Author: (Bergh, 1874)

Order: Nudibranchia  Family: Arminidae

Maximum Size: 80 mm

Sightings: Sunshine Coast

_________________________________

Dermatobranchus ornatus (Bergh, 1874)

Dermatobranchus, along with Armina, is a dominant genus in the family Arminidae. The members of this family have a distinctive oral veil, an elongate body with a broad mantle that often carries numerous longitudinal ridges and rhinophores with clubs bearing vertical primary lamellae. The major externally observable differences between these two genera are that Armina have a mantle edge that is continuous anteriorly behind the rhinophores and they also carry secondary respiratory leaflets in the hyponotum (region between underside of mantle and foot). Both of these features are absent in Dermatobranchus, with the mantle edge being incomplete anteriorly and fused to the body behind the rhinophores.

Dermatobranchus ornatus is one of the larger, if not the largest, species of the genus, growing to a maximum recorded size of 80 mm. It is also unusual in being one of the few species in the family without distinct longitudinal ridges having instead many small and large tubercles on the notum. These tubercles are raised and flat-topped, sometimes crater-like, and most often with orange apices or orange rings around the crater edge, although other shades including pink and red are known. The smaller tubercles are simply dome topped. The orange colouration is also borne by the edges of the mantle, foot and oral veil. The base colour of the mantle is variable, most often grey but may be darker or even much lighter to almost creamy white. Black spots are evident submarginally on the mantle, foot and oral veil, occasionally forming short lines. The foot and oral veil are both otherwise white. The rhinophore clubs are black with vertical lamellae edged in white whilst the stalks are translucent white but bearing black markings on the anterior face.

This species feeds upon gorgonian corals stripping off the polyps and all external tissue leaving behind just the calcareous skeleton. It is believed that distasteful chemical compounds are obtained from the gorgonian tissue and accumulated in glands under the mantle edge for defence purposes against predators.

Distribution is across the Indo-Pacific from the Red Sea east and north to Japan and south to the sub-tropical coasts of western and eastern Australia. Most of the colour variations appear related to certain geographical locations.

Originally described as Pleuroleura ornata.

References:
– Bergh, L.S.R. (1873/4). Malacologische Untersuchungen. In: C.G. Semper, Reisen im Archipel der Philippinen, Wissenschaftliche Resultate. Band 2, Heft 5: Pl 25 – 1873 and Heft 6: 278-285, Pls 34 & 35 – 1874.

– Baba, K. (1977). Two New Species and Five Common or Rare Species of the Genus Dermatobranchus from Japan. The Veliger, Vol. 19; No. 1.

– Rudman, W.B., 2008 (Apr 8). Comment on Dermatobranchus ornatus – Feeding & mantle glands by Gaetan White. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/20878

– Gosliner. T.M. and 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, 2011, 161, 245–356

– This Species Profile has been modified from a previously published article in Dive Log Magazine’s – Critter ID with NudiNotes Column, Issue: #367 (February 2019):12 by David A. Mullins

David A. Mullins, July 2019