The Cyclostremellidae, a New Family of Prosobranch Mollusks! Donald R

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THE CYCLOSTREMELLIDAE, A NEW FAMILY OF PROSOBRANCH MOLLUSKS! DONALD R. MOORE Institute of Marine Science, University of Miami

ABSTRACT A new family of minute gastropods is described for the genus Cyc/ostremella. The family consists of about three species of marine gastropods found on both coasts of North America. Special characters are a heterostrophic protoconch, planispiral shell, elevated dorsal channel, and paucispiral operculum. Anatomy of the soft parts is as yet unknown.

The genus Cyclostremella Bush, 1897, was erected for a single species of minute gastropod, C. humilis Bush, found off the coast of North Carolina. Bush placed the genus in her new family Vitrinellidae along with Vitrinella, Circulus, and a number of new genera. In 1907, Bartsch described Cyclostremella californica, in 1910, C. dalli, and later, in 1920, C. concordia. The latter was figured in 1927. All three of these species are found on the Pacific coast of the United States. In 1915, Bartsch described two species from South Africa, C. africana and C. farica. These two species are obviously not related to Cyclostremella and must be placed elsewhere. Baker, Hanna, & Strong (1938) revised the species of the genus found in the eastern Pacific. They confused Cyclostremella with Delphinoidea Brown, 1827. However, Delphinoidea is an objective synonym of Skenea Fleming, 1817, and this genus is not closely related to Cyclostremella. Of the 13 species listed by Baker et ai., possibly only two of the species described by Bartsch, C. californica and C. concordia are true Cyclostre- mella. The writer has examined paratypes of C. concordia, and found this species to be very similar to the type species. Pilsbry & Olsson, 1952, included a single species, which they did not see, in the fauna of the Panamic Province. As far as the writer is aware, the only mention of the genus in the fossil record is the description of Delphinoidea coronadoensis Arnold from the Pleistocene of California, and the description of Cyclostromella venezuelana Weisbord from the late Cenozoic of Northern Venezuela. Grant & Gale (1931) have commented on the similarity of C. coronadoensis Arnold to C. californica Bartsch. The writer examined the holotype of Cyclostromella (misspelling for Cyclostremella) venezuelana Weisbord, 1962. It is a larval shell of 1!0 whorls plus about half a postlarval whorl. It is not a Cyclostremella. The writer included the genus in his studies of the family Vitrinellidae in the Western Atlantic. Examination of a series of specimens from the

'Contribution No. 696 from the Institute of Marine Science, University of Miami. 1966] Moore: A New Family of Mollusks 481

4 FIGURES1-5. Shell and operculum of Cyclostremella humilis Bush. 1, Upper view of adult shell showing base of protoconch, X62.5.-2, Lower view of shell showing apex of protoconch in the umbilicus, X62.5.-3, Outer view of operculum, x93.-4, Lateral view of shell, X62.5.-5, Protoconch, oriented 1800 from its position in Figure 4, X125.

Gulf of Mexico soon showed that there were major differences between Cyclostremella and the Vitrinellidae. Since the genus does not fit into any other known family, a new family is hereby erected for Cyclostremella.

Cyclostremellidae, new family Minute gastropods with a transparent planispiral shell, with a heterostrophic protoconch, and a thin chitinous oval paucispiral operculum. Near the suture the whorls are slightly angulated to form a dorsal channel. The outer slope down to the periphery is somewhat flattened, but the base is evenly rounded. A labral sinus is present adjacent to the suture. Anatomical details are as yet unknown. The family contains a single genus, Cyclostremella Bush, 1897. Type species of the genus is C. humilis Bush, 1897, by original designation.

DISCUSSION The heterostrophic protoconch, oval paucispiral operculum, dorsal channel, and labral sinus are all features foreign to the Vitrinellidae. The Tornidae, often confused with the Vitrinellidae, do have a paucispiral operculum, but Jack the other features mentioned above. The writer considers Cyclostremella to be a prosobranch until evidence 482 Bulletin of Marine Science [16(3 )

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95· 90· 85·, 80· FIGURE 6. Distribution of Cyclostremella humilis Bush. The Gulf of Mexico localities are new records. to the contrary can be produced. While the heterostrophic protoconch is usually considered to be an opisthobranch character, it is also charac- teristic of the prosobranch families Architectonicidae and Mathildidae. In addition, some members of the prosobranch families Epitoniidae, Janthinidae, Eulimidae, and Aclididae also have been reported to have a heterostrophic protoconch (Fretter & Graham, 1962). The Archi- tectonicidae have flattened discoidal shells, a heterostrophic protoconch, and oval paucispiral opercula, but do not have an elevated dorsal channel or labral sinus as is found in the Cyc1ostremellidae. Actually, Cyclostremella has a rather primitive appearance. It bears a striking resemblance to some of the Paleozoic and Mesozoic Euomphalacea which also have an elevated dorsal channel and labral sinus. Whether the similarity is artificial or actually shows a close relationship may prove to be an interesting field of investigation. Cyclostremella appears to be confined to the temperate coasts of North America. A single species, C. humilis Bush, is found off North Carolina 1966] Moore: A New Family of Mollusks 483 in about 29 m, in beach drift in the Gulf of Mexico at Cape San BIas, Florida, in 26 m off Panama City, Florida, and in drift at Port Aransas, Tcxas. On the Pacific coast, Bartsch described three species. Of these, C. concordia and C. californica are true Cyclostremella. The type of C. dalli, however, has been found to be a vitrinellid. C. concordia is found on the coast of Washington, and C. californica from San Diego north to Monterey Bay, California. The genus is very poorly known in late Tertiary strata, for it appears to have been reported only from the Pleistocene of California. The small size of the species and possibly the habitat would be contributing factors to our lack of knowledge. Almost nothing is known of the biology of Cyclostremella. However, the presence of a heterostrophic protoconch makes it almost certain that there is a free swimming veliger stage. All the material that the writer has examined was found on siliceous sand in shallow water, mostly where the water was somewhat turbid. Some material collected at low tide at Port Aransas was alive when collected. Thus the known depth range of C. humilis is from the intertidal zone to a depth of 29 m.

ACKNOWLEDGMENTS The writer is deeply grateful to Mrs. Winnie Rice for material collected at Cape San BIas, Florida, and Port Aransas, Texas; to Dr. Harold Rehder for the opportunity to examine the two type specimens of C. humilis, and to Dr. Katherine V. W. Palmer for permission to examine the holotype of "Cyclostromella" venezuelana. Thanks are also extended to the National Science Foundation. The preliminary work was done under NSF grant 0-14521, and the work was completed under NSF grant GB 3104.

SUMARIO CYCLOSTREMELLIDAE, UNA NUEVA FAMILIA DE MOLUSCOS PROSOBRANQUIOS K. J. Bush estableci6 el genero Cyclostremella en 1897 basandose en una sola especie de una pequeno gaster6podo encontrado frente a la costa de North Carolina. Bush coloc6 eI genero en la familia Vitrinellidae. Desde entonces se han descrito varias especies procedentes de la costa occidental de Norte America, Sur Africa y de dep6sitos terciarios recientes de Norte y Sur America. POl' 10 menos doce de las especies descritas no pertenecen a este genero, y tres especies de Norte America parecen ser los unicos representantes vivientes. Un numero de caracteres encontrados en Cyclostremella son foraneos para Vitrinellidae. Ellos son: una protoconcha heterostr6fica, operculo pauciespiral oval, canal dorsal y sinus con labrum. Puesto que ninguna otra familia de gaster6podos tiene esta combinaci6n de caracteres, se establece para este genero una nueva familia: Cyclostremellidae. 484 Bulletin of Marine Science [16(3)

La familia Architectonicidae, tambien tiene una protoconch a hetero- str6fica y operculo pauciespiral, pero carece de canal dorsal y sinus con labrum. Cyclostremella parece que se asemeja a la Enomphalacea del Paleozoico y Mesozoico, pero no se sabe si tienen relaci6n. La anatomfa de las partes blandas y la biologfa de Cyclostremella son desconocidas. Sin embargo, ejemplares de C. humilis han sido recolectados desde la orilla de la playa hasta profundidades de 29 m. El sustrato era arena siHcea y el agua algo turbia.

REFERENCES ARNOLD, R. 1903. The paleontology and stratigraphy of the marine Pliocene and Pleis- tocene of San Pedro, California. Mem. Calif. Acad. Sci., 3: 9-420, pis. 1-37. BAKER, F., G. D. HANNA, AND A. M. STRONG .I938. Some Mollusca of the families Cerithiopsidae, Cerithiidae, and Cyclostrematidae from the Gulf of California and adjacent waters. Proc. Calif. Acad. Sci., 23 (15): 2.17-244, pis. 17-23. BARTSCH, P. 1907. New mollusks of the family Vitrinellidae from the west coast of America. Proc. U. S. nat. Mus., 32 (1520): 167-176, 11 figs. 1910. Descriptions of new mollusks of the family Vitrinellidae from the west coast of America. Proc. U. S. nat. Mus., 39 (1785): 229-234, pis. 39,40. 1915. Report on the Turton collection of South African marine mollusks, with additional notes on other South African shells contained in the United States National Museum. Bull. U. S. nat. Mus., 91: 1-305, pIs. 1-54. 1920. The Caecidae and other marine mollusks from the northwest coast of America. J. Wash. Acad. Sci., 10 (20): 565-572. 1927. New west American marine mollusks. Proc. U. S. nat. Mus., 70 (2660): 1-36, pis. 1-6. BUSH, K. J. 1897. Revision of the marine gastropods referred to Cyclostrema, Adeorbis, Vitrinella, and related genera: with descriptions of some new genera and species belonging to the Atlantic fauna of America. Trans. Conn. Acad. Sci., 10 (3): 97-144, pis. 22, 23. FRETTER, V. AND A. GRAHAM 1962. British prosobranch mollusks. Ray Society, London, XVI + 755 pp. GRANT, U. S. AND H. R. GALE 1931. Pliocene and Pleistocene Mollusca of California. Mem. San Diego Soc. nat. Hist., 1: 1-1036, pis. 1-32. MOORE, D. R. 1964. The family Vitrinellidae in South Florida and the Gulf of Mexico. Ph.D. dissertation, Univ. of Miami, 235 pp., 35 figs. PILSBRY, H. A. AND A. A. OLSSON 1952. Vitrinellidae of the Panamic Province: II. Proc. Acad. nat. Sci. Philadelphia, 104: 35-88, pis. 2-13. WEISBORD, N. E. 1962. Late Cenozoic gastropods from northern Venezuela. Bull. Amer. Paleo., 42 (193): 1-672, pis. 1-48.