Trapezia and Tetralia Ectoparasites — Knudsen 
57 
makeup of the chief source of food, that is, 
the mucus secreted by the coral animals. In our 
collections at Eniwetok Marine Laboratory we 
isolated a large number of corals by species and 
carefully separated the parasitic and commensal 
crabs found therein. The identification of these 
animals may well reveal a more definite species - 
| to-species relationship between crabs and corals. 
These data and others will be recorded in an- 
other paper, along with additional experimenta- 
tion to be conducted at the Eniwetok Marine 
Biological Laboratory. 
CONCLUSIONS 
The literature, our field collections, and field 
experimentation confirmed that an obligate host 
specificity exists between the crab genus Trapezia 
and Pocilloporidae corals, and between the crab 
genus Tetralia and Acroporidae corals. Further- 
more, these crabs require living corals as a 
source of food, in addition to protection, and 
should be recognized as obligate ectoparasites 
of their respective host corals. There may be a 
relationship between the food brush and comb 
size and the apparent ability of the two coral 
families to secrete mucus which governs the host 
preference displayed by Trapezia and Tetralia. 
ACKNOWLEDGMENTS 
The writer is indebted to the National Sci- 
ence Foundation and to Dr. Robert Hiatt, 
Director of the Eniwetok Marine Biological 
Laboratory, sponsored by the Atomic Energy 
Commission, for support and assistance ; to 
Dr. John S. Garth, who worked long hours to 
help review and identify Eniwetok crab speci- 
mens; and to my students, Jack Shannon and 
Dave Pearson, who diligently aided in our field 
research. 
REFERENCES 
Borradaile, L. A. 1903. Marine Crustaceans. 
III. The Xanthidae and some other crabs. 
In: J. Stanley Gardiner, The Fauna and 
Geography of the Maidive and Laccadive 
Archipelagoes 1 (3) :237-271. 
Crane, J. 1947. Eastern Pacific Expeditions of 
the New York Zoological Society. XXXVIII. 
Intertidal brachygnathous crabs from the west 
coast of tropical America, with special refer- 
ence to ecology. Zoologica N. Y. 32(2) : 69— 
96. 
Garth, J. S. 1964. The Crustacea Decapoda 
(Brachyura and Anomura) of Eniwetok 
Atoll, Marshall Islands, with special refer- 
ence to the obligate commensals of branching 
corals. Micronesica 1 (1-2) : 137-144. 
Gerlach, S. A. 1961. The Tropical Coral Reef 
as a Biotope. Atoll Research Bull., Pt. 80, 
PP . 1-6. 
Miyake, S. 1939. Notes on Crustacea Brachy- 
ura collected by Professor Teiso Esaki’s 
Micronesia Expeditions of 1937-1938, to- 
gether with a check list of Micronesian 
Brachyura. Rec. Oceanogr. Work Japan 
10(2) :l68-247. 
