SYSTEMATICS, ECOLOGY, AND DISTRIBUTION OF THE MOLLUSKS OF LOS ROQUES, VENEZUELN ROBERT C. WORK Institute of Marine and Atmospheric Sciences, University of Miami ABSTRACT One hundred and twenty-five species of mollusks of the Los Roques Archipelago are treated. The habitat and associated fauna of each molluscan assemblage are discussed. An attempt is made to establish accurate geographic ranges for each species. Notes concerning the feed- ing habits of ten species of gastropods are included, and the egg capsules of three species are illustrated. INTRODUCTION This paper is based upon the mollusks collected in Los Roques Islands, Venezuela, during the month of August 1963, at which time the author took part in an expedition initiated and partially supported by the Fundaci6n Cientifica Los Roques under the supervision of Dr. Guillermo Machado of Caracas. The University Central de Venezuela, Harvard University, and the Institute of Marine and Atmospheric Sciences of the University of Miami participated. The base of operations was located on the south island of Dos Mosquises, where the Fundaci6n Cientifica Los Roques maintains comfortable living quarters and laboratory facilities (see inset, Fig. I). An illustrated, popular narrative of the 1963 Los Roques Expedition has been published by de Sylva (1964). The purpose of this paper goes, hopefully, beyond being a simple check list. Through literature research, personal communication with reliable authorities, and personal experience, an attempt has been made to determine the actual ranges of the species listed and the zoogeographic affinities of the Los Roques Archipelago to other regions. It is hoped that the descriptions of the collecting localities will give some idea of the general ecology of some of the species. In the systematic treatment, additional notes pertinent to the ecology of some of the species are included. Information on the feeding habits is given for some species, and the egg capsules of several species are figured. This list of species is unquestionably far from being complete. However, only through many such incomplete lists compiled by interested investigators will an ultimate composite understanding of the Caribbean fauna become a reality. 1Contribution No. 1050 from the Institute of Marine and Atmospheric Sciences, University of Miami. This research was supported in part by the Office of Naval Research Grant Nonr-(G)- 0031-64 and was submitted to the faculty of the Graduate School of the University of Miami in partial fulfillment of the requirements for the degree of Master of Science. 1969] Work: Mollusks of Los Roques 615 ACKNOWLEDGMENTS Sincere appreciation is extended to the Fundaci6n Cientifica Los Roques for the financial aid, companionship, and able assistance given by its members: especially Dr. Guillermo Machado, Mr. Francisco Nunez, Mr. and Mrs. William H. Phelps, and Mr. Freddy Behrens. The author is particularly grateful to the United States Office of Naval Research for its support through grant Nonr-( G) -0031-64. With great pleasure the author accepted the friendship and cooperation of the following expedition members from the Universidad Central de Venezuela: Dr. Franz Weibezahn, Mr. Francisco Mago Leccia, Miss Tania Cobo, Mr. Otto Infante, Mr. Jose de Gregario, and Miss Elizabeth Izaguirre. The author owes special thanks to the latter for her particular interest in the collection of invertebrates. In addition, thanks are due to many members of the Venezuelan Navy, especially to Captain Noel Sanchez-Gomez, captain of the Navy vessel "HO-1," which transported expedition members to and from Los Roques; and to Lieutenant Leopoldo Salas-Romer, who was the liaison officer with the Venezuelan Navy and who also helped with the collections. Thanks, of course, are extended to the author's two companions from the University of Miami, Dr. Donald P. de Sylva, ichthyologist and chief sci- entist of our team, and Dr. John M. Greene, who was a graduate student in ichthyology at the time of the expedition. Special thanks are due Dr. Gilbert L. Voss of the Institute of Marine and Atmospheric Sciences for having chosen me to be included among the expedition members. Further appreciation goes to Dr. Voss and Dr. Frederick M. Bayer for encourage- ment and guidance while writing this paper. The author is grateful to the following specialists for assistance with identifying some of the non-molluscan fauna: Dr. Frederick M. Bayer for all alcyonarians, with the exception of a few generic field identifications by the author; Dr. Lowell P. Thomas for the greater part of the ophiuroids; Dr. Elisabeth Deichmann for all holothurians, with the exception of the author's field identification of Ludwigothuria mexicana (Ludwig); and Dr. Anthony Provenzano for all pagurids. The author is responsible for the determinations of all of the remaining non-molluscan invertebrates included herein. The following individuals are gratefully acknowledged for specific de- terminations of special groups of mollusks: Drs. Eveline and Ernst Marcus for all opisthobranchs other than Bulla; Mr. Edward T. Laroe for all chitons; and Dr. Gilbert L. Voss and Dr. Richard Young for all cephalo- pods. For the loan of specimens of Astraea and Laevicardium for comparative purposes, appreciation is given to Mrs. Ellen Crovo; Lt. Col. Corrine Ed- wards, U.S.A.P. (Ret.); Mrs. Louise Futch; and Mrs. Adele Emery. 616 Bulletin of Marine Science [19(3) HISTORICAL RESUME This resume includes literature only for the islands and continental shores of the Caribbean proper, with the exception that the entire Yucatan Peninsula is here considered geographically as Caribbean. By the same token, the northern shores of the Greater Antilles are considered to be part of the Caribbean. One may consult the list of references for pertinent literature concerning the Caribbean fauna in the remainder of the Gulf of Mexico, the southeastern United States, the Bahamas, Bermuda, and the Atlantic coast of South America. Among the very early publications concerning Caribbean mollusks are those of Orbigny (1842, 1853) dealing with the fauna of Cuba, and Adams (1845, 1846, 1850) who listed and described many new species of mollusks from Jamaica. Following these, Beau (1858) published a cata- logue of shells from the island of Guadeloupe, and Krebs (1864) and March (1863, 1875, 1876, 1877) published lists of West Indian marine shells, many from the island of S1. Martin. Coomans (1958) has reviewed the work of Krebs and part of that of March and has brought Krebs' nomenclature up to date. Also during the 19th Century, a number of new Caribbean species were described in brief papers by P. Fischer, H. Crosse, and Bernardi, individually and in various coauthorships, mostly published in the Journal de Conchyliologie. In this century Dall & Simpson (1901) published an important systematic work on the mollusks of Puerto Rico. More recently, Warmke & Abbott (l961) have treated Caribbean mollusks based mainly on collections from Puerto Rico. McLean (1951) treated the pelecypods of Puerto Rico and the Virgin Islands. Many of his Puerto Rican records are based on the above mentioned work of Dall & Simpson. From Playa de Vega Baja, Puerto Rico, Arnow et aZ. (1963) listed and gave notes concerning 224 species of mollusks. For the Virgin Islands, Usticke (1959) has published an annotated checklist of shells at S1. Croix, and Weber (1961) has listed the marine shells of Water Island at S1. Thomas. Aguayo & Jaume (1947-1952) compiled a catalogue of Cuban mol- lusks, but unfortunately it was never officially published. Abbott (1958) has treated ecologically and systematically the mollusks of nearby Grand Cayman. For the islands of the lower Caribbean, publications in this century include Schepman's (1915) work on the Netherlands West Indies and Benthem Jutting's (1927) list of mollusks from the island of Cura<;ao. More recently Coomans (1958) has reviewed the gastropods of the Nether- lands West Indies and other Caribbean islands. This is a good reference for the gastropods of Bonaire, Aruba, and Cura<;ao. Rehder (1962) has published a brief but excellent paper on a small collection of mollusks from Los Rogues and nearby La Orchilla. Rodriguez (1959) included 1969] Work: Mollusks of Los Roques 617 information on the ecology of certain mollusks on Margarita Island. Lewis (1960) discussed some of the mollusks of rocky shores at Barbados and (1965) gave an interesting list of benthic mollusks from that island. Less information is availab]e concerning collections of mollusks from the continental Caribbean coast. Fluck (1900, 1901, 1905) published a series of short articles on the shells of the Caribbean coast of Nicaragua. Weisbord (1926) and Jaume (1946) listed mollusks collected from the Yucatan Peninsula. Olsson & McGinty (1958) published an extensive list of mollusks from the Caribbean coast of Panama. This paper included the descriptions of new genera and species. Weisbord's (1962, 1964) publications on the Cenozoic mollusks of northern Venezuela include some species of the Recent horizon, and Flores (1966) has treated the cassidids of northern Venezuela and the Venezuelan islands. Most recently, Hou- brick (1968) treated the mollusks of the Caribbean coast of Costa Rica. The cephalopods of the Caribbean have been described by Adam (1957), Rees (1950), and in papers by Voss (1955, 1956, 1958) for Cuba, the Bahamas, the southwestern Caribbean and numerous individual localities. PHYSICAL SETTING The archipelago of Los Roques is located about 120 kilometers north of the coast of Venezuela. Rough]y, the chain of islands forms a rectangle with an east-west dimension of 36.6 kilometers and a north-south dimension of 24.6 kilometers. The extremes of the boundaries are between 110 44' 45" and 110 58' 36" North latitude and between 660 32' 4" and 660 52' 27" East longitude. The south-central portion is occupied by a very large, shallow lagoonal area with a depth of about 1 to 1.5 meters. It is around this lagoon that the 42 islands, and more than 250 sandbanks and reefs, are situated.