Plakobranchus ocellatus

Plakobranchus ocellatus is a species of sea slug, a sacoglossan, a marine opisthobranch gastropod mollusk in the family Plakobranchidae.^[1] It is found in shallow water in the Indo-Pacific region.

Plakobranchus ocellatus
Two Plakobranchus ocellatus sea slugs facing in opposite directions
Scientific classification
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Gastropoda
Family:	Plakobranchidae
Genus:	Plakobranchus
Species:	P. ocellatus
Binomial name
Plakobranchus ocellatus (van Hasselt, 1824)
Synonyms[1]
Elysia ocellata Pease, 1860 Placobranchus gracilis Pease, 1871 Placobranchus guttatus Stimpson, 1855 Plakobranchus guttatus Stimpson, 1855 Placobranchus ianthobaptus Gould, 1852 Plakobranchus ianthobaptus Gould, 1852 Placobranchus ocellatus van Hasselt, 1824 (an incorrect subsequent spelling by Férussac (1824) in a translation of van Hasselt's work.) Placobranchus variegatus Pease, 1871 Plakobranchus argus Bergh, 1872 Plakobranchus camiguinus Bergh, 1872 Plakobranchus chlorophacus Bergh, 1873 Plakobranchus laetus Bergh, 1872 Plakobranchus priapinus Bergh, 1872 Plakobranchus punctulatus Bergh, 1872

Distribution

This species occurs in the Indo-Pacific.^[1] Recent work on the photosynthetic abilities of Plakobranchus reveals that P. ocellatus is actually a species complex consisting of at least four distinct clades.^[2]

Description

Plakobranchus ocellatus, head end towards the left

The body is broad, truncate, and rather flattened, up to 4 cm (1.6 in) long.^[1] The head is flat and squarish, the rhinophores being folded longitudinally. The mouth is at the front apex of the head and the eyes are very close together, being visible through the semi-transparent skin of the head. The dorsal surface of the sea slug has a number of longitudinal ridges, but when at rest, the parapodia are folded up over the midline of the body so that the dorsal surface is concealed from view. On the underside, the foot is broad and long, but is not clearly demarcated from the mantle.^[3] The ground colour of this sea slug is usually pale green, beige, or cream with large ocelli (spots similar to eyespots) of cream, brown, pink, and purple in varying shades. The sole of the foot also has ocelli.^[1]

Dorsal view of a freshly collected intact Plakobranchus ocellatus showing its head, rhinophores and parapodia.

Dorsal view of an anesthetized individual of Plakobranchus ocellatus with spread parapodia. Stomach and branched digestive glands are visible. The tissue region in the red square was dissected and used for DNA extraction in the study by Maeda T. et al. (2012).[4]

Habitat

These seaslugs live in sheltered, shallow water habitats with stones or gravel and silt.^[1] They feed on a broad food spectrum, including members of the genera Halimeda, Caulerpa, Udotea, Acetabularia and further unidentified algae, with an emphasis on Halimeda macroloba.^[2]