USVI Public Records

Document text

A NEW CAECUM FROM PUERTO RICO AND THE VIRGIN ISLANDS! DONALD R. MOORE University of Miami, Rosenstiel School of Marine and Atmospheric Sciences ABSTRACT A new species of Caecum is described from the Puerto Rico and Virgin Island platform. The new species appears to be confined to this island group in contrast to the wide distribution of most species of the Caecidae. Scan- ning electron microscope photographs illustrate the microsculpture of the new gastropod and of two closely related species, C. imbricatum and C. floridanum. In June ] 96], Raymond B. Manning and I were on St. John, Virgin Is- lands, to collect animals living in Thalassia testudinum, the common marine turtle grass. Before leaving the island, a I-liter bottom sample was taken in a depth of 1.5 m. This location was near the head of the bay on open sandy bottom near Thalassia and scattered reef corals. Micromollusks were abun- dant in the sample, and one of the most common was a species of Caecum. This species was found to be figured and briefly described by Warmke & Abbott (1961) as Caecum insigne Folin, 1867. The identification seemed correct, but two years later I was able to examine the types of C. insigne at the Laboratoire de Malacologie in Paris. Both C. insigne and C. coronatum, another species described in the same paper from the same locality, are con- specific with C. imbricatum Carpenter, 1859. The Virgin Island specimens, however, belong to a different species. It appears that this species has never been named or adequately described. Additional material from Puerto Rico was later submitted to me by Ger- maine Warmke. Collections from various parts of the Caribbean have given some indication of its geographical distribution, mostly by negative evidence. The species appears to be confined to Puerto Rico and the northern Virgin Islands, although admittedly the Caecidae are poorly known throughout the West Indian area. However, beach drift and shallow-water bottom samples from St. Croix, Haiti, Jamaica, the lower Bahamas, and the lesser Antilles have been examined without finding the new species. Since this Caecum is apparently restricted to a small group of islands, an appropriate name and a full description are given below. 1 Contribution No. 1178 from the University of Miami, Rosenstiel School of Marine and Atmo- spheric Sciences. 1970] Moore: A New Caecum 369 Caecum insularum, new species Caecum insigne, Warmke & Abbott, 1961: 68, fig. 15 F, not Folin, 1867: 52-53. Description.-The shell of the adult C. insularum is only slightly curved, and tapers evenly from the anterior to the posterior end. The septum is even with the posterior end of the shell. The mucro is strong and forms a right-angled triangle when seen from the side; it forms an equilateral triangle when seen from the ventral aspect. The shape of the mucro varies a little from specimen to specimen. The aperture is circular. It is not expanded, and there is no terminal varix. The terminal annular rib is contracted, nar- row, smooth, and is often colored brown. Color in the remainder of the shell is somewhat variable. It is usually white, sometimes with indistinct banding. Many specimens are tinged with brown, either near the aperture or suffused over the entire shell. There are three orders of sculpture. The strongest is the annular ribs. They are low, flattened, and very close together. They number about 35 to 50 in the adult. Longitudinal sculpture is made up of poorly defined low ribs with wide interspaces. They are weak, irregular, and often difficult to observe. The third type of sculpture consists of microscopic longitudinal striations. The protoconch was not observed. The juvenile second stage varies greatly in size; some shells are short and thick while others are long, slender, and attenuated. The sculpture of the second stage is similar to that of the adult, but the mucro is more slender and pointed. The operculum is brown, circular, and muItispiral. The outer face is con- cave in dry specimens, and shows more than ten whorls. The inner face is convex and smooth, showing no trace of the spiral turns. The operculum of one typical adult specimen measured 0.52 mm in diameter. Size of mature specimens varies considerably. Two specimens represent- ing the extremes in size are contrasted below. Total length Anterior diameter Posterior diameter Large 3.36 mm 0.76 mm 0.54 mm Small 2.36 mm 0.55 mm 0.42 mm Material.-Type-material was placed in the following institutions: United States National Museum (USNM); Academy of Natural Sciences of Phila- delphia (ANSP); American Museum of Natural History (AMNH); Mu- seum of Comparative Zoology (MCZ); and the Museum of the Rosenstiel School of Marine and Atmospheric Sciences of the University of Miami (UMML). 370 Bulletin of Marine Science [20(2) A B o FIGURE 1. West Indian Caecidae: A, Caecum insularum, new species, X 19; B, microsculpture of C. insularum, X 190; C, Caecum imbricatum, X 20; D, microsculpture of C. imbricatum, X 200. Type-Specimens.-HoLOTYPE: Lesser Lameshur Bay, S1. John, Virgin Is- lands, 7 June 1961. Measurements: total length, 3.28 mm; anterior diam- eter, 0.68 mm; posterior diameter, 0.48 mm. USNM No. 679178. PARATYPES: Lesser Lameshur Bay, St. John, Virgin Islands. 7 adults 1970] Moore: A New Caecum 371 A B FIGURE 2. West Indian Caecidae: A, Caecum floridanum, X 23; B, micro- sculpture of C. floridanum, X 190. and 5 juveniles, USNM No. 679179. 7 adults and 3 juveniles, ANSP No. 315477. 8 adults and 3 juveniles, MCZ No. 271305. 7 adults and 3 juve- niles, AMNH No. 147965. 6 adults and 8 juveniles, UMML No. 30:3203. More than a hundred paratypes from this locality, many worn or broken, have been kept by the author. West coast of Puerto Rico, 29 specimens, G. L. Warmke. Type-Locality.-Open sandy bottom at the head of Lesser Lameshur Bay, St. John, Virgin Islands, depth, 1.5 m. Remarks.-Caecum insularum is distinguished from pther western Atlantic species of Caecum by its slight degree of curvature, absence of a terminal varix, strong triangular mucro, and glistening appearance due to the fine longitudinal striae. The type-specimens of C. insigne and C. coronatum were collected in Jamaica, an island apparently outside the range of C. insularum. The speci- mens were probably picked out of the same sample, for those named C. coronatum were in good condition, while those named C. insigne were worn and in poor condition. They were all C. imbricatum Carpenter, a wide- spread west Indian species. C. imbricatum appears to be the closest relative of C. insularum. The following characters can be used to separate the two species. C. imbricatum is more strongly curved, has stronger longitudinal ribs, and terminates with a varix around the aperture; C. insularum has no varix. Worn or immature specimens are sometimes difficult to identify. C. imbricatum has more nu- 372 Bulletin of Marine Science [20(2) merous and stronger longitudinal striae, but this feature is difficult to dis- tinguish through a stereoscopic microscope. C. insularum might also be confused with C. floridanum Stimpson, 1851, but the resemblance is weaker. C. floridanum has strong annular ribs with deep interspaces. The last two or three ribs are larger and well separated from the others. The last one forms a strong terminal varix. The septum is recessed, and the mucro projects up from this like a spike. Longitudinal striae are very well developed. Both C. floridanum and C. imbricatum are widespread throughout the West Indian region from Florida to South America. C. insularum appears to be restricted to shallow, warm, oceanic waters surrounding a small group of islands. The Puerto Rico-Virgin Islands plat- form is an elongate structure aligned in an east-west direction from 64°08'W on the east to 67°27'W on the western end. This includes the islands of Puerto Rico, Vieques, Culebra, several small islands near Culebra, and all of the Virgin Islands except St. Croix. The platform is separated from the lesser Antilles by Anegada Passage with depths of more than 2000 m. St. Croix is separated from Puerto Rico by depths approaching 1800 m and from the remainder of the Virgin Islands by depths ranging up to 4000 m. In the west, Mona Passage between Puerto Rico and Hispanola is not as deep, but most of the passage has depths exceeding 400 m. Three small islands (Mona Island is the largest) and several banks occuPy part of the area, but the main passage is more than twenty nautical miles across, with depths exceeding 360 m. C. insularum may well have been derived from the much more widespread C. imbricatum. Apparently, C. insularum has a much reduced, or possibly even absent, pelagic larval stage. This, and a preference for quite shallow water, has kept it confined to a relatively small area. Depths of the water surrounding the Puerto Rico-Virgin Island platform are such that they would effectively prevent migration during periods of lowered sea level due to glaciation during the Pleistocene. ACKNOWLEDGMENTS I am very grateful to Wayne D. Bock and W. W. Hay for the scanning electron microscope photographs of the specimens illustrated. I also wish to thank Professor E. Fischer-Piette and his staff at the Laboratoire de Ma]acologie in Paris for the opportunity to study Folin's type-specimens of Caecum. This work was supported by National Science Foundation Grants GP-4783 and GB-5055. SUMARIO UN NUEVO Caecum DE PUERTO RICO Y LAS ISLAS VIRGENES Una nueva especie de Caecum es descrita procedente de ]a plataforma de 1970] Moore: A New Caecum 373 Puerto Rico y las Islas Virgenes. La nueva especie parece estar confinada a este gropo de islas en contraste con la amplia distribuci6n de la mayoria de las especies de Caecidae. Fotografias hechas con el microscopio electr6nico "scanning" ilustran la microescultura del nuevo gaster6podo y de dos espe- cies muy relacionadas con ella, C. imbricatum y C. floridanum. LITERATURE CITED CARPENTER, P. P. 1859. First steps toward a monograph of the Caecidae, a family of rostrifer- ous gasteropoda. Proc. zoo\. Soc. Lond., 26: 413-444. FOLIN, L. DE 1876. Descriptions d'especes nouvelles de Caecidae. J. Conch., Paris, 15: 44-58, pIs. 2 & 3. WARMKE, G. L. AND R. T. ABBOTT 1961. Caribbean Seashells. Livingston Publishing Co., Narberth, Pennsyl- vania, 346 pp.