MORPHOLOGICAL DEVELOPMENT OF THE RADULA OF FOUR SPECIES OF THE NEOGASTROPOD FAMILY MURICIDAE

Radular ontogenies of four species of the neogastropod family Muricidae are described through comparisons of early post-metamorphic and adult developmental stages, with specific focus on the rachidian (central) tooth. The degree of rachidian transformation during ontogeny varies from minor shape change to addition or loss of structural features important for assigning taxa to subfamilies. Changes include: flattening of the rachidian base and a switch from a short, beak-like to a long, flattened central cusp in the rapanine Stramonita biserialis; a switch from variable, asymmetric to regular, symmetric expression of inner lateral denticles in the basal muricid Timbellus phyllopterus; curvature of the rachidian base at the margins and separation of the pointed base endpoint from the radular membrane to form a marginal cusp in the muricine Chicoreus dilectus; and moderate straightening of the rachidian base in the ocenebrine Vokesinotus perrugatus. From these observations and previous work, we propose a plesiomorphic developmental sequence for the Muricidae and provide supporting evidence for the developmental origins of novel features of the muricid radula.