The Biology and Functional Morphology of the Placental Embryo-BroodingNeolepton salmoneum, a Comparison withNeolepton subtrigonum(Bivalvia: Cyamioidea: Neoleptonidae), and a Discussion of Affinities

Abstract

Abstract: The anatomies of two species of Neoleptonidae are described. Clearly heterodont with cardinal and lateral hinge teeth, the shell also has an internal, parivincular ligament. Shell form suggests a shallow burrowing mode of life in coarse gravels in coastal waters. The labial palps are small and the intestine short further suggesting deposit feeding in well-sorted gravels. A pronounced prodissoconch (II) with a marginal ridge argues for lecithotrophic development further facilitating re-colonization of a narrow niche. In most anatomical respects, the two species are simplified with conjoined inhalant and pedal apertures and few posterior sensory mantle papillae. The ctenidia comprise subequal demibranchs with the outer reduced and the inner modified for internally fertilized embryo brooding. The attachment of each embryo chord to the demibranch filaments is probably from secretions produced by basal glands developed on their abrofrontal surfaces. There may also be secondary external pallial broodi...