A study of the Eastern Pacific representatives of the genus Callianassa (Crustacea, Decapoda, Callianassidae)

The present study was conceived while research was under way on the western Atlantic species of the genus Callianassa, commonly known as ghost shrimp or burrowing shrimp. The collection of the Smithsonian Museum of Natural History was found to contain a sizeable amount of callianassid material collected by the Allan Hancock Pacific Expeditions, primarily during the 1930's. With the completion of the study of the Atlantic species, the Pacific material was made available to me. Preliminary examination showed that a relatively large number of species were involved and that many of these were new or the records provided major extensions of the existing species' ranges. Perhaps more important was the discovery that at least half a dozen of the species were very closely related to or identical with western Atlantic species. While this situation was not unexpected because of research on other decapod groups, there had been only one previous publication dealing in a way with thalassinidean relationships in these two faunal areas (Chase, 1962). Furthermore, no comprehensive study of the eastern Pacific representatives of Calianassa had ever been made. After supplementing the Hancock material with specimens from other sources, additional taxonomic problems came to light, an it was obvious that a review of all the callianassid species from the eastern Pacific would be desirable. At the beginning of the study, a total of fourteen species had been described, and of this number, only nine could actually be identified. Records for all species other than the three from the coast of the United States were few in number and often scattered throughout the literature. This points to one of the major problems in working with this group of animals. The number of specimens is rarely great enough from within a single geographic area to provide a knowledge of the full range of character variation, and descriptions of species have often been based on less than half a dozen specimens. De Man noted in 1928 that of the 76 species of Callianassa then known, 46 had not been found since their original description. While the percentage has certainly decreased, I would still estimate that about half of the more than 120 species described are known from a single record, and that number would increase substantially if species with only two or three records were considered. The prolonged period between collection of some species explains in part my willingness to complete this study despite the lack of material on which to base decisions concerning the status of several of the species....