DEVELOPMENT OF THE EOLID NUDIBRANCH CUTHONA NANA (ALDER AND HANCOCK, 1842), AND ITS RELATIONSHIP WITH A HYDROID AND HERMIT CRAB

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Abstract
The development and ecology of C. nana was investigated in waters off New Hampshire, USA. A previous report suggested that C. nana may possess 2 modes of development, but only nonpelagic lecithotrophic development was observed during this study. Hatching occurred within 19 days at 11-13.degree. C. The lecithotrophic veligers remained benthic and proceeded to metamorphose within another 2 days. Adult nutrition did not affect egg size or subsequent development and metamorphosis. Embryogenesis, hatching and metamorphosis were unaffected by the presence or absence of the adult nudibranch''s prey, the hydroid Hydractinia echinata. Different temperatures altered the rate of development and of metamorphosis but not the type of development. Newly metamorphosed specimens of C. nana survived for up to 6 wk at 11-13.degree. C and 10 wk at 4.degree. C in the absence of H. echinata. C. nana fed specifically on H. echinata, which was found predominantly on shells occupied by Pagurus acadianus. As the hermit crabs moved about, postlarvae of C. nana were swept up by the gastrozooids of H. echinata, were not eaten by the polyps but reoriented and fed on hydroid tissue. C. nana did not kill the H. echinata colonies it preyed upon, but only cropped some of the polyps before leaving the colony to find a mate or deposit eggs. Lost polyps were subsequently regenerated.
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