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Dermatobranchus semilunus is characterized by a U-shaped brownish patch at the anterior third of the notum.
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.
Let me quote Gosliner & Fahey (2011): "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 pigment at the anterior third of the notum. Along the mantle edge are evenly spaced, dark ocellated spots of pigment. The posterior edge of the mantle has a yellowish or tan hue. The rhinophore stalk is white and the club is dark. The oral veil is opaque white with some dark irregular spots."
Dermatobranchus cf. semilunus differs from Dermatobranchus semilunus by pink pigment at the margins of the mantle and the oral veil.
There is a picture of a specimen with pink margins taken by Terry Gosliner at Verde Island at iNaturalist.org, he labels it Dermatobranchus semilunus, though it differs from the description.
Dermatobranchus semilunus is Dermatobranchus sp. 7 in IPN at page 311
Gosliner, Terrence M. & Fahey, Shireen 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. 2011 February; 161(2): 245–356.
This text is completely online at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3073124/
Gosliner, Terrence M., David W. Behrens & Ángel Valdés. 2008. Indo-Pacific Nudibranchs and Sea Slugs. Sea Challengers Natural History Books.
Gig Harbor, Washington. 426 pp.
Pretty similar are:
Dermatobranchus semilunus, which lacks the pink pigment at the margins of the mantle and the oral veil,
Dermatobranchus fasciatus, which differs by two transverse brownish bands/patches,
Dermatobranchus sp. 13 which has a solid white oral veil, and
Dermatobranchus sp. 14 which differs by series of minute brownish spots on the longitudinal ridges,
Dermatobranchus tuberculatus, which lacks the prominent longitudinal ridges, and differs by rounded tubercles on the dorsal surface.
Dermatobranchus sp. 12 which differs by network of brownish-orange longitudinal lines, by an orange margin on the oral veil, and by black rhinophore clubs with white edges.
How to cite:
Köhler, E. (2019), published 14 February 2019, Dermatobranchus cf. semilunus Gosliner & Fahey, 2011
available from https://www.Philippine-Sea-Slugs.com/Nudibranchia/Cladobranchia/Dermatobranchus_semilunus_cf.htm