Summary
The elusive Rosy nudibranch, like many of its fellow Opisthobranchs, has adapted to life in the ocean without the use of a protective chitinous outer-shell. Instead, this species has diverged from the characteristic molluscan body plan and evolved into a soft-bodied invertebrate displaying a strikingly beautiful magenta colouration across its entire body. This species bears up to 4 pairs of white bifurcated cerata containing ‘naked gills’, that allow the organism to obtain oxygen from the water column. The pair of bright, blood red, palmate chemosensory rhinophores, located towards the anterior end of this nudibranch, are characteristic of this particular species. To compensate for the lack of an outer-shell, Marianina rosea employs the use of aposematic colouration and chemical defences to escape predation on the coral reefs that it inhabits throughout the tropical indo-west pacific region.
The uniqueness and highly specialised body plan of this nudibranch has led to the re-evaluation of M. rosea into a suitable family. This species is known to feed exclusively upon hydroids, unlike many Tritoniids that feed on alcyonarian soft corals and gorgonians. The cerata of most Tritoniids lack cnidosacs that should contain cnidocytes utilised by the nudibranch from the food it ingests as its primary defence mechanism. As this species is considered to feed upon hydroids, at present no studies have been performed on M.rosea to determine whether or not this nudibranch utilises the cnidocytes from its food source as a defence mechanism against predation, or simply employs the use of a chemical defence mechanism. A detailed anatomical research study was performed at the Heron Island Research Station, and at the St. Lucia campus of the University of Queensland to determine the defence mechanism of this species.
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