Nerita fulgurans Gmelin, 1791 Antillean Nerite Page Two

    Taking into account the demonstrated variation in color pattern, ribbing, etc., one is left with two overriding differences between these morphs: (1) the greater prominence of the apertural armature, i.e.,  denticles/beading on the parietal shelf and labral folds/denticles, and (2) the more coarsely crenulate outer aspect of the labrum in the Brevard Co. shell, hereafter the "robust form."

    Except for the elevated spire and more constricted, less oblique aperture, characters shown above to be growth-dependent, the Nassau Co. specimen is quite similar to the 17 mm. figured holotype and paratype of Nerita lindae Petuch, 1988 (pl. 30, figs 4, 5, 11) described from Palm Beach County. Size notwithstanding, this morphology typifies Nassau Co. shells. Likewise the Brevard Co. ones are consistently of the robust form; see images on the previous page.

    Are N. fulgurans and N. lindae different biospecies? At this point, it certainly appears the morphological differences cannot be explained by ontogenetic factors alone. If there is a any zoogeographical dissociation between the two, it is not readily apparent. Our work shows no evidence for a north-south gradient from Palm Beach to Nassau Co. since the robust form has been documented from most east Florida counties, e.g. Brevard, Volusia, St. Johns, and Duval between the type locality of N. lindae and the Nassau Co. outpost. Considering published and unpublished work by others along with his own conchological and ecological observations, nerite expert Tom Eichhorst reports that there are no opercular, radular, or molecular phylogenetic differences between topotypical N. lindae and sympatric typological N. fulgurans.

    Then what drives these nerite populations with close to, or entirely, identical constitutions to sort out into two reasonably distinct morphs? The answer may be the (micro)habitat. There are hosts of reports dealing with ecological influence on shell form of a diversity of marine gastropod species, and the nerites are certainly among them. these include (1) the level of competition for food in Nerita atramentosa Reeve, 1855 (Underwood, 1976), (2) the predation pressure by crabs on that species (Chilton and Bull, 1984), and (3) the density of Neripteron violaceum (Gmelin, 1791) populations (Murty and Rao, 1978). Perhaps the most visibly arresting impact resulted from (4) experimental work by Minton and Gundersen (2001), which revealed that the color pattern in the nerite Puperita pupa (Linnaeus, 1767) was driven by the salinity of the microhabitat rather than genetic factors as was the accepted theory and basis for the taxon P. tristis (d'Orbigny, 1842). These workers were able to show abrupt and profound changes in color pattern (essentially from one "species" to the other) by simply transplanting living snails between tide pools with different salt concentrations on the same rocky shoreline. Perhaps the Nassau County nerite population could be subjected to a comparable experimental manipulation of environment to test the phenoplasticity of its shell morphology and thus the phylogenetic basis for Nerita lindae?

Chilton, M.B. and C.M. Bull, 1984. Influence of predation by a crab on the distribution of size-groups of three intertidal gastropods in South Australia. Marine Biology 83: 163-169.
Minton, R.L. and R.W. Gundersen, 2001. Puperita tristis (d'Orbigny, 1842) (Gastropoda: Neritidae) is an ecotype of Puperita pupa (Linnaeus, 1767). American Malacological Bulletin 16(1/2): 13-20.
Murty, A.S. and M.B. Rao, 1978. Effect of environment on the shell shape of a tropical estuarine snail Neritina violacea (Gastropoda: Neritacea). Journal of Molluscan Studies 44: 265-271.
Petuch, E.J., 1988. Neogene History of Tropical American Mollusks. Biogeography & Evolutionary Patterns of Tropical Western American Mollusca.The Coastal Education & Research Foundation (CERF), Charlottesville, VA. [vi] + 1-217 (including 39 plates). 15 Dec.
Underwood, A.J., 1976. Food competition between age classes in the intertidal neritacean Nerita atramentosa (Gastropoda: Prosobranchia). Journal of Experimental Marine Biology and Ecology 23: 145-154.