Indirect evidence for ecophenotypic plasticity in radular dentition of Littoraria species (Gastropoda : Littorinidae)

In examination of radulae from all but one of the 36 species of the littori nid genus Littoraria we found extraordinary intraspecific variation in thos e occurring on a range of substrates. Radulae from rock showed a less well developed 'hood' on the rachidian tooth, a strikingly enlarged major cusp o n each of the five central teeth, fewer cusps on the outer marginal teeth a nd the radular ribbon was longer, when compared with radulae of conspecific s from plant substrates. The radulae of species found exclusively on rock d iffered in similar ways from those restricted to plant substrates (mangrove s, driftwood and saltmarsh). We suggest that this may be an example of phen otypic plasticity of radular form, induced by substrate and/or diet, as rec ently shown experimentally in another littorinid genus. The mechanism of in ducible plasticity deserves further study. Ecotypic variation in the radula may be widespread in littorinids, and radular characters should therefore be used with caution in studies of taxonomy, phylogeny and adaptation.