Table Of ContentTAXONOMY AND DISTRIBUTION OF THE ANOMALOUS
"STRAIGHT-LINE" PAGURIDS (CRUSTACEA)
OF THE EASTERN PACIFIC
A Thesis
Presented to
the Faculty of the Department of Zoology
The University of Southern California
In Partial Fulfillment
of the Requirements for the Degree
Master of Science
by
Bryce C. Walton
August 1950
UMI Number: EP67197
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2. ' n oj
This thesis, written by
....BRYGE„C...W^Tg.N..................
under the guidance of his.... Faculty Committee,
and approved by all its members, has been
presented to and accepted by the Council on
Graduate Study and Research in partial fulfill
ment of the requirements for the degree of
MASTER OF SCIENCE
AUG 1950
Date.
Faculty Committee
Chairman
TABLE OF CONTENTS
Page
Introduction ............... 1
Acknowledgements..................... 4
General Objective ................................ 5
Specific Objectives.............................. 5
Definition of Terms . • ......................... 7
Status of Sub-families............................ 9
Systematic Section ............................ 14
Conclusions on Distribution ..................... 71
Summary.......................................... 75
Literature Cited ................................ 76
Charts • ...................................... 82
Plates 91
INTRODUCTION
Within the family Paguridae, the so-called "Hermit
Crabs," there is a small group which differs from the rest
of the family in the possession of an uncoiled abdomen, and,
in most cases, a symmetrically developed tail fan, although
the abdominal appendages are completely suppressed on the
right side.
The collections of the Allan Hancock Foundation at
the University of Southern California include the greatest
aggregation of Pacific straight-line pagurids available in
any one place. These collections from the Eastern Pacific
between Oregon and Ecuador, made in the period from 1931 to
date, are the basis for the present study. A total of over
600 specimens from this anomalous group were examined.
In the majority of the pagurids the abdomen is strongly
coiled to the right, an arrangement which admirably adapts
them for life in the cast-off shells of gastropods, which, as
a rule, are dextrally coiled. This asymmetry has a strong
hereditary basis and persists in forms which do not live In
spiral shells, such as Troglopagurus which lives in holes
In coral, and in the common California species, Paguristes
bakeri, which often is found in sponges. Milne-ldwards and
Bouvier (1893) report that the dextral coiling also persists
in those rare abnormal individuals that adapt themselves to
2
a sinistral shell. Another indication that this coiling is
more than superficial is given in the results of a behavior
study (McKay 1945) in which Calcinus herbsti de Man was
shown to turn predominately to the left when placed in a f,Ttf
shaped tunnel, as would be expected from animals that are
spirallj/ constructed.
Alcock (1905) believes that the straight-line pagurids
are derived from coiled forms and that their symmetry is
secondarily acquired and superficial as ^proved by the fact
that the posterior abdominal appendages .... exist only on
the left side.* However, if the possibility is considered
that unilateral development of abdominal appendages is not
necessarily a secondary result of coiling of the abdomen,
but to be regarded as a separate phenomenon, part of this
straight-line group might prove to be useful in determining
the more immediate steps in the phylogenetic development of
the Paguridae from the supposed pylochelid ancestors. It is
quite possible that a detailed study of this group might dis
close that some of them stem, not from asymmetrical forebears,
but directly from the Pylochelidae. This family, which is
paguroid in general form, resembles the Macrura in the
possession of well formed and calcified abdominal terga and
in the bilateral development of the abdominal appendages
although the pleura have been lost as in the Paguridae.
The postulation of a stage in which reduction of
3
the terga, and unilateral suppression of abdominal appendages
has occurred, but in which the abdomen remains primitively
uncoiled, would fill a rather large gap now existing in the
very gradual intergradation between forms having macruran
characters and the Brachyura, or true crabs, Several of
these straight-line forms seemingly agree with this postu
lated phylogenetic stage.
The pagurids which possess this anomalous uncoiled
abdomen fall into seven genera, all quite small:
Cancellus Milne-Edwards 1836
Paguropsis Henderson 1888
Tylaspis Henderson 1888
Pylopagurus Milne-Edwards & Bouvier 1893
Xylopagurus Milne-Edwards 1880
Ostraconotus Milne-Edwards 1880
Orthopagurus Stevens 1927
Of these, Paguropsis, Tylaspis. and Ostraconotus are
monotypic and none have been reported from the Pacific Ocean,
From the Eastern Pacific there have been reported to
date, only a single specimen of Cancellus, nine species of
Pylopagurus, two species of Orthopagurus, and one species of
Xylopagurus,
ACKHOWIiEDGEMERTS
The writer wishes to express his appreciation to
Captain Allan Hancock and the Director of Research of the
Allan, Hancock Foundation for the great privilege of using
the collections and facilities of the Foundation for this
study, and to Dr. John S. Garth for his guidance and for
assistance in preparing this manuscript.
(4)
GENERAL OBJECTIVE
The knowledge of any group of animals is usually
founded upon taxonomic studies which establish morphological
boundaries for genera and species, and make possible the
identification of the animals for further, more detailed
studies, such as of the physiology, development, and ecology
of the group. The general purpose of this paper is to thus
lay the groundwork for a greater understanding of these
anomalous pagurids; to facilitate their accurate identifica
tion; and to report fully their occurrence off the Pacific
coast.
SPECIFIC OBJECTIVES
I. The description of new forms.— The extensive
nature of the Hancock collections in areas never before
thoroughly collected has resulted in the discovery and de
scription of one species and one sub-species.
II. The redescriptioh of all Pacific species. — The
original descriptions were written by no less than eight
different authors, some of them many years ago. Consequently,
there is no uniformity of either style or characters describ
ed, which makes the identification of similar species very
(5)
6
difficult. To insure the description of all significant
characters, and a parallel style, which would facilitate
comparison of characters, the following outline for specific
descriptions was developed:
1. Ghelipeds
a. Major cheliped
(1) merus
(2) carpus
(3) manus
2. Carapace
a, Precervical portion
b. Postcervical portion
3. Eyes
a. Stalk
b. Cornea
c. Scales
4. Antennae
a. Acicle
b. Peduncle
c. Elagellum
5. Antennuies
a. Peduncle
b. Flagellum
6. Pereiopods
a. Ambulatory legs
(1) merus
(2) carpus
(3) propodus
(4) dactylus
b. Fourth and fifth legs
7. Abdomen
a. Appendages
b. Terga
8. Tail fan
a. Telson
b, Uropods
III. The discovery of new specific characters. — On
