University of Southern California Dissertations and Theses

Some variations in the molluscan genus Acmaea

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Some variations in the molluscan genus Acmaea

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Content SOME V IATIONS
IN THE OLLU C
A Thesis
Pre~ented to
the Faculty of the Department of Zoology
University of Southern California
In Partial Fulfillment
of th requir ments for the Degree
aster of rts
by
Edwin Frederick edon
.Tune 1935
This thesis, written under the direction of the
candidate's Faculty Committee and approved by
all its members, has been presented to and ac
cepted by the Council on Graduate Study and
R esearch in partial fulfillment of the require
ments for the degree of
s. r ... of .. .Ar.t.s. ................... ,,... ............................................. .
Dean
Date..... ahr.u.ar.~.193.5 ............. .
Faculty Committee
(,
The writer desires to express his appreciation tor
the assistance given by the Los ngeles County M~seum .
The Director, Dr. 1111 m A.Bryn, permitted him to have an
employee's right of entr nee as well as full access to the
facilities of the institution. r r. Hoard R. Hill ,
Zoologist , most considerately provided in his on office,
the space and drawers indispensable for this vork . Even
more important was his interest, which was manifested by
numerous pertinent suggestions and criticisms that greatly
aided the pursuit of this study.
In addition, the riter is indebted to his thesis
co ittee and particularly to Dr. F •• Baldwin for his
ever helpful and kindly guidance.
TABLE OF CONTENTS
C HAPrER
PAGE
I.
II.
III .
STATEMENT OF THE ROBL
LITERATURE ••••••
History of the problem
AND REVIEW OF 'rHE
• • • • • • • • • • •
• • • • • • • • • • •
V
Review of the literature
Statement of the problem
• • • • • • • • • •
• • • • • • • • • •
Soape of the study
• • • • • • • • • • • e •
Organization of the remainder of the thesis.
TERIALS AND TECHNIQUE ••••••••••••
aterials ••••••••••••••••••
'rechnique • • • • • • • • • • • • • • • • • •
IATION IN THE UB PEC IES OF C A CASSIS
ESCHSCHOLT~ -' • •
• • • • • • • • • • • • • • •
General classification
• • • • • • • • • • •
1
1
2
4
6
8
9
9
10
13
13
Acmaea cassis pelta Eschscholtz. • • • • • • 14
Acmaea cassia olympica Dall ••••••
omaea cassia nacelloides Dall
• • • •
• • •
• • •
19
21
cmaea cassia monticola Carpenter. • • • • • 22
Summary • • • • • • • • • • • • • • • • • • • 23
IV. VARIATIONS IN ACMA
DIGIT.ALIS ESCHSCHOLTZ
AND ITS SUBSPECIES
• • • • •
Classification
• • • • • • •
omaea digitalis Eschscholtz
• • • • • • • •
• • • • • • • •
• • • • • • • •
25
25
25
CHAPT ~R
Acmaea digitali umbonata Reeve
• • • • • • • •
Acmaea digitalis textilis Gould
• • • • • • • •
Summary
•
•
• • •
• • • • • • • • • • • • • • •
v. v~ I TIO~S IN SOaE [ISCELL NEOUS SUBSPECIES
•
• •
Classification
• • • • • • • • • • • • • • • • •
Acmaea soutum cribraria Carpenter
• • • • • • •
cmaea limatula Carpenter
• • • • • • • • • • •
Acmaea persona strigillata Carpenter
• • • • • •
VI. SUlv RY OF FINDINGS ND CONCL US IO S
• • • • • • •
BIBLIOGR
PENDIX
HY • •
• • • • • • • • • • • • • • • • • •
• • • • • • • • • • • • • • • • • • • • • •
• •
• •
V
P GE
27
29
30
33
33
33
33
35
39
43
64
LIST OF PLATES
PLATE
PAGE
I. ACMAEA CASSIS PELTA Eschscholtz. • • • • • • • 49
II. AC .. ~.-A CASSIS PELTA Eschscholtz. • • • • • • • 50
III. ACMAEA CASSIS OLYMPICA Dall. • • • • • • • • • 51
IV. ACMAEA CASSIS NACELLOIDES Dall
• • • • • • • •
v. ACMAEA CASSIS iONTICOLA Carpenter
• • • • • • •
VI. Composite of subspecies of AC AEA CASSIS
VII.
VIII.
IX.
x.
Eschscholtz •••••••••••••
AC EA DIGITALIS Eschscholtz •••••
AC DIGITALIS UMBON TA Reeve ••••
AC~u~~A DIGITALIS TEXTILIS Gould ••••
Abnormal forms of ACMA DIGITALIS
• • • •
• • • •
• • • •
• • • •
52
53
54
55
56
57
Eschscholtz. • • • • • • • • • • • • • • • • 58
XI. AC~-........ SCUTUM CRIBRARIA Carpenter • • • • • • • 59
XII.
XIII.
XIV.
x:v.
AC AEA LillATULA Carpenter •••••••••••
ACM.A A PERSONA STRIGILLATA Carpenter • • • • •
AC EA PERSONA STRIGILLATA Carpenter •••••
AC EA PERSONA STRIGILLATA Carpenter •••••
60
61
62
63
CHAPTER I
STATEMENT O F THE ROBLIDJI AND REVIE iV O F THE LITER TURE
Dr. Philip P. Carpenter in a report made in 1856 to
the twenty-sixth meeting of the British Association for the
Advancement of Science said:
The earliest known collector on the North-west shores
of America was the justly celebrated Dr. Johann Friedr .
Eschscholtz, Professor and Director of the Zoological
useums in the University of Dorpat. He accompanied an
expedition in the Russian ship Predpriaetie, commanded
by Capt. Kotzebue, during the years 1823-6 •••• The
description of the new species was commenced by Esch
scholtz in the "Zoologischer Atlas, enthaltend Abbild
ungen und Beschreibungen neuer Thierarten, Berlin, May
1829:" but he died of nervous fever, May 7, 1831, at the
early age ot 37 years. The work was brought to a con
clusion in the year 1833 (from the author's MSS.) by
Dr. Martin Heinrich Rathke,
1
who appears to have succeeded
him in the chair at Dorpat.
The genus Acmaea (limpets) has been accumulating
species and subspecies since 1830, when Eschscholtz named the
type for the genus. Subsequently, a great many individuals
collected specimens that have reachea the hands of various
persons ho classified and named them, frequently with no
knowledge of, or regard for, the work done by others. As a
result the classifiers usually disagreed with one another
1
Philip P. Carpenter, "Report on the present state ot
our knowledge with re ard to the ollusca of the est Coast
or North America." Report of the Twenty-Sixth eeting of
the British Association for the Advancement of Soienoe, 1856,
p. 159.
and, what was more disastrous, gave different names to the
same shell, a happening which need ocoasion no amazement.
Naturally great confusion resulted and the need for correla
tion and revision became imperative.
2
The first reviser who attempted to correlate the work
of his predecessors was Dr. Philip P. Carpenter, an English
conchologist who later in life was with the Smithsonian In
stitution. He published three papers; the first in 1857
entitled, "Report on the present state of our knowled e with
regard to the Mollusca of the est Coast of North .America",
1
the second in 1864 entitled, "Supplementary Report on the
Present State or our Knowledge with regard to the M ollusca
of the est Coast of North America",
2
and the third entitled,
3
"On the Acmaeidae of the Vancouver and California province" •
• H. Dall, who for over fifty years was with the
Smithsonian Institution, much of the time as Curator of
ollusks, was the author of the next contribution published
in 1871, entitled, "On the limpets, with special reference to
-------~
1
Philip P. Carpenter, Report of the Twenty-Sixth
eeting of the British Association for the Advancement of
Science, 1856, pp. 159-368.
2
Philip P. Carpenter, Report of Thirty-Third eeting
of the British Association for the Advancement of Science,
1863, pp. 51?-686.
3
Philip P. Carpenter, .American Journal of Conohology,
Vol. II, No. IV, PP• 332-348.
the species of the west coast of America, and to a more
natural classification of the groupn.
1
In 1891, an article
written by Tryon and Pilsbry entitled, onographs of the
3
Aomaeidae, Lepetidae, Patellidae and Titisoan11dae"
2
was
published. The most recent contributions in this field are
by William H. Dall, his "Notes on some northwest coast
Aemaeas"
3
appearing in 1914, and his "Summary of the marine
shellbearing mollusks of the northwest coast of America, ••
• • "4 in 1921. This last publication is used very
extensively by conchologists interested in west coast shells.
In the 1914 article when speaking of the need of re
vision, Dall says:
Since Dr. Philip Carpenter's review of the Acmaeas of
the Northwest Coast {Am. JOUrn. Conch., II, 1866) all
writers on the subject, including myself, have to a
large extent, if not entirely, accepted his conclusions
as to their nomenclature.
Having occasion to revise the magnificent series of
these shells in the National Museum, I have recently
reviewed the whole nomenclature from the beginning, and
to my surprise and dismay found that Dr. Carpenter, in
1
• H. Dall, American Journal of Oonchology, Vol. VI,
Part III, pp. 227-282.
2
George w. Tryon, Jr., and Henry A. Pilsbry, Manual
of Conchology. Vol. XIII, pp. 5-195.
3
W illiam H. Dall, The Nautilus, XXVIII {June, 1914),
13-17.
.
4
1illiam Healey Dall, (United States National Museum,
Bulletin 112. Washington: Government Printing Office,
1921), pp. 168-170.
4
his desire to perpetuate the manuscript names of his
friend Thomas Nuttall, had frequently ignored the rules
altogether, had adopted names which he knew to be pre
oooupied, and in several cases misidentified early
authors' species. Mr. Robson of the British Museum
had intimated to me some time ago that the nomenclature
of these limpets was in a very bad state of confusion,
but until I oame to work over them myself I had no
realization of the true condition.
In extenuation it must be remembered that fifty years
ago the necessity of strictly conforming to the rules
was little appreciated, and many excellent naturalists
or that day are responsible through their carelessness
for much of the trouble now encountered.
In reviewing the work of an author who like Eschscholtz
gave several names to mutations of the same species, the
most acceptable way is to take his first name for the
consolidated species and put the others in synonymy. Dr.
Carpenter, however, in choosing in such cases did not
follow this method. However, as the first reviser, his
selection may be considered final, or we should practi
cally have to change all his names. In the space here
available it is not practicable to give a full discussion,
but the final results may be noted.
In spite of all the v ~rk with Aomaeas, conohologists
of today still find themselves in a state of great confusion
and uncertainty concerning those species which have sub
species. This confusion exists because or the extreme
variations of the Aomaeas themselves, which seem to be
caused by differences in food and station, and because of the
very inadequate descriptions which exist for some of the
Acmaeas. For example, the following which appears when
Carpenter is speaking of Aomaea pelta Eschscholtz (Acmaea
cassia pelta Eschscholtz) is the only description to be
found for omaea cassia monticola Carpenter:
In its early adolescence, irregular decorticated shells
are the A• monticola of Nutt., ms.; some specimens not
bein~ distinguishable internally f"rom Lottia onychina,
Gld.
The difficulty from the standpoint of variations has
always been recognized by students as witness the following
statement made by Dr. Carpenter, in 1856, when referring to
the work of Conrad upon the shells collected by Nuttall, in
1834-5, on the shores of California:
5
The work bears the appearance of undue haste; the genera
are grouped together without the least regard to arrange
ment; a large proportion of the species are named either
Californicus or Nuttall!; the difficult geRera, such as
Acmaea and Chiton are not touched; ••••
It appears that the only way to understand the subspecies is
to study the variations to be round and then to clarify the
confusion arising because of these variations. Dall lists
thirty-two species and subspecies in the genus Acmaea.
3
The
following are the subspecies with the parent species in eaoh
1
Philip P. Carpenter, "On the Acmaeidae of the
Vancouver and California province." .American Journal of
Conchology. Vol. II, No. IV, of the Conchological Section of
the (Philadelphia] Academy of Natural Sciences, · 1866, p. 337.
2
Philip P. Carpenter, "Report on the present state of
our knowledge with regard to the Mollusca of the est Coast
of North America." Report of the Twenty-Sixth Meeting of
the British Association for the Advancement of Science, 1856,
p. 193.
3
William Healey Dall, Summary of the marine shell
bearing mollusks of the northwest coast of America, ••••
(United States National Museum, Bulletinll2. ashington:
Government Printing Office, 1921), pp. 168-170.
case:
Aomaea mitra Eschscholtz, 1833
Aomaea mitra funiculata Carpenter, 1864
Acmaea
Aomaea
Aomaea
Aomaea
Acmaea
Acmaea
Acmaea
Acmaea
Aomaea
Acmaea
Acmaea
cassis
cassia
cassia
cassis
cassia
soutum
soutum
soutum
scutum
scutum
scutum
schsoholtz, 1833
pelta Eschscholtz, 1833
olympica Dall, 1914
naoelloides Dall, 18?1
monticola Carpenter, 1866
Eschscholtz, 1833
patina Eschscholtz, 1833
pintadina Gould, 1846
oribraria Carpenter, 1866
ochracea Dall, 18?1
parallels Dall, 1914
Aomaea digitalis Eschscholtz, 1833
omaea digitalis umbonata Reeve, 1855
Aomaea digitalis textilis Gould, 1846
Acmaea limatula Carpenter, 1866
Acmaea limatula m~rchii Dall, 18?8
Acmaea persona Eschscholtz, 1833
Acmaea persona strigillata Carpenter, 1866
This thesis embraces only those species with
subspecies to be found on the coast from Santa Monica to
Balboa Beach; consequently, the following are not included:
Acmaea cassis Eschscholtz--not found south of San
Francisco
Acmaea scutum pintadina Gould--not found south of
Monterey
Aomaea scutum ochracea Dall--found only at onterey
Acmaea scutum parallela Dall--found only in Alaska
Acmaea limatula mBrchii--found only at Tamales Bay,
6
7
California
Ac aea mitra Eschscholtz, which is usually found below
the extreme low tide lines, and Aomaea a i tra funioulata Car
penter, a dredge shell, are not studied for the reason that
they are clearly distinguishable. Acmaea scutum Eschsoholtz,
Acmaea scutum patina Eschscholtz, and Aomaea persona
Eschscholtz were not collected by the author. The
Conchologioal Club of Southern California reports that its
members have not found these shells in this locality, even
though Dall gives the range in eaoh case as being south to
Socorro Island. These spells are likewise omitted . It thus
appears that there are ten species and subspecies occurring
locally which because of their variations are causing
conchologists difficulty and these ten are all included in
this study:
Aomaea cassis pelta Eschscholtz
Aomaea cassis olympica Dall
Acmaea cassia nacelloides Dall
Acmaea oassis monticola Carpenter
Aomaea scutum. cribraria Carpenter
Aomaea digitalis Eschscholtz
Aomaea digitalis umbonata Reeve
Acmaea digitalis textilis Gould
Aomaea limatula Carpenter
Acmaea persona strigillata Carpenter
It is the purpose of this thesis to analyze variations
occurring in the shells listed above with the hope of elimi-
8
nating many of the problems QOnfronting conchologists in this
respect. Dall's arrangement of species and subspecies has
been followed as nearly as possible. For convenience of study
the shells have been divided into groups which are discussed
under the following chapter headings:
CHAPTER III VARIATIONS IN THE UBSPECIES OF ACMAEA
CASSIS ESCHSCHOLTZ
Acmaea cassis pelta Eschscholtz
Aomaea cassis olympica Dall
Aomaea cassis nacelloides Dall
Acmaea cassis monticola Carpenter
CHAPTER IV VARIATIONS IN AC AEA DIGI ALIS ESCH
SCHOLTZ AND ITS SUBSPECIES
Acmaea digitalis Eschscholtz
Acmaea digitalis umbonata eeve
Acmaea digitalis textilis Gould
CHAPTER V V IATI NS IN SO MISCELLANEOUS
SUBSPECIES
Acmaea scutum cribraria Carpenter
Aomaea limatula Carpenter
Acmaea persona strigillata Carpenter
CHAPTER VI SUMMA Y OF INDINGS AND CONCLUSIONS
CHAPTER II
MATERIALS .AlID TECHNIQUE
The most desirable method of studying the different
species and subspecies that have been selected ould be to
actually grow them under control conditions; however, the
lack of facilities precludes any such endeavor. The same,
or very nearly the same, results may be obtained by collect
ing large numbers of shells and then thoroughly studying
these specimens, basing the study upon the work of prominent
conchologists. Only by collecting large numbers of shells
can one be reason~bly certain of securing the maximum number
of variations.
The author has collected shells over a period of five
years (1929-1934) at the following places from Santa Monica
to the Balboa jetty:
Santa Monica Pier
Lick Pier at the foot of Navy Avenue, Ocean Park
Amusement Pier at the foot of lindward Avenue, Venice
Sunset Pier at the root of N. Venice Boulevard, Venice
Board wall at the foot of ashington venue, Venice
Playa del Rey Pier
El Segundo Pier
[anhattan Beach Pier
Hermosa Beach Pier
Redondo Beach Pier
Rooks at Pt. Vincente
Rocks st Portuguese Bend
Rocks at Long Point
Rocks at Pt . Fermin
Pt . Fermin Breakwater
Various pilings at Los eles Harbor
Amusement Pier at foot of Pine Avenue, Long Beach
Rocks of jetty by power plant at Seal Beach
Bridges over entrance of Alamitos Bay
Seal Beach Pier
Huntington Beach Pier
Newport Beach Pier
Balboa Beach Pier
ocks of Balboa jetty
10
In all, more than thirty-five different collecting
trips were made. The tide was very favorable for eaoh trip,
ranging, with few exceptions, from -.5 to -1.a.
Because of the need of obtaining large numbers of speci
mens, no consideration was given to selection during the
actual collecting but just as many shells vere taken as could
be secured while the tide remained favorable. The specimens
were obtained by quickly inserting a thin bladed knife under
the edge of the shell, pushing the knife forward, and at the
11
same time raising the handle hich caused the shell to come
loose. A small sized _ can, such as a one~pound coffee can,
makes a good receptacle in mich to receive the falling shell.
The specimens were then cleaned by plunging them for about
thirty seconds into boiling water which freed the fleshy
material from the shells so that they could be readily sepa
rated. After drying, the shells ere placed in co~tainers,
labelled, and set aside ror future study. Thousands or
specimens were thus secured.
She~ls from a given location were studied together.
Each shell was examined and placed with other shells which
seemed to be the same. These shells of a like kind ere
then individually examined again so as to be certain that
no errors of the original selection ere allo ed to go un
corrected. The different groups of shells thus segregated
were identified. Each shell as then critically examined
for individual differences wid grouped in accordance with
the variations discovered. At elve-power hand lens and a
binocular microscope were frequently necessary. The varia
tions ere then studied in an effort to find intergrading
and other differences which might lead the conchologist
astray in his effort to identify the different species and
subspecies. The collection has been divided into two units:
first, a collection of adult specimens designed to reveal
whether or not an intergrading is to be found when large
numbers are examined, an secondly , a g series designed to
show whether at any certain degree of development variations
begin to appear.
12
Photog a taken in order to illustrate the important
points discovered, along witl discussions thereof, have been
incorporated into this thesis, and constitute its chief
utility.
CHAPI'ER III
VARIATIONS IN THE SUBSPECIES OF ACMAEA CASSIS ESCHSCHOLTZ
General Classification
The genus ACMAEA is plaoed in the Family ACMAEIDAE.
The following description is from Oldroyd:
Family ACMAEIDAE
Genus AC EA Eschscholtz, 1830
Shell conical, patelliform, apex more or less anterior.
The shells may generally be distinguished from Patella
by the different texture and margin border of the inside.
(Tryon and Pilsbry, anual of Conchology.)
Type. Acmaea mitra Eschscholtz
Distribution. North Atlantic and Arctic, western coast
of North America ind South America, West Indies, Japan
and Indo-Pacifio.
The Acmaeas considered in this thesis are classified
under Section COLLISELLA Dall, 1871, which was originally
described as:
Subgenus COLLISEllA, Dall
Lottia, Aom.aea, Teotura, and Patella, sp. auct.
l Ida Shepard Oldroyd, The Marine Shells of the West
Coast of North America, Vol. II, Part III (Stanford
University, California: Stanford University Press, 1927),
p. 144.
14
Animal without any vestige of a branchial cordon.
Muzzle-trill simple, entire, not produced into lappets or
tubercles. Radula with the two inner laterals anterior,
approximate, simple, with long cusps; next two posterior,
with large, broad usually simple cusps; outer laterals
minute, closely appressed and opposed to the cusps of the
second pair; pleurae provided with one or two very minute
uncini close to the posterior corner of the area. Fonnula
0
2 or 1(2-1.1-2}1 or 2.
This subgenus differs from Acmaea in the simple
muzzle-trill, the relative position and unequal size of
the lateral teeth, and in the very minute uncinus, which
from its small size, is very liable to be overlooked.
The fact that the type of the genus Tectura belongs to the
restricted genus Acmaea , prevents the use of that name for
this group for which it might have been advantageously
employed.
The majority of the Acmaeidae of the eit American
coast belong to this section of the genus.
here are four subspecies of the species Acmaea cassia
Eschsoholtz:
I. Acmaea cassia pelta Eschscholtz
II. Aomaea cassis olympica Dall
III. Acmaea cassia nacelloides Dall
IV. Aomaea cassia monticola Carpenter
I. Acmaea cassia pelta Eschscholtz ~
Description
1
• H. Dall, "On the Acmaeidae of the Vancouver and
California province." .American Journal of Conchology,
Vol. VI, Part III, pp. 245-246.
Acmaea cassia pe1ta Eschscholtz, 1833
Zoological Atlas, 19. Tryon and Pilsbry, Manual of
Conchology, 13: Pl. 8, figs. 90, 91.
15
Testa ovato-oblonga depressiuscula, extus fusco
olivacea, intus alba aut caerulescente, macula sub fornice
fusoa irregular!, striis transversis subtil1ss1mis, costa
~arum elevatis latis, vert1s, exoentrico subinflexo.
(Esohscholtz.)
Die Schale 1st auswendig glatt, sehr dunkel, olivengrun,
und in der Nahe des Randes zwisohen den Rippen mit einigen
gelblichen Langsstreifen versehen. Die vordere Halfte des
breunen Fleokens 1m Innern der Schale 1st bei allen mir
vorliegenden Exemplaren verwischt. Am Rande kommt inwendig
ein schmaler brauner oder braun un gelb gefleokter Saum
vor. Lange 1 Zoll 1 Linie, grosste Breite 10 Linien, lfohe
5½ Linien.
Hieher glaube ich als blosse Spielart eine andere Schale
zahlen zu mussen, die etwas grosser und auwwendig nicht
glatt, sondern etwas rauh 1st, bei der auch die Rippen
nicht so deutlich hervortreten, die gelben Langsstreifen
fehlen und der Gipfel nicht im mindesten ubergebogen 1st.
Ich habe mehrere Schalen in Handen, die deutlich einen
Uebergang in diese Varietat machen. (Ksohscholtz.)
Shell oval, conical, apex a little in front of the
middle. Surface having rather coarse low ribs. Dark
bo~der of the inside very narrow, or reduced to a series
of dark scallops. (Tryon and Pilsbry, l anual Q!.
Concholog~. )
Type in St. Petersburg. Type locality?
Range. Okhotsk and Southern Bering Sea, N~shsgak,
Alaska, Aleutian Islands to Lo er California.
Acmaea cassia pelta Eschscholtz is one or the most
variable of the limpets to be found along our local shore line.
l Ida Shepard Oldroyd, The [arine Shells of the West
Coast of North America, Vol. II, Part III (Stanford
University, Californi a : Stanford University Press, 1927),
P• 146.
16
The most noticeable variations are those of markings and
height of apex. Occasional specimens have more or less
prominent ribs. Some shells are very light in tone while
others are strongly marked with stripes of white which often
divarioate or break into a tessellated pattern superimposed
on a light background. Shells of the same size may differ
so widely as to the height of apex that one might question
whether they were the same species. Occasionally the apex or
one shell will be as much as three times as high as the apex
of another shell of the same circumference. In fact, there
appears to be an almost distinct variety having the low apex.
However, this low apex variety may readily be united with the
typical high apex specimens by means of intermediate shells
which clearly complete the series. The specimens shown in
PLATE I are the typical Acmaea cassis pelta having the high
apex.
The most startling variations to be found in this
species are the dark caps which occasionally appear on some
specimens which are otherwise typical. PLATE II shows a
series of such shells. It is to be noticed that the small
specimens show the Acmaea cassia Relta characteristics at the
margin only. Otherwise they appear to be Aomaea cassia
nacelloides Dall shown in PLATE IV. An examination of all the
caps reveals the same appearance and were it not for the
Acmaea cassia pelta characteristics below the cap they would
17
all be identified as Acmaea cassia naoelloides. It is
possible to run these small specimens right into Acmaea
cassis nacelloides so that one cannot tell by looking at a
small specimen of this species whether it will remain an
Aomaea oassis naoelloides or later by changing its appearance,
grow into an Acmaea cassia pelta.
Hemphill seems to have been the first to notice this
unusual relationship. The following is a portion or his
letter read by Mr . Tryon at a meeting of the Philadelphia
Academy of Natural Sciences on April 19, 1881:
I will now call your attention to Nos. 45?, 458, 459
and 460. I have made two trips to onterey, Cal., this
winter. During my rirst visit I collected a few speci
mens of Acmaea pelta and its vars., and when I returned
home and began to clean the specimens I was very much
puzzled over some specimens of No. 458. Several years
ago I had collected shells of No. 459 at Monterey , which
at that time I called Nacella instabilis, but these halt
and half varieties did not appear at that time. After
a little reflection on the matter , I began to suspect
the true condition of the subject and beoame so much
interested in it, that I concluded to go to Monterey
again and try to work it up, and I think I have done so.
It is simply a 4uestion of station.
W hen the young of!• pelta stations itself on the
kelp {Phyllospora menziesii, Ag.), it assumes the aspect
of Naoella, and as long as it remains on the kelp it
does not change its color in the least, and only varies
its form to suit the shape of the stems of the kelp to
which it attaches itself~ But when from any cause it
leaves the kelp and takes to the rooks, it seems to
begin immediate·ly to paint up and ornament itself after
the fashion of the specimens I have sent you.
When it remains on the kelp a long time and completes
its growth, we then have Naoella instabilis, and if living
in an exposed position its apex becomes worn, the sculp
ture faint, etc. When the young station themselves on
18
the rocks they do not assume the Nacella aspect at all,
but commence immediately to adorn themselves in gay and
beautiful colors as you will see by the fine series of
No. 457. Now for the facts and reasons why I catne to
this conclusion. I collected about 200 living specimens
on the kelp in all stages of . growth, and out of the 200
I found but two specimens that varied their color at all;
one was a very young and small specimen, with a few light
dots on or near the apex, and the other was a large
specimen with a tesselated border on the inside. I also
collected about 200 on the rocks, ad every one was more
or less variegated with either the square dots or alter
nate rays of white and black, while those that had evi
dently been on the kelp had their tesselated borders well
advanced. e must also take into consideration the fact
that onterey is the most southern point at which Naoella
instabilis has been found, and it is quoted by Dall as
rare there. The water of the bay here these half and
half No. 458 are found, and also others, is comparatively
smooth t o what it is on the outside where the typical
Nacella is found, which will account for the preservation
of the apex and sculpture and may have something to do
with t he form, ani undoubtedly is the cause why it is
rare at onterey.
It is to be observed that Hemphill refers to Nacella
instabilis, but Tryon in mentioning Hemphill's findings says,
"The specimens collected by Henry He phill and described by
him in Proc. Acad. Nat. Sci. Phila. 1881, p. 8?, under the
name instabilis, are typical nacelloides."
2
All of the speci
mens I have collected are clearly nacelloides. I was able to
1
Henry Hemphill, "Portion of a letter.n Proceedings
of the Academy of Natural Sciences of Philadelphia for 1881,
PP• 87-88.
2
George • Tryon, Jr. and Henry A. Pilsbry,
"M onographs of the Acmaeidae, Lepetidae, Patellidae and
Titisoaniidae." Manual of Conchology, 1st series, Vol. XIII,
of the Conchological Section, [.PhiladelphiEil Academy of
Natural Soienoes, 1891, p. 18.
19
examine, in the Los Angeles County useum, capped specimens
from Monterey which also proved to be typical naoelloides.
It appears certain that Hemphill misnamed his specimens.
Apparently this pecularity in regard to caps has not been
observed or studied elsewhere as the literature is barren of
any such sug estion.
All of my specimens were taken from pilings or rocks.
On these same pilings and rocks were foun nacelloides, many
of them mature; but still not showing the slightest tendency
to develop the decorated margin . While Hemphill's observations
may state a general truth it is certain that the mere fact
that a nacelloides is not on kelp does not guarantee that it
will change over into an Acmaea cassis pelta, for it may grow
to maturity without oing so. Certainly the relationship is
so close and intimate as to show these to so-called
subspecies are variations of but one and the same subspecies.
II. Acm ea cassis olympioa Dall
Description
Acmaea cassis olympica Dall, 1914
Plate 94, figs. 12, 13
Nautilus, 28:14. Tryon and Pilsbry, Manual of Conchologl,
13: Pl. 8, figs. 92-94.
Shell small, conical, el vated, having much the shape
of A. mitra. The color outside is gray, pink, or light
purple , painted with a few or many black stripes. A dark
20
spot is inside. Ribs obsolete. Length, 25-30 mm. (Tryon
and Pilsbry, Manual of Conchology.}
Type in United States National useum. Type locality,
Olympia, Washington.
Range.
1
Alaska Peninsula to San Diego, California.
Acmaea cassis olympica Dall, (PLATE III), was first
collected by Hemphill at Olympia, Puget Sound, Washington,
being found on Mytilus edulis.
2
He sent a collection to the
Philadelphia Academy of Natural Sciences in 18 1. These
shells were not named, however, until Dall in 1914, called
them olympica. They are to be found locally on Mytilus
oalitornianus in plentiful quantities. In shape and general
appearance they closely resemble Acmaea cassis naoelloidea
Dall, {PLATE IV), but lack the horny appearance and solid
black or brownish color of the latter. Acmaea cassia
olympioa usually has more or less striping of white which
generally does not persist near the apex. The larger shells
grade down to young specimens which are indistinguishable
from the young of nacelloides, thus further complicating the
l Ida Shepard Oldroyd, The Marine Shells of the
est Coast of North America, Vol. II, Part III (Stanford
University, California: Stanford University Press, 192?),
p. 147.
2
George • Tryon, Jr. and Henry A. Pilsbry,
' onographs of the Acmaeidae, Lepetidae, Patellidae and
Titiscaniidae." anual of Conchology, 1st series, Vol. XIII,
of the Conchological Section, [Philadelphia] Aoademy of
Natural Sciences, 1891, p. l?.
distinction between the subspeoies or Aomaea cassia.
III. Aomaea cassia naoelloides Dall
Description
Aomaea cassia nacelloides Dall, 1871
Plate 94, figs.?, a, g
21
American Journal of Conchology. 6:247; Pl. 17, figs. 36,
a-c.
A very distinct variety of this species (Collisella
pelta Esch.) has exactly the aspect of Naoella instabilis
externally. It is of a blackish-brown, with sharp,
radiating grooves sometimes obsolete near the apex.
Several shells beginning in this way have a margin with
the normal characters of~. pelta. It is quite distinct
from the variety montioola Nutt., as described by Dr.
Carpenter in the .American Journal or Conohology, 2:33[7],
and might readily be taken for a distinct species, as
the sculpture differs entirely from that of the normal
pelta, which is sparsely furnished with prominent bulging
ribs. (Dall.)
Type in United States National Museum. Type locality,
California.
Range. Attu Island, Aleutian, to San Diego, California.
Described as Collisella pelta naoelloides.
1
Aomaea cassia naoelloides Dall, (PLATE IV), may be
found on rooks, pilings, or Mytilus californianus. The brief
description of this subspecies under Acmaea oassis olympica
l Ida Shepard Oldroyd, The Marine Shells or the West
Coast of North .America, Vol. II, Part III (Stanford
University, California: Stanford University Press, 1927),
P• 147.
necessitates no further tre tment here.
IV. cmaea cassis monticola Carpenter
Description
Acmaea cassis monticola C rpenter, 1866
The only description that can be found for this sub
species , and a very unsatisfactory one , appears when
Carpenter in speaking of Acmaea pelta Eschsoholtz ( cmaea
cassis pelta Eschscholtz) said:
In its early adolescence, irregular decorticated
shells are the A. monticola of Nutt., ms.; some speci
mens1not being distinguishable from Lottia onychina,
Gld.
Apparently this description means that adolescent,
22
irregular, decorticated shells, belonging to Acmaea cassia
pelta, are called cmaea cassis monticola . No type specimen
is known nor is any locality iven. rs. Oldroyd has not
recognized this subspecies
2
and it would appear obvious
from its description that it is only a variation of Acmaea
cassia pelta. Some shells, coming within this description,
1
Philip P. Carpenter, "On the Acmaeidae of the
Vancouver and California province." American Journal of
Conchology, Vol. II, No. IV, of the Conohological Section of
the [Philadelphia] Academy of Natural ciences, 1866, p. 337.
2
Ida Shepard Oldroyd, The Marine Shells of the est
Coast of North America, Vol. II, Part III (Stanford
University, California: Stanford University Press, 1927).
are of such a nature that it is impossible to detennine
whether they are more similar to Acmaea cassis E,__elta or
Aomaea oassis olympica. Specimens of this so-called sub
species are shown in PLATE V.
Summary
23
The rudimentary form or these subspecies seems to be
Aomaea cassis nacelloides. The young of this subspecies, or
young indistinguishable from it, ma develop into the capped
form of Aomaea cassia pelta, into Acmaea cassia olympica, or
remain Acmaea cassia nacelloides. This extreme intermingling
shows that these three subspecies are really all variations
of the subspecies Acmaea cassis pelta and not true subspecies.
It also explains why conchologists have been so confused in
regard to them. Acmaea cass is monticola is not found in the
youn stage at all but is always adolescent. This shell is
clearly an irreg lar, adolescent cmaea cassia pelta which
has become decorticated.
The conclusion is that these four s~bspecies are all
variations of Acmaea cassis pelta which blend one into the
other so that certain speci1 ens cannot be placed positively
in any of the subspecies and must, therefore, be called Acmaea
cassis pelta. It is a question whether it is ise to attempt
to distin uish between these subspecies. Certainly one must
recognize that any such distinction is purely arbitrary.
24
PLATE VI is arran ed to denonstrate how even the
typical members of these ifferent subspecie constitute a
connect ed series. The five specimens of Aomaea cassia pelta
shown in group 1, ran e progressively fro1 the typical
cassia pelta on the left, to the form on the right
almost completely covered by a cap which is so similar to
the Acmaea cassis nacelloides shown in group 2 . Acmaea
cassia olympica shown in roup 3, closel approaches Acmaea
cassia nacelloides at one extreme and at the other, Acmaea
cassis olympica shown in group 4. Since there is this
intergrading in even the typical specimens of the subspecies ,
one may readily see that the variable members of these
subspecies 1ould blend one into the other to such an extent
that n accurate d etermination of subspecies would be
i possible.
CHAPI'ER IV
VARIATIONS IN ACMAEA DIGITALIS ESCHSCHOLTZ AND IT SUBSPECIES
Classification
The species Acmaea digitalis Eschscholtz and
subspecies will be discussed in the following order:
I. Acmaea digitalis schscholtz
II. Acmaea digitalis umbonata Reeve
III. Acmaea digitalis textilis Gould
I. Acm.aea digitalis Eschscholtz
Description
Aomaea digitalis Eschscholtz, 1833
Plate 85, figs . 6, 9; Plate 94, figs . 10, 11
Zoological Atlas, 5:20; Pl . 23 , figs.?, 8
its two
Testa ovato-elliptica, convexa, intus albida, macula
sub fornice fusca, irregulari obsoleta, costis nonnullia
latis tuberculosis, vertice submarginal1 compresso. (Es
chscholtz.)
Der Gipfel berindet sich an dem vordern End , und nicht
gar fern van dem Rande der Schale . Seitwarts van ihm
fillt die Schale rast ganz gerade und sehr absohussig ab,
nach hinten aber steigt die Schale var ihm erst etwas,
obsohon an einingen Examplaren mehr, an andern weniger in
die Hohe, und fallt dann allmahlig und mit einer starken
Wolbung ab. An dem vordern Theile der Schale sind
zwischen dem Gipfel und dem Rande Keine Rippen zu
bemerken, nach hinten aber werden sie allmahlig starker,
und die jenige, welche van Gipfel zu dem hinterne Ende
des Sohalenrandes verlauft, 1st nicht blos die langste,
26
sondern auch die hochste und dickste. Den grossern
Rippen entsprechen schwache rinnenformige Vertiefungen
an der innern Seite der Schale. Einige Schalen sind in
der Gegend des Gipfels starker zusammengedruokt, als
andere, und danach richtet sich denn auch hauptsachlich
die Form des nur massig grossen braunen Fleckens , der sich
und der innern Flache der Schale befindet. Doch 1st in
manchen Exemplaren statt dieses Fleckens nur ein
leiohter brauner Anflug vorhanden • .Am Rande 1st inwendig
ein schmaler braunlicher oder auch braun und gelb
geflecter Saum . Die Grundfarbe der aussern Flache 1st
ein unreines 'eiss. An einigen Exemplaren liefen auf
diesem einige dunk:, elbraune Binden von dem einen
Seitenrande Uber die Wolbung der Schale, etwas schief zu
dem andern Seitenrande quer herliber. Bei den meisten
aber waren die Binden oder auch nur der mittlere Theil
deraelben abgerieben oder auch gleichsam verwischt. Die
Lange der grossten Exemplare betung 1~ Linien, ihre
grHsste Waite 8 Linien und ihre H~he 6 Linien.
(Eschschol tz. )
This is the most usual form found north of San
Francisco Bay. It is dull, lusterless, whitish, with
stripes and zigzags of blackish-brown. The apex is
usually decidedly anterior and elevated; the front ribs
are obsolete, the posterior ribs strong, rounded, often
uneven. Inside margin conspicuously tessellated; central
area generally dark and rather narrow.
This is the oregona of Authers, and probably radiata
of Eschsoholtz . It ~esembles the striped variety of the
Chilean A. ceciliana so closely that it would be
absolutely impossible to separate a mixed lot. (Tryon
and Pilsbry , lVIanual of Concho logy.)
Type in St. Petersburg. Type locality?
Range .
1
Aleutian Islands to Monterey , California.
1
Ida Shepard Oldroyd, The Marine Shells of the West
Coast of North America, Vol. II, Part III {Stanford
University , California: Stanford University Press, 192?),
pp. 151-152.
27
cmaea digitalis Eschscholtz, (PL TE VII), is a common
local species living on the vertical races of the large rocks
where the surf strikes with full ~orce. Many of the shells,
therefore, become badly eroded and their m rkings become
indistinct or disappear entirely. ven the usually strong
ribs may become badly worn. Because of this erosion a very
large proportion of the shells collected are of little value
for the purposes of critical examination. The typical speci
mens are easy to select but they are rathe r rare . In any
collection of digitalis, specimens commonly vary from the
typical in many respects. The apex is often located more
posteriorly and is less elevated. The ribs in some shells
are not nearly so strong; occasionally they almost disappear.
The vivid tessellations of the inside margin sometimes
disappear and instead there is a solid, or nearly solid, black
border. The characteristic white porcelain-like interior at
times assumes an unmistakably pale blue color.
fuile Acmaea digitalis is exceedingly variable it is
not more so than its subspecies.
II. Acmaea digitalis umbonata Reeve
Description
Acmaea digitalis umbonata Reeve , 1855
Conchologia Iconica, 8: fig. 107.
28
Shell globosely convex, apex altogether anterior, sharp
ly hooked, radiately ridged, ridges few, irregular,
obtusely crenated; ash-black, sculptured with white im
pressed punctate [Punctures] , punctures more numerous
toward the margin, interior bluish-white, chestnut in the
middle. (Reeve.)
Type in Museum Cuming. Type locality, Upper California.
Range. Saginaw Bay, Alaska, to California.
1
Acmaea digitalis umbonata Reeve, (PLATE VIII), seems
to be about intermediate in many characteristics between
Acmaea digitalis and cmaea digitalis textilis. The apex is
not so anterior as in digitalis and generally not so posterior
as in textilis. It is less prominent than in digitalis and more
so than in textilis. The shell is arched about like digitalis
and more than textilis. lliile the ribbing in umbonata is
very similar to textilis, except that it is more beaded, it is
not nearly so prominent as in digitalis.
The interior of umbonata is of a bluish-white color
which becomes progressively lighter from the margin to the
chestnut spot in the center. The dark border is sometimes
almost black and rarely shows any tendency to tessellate. The
characteristics mentioned are not at all constant but vary so
much that frequently it is impossible to determine the nature
of the exterior, if one examines the interior only.
1
Ida Shepard Oldroyd, The Marine Shells of the est
Coast or North America, Vol. II, Part III (Stanford
University, California: Stanford University Press, 192?),
p. 152.
29
III. cmaea digitalis textilis Gould
Description
Aomaea digitalis textilie Gould, 1846
Proceedings of the Boston Society of Natural History,
2:152. Mollusca and Shells of the United States Ex-
ploring Expedition, Pl. 29, fig. 456. -
Testa depressa, oblique conica; apice anteriori, acuto;
oostis latis, elevatis, subplanulatis, nodosis ad 15
radiantibus; epidermide viridi, punctis albidis quadratis
reticulate; basi ovato-rotundato, limbo marginal!
albido et fusco-viridi fimbriato: faoies interior albida;
tundo pioeo. Long., l; lat., 3/4; alt., 3/10 in.
(Gould.)
Type in State Museum, Albany , No . (A ] 6347.
Range. Cresc
1
nt City, California, to Cedros and
Socorro Islands.
cmaea digitalis textilis Gould, (PLATE IX), is found
all along the local coast. The apex is less elevated than
either Acmaea digitalis or Acmaea digitalis umbonata; the
shell is frequently markedly depressed. The sides are usually
wide and relatively flat. The interior is very similar to
umbonata. The virtually black border of textilis is often
more sharply defined, and the blue oolor running to the central
spot is generally deeper, than in umbonata. The margin is
orenate to about the same degree as in umbonata but less than
l Ida Shepard Oldroyd, The Marine Shells of the Wes t
Coast of North America, Vol. II, Part III (Stanford
University, California: tanford University Press, 192?),
P• 152.
30
in digitalis.
Summary
Acmaea digitalis and its subspecies, Acmaea digitalis
umbonata and cmaea digitalis textilis, comprise a group that
is very confusing because of the many variations which occur.
The typical specimens of each division are quite distinct and
present no difficulties in identification. Unfortunately,
the typical specimens are greatly in the minority , and as a
result, the shell collector will rind that most of his speci
mens are not easily identified.
Hard and fast criteria for identification cannot be
formulated. It is useless to attempt to find some one
characteristic which may be relied upon to tell the collector
what he wishes to know. Instead, one must carefully note the
general characteristics of the form under examination and a
familiarity with these will usually serve to identify the
species. The distinguishing characteristics are not readily
learned from reading alone, but can be much more easily
recognized after an intensive study of the specimens. No
matter how careful or thorough the conohologist may be, he
will find specimens which show characteristics that do not
belong to either digitalis, umbonata, or textilis alone, but
are instead, a combination of characteristics of two or more
of these. Such specimens obviously cannot be definitely
31
identified but must be called Acmaea digitalis. The subspecies,
Acmaea digitalis umbonata and cmaea digitalis textilis, are
purely variations of Acmaea digitalis and blend so readily
into it, and into each other, that one is forced to conclude
that they are unstable variations whose differentiation is of
little value to the conchologist.
A series of abnormal Acmaea digitalis is shown in
PLATE X. The small shells appear so little like Acmaea
digitalis that one examining them is in oubt as to their
identity until the older shells, which have acquired the
digitalis border, are found. This variation is simply another
example of the curious, unexplained variations found in the
Aomaeas.
CHAPTER V
VARIATIONS I SOE 1ISCELLANEOUS SUBSPECI S
Classification
----------
The three subspecies to be considered in this chapter
will be discussed in the following order:
I. Acmaea scutum cribraria Carpenter
II. Acmaea limatula Carpenter
III. Acmaea p rsona strigillata Carpenter
I. Acmaea scutum cribraria Carpenter
Description
Acmaea scutum cribraria Carpenter, 1866
American Journal of Conchology, 2:335.
This shell when young is dark olive closely dotted all
over with white, the eroded apex black; when adult it is
usually uniform dull slate-color outside with a ring of
light around the black apical spot ; inside it has a wide
dark border , a large, irregular central dark patch, and .
generally is suffused with dark brown all over. Sculpture
obsolete. (Tryon and Pilsbry , anual of Conchology.)
Type in? Type locality, California.
Rang!• Neah Bay, ashington, to Santa Barbara , Cali
fornia.
1
Ida Shepard Oldroyd, The arine Shells of the est
Coast of North America, Vol . II, Part III (Stanford
University, California: Stanford University Press, 1927),
p. 149.
33
Acmaea scutum oribraria Carpenter , (PLATE XI) , is
included in this study not because of any particular
variations , for there is none, but because all subspecies
occurring locally are considered . s a matter or fact , none
of the subspecies proved to be as free from variations as
this one. In collecting specimen from twenty- four different
places, I was only able to find oribraria at or around
the Pl ya del Rey Pier here it s re sonably plentiful .
he shells accord 1th the description very satisfactorily
an re e sily recognized.
closely or blend into ny o
Cribrari does not resemble
the other loc 1 species or
subspecies of limpets. he characteristics persist from
e urly youth into the adult specimens 1th the exception of the
small hite dots on the exterior. s the shell becomes older
the rhite dots disappe r progressively, co encin t the apex ,
until i n the old adult they have tot ly disappe red , or at
the best, remain s narro rgin.
The constancy of cmaea scutum oribrari , in such
variable company, is exceedingly refreshing and , to some
degree, restores one's faith in a reasonably well ordered
Nature .
II .
Description
34
Aomaea limatula Carpenter, 1866
American journal of Concholo~!• 2:340. Tryon and
Pilsbry, anual of Conchology,:14; Pl. 3, figs. 38-40.
xtus sculptura normali; seu intensiore, lirulis qui
busdam majoribus, valde nodosis; intus albida, nitida;
limbo lato nigro, seu rarious tessellate; spectro saepius
fusoo maculato. (Carpenter.)
Outer layer of the shell black, covered with an olive
green , or sometimes li ht bluish, epidermis; inside border
black; a deep brown central spot. (Tryon and ilsbry,
anual of Conchology.)
Type in? Type locality, San edro, California.
an e. Crescent City , California , to Cerros and
ocorro Islands.
Described as cmaea scabra limatula.
1
cmaea limatula Carpenter , (PLATE XII) , is one of the
most common of the local species . It is found all alon the
coast where there are rocks, and occasional specimens are
found on pilings . It is usually confined to a narrow space
about the mid-tide line. Acmaea limatula is decidedly var
iable within the species but locally it does not intergr de
ith any other species, or subspecies, sufficiently to make
identification difficult.
The shell varies a great deal as to the height of apex,
some specimens of the same size being twice as elevated as
1
Ida Shepard, Oldroyd, The arine Shells of the Vest
Coast of orth America, Vol. II, Part III (Stanford
University, California: Stanford University Press, 192?),
pp . 152-153.
35
others. The ones with the lower apex seem to be found on
shores lined with "nig er-head" boulders. These shells become
incrusted so that the characteristic rough, file-like
appearance is totally obscured or can be detected only around
the margin . he most striking variation is the somewhat rare
pale limatula. This shell is exactly the same as the dark
limatula except that it is almost albino in appearance having
a pale tannish- yellow, or nearly white color. he pale
specimens do not seem to be caused by conditions of station
or of food as they are found in the same places where the
darker variety is groin. It is not impossible that they
appear in accordance 11th the endelian law of heredity . The
five specimens on the left-hand side of PL TE II are the pale
limatulas hile the five specimens on the right-hand side are
the dark limatulas. They differ more markedly in color than
is apparent in the plate.
III. Aomaea persona strigillata Carpenter
Description
Acmaea persona strigillata Carpenter, 1866
Supplementary Report , British Association ror the
Advancement of Science , 1863, 618.
A. testa A• mesoleucae simili, sed minore, haud viridi;
striolis mini is, confertissimis, plerumque erosis
tenuissime sculpta; albida, strigis olivaceo-fuscis,
plerumque radiantibus, interdum oonfluentibus piota;
apice saepius nigro; intus albida, margine satis lato,
strigis tessellate. Long., 9; lat., ?4; alt., 3 poll.
(Carpenter.)
The shell is ovate, a little wider behind, elevated;
apex at the front fourth of the length. Young with
excessively fine close radiating striae crossed by
growth-lines, largely worn off in adult specimens. Apex
very acute in young, eroded, dark brown and polished in
old shells. Coloration: Marked with irregular, forking
black stripes on a white ground, interspersed around the
apex when not eroded, with dots and small narrow or
needle-shaped white streaks. Inside bluish-white, with
the central area indistinctly irregularly clouded with
brown. Border wide, vividly tessellated with blackish brown. Length, 19; breadth, 14; hei ht,? mm. (Tryon
and Pilsbry , anual of Conchology.}
36
Type in United tates National [Useum. Type locality?
ange. itka, laska, to .a dalena Bay, Lower
California .
This equals_. strigatell Carpenter.
1
Aomaea persona strigillata Carpenter , (PLATES XIII,
XIV, and XV), is a subspecies, which locally, is not readily
confused with any other species or subspecies , but which,
nevertheless, does show great variation within its own group .
An examination of the exterior of large numbers of these shells
will show that they may be divided into three groups; one
predominately striped , one predominately mottled, and one
neither distinctly striped nor mottled. A person examining
the striped form and the mottled form might readily conclude
1
Ida Shepard Oldroyd , The arine Shells of the West
Co st of North America, Vol. II, Part III (Stanford
University, California: Stanford University Press, 192?),
p. 155.
3?
that they ere not closely related. A study of more specimens,
however, will prove that these two forms may be readily con
nected by intermediate forms . PLATE XIII shows, in the left
hand row, an age series of striped shells and , in the right hand row, an age series of ottled shells . These two
extremes are connected by the cross row. PL E XIV shows an
interior view of the same specimens appearin in PLATE XIII .
It 111 be noticed that the striped shells have a tessell ted
border hile the mottled shells have a soli borer. The
connecting shells hoJ e er tessellations as the tripin s
disappear . ·
A pee liar o of what is in reality Acmaea persona
strigillata (P TE V) is occasionally found . his form has
a 11 ht, pale shell w ich is ore or less translucent. The
shell is not stron like the typical strigillatas but is thin
and sees fragile. Often the stripings are not present and
some specimens are almost totally free fro any markings .
Intermediate specimens readily constitute a series connecting
this attenuated form with the typical strigillatas. Other wise , one would be certain they ere unrelated. The left
hand shell in PLATE X:V is a normal strigillata. The next
three specimens are transition or intermediate shells,
connecting the normal form with the attenuated form. Just
what conditions produce this weak form 1s not known.
Because of the general appearance of the perfect series
running into the typical form , one is tempted to hazard the
opinion that this variation may be nutritional in nature.
Nothing that I have seen would either substantiate or
contradict this gratuitous opinion. It is a matter to be
determined only after considerable study.
38
CHAPTER VI
sm RY OF !'INDINGS AND CONCLUSIONS
The great range of variations sho 1n in this thesis to
exist in the ten species and subspecies of omaeas studied
explains why these shells have been so perplexing to the con
ohologist who wished to identify them. The followin are the
conclusions reached:
1. The rudimentary form of cmaea cassis pelta,
cmaea cassis olympica, and _cmaea cas is naoelloides seems
to be cmaea cassis naoelloides. The young of this subspecies,
or young indistinguishable from it, may develop into the
capped for of omaea o ssis pelta, into ___ cassis olympica,
or remain omaea eassis naoelloides. This extreme intermin
gling shows that these three subspecies are really all
variations of the subspecies----~---- ___ pelt and not true
subspecies. It also expl ins why conoholo ists have been so
confused in regard to them. cmaea cassis montioola is not
found in the youn stage at all but is al ays adolescent .
This shell is clearly an irregul r, adolescent Acmaea oassis
Relta ~hich has become decorticated.
2. omaea digitalis and its subspecies, Acmaea
digitalis umbonata and cmaea digitalis textilis, comprise a
group that is very confusing because of the many variations
which occur. The typical specimens of e ch division are
40
quite distinct and present no difficulties in identification.
Unfortunately, the typical speci ens are rather rare, and as
a result, the shell collector 11 find th t nest of his
spec ens are not easily identified.
for identification c nnot be formul ted.
d an f st criteria
e subspecies,
cmaea digitalis igitali textilis, are
purely variations of ________ digitalis and blen so readily
into it, and into ch other, th tone is forced to conclude
t at they e unstable v r1 tions ose ·rrer ntiation is of
little value to the cone ologist .
3 . omaea soutum oribraria arpenter i v ry stable
11 pet ioh does not resemble closely or blen into ny of
the other lac 1 ~pecies or subspeci sot 11 pets .
I
4.
ithin the species but locally it does not intergra e with
any other specie or subspecies surficiently to ake
identification difficult. The most striking vari tion is the
some hat rare pale limatula.
5. omaea person strigillata Carpenter is a sub-
species, hich locally is note sily confused 1th any other
peoies or subspecies, but hich, nevertheless, does show
reat vari ~tion ithin its om roup. An exa ination of the
exterior of 1 rge numbers of these shells will how that they
may be divided into three groups ; one predominantly striped,
one predominantly mottled , and one neither distinctly striped
nor mottled. A person examining the striped form · nd the
mottled form might re· dily conclude tha t they were separate
subspecies. study of more specimens, ho rever, will prove
41
thut these t w o forms may be readily connected by intermediate
forms.
peculi r attenuat ed fo of cmaea persona
strigill ta is occasionally found. This form has a light,
p le shell hich is more or less translucent. The shell is
not strong 11 e the typical trigillatas but 1s thin a nd
sees fragile. 0 t en the stripings are not pre sent and some
specimens re lmost tot lly free fro m ny m r kin s.
Intermediat specimens rea ily constitute a series connecting
t his at tenu te ro rit h the typi al strigillatas.
6. lhile it is pos s ible in each species or subspecies
to choos e typi cal spec unens ich allo no possibility of
doubt s to their proper classification, such specimens are
•
not co on . o single constant ch racteristic has been found
hich may be relied upon s a sure guide, but a thorough
kno ledge of t he general characteristics of the species and
subspecies pplied to a particul r specimen, 11 usually
lead to a certainty, or reasonable certaint y, of correct
identification. ast numbers of shells sho characteristics
of t o or ore groups ich are so blended that it is often
i possible to classify accurately the specimens. 1th such
42
shells it is un,ise to attempt ore than a species classifi
c tion.
7. fter seein the surprising v riations disclosed
in the cmae sunder consider tion, one is immensely fas
cinated by the contempl tion of the causitive factors. De
spite the collectin of many thousands of specimens, I can
dvance no theory or expl n tio hie seems of ny real
merit . The 1 in concholo ist o the ,orl have almost
un nimou l rem ine silent o this tter . r . . 1111
•
Dall o ered the ollo , in his be t thou ht on the
proble :
In studyin these ollus sit is nece s ry to remember
that the ifferent pecies o te ha e n almost identi
cal seri s of color variations, o hat if one is guided
chiefly by color, there is liability to put together
mut tions belon in to different species . here is
little doubt t t food e 1--tly influence and ireotly
ch· es both the color an texture of the outer layers
of the shell , rile the form is directly related to the
situs o the individual.
1
The proving, or disprovin , of Dr . all's theory, offers
itself as a difficult problem Qnd as a real challenge to any
student of zoology interested in the field of ecology.
1
omaeas . '
illiam H. Dall, 'Notes on some northffest coast
The autilus, XXVIII (June, l 14), P• 15.
BIBLIOG PHY
BIBLIOGRAPHY
rnold , ugusta Foote , The Sea-Beach at Ebb- Tide . New York :
The Century Co., 1903. 490 pp .
Carpenter, Philip P . , " eport on the present state of our
knowledge with egard to the ollusca of the est Coast
of North America . " Report of the Twenty- Sixth ·!eating of
the British ssociation for the Advancement of Science ,
1856 , pp . 159- 368.
A swnmation of all knowledge at that tie concerning
mollusks of the west coast of orth America .
Carpenter, Philip P., "Supplementary Re ort on the Present
State of our Kno ledge 1th regard to the ollusca of
the est Coast of orth unerica. " Report of the Thirty Third eeting o the British ssociation or the
dvanoement of Science, 1863 , pp . l? - 686 .
This re port supplements the one of 18 6 . A reprint
appe sin volume ten , of the S ithsonian iscellaneou
Collections, Smithsonian Institution .
Carpenter, Philip . , "On the cmaei ae of the ancouver and
California province . ' American Journal of Cone ology ,
Vol . II , o . I , of the Conchological ection of the
[Philadelphia] cademy of atural Sciences , 1866 , pp .
332- 348.
hi article consolidates the previous reports of 1856
and 1863 , and in addition , includes all other available
information on the cmaeidae .
Dall , • H., "On the limpets; with special reference to the
species of the west coast of America , and to a more
natural classification of the group . " American Journal
of Conchology , Vol . VI , Part III , of the Concholog i cal
Section of the CPhiladelphi ,:il Academy of Natural
Sciences , 18?1 , pp . 227- 282 .
Includes a classification of the limpets based on the
dentition .
Dall , dilliam H., " ates on some northwest coast Acmaeas . '
The Nautilus , XXVIII {June , 1914) , 13-15 .
monthly journal devoted to the interests of conchol o-
45
gists. Gives Dall's exceptions to the classification of
the · omaeidae in Carpenter's article of 1866.
Dall, 1111 He ley, Summ ry of the Marine Shellbearing
ollusks of the Northwest Coast of ~eric, from an
Diego, California, to the Polar Sea, mostlr contained in
the collection of the United tate tional useum, 1th
illustrations of hitherto unfigured species. United
States ation l useum, o. 112. Washington: Government
Printing Office, l 21. 217 pp.
annot te ct lo ue of t e arine ellbe rin
ollusk o th north ·est co st o erioa.
Flatt ly,
e Yor:
1th an introduction by J. A thur ho on.
He phill, en y,
.. c demy of
pp . 87-88.
lett r. ' rooeedings o the
hiladelphia for 1881,
Johnson, yrtle lizabeth, and noo, Harry James, ea-Shor~
Anim ls of the Pacific Coat . e York: The ac illan
Company, 192?. 659 pp .
Keep , Josiah, et erican hells. San Francisco: The
lhitaker & Ray Company, 1904. 360 PP•
description in r niliar ter s of the principal marine,
fresh ater, and land mollusks of the United States found
est of the ocky ountains as ell as ose of British
olum.bia and laska. lso a classified reference list of
the species and varieties known to exist within the
above limits. Fully illustrated.
Keep , Josiah, est Co st Shells. Revised edition; San
Francisco: The tThitaker & Ray- iggin Company, 1911.
346 PP•
A desc iption of the principal marine mollusks living
on the west coast of the United States , and of the land
shells of the adjacent r~ion. Also a chapter on the
fresh rater mollusks of the Pacific Slope by Harold
Hannibal. Fully illustrated .
endes da Costa , Emanuel , Elements of Conchologz. London :
Printed for Benjamin mite , 1776 . 318 pp .
orrison , • L., _ study of molluscs found at Mission Bay,
an Diego , California ; their classifi cation and special
attention to their distribution. Unpublished aster' s
thesis , University of Southern California , Los Ang el es,
Cali~ornia , 1930 . 94 pp .
ewbigin , Marion , Life~ The Seashore . evised edition;
London: George llen , 1931. 296 PP•
Oldroyd , I da Shep rd , The arine hells of the est Coast
46
of North America. Vol . II , Part III . Stanford University ,
California : Stanford Unive sity Press, 1927 . 339 pp .
An invaluable book for t he conchologist . A description
with type and range is g iven for each species, and m ny
of the species are in addition figured . Contains a
bibliography .
Packard, E . L., h
1
Iolluscan Fauna from San rancisco Bay.
University of California publication in Zoology, Vol . XIV,
No . II . Berkeley: University of California Press , 1918 .
253 pp .
An excellent study which is edited by illiam Emerson
Ritter and Charles Atwoo d Kofoid .
Pycraft, • P . , The Sea- Shore . New York: The iacmillan
Company , 1920 . 156 pp .
Reeve, Lovell ugustus , Conchologia Icanica . Vol. VIII ,
Conohologia Ioonica , Lovell Reeve, editor, 20 vols . ;
London : Lovell eeve , 1843- 1878.
This monumental ork contains descriptions of species and
is magnificently illustrated in color, by G. B. Sowerby,
.Tun .
Rogers , .Tulia Ellen , The Shell Book. The ature Library ,
Vol . IV, Part II . New York : Doubleday , Page & Company ,
1914. 485 pp .
A popular guide to a knowledge of the families of the
living mollusks , and an aid to the identification of
shells, native and foreign . Illustrated by 8 plates in
47
colour and 96 in black and hite, mostly from photo
graphs by A. R. Dugmore.
ussell, F. s., and Yonge, c. M., The Seas. Lon on: Frederick
arne & Co. Ltd., 1928. 379 pp.
Sowerby, George Brettingha , Popular British Cone ology.
Lon on: Lovell Reeve, 1854. 304 pp.
fru iliar history of the molluscs inh biting the
British Isles. Colored illustrations.
Strong , •• , and na, G •• , rine ollusc of
Gu lupe Isl nd,
fornia cad y of
1930}, PP• 1-6.
1 exico. Prooeedin~s of t e C 11-
ciences, Fourt Series . X (June,
Strong , • . • , nd Hann , G.D., arine .ollusca of the
Revillagigedo Isl nds, exioo. Prooe dings o the
C li orni .ca emy of Sciences, Fourt Series . I
(June, 1930), pp. ?-12.
Strong , •• , and Hanna , G. D., arine
aria Islands, exico.' Proceedings
cademy of cienoes, ourt eries.
pp. 13-2.
olluso of the Tres
of the C li ornia
( June, 1 30 } ,
Tr on , Gear e ~ . jr., and Pil bry, Henry ., 'ono r phs
oft e cmaeidae, Lepetidae, P tellid e an Titisc n
iid e. anual of Conohology, 1st series, Vol. III,
of the Cone olo ic 1 Section , [:Philadelphi ~ Academy
of atural ociences, 1891, pp. 5-195.
The material studied in cmaeidae is exceptionally
extensive. A large number of previously unfigured
forms a e figured. o effort was spared to make the
synonomy and re erences complete nd reliable .
....
LA
49
E I
•
p ~
sch c oltz
•
}S I S
•
B.
c.
I
schscholtz (X 2/3)
To ie
Side view
Inside view
PLATE I
A
B
50
L E II
C C IS L schscholtz
•
C
II
.. SI P LT schscholtz ( 2/)
•
•
•
Top ie
Si e view
Inside view
PL TE I\
A
B
C
I
( 2/3)
•
•
I e
PL TEIII
•
B
C
C C
•
•
•
I
C LLOI E al ( 2/)
o 1
de 1
Insid
PL TE IV
---~----------~
A
B
C
PL
• op
B. i e
Cr n r { 2/3)
•
nsid vi
PLATE V
A
B
C
1.
2.
3.
C
C
•
B.
VI
ubspecies o
oltz ( 2/3)
op vie
i vie
C. Insi vie
C
C
IS L ~ ohso oltz
IC
I .10 I 0
11
11
ar en er
PLATE VI
111
l
2.
A
1
2, J
B
,.
♦
C
I L
•
•
•
0
1
n
I
C S O Z ( 2/ )
ie
ie
PLATE VII
A
B
C
I s
•
•
•
0
1
Ins
III
V
V ( / )

I
•
B.
•
ILI
op vie
Side vi
Insid
uld (X 2/3)
PLATE I
B
C
0
C z 2/)
•
0
•
•
1
PLATE X
B
C
C
L
I
•
0 i
• 1 e vi
• In 1
I
t
( /3}
PLATE XI
A
B
C
C p n e ( 2/
•
B •
• I s1 1
PLATE XII
A
B
C
I
( p ie• )
•
i d
•
•
0 0
A
A
C
{ n
)
•
•
0
•
0
A

•
•
•
GIL
ie
1
pent
1
P L ATE xv
C
I
LOC !TIES OF P OTOG HED HELLS
In all the plates, the horizont 1 ro are numbered
ro left tori ht; th v rtic 1 ro ro top to bottom .
L T I
11 ro
• • • • • • • • • • • • •
umber l
ro t
2 1
1
th o a
. Ply
in 1
e
i
e i
0 itt
•
I
I lJ
1, 2
• • • • • • • • • • • • • • • •
I • • • • • • • • • • • • • • • •
1 ot e
• • •
'
0
C
l, 4 , ? , 10 , l • •
11 others ••••
• • • • • • • • •
' a , n 1 0
sid 1 •
C IS
III
I
• • • • • • • • •
• • • • • • • • •
0 0 0 z
1 1 r
ier, ind-
venue,
0 io
p 1 1
all
anta onioa
unset Pier,
e ice
Pier
vie
ier
enice
Number 17 of the top nd inside vies is o itted
fro the side vi •
PLATE IV
.
C C IS CELLOIDES Dall
11 from
• • • • • • • • • • • • • •
unset Pier, Venice
Numbers 5 and 11 of the top and inside views are
omitted from the side vie r.
66
PLATE V
C EA CASSIS ONTICOLA Carpenter
2, 3 ••••••••••••••••• Santa ·onioa Pier
6, 11 •••••••••••••••• Sunset Pier, Venioe
All others •••••••••••••• Playa del Rey Pier
1,
3-
6,
?
P TE I
Composite or subspecies or AC C SSIS schscholtz
2, 11, 13, 14
•
'
12
• • • • •
8-10
• • • • •
• • • • • • • •
• • •
•
• •
• • •
• • •
• • •
• • •
• • •
• • •
IGI L
•
•
•
•
••• Playa del ey Pier
••• Amussnent Pier, in -
ard venue, Venice
••• Sunset Pier, Venioe
••• ant onica Pier
VII
schsoholtz
1-3, , 7 , 12-1 • • • • • • • • • • Plays del Rey Pier
a,
10
• • • • • • • • • • • • • • • • • • us ent Pie , ind
r venu, Venice
••••••••••••••••• Lio Pier, Oo n Park
•••••••••••••••••• Boa all at oot or
ashingto venue,
enioe
11 • • • • • • • • • • • • • • . • • • u e ent Pier, ind
ard venue, enice
1-3, 6, 7, 9-15
4 • • • • • • •
5 I 8 • • • • • •
T III
IGIT I Reeve
••••••••••• Lick Pier, Ooean Park
••••••••••• Santa 'onioa Pier
• • • • • • • • • • • usement Pier, uind
ard Avenue, Venice
PLATE IX
c ... ,.. ........ A IGIT... I TEXTILI Gould
1
• • • • • • • • • • • • • • • • • •
Amusement Pier, nd
ward Avenue, Venice
2-6, 16 ••••••••••••••• Sunset Pier, Venice
7, 8, 11-13 • • • • • • • • • • • • • Newport Beach Pier
67
9, 10, 14, 15 •••••••••••• Liok Pier, Ooean Park
1 • •
2, 3
4, 5
PLATE X
bnormal forms of Caui&~~ DIGITALIS Esohsoholtz
•••••••••••••••• Balboa jetty
• • • • • • • • • • • • • • • • unset Pi er, Veni oe
• • • • • . • • • • • • • • • • u ement Pier, ind-
ward venue, Venice
6 •••••••••••••••••• Board all at toot ot
ashingto venue,
enioe
7-10, 13, 14 •••••••••••• anta onica ier
11, 12 ••••••••••••••• Liok ier, Ocean P rk
L XI
UTUl RIB
11 rrom
• • • • • • • • • • • • • •
C rpenter
laya de y 1 r
5 • • •
• • • •
11 ot rs
• •
C
•
1, 2, 5, 13
19-23
• •
11 others
1 te II
C LI Cr en er
. ...•...... t. e 1n
••••••••••• Jetty by o r pl nt
at el Beao
LA XIII
p
0 T IGILL C rpenter
• • • • • • • • • •
Playa del Rey Pier
• • • • • • • • • • •
Amusem nt Pier, ind-
ard venue, enioe
• • • • • • • • • • •
anta onioa Pier
B. 1 . . . . . .
• • • • • • • •
• Seal Beaoh Pier
11 others ••
• • • • • • • •
• Liok Pier, Ocean Park
c. All from.
• • • • • • • • • •
• Newport Beach Pier
•
•
c.
1. 2. 5, 13
19-23 • • •
11 others •
68
PLATE XIV
T IGILL T Carpenter
•••••••••• Playa del ey ier
• • • • • • • • • • u ement Pier• lind
ard venue, enice
• • • • • • • • • • anta ·onio r
1
1
• • • • • • • •
••••••• e 1 Beaoh Pi
••••••• Lio Pier. Oo oth r
• • • •
1 0
• • • • • • • • • • • •
0 eao
n P rk
1 r
C r t r
1-, 17. 8 • •
• • • • • • • • • • •
in -
• • • • • • • • • • • •
•
, Oo

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Asset Metadata

Creator Whedon, Edwin Frederick (author)

Core Title Some variations in the molluscan genus Acmaea

School Department of Zoology

Degree Master of Arts

Degree Conferral Date 1935-06

Publication Date 02/01/1935

Defense Date 02/01/1935

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag OAI-PMH Harvest

Format theses (aat)

Language English

Contributor Digitized in 2022 (provenance)

Permanent Link (DOI) https://doi.org/10.25549/usctheses-oUC112723838

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Document Type Thesis

Format theses (aat)

Rights Whedon, Edwin Frederick

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