LARVAL GROWTH AND THE INDUCTION OF METAMORPHOSIS OF A TROPICAL SPONGE-EATING NUDIBRANCH

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Abstract
The Hawaiian dorid nudibranch Hypselodoris infucata (R€ppell & Leuckart, 1828) was reared to metamorphosis in the laboratory. Egg diameter averaged 88 μm and veligers hatched, after about 5 days at 25°C, with a coiled shell averaging 149 μm in length. Larvae fed on phytoplankton grew to a maximum shell length of 306 μm in about 15 days. Larval growth was affected by both quality and quantity of the algal diet. Some larvae were competent to metamorphose 16 days post-hatching at 26°C, and competence could be retained for at least one week. Metamorphosis is complete within 24 hours of exposure to an inducer. At least three species of sponge, Halichondria coerulea, Sig-modocia sp., and Tedania macrodactyla, in addition to the nudibranch's adult prey species, Dysidea sp., induced metamorphosis of competent larvae. Primary films grown on glass slides also induced metamorphosis in some larvae, as did 20 μM excess potassium ions in seawater. These data suggest that nonspecific induction of metamorphosis occurs in this species even though the adult nudibranchs are highly prey specific. This implies that in the field, H. infucata find Dysidea sp. after settlement and metamorphosis