New Pleurotomariid Gastropods from the Western Atlantic, with A

BULLETIN OF MARINE SCIENCE VOLUME 15 1965 NUMBER 4 NE\V PLEUROTOlVIARIID GASTROPODS FROM THE \VESTERN ATLANTIC, vVITH A SUMMARY OF THE RECENT SPECIES' FREDERICK M. BAYER ImtitU/e of Marine Science, University of Miami ABSTRACT Three new species of pleurotomariid gastropods from the Western Atlantic, Perotrochus midas, P. lucaya, and P. gemma, are described and figured. All previously known Recent species of the family are reviewed briefly and illustrated. The type specimens of Perotrochus quoyanus, P. teramachii, and Entemnotrochus rumphii are figured. The generic groups are discussed and defined. INTRODUCTION Owing to their long geological history and comparatively recent discovery in the living state, their striking appearance, and their general rarity, perhaps no mollusks have attracted more concentrated interest on the part of both scientists and laymen than have the pleurotomarians. The surviving family, Pleurotomariidae, extends back in geological time to the beginning of the Mesozoic, and related extinct families carry the line back to the Cambrian. The discovery, in 1856, of the first living representative of a predominantly Paleozoic family naturally excited much interest. During the ensuing 48 years, five more species were discovered, three in Japan, one in the East Indies, and another in the West Indies. For many years, each new specimen elicited individual attention. Bouvier & Fischer (1899) reviewed all the reported examples of the four species known up to that time. After the publication of Pleurotomaria hirasei by Pilsbry in 1903, no further new species of pleurotomarians were discovered for 45 years, tending to corroborate the idea, supported by Lindholm (1927), that the survivors of this once numerous group are few in number of species and rare in individuals, indicating the approach of total extinction. Then, in 1948, Tomlin announced the discovery of a seventh species, in South African waters far from all previously known habitats of living pleurotomarians. This was followed, in 1955, by Kuroda's report of a new species IContribution No. 651 from the Institute of Marine Science, University of Miami. This paper is one of a series resulting from the National Geographic Society-University of Miami Deep-Sea Biology Program. Some of the material reported herein was obtained during deep-water ope rat ions of R IV G ERDA supported by grant G B-1204 from the National Science Foundation. 738 Bulletin of Marine Science \15(4) from Japan, Perotrochus teramachii, the indications by Kira (1961) and Habe (1962) of still another species (misidentified as P. teramachii) from Japan, and the description of Mikadotrochus schmalzi by Shikama (1961). The number of described West Indian species remained unchanged, however, for nearly 100 years. Then, on June 21, 1963, the research vessel GERDA,of the Institute of Marine Science, University of Miami, while trawling off Sombrero Light in the Florida Keys, obtained a handsome pleurotomariid which at first glance was thought to be Perotrochus quoyanus because of its comparatively small size and shallow slit. Examination in the laboratory immediately revealed that it was not P. quoyanus as originally believed. Comparison with specimens of the various species in the collections of the U.S. National Museum confirmed that it represented an undescribed species, which subsequently was described under the name Mikadotroehus amabilis (Bayer, 1963), the third pleurotomarian species known from the Western Atlantic Ocean. Continued operations of R/V GERDA failed to reveal any further pleurotomarian material until March 1965, when a haul off Grand Bahama Island produced two large fragments of Entemnotrochus adansonianus (Crosse & Fischer). On the assumption that such fragments indicated the presence of a living population nearby, intensive exploration of the area was planned for the first opportunity. This came in July 1965, when R/V GERDAduring cruise G-6528 worked northward in the Straits of Florida to approximately 27°30'N., then around the northwestern extremity of Little Bahama Bank, and finally into Northwest Providence Channel. Dredging and trawling was undertaken in the general area where fragments of adansonianus had been found in March. During three days of operation (July 20, 21 and 22), three species of pleurotomarians were obtained, two of them new, constituting one of the most important biological finds made aboard the GERDA. In the course of reviewing pleurotomarian material for this report, a number of museum specimens from Western Atlantic localities were examined, among them two Perotrochus from Barbados, loaned by the Academy of Natural Sciences of Philadelphia, through the kindness of Dr. R. Tucker Abbott. These proved to be different from the type of Perotrochus quoyanus and from the specimens trawled by R/V GERDA, and are here treated as a third new species. Accordingly, six pleurotomarian species are now known to occur in the Western Atlantic. ACKNOWLEDGMENTS The specimens that stimulated the preparation of this paper were obtained during deep-water biological operations co nd u cte d aboard R/V GERDAof the Institute of Marine Science, University of Miami. To Captain William Dickinson and the crew of R/V GERDA, and to the scientific personnel of cruise G-6528, consisting of Martin Roessler (party 1965 J Bayer: Pleurotomariid Gastropods 739 chief), Dr. Donald F. Squires (visiting scientist), Jon C. Staiger, R. H. Chesher, R. J. Livingston, D. G. Smith, and Koesoebiono (biologists), 1 express sincere appreciation for a highly successful cruise. I am no less grateful to Dr. Joseph Rosewater, Curator of Mollusks at the U.S. National Museum, who made available the facilities of his laboratory; to Mr. W. J. Byas, of the U.S. National Museum, who extracted the soft parts of the pleurotomarians for dissection; to Dr. R. Tucker Abbott of the Philadelphia Academy, and to Mr. John Finlay, who made available to me the specimens from Barbados here described as new; to Drs. William J. Clench and Ruth D. Turner of the Museum of Comparative Zoology, who provided specimens and photographs from their collections; to Professor Tokubei Kuroda of Kyoto University, who provided photographs of Entemnotrochus rumphii, Perotrochus teramachii, and Mikadotrochus schmalzi; to Dr. A. W. Janssen of the Natuurhistorisch Museum, Rotterdam, who provided photographs of the type specimen of E. rumphii; and to my colleagues at the Institute of Marine Science who have unfailingly extended to me the benefit of their knowledge and experience. The biological operations of R/V GERDAhave been supported by the National Science Foundation through grant GB-1204 and the research has been supported by the National Geographic Society through a most generous grant for investigations of deep-sea biology. The assistance of both of these agencies is gratefully acknowledged. The publication of the colored figures of Perotrochus midas contained in this paper was made possible by the International Oceanographic Foun- dation through a grant to defray part of the printing costs. Family PLEUROTOMARIIDAESwainson, 1840 As recognized by Knight et al. (1960: 219), this family includes eleven genera, of which three contain Recent species: Entemnotrochus P. Fischer, 1885; Perotrochus P. Fischer, 1885; and Mikadotrochus Lindholm, 1927. The type-genus, Pleurotomaria Defrance, 1826, is extinct, ranging in time from Lower Jurassic to Lower Cretaceous. The differences separating these taxa appear to be of a rather superficial nature and might have been considered less important in any group not subjected to the close scrutiny that the Recent pleurotomariids have attracted. However, it does appear that no species with the nodose sculpture of typical Pleurotomaria has lived since the Lower Cretaceous, and possibly this is adequate justification for treating the Recent forms as generically distinct. SYSTEMATICCHARACTERS The usual conspicuous features of the shells form the chief basis for the separation of pleurotomarian species. Among these are size, shape, depth and location of slit, sculpture, and color, most of which have never been expressed in any really objective manner. A major difficulty, not soon to 740 Bulletin of Marine Science 115(4) be overcome, is the very small number of specimens available for study. No meaningful evaluation of the reliability of morphological characters can be expected until a substantial number of specimens can be obtained. The significance of this problem can be suggested by pointing out that one of the largest collections in the world, that of the United States National Museum, contains only 13 specimens representing 7 species, viz.: adansonianus (1), africanus (I), amabilis (1), beyrichii (1), hirasei (4), quoyanus (4), and salmianus (1). Following the publication of this paper, those numbers will increase by one specimen each of two new species described herein. Only one species of pleurotomarian is well represented in collections, Perotrochus hirasei (Pilsbry) from Japan. The various specimens show minor differences but on the whole are reasonably constant as to size, shape, sculpture and color. Small individuals are clearly recognizable specifically and easily separated from other species living in the same region. The known specimens of P. amabilis, M. beyrichii, E. adansonianus and E. rumphii are similarly consistent but the number of specimens from which to draw conclusions is extremely limited. Size.- The maximum size attained by each species is characteristic, but the value

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