Larval Development of the Coquina Clam, Donax Variabilis Say, with a Discussion of the Structure of the Larval Hinge in the Tellinacea

Adult specimens of Donax variabilis were spawned in the laboratory and the larvae reared to metamorphosis. Larval length increases from 70 µ to 340 µ during pelagic stages. Height is originally 10 µ to 15 µ less than length. Height increases less rapidly than length and may be 50 µ less than length at metamorphosis. Depth is originally 50 µ less than length. It also increases more slowly than length and may be 150 µ to 170 µ less than length at metamorphosis. Length of the hinge line is 50 µ to 60 µ Round umbos form when larvae are 100 µ to 120 µ long. Umbos protrude above the shell as knobby projections at lengths above 170 µ. The anterior and posterior ends are equally rounded until, at about 250 µ, the posterior end becomes more pointed. Larvae metamorphose at lengths from 275 µ to 340 µ.

The hinges of the larvae of D. variabilis and Tellina agilis consist of numerous small irregular teeth. Descriptions of taxodont dentition in larvae of other Tellinacea are probably in error and refer to these small irregular teeth. The large special teeth, frequently described in larvae of this group, probably do not develop until after metamorphosis.