RADULAR ONTOGENY OF THE MURICID TROPHON GEVERSIANUS

PIO, M.J.; HERBERT, G.; PASTORINO, G.

Puerto Madryn

Congreso; Congreso Latinoamericano de Malacologia; 2011

Asociacion Lationamericana de Malacologia

The radulae of many gastropods undergo dramatic changes in the number, type, and structural complexity of teeth between the pre-metamorphic larval stage, when the radula first forms, and adulthood. Several authors have hypothesized that evolution of the rate or timing of these developmental trajectories (e.g., paedomorphosis) might be capable of inducing sudden emergence of novel structures, the origins of which were previously difficult to explain. Here, we study the radular ontogeny of the trophonine muricid Trophon geversianus, a taxon known from molecular and soft anatomical data to bridge the gap between basal muricids of the subfamily Muricinae and a more derived group, the Ocenebrinae. Our goal was to determine whether novel characters of the Ocenebrinae and absent in basal muricines are present at any ontogenetic stages of intermediate taxa, such as T. geversianus. Major features of the ocenebrine rachidian tooth are (1) central and lateral cusps that project strongly from the rachidian base, (2) a short, recurved central cusp, and (3) a bifid (cleft into two parts) and deep base. In muricines, the central and lateral cusps do not project much from the base, and the rachidian margins are often barren of cusps and shallow. Ontogenetic analysis of the rachidian of T. geversianus reveals strong differences in morphology between the juveniles and the adults. Adults are mostly of the muricine type, including low projection of central and lateral cusps from the base, a long, flat central cusp, and a single marginal cusp at either end of the shallow rachidian base. By contrast, the juvenile rachidian has strongly projecting central and lateral cusps and a short, recurved central cusp, as in ocenebrines, as well as a deep, near-bifid base. These results confirm the evolutionary importance not only of developmental timing in the evolution of the Muricidae but also the Trophoninae as a key taxon bridging the gap between basal and more derived muricids. Future ontogenetic studies of theTrophoninae, including anatomy and shell features, will reveal whether developmental evolution that led to ocenebrine synapomorphies was global (whole organism) or restricted to particular character systems.