Cephalopyge is a genus of pelagic nudibranchs comprising the single species Cephalopyge trematoides, a free-swimming marine gastropod in the family Phylliroidae.
Etymology Cephalopyge is a contraction of cephalus (Greek: κεφαλή , "head") and (πūγή, "behind") referring to the position of the anus close to the head. The species epithet trematoides expresses a likeness to flukes.
Description Cephalopyge trematoides grows to in length. It swims at approximately , by passing several undulatory waves down its body each second.Sea Slugs of Hawaii It is flattened and transparent; its internal organs are visible.Marine species identification portal: Cephalopyge and Cephalopyge trematoides.
Pelagic nudibranchs Of the approximately 3000 species of nudibranch, the vast majority are benthic, only a couple are neustonic, and Cephalopyge trematoides is very unusual in that it is pelagic.J.E. Steinberg, The pelagic nudibranch, Cephalopyge trematoides (Chun, 1889), in New South Wales with a note on other species in this genus, Proceedings of the Linnean Society of New South Wales 81:184-192 (1956) G.M. Mapstone & M.N. Arai, Siphonophora (Cnidaria, Hydrozoa) of Canadian Pacific Waters, p.33. "The best documented predators of pelagic cnidarians from the phylum Mollusca are the neustonic nudibranchs and snails [...and] the pelagic nudibranch [...]" It is estimated to be one of only five planktonic nudibranch species (another epipelagic example is Phylliroe bucephala).Orso Angulo-Campillo, Gerardo Aceves-Medina and Raymundo Avedaño-Ibarra, Holoplanktonic mollusks (Mollusca: Gastropoda) from the Gulf of California, México
Further information (including photos): Nudibranch Encyclopedia Kousuke Chibi (in Japanese) Seaslugs of Hawai'i by Cory Pittman and Pauline Fiene
References
External links film of Cephalopyge swimming