Melibe leonina (Gould, 1852) : Hooded Nudibranch
Phylum Mollusca / Class Gastropoda / Subclass Opisthobranchia / Order Nudibranchia / Family Tethyidae

OK, so this isn’t really a planktonic animal. On occasion though, this bizarre nudibranch can swim by flexing the body, albeit not in a particularly graceful fashion. Most nudibranchs, more commonly known as “sea slugs”, are quite colorful and live a benthic existence. The hooded nudibranch is a bit of an oddball, having a body that’s more gelatinous than the typical sea slug and bland yellowish brown or pale gray color. It can be quite large, reaching lengths of 15 cm. Melibe typically hang on eelgrass, fronds and blades of giant kelp, or other substrates using a large foot. While attached, they capture zooplankton prey with a large, distinctive oral hood that is swept downward (another unusual characteristic for a nudibranch). The dorsal surface of the posterior half of the body bears 5 or 6 pairs of leaf-like cerata. In certain locations, such as Monterey Bay, Melibe can blanket giant kelp plants with incredible aggregations of many hundreds (maybe thousands) of individuals (see video below). Hooded nudibranchs range from nearshore waters of Alaska to the Gulf of California (Sea of Cortez in Mexico). One area where you may witness swimming individuals is the Pacific Northwest during fall and winter, when storms often dislodge them from their eelgrass perches.

Melibe leonina, video courtesy of Patrick Anders Webster, Monterey Bay CA, July 2013

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