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Tenellia sibogae

Species Profile

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Tenellia sibogae

Author: (Bergh, 1905)

Order: Nudibranchia  Family: Fionidae

Maximum Size: 35 mm

Sightings: Sunshine Coast

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Tenellia sibogae (Bergh, 1905)

An aeolid nudibranch with an elongated, narrow body. The anterior foot corners are developed into blunt propodial tentacles and the tail is short and pointed. The rhinophores are long slender tapered and smooth and the oral tentacles similar but shorter. Cerata are smooth, tubular and of a reasonable length, just shorter than the rhinophores, with an abruptly pointed tip. They are arranged in clusters, approximately eight on each side of the notum down the length of the body, and sited on elevated ridges. 

Tenellia sibogae is consistently found with a particular colour arrangement on the Sunshine Coast; body: pale lilac (looking pink at times) to dark purple, rhinophores and oral tentacles: much darker than the body colour especially, at least, the distal half, cerata: most usually similar in colour to the body but with a dark subapical band ranging from a deep purple to almost a deep maroon then tipped with golden yellow. Sometimes, but not always, the outermost, smaller cerata in each cluster are golden yellow, however close examination shows that even on those, the ceratal base is still purple. However, there is a graduation of intraspecific variation, the extent of which is probably not completely apparent, as yet. Body colour from light pink to dark purple; cerata colour from white to pink to yellow to lilac, and their tips, yellow, orange, red or white with extent of tip colour varying sometimes within same specimen. The subapical band too, may vary remarkably in colour. The variation of colour within the clusters is a striking characteristic.

It may transpire that there exists a cluster of species waiting to be revealed through molecular investigation, but that can only be speculation at the moment.

Regarding the colours in the original description, the following is a translation from Bergh’s original German:
The colour appears to have been red-violet, some of the papillae, at least their tips, lemon yellow.
and
The colour was a dirty yellowish colour throughout.”

Those confusing words, together with the somewhat fuzzy and small illustration (see image gallery) accompanying the description, does not allow for a very clear interpretation for comparison to living specimens. 

Tenellia sibogae is most usually sighted upon its food – arborescent hydroids of the Sertularella genus (usually identified as Sertularella diaphanous or Sertularella quadridens) – and feeding on the polyps. Sertularella can be a large and bushy colony or merely growing as just a struggling few stems. The colour of stems and branches is orange to golden brown with the expanded polyps a translucent white.

Distribution is widespread in the Western Pacific and Indian Oceans.

– Originally described as Hervia sibogae, from a trawled specimen at Kangean Island, north of Bali in Indonesia.
– Depending on date of publication and/or taxonomy followed the names Trinchesia sibogae or Cuthona sibogae may be seen.

David A. Mullins – January 2024

References:
– Bergh, L. S. R. (1905). Die Opisthobranchiata der Siboga-expedition. Siboga-Expeditie. 50: 1-248, pls 1-20.

– 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. 257 pp. Backhuys: Leiden.

– Rudman, W. B., (2003 October 20). Cuthona sibogae (Bergh, 1905). [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/factsheet/cuthsp4 and associated messages.

– Debelius, H & Kuiter, R. H. (2007). Nudibranchs of the World. IKAN.

– Yonow, N., (2008) Sea slugs of the Red Sea. Pensoft Publishers, Sofia

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

– Davie, P., Cranitch, G., Wright, J. & Cowell, B. (2011). Queensland Museum. & Port of Brisbane Corporation (Qld.). Wild guide to Moreton Bay and adjacent coasts. Queensland Museum.

– Gosliner, T. M., Valdés, Á., and Behrens, D. W. (2018). Nudibranch & Sea Slug Identification: Indo-Pacific – 2nd Ed. New World Publications: Jacksonville, FL.

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