Embryonic development of the sea butterfly Desmopterus papilio (Gastropoda: Thecosomata)

The embryonic development of the thecosome Desmopterus papilio is described for the first time. The mature individual produced a round-shaped egg mass containing ca. 200 fertilised eggs. First cleavage was observed 15 min after the release of the egg mass. Embryos showed typical molluscan spiral cleavage: macromeres produced the first and second quartets of micromeres in clockwise and counterclockwise directions, respectively. A trochophore larva hatched from the egg capsule 28 h after the release of the egg mass. Thereafter, the larva secreted a primary shell at the posterior part, developing into the veliger stage. These findings may be useful for future work on postembryonic development, especially on the loss of the veliger shell, in the genus Desmopterus which is the only group of thecosome species without a shell in the adult stage.