Author: (Angas, 1864)

Order: Nudibranchia  Family: Chromodorididae

Maximum Size: 65 mm

Sightings: Sunshine Coast

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Goniobranchus splendidus (Angus, 1864)

The colouring and marking of Goniobranchus splendidus serve to make it a most conspicuous nudibranch. I even recall spotting a specimen, down on the seabed from the surface prior to descending for a dive in over 12 metres of water.

It is a large nudibranch of up to 65 mm in length but most often seen in the 30 to 40 mm range. The mantle exhibits a relatively large overlap, is bright white, marked with a few large blood-red blotches or many red spots depending on locale, and trimmed around the margin with golden yellow. The rhinophore clubs too are blood-red in colour with white to the very edge of the lamellae. Most of the stalk is translucent white. The gills are quadrangular in cross-section being translucent white with distinct red lines traversing from the tip of each down all of the four corners and joining across to the next. The posterior end of the foot is not always visible but when it is it may or may not exhibit a gold margin like that of the mantle however the rest of the foot is without a coloured border.

The currently reported distribution is quite limited extending only from southern New South Wales to central Queensland on the east coast of Australia and is considered a common species in some of those coastal waters. It is listed in Nimbs & Smith’s 2017 Sea Slug Inventory of NSW as far south as Narooma but It does not appear in Burn’s 2006 Checklist of Opisthobranchia of Victoria and Bass Strait. Northern limit is currently recorded as the Percy Isles, just south of Mackay as reported in Wilson, Winters & Cheney’s 2016 paper: Tropical Range Extension for the Temperate, Endemic South-Eastern Australian Nudibranch Goniobranchus splendidus (Angas, 1864).

In its southern range Goniobranchus splendidus displays a more spotted arrangement of mantle markings compared to the large single or couple of smaller blotches of those sighted further north as illustrated above. At the extreme northern extent of its range the blotches again revert to spots. This spotting gives it a somewhat similar appearance to a number of other dorids including Goniobranchus daphne and Mexichromis festiva that have a much similar distribution. This is quite possibly an example of aposematic colouration whereby a group of animals display similar colour and pattern in order to spread the load of warning (“teaching”) potential predators, mainly fish, that they possess distasteful/poisonous mantle glands. Just to confuse even more though, specimens of what is believed to be G. splendidus, devoid of any red markings at all on the mantle, have been found. These plain variants are not particularly common. At times individuals will also turn up with markings that are orange rather than blood-red and this paler colour usually extends to the gills and rhinophores as well.

This species lays an anticlockwise bright yellow upright egg spiral with large egg capsules and extra-capsular yolk and the larvae are believed to develop lecithotrophicly whereby after hatching they only spend a very short time in the plankton and do not feed there.

Goniobranchus splendidus feeds upon a number of different sponges of the Darwinella genus that are mainly pink or yellow and also a Dictyodendrilla sp. that is very dark in colour.

Previously known as Chromodoris splendida.

Originally described as Goniodoris splendida.

Goniobranchus splendidus moving across the substrate in search of its sponge prey. Note its left (at top) rhinophore actually rotating as it samples the chemical cues in the water column.

David A. Mullins, July 2019

References:
– Angas, G.F. (1864). Description d´éspèces nouvelles appartenant à plusieurs genres de mollusques nudibranches des environs de Port-Jackson (Nouvelle-Galles du Sud), accompagnée de dessins faits d´après nature. Journal de Conchyliologie. series 3(12): 43-70., page(s): 55-56, Pl. 5, Fig. 2

– Rudman, W.B. (1983). The Chromodorididae (Opisthobranchia: Mollusca) of the Indo-West Pacific: Chromodoris splendida, C. aspersa and Hypselodoris placida colour groups. Zoological Journal of the Linnean Society, 1983, 78, 105–173.

– Rudman, W.B. (1984). The Chromodorididae (Opisthobranchia: Mollusca) of the Indo-West Pacific: A review of the genera. Zoological Journal of the Linnean Society, 1984, 81, 115–273.

– Rudman, W.B. (1990). The Chrornodorididae (Opisthobranchia: Mollusca) of the Indo-West Pacific: further species of Glossodoris, Thorunna and the Chromodoris aureomarginata colour group. Zoological Journal of the Linnean Society, 1990, 100, 263–326.

– Rudman, W.B. (1991). Purpose in Pattern: the evolution of colour in chromodorid nudibranchs. Journal of Molluscan Studies, 57: 5-21.

– Marshall, J.G., Willan, R.C. (1999). Nudibranchs of Heron Island, Great Barrier Reef: A survey of the Opisthobranchia (sea slugs) of Heron and Wistari Reefs; Backhuys: Leiden, The Netherlands, 1999.

– Rudman, W.B., 2003 (Mar 11). Comment on Chromodoris splendida laying eggs by Leanne & David Atkinson. [Message in] Sea Slug Forum. Australian Museum, Sydney.

– Burn, R. (2006). A checklist and bibliography of the Opisthobranchia (Mollusca: Gastropoda) of Victoria and the Bass Strait area, south-eastern Australia. Museum Victoria Science Reports 10: 1-42 (2006).

– Rudman, W.B., Bergquist (2007) A review of feeding specificity in the sponge-feeding Chromodorididae (Nudibranchia: Mollusca). Molluscan Research, 27(2): 60-88.

– Rudman, W.B., 2008 (Feb 4). Comment on Re: Chromodoris splendida laying eggs by Leanne & David Atkinson. [Message in] Sea Slug Forum. Australian Museum, Sydney.

– Johnson, R.F., Gosliner, T.M. (2012). Traditional taxonomic groupings mask evolutionary history: A molecular phylogeny and new classification of the chromodorid nudibranchs. PLoS One 7 (4): e33479.

– Wilson, N.G., Winters, A.E., Cheney, K.L. (2016). Tropical Range Extension for the Temperate, Endemic South-Eastern Australian Nudibranch Goniobranchus splendidus (Angas, 1864). Diversity 2016, 8, 16.

– Nimbs, M.J., Smith, S.D.A. (2017). An illustrated inventory of the sea slugs of New South Wales, Australia (Gastropoda: Heterobranchia). Proceedings of the Royal Society of Victoria 128: 44-113.

– Winters, A.E., Wilson, N.G., van den Berg, C.P., How, M.J., Endler, J.A., Marshall, N.J., White, A.M., Garson, M.J., Cheney, K.L. (2018). Toxicity and taste: unequal chemical defences in a mimicry ring. Proceedings of the Royal Society B 285: 20180457.

– This Species Profile has been modified from a previously published article in Dive Log Magazine’s – Critter ID with NudiNotes Column, Issue: #362 (September 2018): 12 by David A. Mullins