Cerion rodrigoi Gould, 1997

Original Description

"Cerion rodrigoi sp. nov.

            Cerion rodrigoi is the first member found on San Salvador of the characteristic Cerion species complex of the southeastern Bahamian islands -- the "triangular" or "tapering" morphotype of Gould and Woodruff (1987, 1990, characterized by a smooth and thick white shell with a triangular outline in cross-section because the later adult whorls continue to increase in width (rather than stabilizing or constricting to produce the barrel shape so characteristic of other Cerion taxa).

            Cerion rodrigoi is the largest of San Salvador Cerion. At the type locality (1225 of Figure 3), ten randomly chosen specimens yield a mean shell height of 26.02 mm, a mean width of 11.64 mm, and grow an average (to the nearest 1/8 whorl) of 7 1/2 postprotoconch whorls.(By contrast, shells at Dall's type locality for C. watlingense range from 22-25 mm. in height.) These ten shells range from 24.6-28.4 m.m. in height, from 11.0 to 12.1 mm in width, and grow from 6 7/8 to 8 1/8 postprotoconch whorls. 

            Cerion rodrigoi has a translucent protoconch followed by one or two finely ribbed juvenile whorls showing mottled coloring on part of the first whorl, after which the shell becomes entirely white and uncolored for the rest of growth. The shell, as is typical for this morphotype, is white, thick, and triangular in cross-section; the aperture is strongly recurved but only modestly thickened.  The adult whorls vary in expression of ribs from entirely smooth and ribless, through occasional and erratically spaced ribs, to a few individuals with weak but persistent ribbing, though always widely spaced in the paucicostate pattern noted in other species of the morphotype (as on Eleuthera -- see Gould, 1988). 

            Geographic distribution: On the most exposed and rocky windward coasts of the Eastern shore of San Salvador.  Pure populations have been found only on Crab and Almgreen Cays.  Populations hybridized with C. watlingense occur both to the north and south along the coast and westward, into the island's interior. 

            Derivatio nominis: The type locality, on the windswept summit of Crab Cay, lies right next to the Columbus monument erected by the Chicago Herald in 1891.Although Columbus surely didn't land on this windward and rocky coast, his ships first spotted the New World on the early morning of October 12, 1492. Probably, the ships then lay east of the island, and the first sight of land may well have been (according to Morison and others) (the reflection of moonlight off the rocky headlands of the highest points on the eastern coast. If so, then Crab Cay is an excellent candidate for the first bit of the New World spotted by Columbus's men. I therefore name this species of Cerion for Rodrigo de Triana, the watchman of the Pinta who first saw land and shouted the cry of "Tierra" on that fateful night. This sailor received little or none of the promised reward, and this posthumous trophy of a snail's name must be cold comfort, while still seeming appropriate.

            Holotype (central specimen of Figure A, Plate I, actual size. The topotype specimens to the left show variation towards greater height and smoothness of shell; and to the right towards greater squatness and ribbiness.These five specimens provide a good idea of the total range). Department of

InvertebratePaleontology,Museum of Comparative Zoology, Harvard University, Locality number 1225 of Gould and Woodruff, on the windswept terrace of Crab Cay adjacent to the Columbus monument.  Height of holotype, 25.2 mm; width, 11.5 mm; 7 3/8 postprotoconch whorls.

Summary statement

            I have recognized two species of Cerion on San Salvador. Dall's C. watlingense, the only name previously available for Cerion from this island, applies to the characteristic form of the ribby morphotype, found as expected along the bank-edge coasts and more sparsely over the island's interior. I found no pure samples of the mottled morphotype, a potential resident of interior areas. Either the mottled morphotype has so extensively hybridized with C. watlingense that well-defined populations no longer exist, or the mottled morphotype never inhabited San Salvador (or died out long ago), and the large range of variation in C. watlingense includes some populations (particularly from interior areas) with strong resemblance to some key features of mottled shells. However, the large, ribless (or sparsely ribbed), entirely white and triangular shells, living on the most exposed parts of the windward eastern coast (Crab and Almgreen Cays), do belong to a second species representing the triangular morphotype of the southeastern islands. I have designated this new species as Cerion rodrigoi.

            Unlike most other Bahamian Islands, which vary extensively in size and degree of connectivity with neighboring islands during Pleistocene eustatic fluctuations, San Salvador lies on its own independent bank, and was neither connected with any other island, nor even very different in size, throughout the extensive sea-level fluctuations of ice age times. This stability in size and isolation may well explain the greatest peculiarity of the current Cerion fauna -- the extensive and continuous variation in shell form among populations throughout the island. Cerion watlingense and Cerion rodrigoi do show centers of relatively "pure" form -- and in the expected places based on our knowledge of Cerion's distribution throughout the Bahamas (see section I of this paper). But populations are extensively and evenly mixed by hybridization throughout the island, forming a virtual blanket of fairly continuous variation in shell morphology -- and thus explaining the biometric results of Fronabarger and Carew in finding mappable patterns of continuous variation throughout the island based on a set of characters measuring shell and aperture size and shape.

            This unusual continuity of variation  --­a probable product of both the relatively small size of the island (with absence of strong geographic barriers to movement), and, especially, of San Salvador's longterm geographic stability -- does make the taxonomy of San Salvador Cerion quite difficult, and is responsible for previous impressions of confusing and intractable variability within a single entity.  But when we apply to San Salvador our knowledge of Cerion patterns throughout the Bahamas, we may then infer the existence of two taxa in their characteristic places, but with extensive and thorough mixture by hybridization (given the opportunities of time and geography mentioned above) throughout the island." (Gould, 1997:84-85)

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