Cittarium pica (Linnaeus, 1758) is the third most important marine invertebrate species eaten by man in the West Indies. Information on it is widely scattered and is newly reviewed here, with original data, questions, and conclusions added. The animal has a relatively large shell and is easily collected, living intertidally and shallow subtidally on rocky shores. Its stocks are depleted at many places, large animals having been selectively removed by fishermen and others. There is only one living species of Cittarium, occurring in Bermuda, southern Florida, and in the greater West Indies. Its closest living relatives are all non-American, the only congener being the recently discovered C. maestratii Lozouet (2002) from the Oligocene of France. Thus the geographical and stratigraphic origins of the genus are still somewhat problematic. In Bermuda and southern Florida, the occurrence of C. pica alive is naturally sporadic. Sometimes sea surface temperatures are too low there for this tropical animal. The following topics are also reviewed: systematics, vernacular names, nomenclature, classification, anatomy and functional morphology, radulae, shell description, internal nacre, sizes and giants; shell strength, dextral coiling, and hermit crab occupancy; ecology and habitats, symbionts (unattached and attached), foods and feeding, reproduction, larval development and life history and movements, shell growth rates and longevity, predators, and escape responses; Pleistocene occurrences and historical extinctions in Bermuda and Florida; human introductions; also, human uses, including cookery, and possible tropical fish poisoning or ciguatera (caused by a toxic dinoflagellate).The most important new findings are: 1) That a shallowly shell-penetrating blue-green alga (Cyanophyta), probably Plectonema terebrans Bornet and Flahault, affecting only the white areas in the external color pattern (reported by Helen A. Randall, 1964), weakens these shell areas only and indirectly brings about differential erosion: the black, often zigzag stripes or marks on old shells become slightly higher in relief than the white areas. 2) Some aspects of multispiral operculum growth, visible externally only, are inferred from its morphology, but major questions remain. With growth, the operculum rotates as very many times as there are coils, and the growing edge is always in the same relative position, posterior, in the ever enlarging shell aperture. The operculum is attached on the inside by muscles arising postero-dorsally in the foot. The opercular muscle attachment and scar move, as they must, while the operculum grows and rotates very many times. How? 3) Occasionally, shells grow extra large in a very shallow, dead coral fringing reef habitat, not “deep”. The largest shell reliably reported is 137 mm wide and is from the Netherlands Antilles. Two from the Bahamas, the first with habitat data, are 132 and 126 mm wide. 4) Clouds of broadcast sperm were once mistaken for an “opaque liquid” causing “alarm” in nearby cittariums.None of these topics is addressed fully or at all by Fretter and Graham (1994) or Hickman (1998). Cittarium is shown to be primitive and in the mainstream of trochid evolution, having few if any noteworthy or remarkable biological specializations such as occur in some other trochids.Examples are given of extreme morphological and functional diversity in other taxa in the family Trochidae, comparing them with those in Cittarium. Trochids are suggested to have the widest adaptive radiation of any marine gastropod family (Hickman, 1996), yet primitive trochids such as Cittarium still exist and indeed thrive. Trochid adaptations tend, though, to be allopatric both as regards geography and ecology.
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Aug 10, 2007
Jeffrey P Blick 
Open Access