Gymnodoris ceylonica (Kelaart, 1858)

Gymnodoris ceylonica is sporadically common at Enewetak Atoll, Marshall Islands. There were not many different occasions when the nudibranchs were sighted, but some times there were a lot of them. The first seven specimens we ran across were on 20 September 1981 crawling up a sandy slope in a swift current next to the pier on Medren Island, not far from the Enewetak's deep water pass. Three days later off Enewetak Island itself, more than 80 specimens were counted at a depth of about 25 meters all crawling roughly northeast along the sandy bottom. If they continued on in the same direction, they would ultimately have gone up the slope to the shallow reef. The next time we ran across them was on 28 February 1982, when numerous specimens were observed off Medren Island at a depth of about 5 meters laying many tangles of egg masses on rocks and Halimeda algae. Over the next year and a half, we spotted an occasional other specimen in lagoon habitats, but never in the quantities observed in the first few sightings. Despite watching at Kwajalein for 19 years, we have not yet seen it here. Specimens measured ranged from about 25 to 80mm.

Gymnodoris ceylonica eats Stylocheilus striatus (below), which it engulfs whole. We never saw it eating anything else, but it would be interesting to see if it eats other sea hares.

On some specimens, the gills seem disproportionately large. The two below are starting to eject their reproductive organs in preparation for mating.

The two shots below show a mating pair of Gymnodoris ceylonica. Like other nudibranchs, these are simultaneous hermaphrodites, and during mating probably practice reciprocal fertilization.

Created 1 January 2007

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