Author: (Kelaart, 1858)

Order: Nudibranchia  Family: Chromodorididae

Maximum Size: 30 mm

Sightings: Sunshine Coast, Capricorn/Bunker Group GBR

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Goniobranchus fidelis  (Kelaart, 1858)

A small but distinctive species of cryptobranch dorid nudibranch fairly common in the central area of its distribution range and having a variable presentation associated with the size, shape and colouration to the scallops of the marginal mantle band.

Goniobranchus fidelis is smooth, elongate oval in shape with the mantle completely overhanging the foot apart from a small portion of the tail.

The mantle dorsum is white to creamy-white. The mantle margin most usually, carries a broad band of orange/red that is formed into several scallops, or “tongue-like patches” – Rudman, intruding upon the white. These tongues may be edged, wholly or in part, with a darker port-wine colour (at times hardly noticeable), or may consist entirely of that darker colour. Where the dorsum is creamy white rather than white, another narrow band of white, following the scalloped outline completely, or intermittently, may be present. The tongues may be quite small and low or may be as large as reaching completely across the dorsum creating compartments of white in between. At times, the tongues may themselves have scalloped edges giving rise to a serrated appearance. The number of these tongues can be from 4 to 6 on each side with one or two more at both the anterior and posterior ends. The foot and tail are white, the tail most often protruding posteriorly from under the mantle. Kelaart’s coloured  illustration of Doris fidelis was not published with his descriptive text in 1858 however Eliot included it with his 1906 paper on nudibranchs of southern India and Ceylon – see image gallery.

Defensive mantle glands are often obvious as lighter coloured spots distributed right around the mantle margin within the orange/red band.

The rhinophores are large with a translucent stalk and a black club (sometimes with a white tip) however there are specimens with quite pale brown clubs. The rhinophores can be withdrawn into a pocket below the mantle surface. The simple gill too is black with white spots often visible along the length of the rachises. It consists of from 5 to 8 branches arranged in a circle, open posteriorly, around the anal papilla. The gill can be withdrawn into a pocket beneath the mantle surface (cryptobranch). There are specimens with a light brown gill to match their brown rhinophores.

Goniobranchus fidelis feeds upon sponges of the Darwinellidae family – Chelonaplysilla spp. including Chelonaplysilla violacea.

Distribution is broadly Indo-Pacific – from the Red Sea to South Africa across the Indian Ocean – from Japan and Hong Kong right down through SE Asia and Melanesia to Fiji, Lord Howe Island and the central coast of NSW.

Rudman (1985) is of the opinion that similar looking specimens from central and northern NSW, possessing red tongues separated from the orange border as patches, are a colour variation of this species.

Goniobranchus fidelis is another of those early described nudibranchs with a subsequent chequered history of names and synonyms.
– Previously known as Chromodoris fidelis
– Originally described as Doris fidelis Kelaart, 1858
– Rudman described a species called Chromodoris krishna in 1973 but had second thoughts and synonymized it with Chromodoris fidelis in 1985.
– Other synonymized names include Chromodoris flammulata Bergh, 1905, Chromodoris lactea Bergh, 1905 and Glossodoris fidelis (used by Pruvot-Fol in 1951, Baba in 1953 and Risbec in 1953).

David A. Mullins – December, 2021

References:
– Kelaart, E. F. (1858). Description of new and little known species of Ceylon nudibranchiate molluscs, and zoophytes. Journal of the Ceylon Branch of the Royal Asiatic Society. 3: 84-139.

– Eliot, C. N. E. (1906). On the nudibranchs of Southern India and Ceylon, with special reference to the drawings by Kelaart and the collections belonging to Alder & Hancock preserved in the Hancock Museum at Newcastle-upon-Tyne. Proceedings of the zoological Society of London, 636-691, pls 42-47.

– Rudman, W. B. (1973). Chromodorid opisthohranch Mollusca from the Indo-West Pacific. Zoological Journal of the Linnean Society. 52: 175-199.

– Willan, R.C. & Coleman, N. (1984). Nudibranchs of Australia, Neville Coleman, AMPI: 26-27

– Rudman, W. B. (1985). The Chromodorididae (Opisthobranchia: Mollusca) of the Indo-West Pacific: Chromodoris aureomarginata, C. verrieri and C. fidelis colour groups. Zoological Journal of the Linnean Society. 83: 241-299.

– Rudman, W. B. (1999 June 1) Chromodoris fidelis (Kelaart, 1858). [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/factsheet/chrofide and associated messages.

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

– Coleman, N. (2008). Nudibranchs Encyclopedia. Neville Coleman’s Underwater Geographic Pty Ltd, Springwood, Qld.

– 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)

– MolluscaBase eds. (2021). MolluscaBase. Goniobranchus fidelis (Kelaart, 1858). Accessed through: World Register of Marine Species at: http://www.marinespecies.org/aphia.php?p=taxdetails&id=597334 on 2021-12-15