Goniobranchus cf rubrocornutus (Rudman, 1985)

This species is relatively common at Kwajalein Atoll on lagoon reefs under dead coral or corrugated aluminum sheets blown into the water during storms. These aluminum sheets acquire nice encrusting sponge growth on their undersides and seem a favored habitat for a number of nudibranchs. The primary difference between these specimens and typical Goniobranchus rubrocornutus is the bright yellow body on the Kwajalein specimens instead of the more typical white. Also, the marginal coloration is a bit different, with a wide orange continuous margin and narrow maroon and white submargins that are also continuous although somewhat irregular in thickness. When we had seen only a few specimens, we thought it might just be a color form of G. rubrocornutus. Now that we have seen several dozen specimens, all with the same dorsal yellow pigment, we are inclined to believe it is different.

The two specimens below are each carrying around a commensal crustacean, near the gills of the first photo and between the rhinophores of the next. On the bottom photo, the commensal looks a bit like the head of a rabbit.

In the specimen below, mantle glands in the skin around the anterior end are visible just inside the bright white submarginal band.

Feeding on dark purple Chelonaplysilla violacea sponge. In the second shot, the animal has turned around, leaving the bare batch where it had been feeding behind (above) it.

The light colored specimen below observed on 2 March 2009 is translucent enough to see its internal organs. The internal orange patch is a mass of orange yolk associated with female portion of the reproductive system. This yolk is used to lay down an orange extra-capsular yolk body adjacent to each ova in the egg mass produced by this species. Most or all other species of Goniobranchus do the same thing.

A tiny juvenle is translucent with only a trace of the yellow dorsal color.

Created 14 December 2005
Updated 14 August 2015

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