This species has been observed on Madagascar Island
Suborder : Dexiarchia
Superfamily : Arminoidea
Distribution : Indo West pacific
Maximal size : 12 mm
Species characteristics :
The ground colour of the dorsum, the oral veil, and the foot is opaque white. The depressions between the dorsal ridges are light grey with dark dots. There is a single dark U-shaped band of dark brown pigment at the anterior third of the notum.
Along the mantle edge are evenly spaced, dark ocellated spots of dark brown pigment, on some specimens there is also a pale yellow coloration
The oral veil is opaque white with some dark irregular spots.
The rhinophore stalk is white and the club is dark grey with white lamellae
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Photo Alain-Benoît Rassat
Madagascar, Nosy Bé, 30 mm
See more about : Sightening and mating periods
Identification proposed by Hsini Lin
The original description does not refer to the marginal pale yellow coloration, but many specimen of this species present this coloration (see philippines seaslug for exemple)
Synonymous : (according Worms)
- No other name
Bibliographic data :
The posterior edge of the mantle has a yellowish or tan hue.
The body shape of the living animal is elongate and triangular, flattened, and narrows at the posterior end.a
The foot does not project beyond the distinct mantle margin b
The widely spaced, club-shaped rhinophores are situated behind the oral veil. They have a series of longitudinal lamellae on the rounded club. The stalk does not narrow noticeably a
There is a series of 10–14 low longitudinal dorsal ridges b
There are no branchial lamellae under the notum a
The oral veil extends forward and has blunt extensions at the corners.b
Marginal sacs are visible along the mantle edge. b
Etymology : The specific name semilunus is from the combined Latin words meaning half-moon, in reference to the dark, semi-lunar shaped marking on the anterior third of the dorsum of this species
Externally D. semilunus looks most similar to D. rodmani, D. tuberculatus, and D. fasciatus.
All four species have a basically white ground colour, a noticeable dark brown band or bands of pigment crossing the dorsum and darker coloured rhinophore clubs.
Of these :
- D. rodmani and D. tuberculatus lack numerous prominent longitudinal ridges found in D. fasciatus and D. semilunus
- D. fasciatus most closely resembles D. semilunus but D. semilunus has a single u-shaped brown marking whereas D. fasciatus has two broader bands of brown. The rhinophores of D. fasciatus are dark brown to black with opaque white spots, whereas those of D. semilunus have white lines along each vertical lamella.
Philippines Seaslug : Dermatobranchus semilunus
Gosliner T.M. & Fahey S.J. (2011) Previously undocumented diversity and abundance of cryptic species: a phylogenetic analysis of Indo-Pacific Arminidae Rafinesque, 1814 (Mollusca: Nudibranchia) with descriptions of 20 new species of Dermatobranchus . Zoological Journal of the Linnean Society 161: 245–356
Other photos of Dermatobranchus semilunus :
Madagascar, Nosy Bé, Baie de Befotaka, 15 m, 21 July 2010
Madagascar, Nosy Bé, Sakatia, 15 m, size : 15 20 mm
More photos from Indian Ocean
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