MORPHOLOGICAL DIFFERENCES BETWEEN THE PEDAL MUSCULATURE OF PATELLOGASTROPOD AND FISSURELLID LIMPETS

In many of the rocky intertidal zones around the world, patellogastrop ods and fissurellid limpets live side-by-side. Although their external appearance is very similar, the allometry and organization of the ped al musculature of these gastropods are quite distinct. For temperate a nd tropical species pairs, allometric analyses indicate that the ratio of the area of the muscle scar to the area of the shell aperture is s maller in the species of patellogastropods studied than in the fissure llids studied. The foot of the patellogastropod Acmaea antillarum cons ists of one homogeneous muscular mass that resembles the columellar re gion of coiled prosobranch gastropods. In contrast, the foot of the fi ssurellid Fissurella barbadensis consists of columellar and tarsic reg ions like those of coiled prosobranchs. The majority of the muscle fib ers in the foot of A. antillarum are oriented dorsoventrally; in F. ba rbadensis the muscle fibers do not show a tendency toward a particular orientation. The large mass of dorsoventral pedal muscles of patellog astropods should permit them to achieve stronger normal tenacities. Th e fewer dorsoventral muscle fibers found in fissurellids may be compen sated for by the increase in the relative size of the surface area of attachment of the pedal musculature to the shell, which should increas e the animal's ability to withstand shearing.