Euselenops luniceps is a most unique member of the family Pleurobranchidae , the side-gilled sea slugs. Unlike other members of this family Euselenops has a very flattened, low relief body, and its foot is much wider than its mantle. In most other pleurobranchs the foot and mantle are of similar size. Looking and behaving more like a cephalaspidean, Euselenops is highly adapted for living in a sandy environments. The large oval veil is edged with a series of long, fine branched sensory papillae, as seen here in Marc's photo and on the Sea Slug Forum . As seen on the Forum, Euselenops dives under the surface of the sand to feed and hide from predators. When completely covered only the white tips of the rhinophores and the pallial siphon, protrude from the substrate.
Some of the body adaptations seen in Euselenops , are common in several other completely unrelated sand dwelling sea slugs. These include Kalinga ornata, some of the Armina's and Cerberilla . They all have a broad foot, flattened body, wide oral veil with sensory papillae or long sensory oral tentacles for locating prey. Like these other sandy bottom predators it is active at night. Little is known about what it feeds on however.
Euselenops luniceps is also a good swimmer, having been observed swimming with body undulations like those used by sea hares or the Spanish Dancer, Hexabranchus sanguineus.
Cuvier derived the name of this species from it's moon shaped body. Specimens may reach 75 mm in length and occur throughout the tropical Indo-West Pacific, where they are found on sandy or fine coral debris bottoms.
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David W. Behrens
Pacific Coast Nudibranchs
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