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

¹ Department of Zoology, University of New Hampshire, Durham, New Hampshire 03824

1. The larval development, metamorphosis, and postlarval growth of the eolid nudibranch, Cuthona nana, is described. Hatching occurred within 19 days at 11-13° C. The lecithotrophic veligers remained nonpelagic and proceeded to metamorphose within another two days.

2. Adult nutrition did not affect egg size or subsequent development and metamorphosis.

3. Embryogenesis, hatching, and metamorphosis were unaffected by the presence or absence of the adult nudibranch's prey, the hydroid Hydractinia echinata.

4. Different temperatures altered the rate of development and of metamorphosis but not the type of development. Egg masses collected in the field and incubated at the temperature at which they were collected invariably produced nonpelagic lecithotrophic veligers which then metamorphosed.

5. Newly metamorphosed specimens of C. nana survived for up to six weeks at 11-13° C and ten weeks at 4° C in the absence of H. echinata.

6. In the presence of abundant food, specimens of C. nana deposited fertile egg masses within 11 weeks after metamorphosis at 11-13° C, and continued feeding and ovipositing for two months.

7. Cuthona nana feeds specifically on Hydractinia echinata, which in Gosport Harbor is found predominantly on shells occupied by Pagurus acadianus. As the hermit crabs move about, postlarvae of C. nana are swept up by the gastrozooids of H. echinata, are not eaten by the polyps but reorient and feed on hydroid tissue.

8. Nonpelagic development in C. nana appears to result in a patchy distribution of postlarvae on the bottom, and an uneven, nonrandom distribution of young nudibranchs on the H. echinata colonies.

9. Cuthona nana does not kill the H. echinata colonies it preys upon, but only crops some of the polyps before leaving the colony to find a mate or deposit eggs. Lost polyps are subsequently regenerated.