Author: S. Johnson, 1984

Order: Nudibranchia  Family: Bornellidae

Maximum Size: 120 mm

Sightings: Sunshine Coast

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Bornella anguilla S. Johnson, 1984

The dendronotinid nudibranchs are not a natural grouping (called a paraphyletic group). Much work still remains to be done to settle the taxonomy of this group. Currently they are all lumped together, for convenience, on the basis of a couple of easily recognized external characteristics. They all possess raised rhinophoral sheaths plus a series of well-developed processes arranged laterally down each side of the length of the body. Some of these processes are highly branched and perform a respiratory function by acting as secondary gills, while others perform a protective function for tufts of secondary gills “sprouting” from their base.

Bornella anguilla is a dendronotinid nudibranch, one of thirteen species currently described and named in the Bornellidae Family. There are several more, known but undescribed, awaiting the attention of taxonomists.

This species is elongate and slender in shape but deep-bodied (laterally compressed). A characteristic, complex mosaic pattern of colours distinguishes this species from its relatives. The background is of a variable brownish colour developed into a network created by the overlay and crowding together of varying sized and irregular shaped patches of white, cream, brown, yellow or orange. The spaces between the larger patches are most often filled by smaller spots of the same colours. A close examination reveals a granular texture to just below the surface of the skin.

Being a dendronotinid of course, a distinctive feature is the dorso-lateral processes. In Bornella anguilla these always present in a consistent arrangement. Posterior to the rhinophores there are firstly, three pairs of processes, each pair consisting of one process on the left side and one process on the right side of the notum, directly opposite each other. These pairings are followed by three individual keel-like processes located down the dorsal midline one after the other. The processes themselves are quite simple, consisting of a short solid stalk topped by a paddle-like extension that is trowel shaped. While the colours of the notum extend to the start of the stalk they are mostly purplish laterally and greyish medially. The paddle itself has a thick orange border around a central dark stripe. White stripes are often interposed between the orange and the dark stripe. Sprouting medially from the base of the stalk of the paired processes are feathery translucent-cream and quite well-developed secondary gills that are afforded protection by the trowel-shaped portion of those processes. They can sometimes also be seen associated with the most anterior of the singular midline processes of larger specimens. Bornella anguilla is considered to have the most developed secondary gills within the genus.

The rhinophores are lamellate, usually pale in colour and protrude from raised protective sheaths. The rhinophore sheath is tall and the colours and patterning of the notum extend thereupon. The brim of the sheath is developed anteriorly into three small thin orange-coloured finger-like papillae and posteriorly into a larger paddle-like flap not unlike those of the dorsal processes and coloured similarly.

The oral veil is divided in two and located on each side of the mouth as a broad oral flap developed anteriorly into 5 or 6 short orange, white-tipped finger-like papillae.

Bornella anguilla feeds upon a number of hydroid species. On the Sunshine Coast of Queensland, Australia we are aware of at least four species of hydroid that it preys upon across four different genera – Aglaophenia, Sertularella, Pennaria and Macrorhynchia. (Refer to the feeding images above.) There are most likely others as well but we have not been able to identify them as yet.

It is known to readily swim, eel-like and head first when disturbed by lateral flexions that travel in waves along the length of the body (anguilla = eel). With this sinuous motion it is the most efficient swimmer in the Bornellidae and probably across all of the nudibranchs. Known to grow to 120 mm in length. Distribution is widespread in the Indo-Pacific from South Africa across to Hawaii.

Prior to its description in 1984 this species was known as Bornella sp.

Above: Bornella anguilla eating hydroids. At one point the jaws of the nudibranch can be seen to be working upon the polyps.

Above: More feeding jaw action of Bornella anguilla as it strips a hydroid colony.

Above: In this video the anterior portion of the foot of Bornella anguilla can be seen clamping a hydroid stalk to steady it against the surge so that stems and polyps can be cut off for consumption.

David A. Mullins – July 2020

References:
– Bertsch, H. (1980). A new species of Bornella from tropical west-America (Mollusca, Opisthobranchia). Spixiana, 3(1): 33-42

– Willan, R.C. & Coleman, N. (1984). Nudibranchs of Australia, Neville Coleman, AMPI: 50-51

– Johnson, S. (1984). A new Indo-West Pacific species of the dendronotacean nudibranch Bornella (Mollusca: Opisthobranchia) with anguilliform swimming behavior. Micronesica, 19, 17–26.

– Rudman, W. B., (1998). Family Bornellidae Pp. 1002-1003 in Beesley, P. L., Ross, G. J. B. & Wells, A. (Eds) Mollusca: The Southern Synthesis. Fauna of Australia. Vol.5 CSIRO Publishing, Melbourne, Part B 565-1234 pp.

– 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., (2000, May 27). Bornella anguilla Johnson, 1984. [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/bornangu and associated messages.

– Pola, M., Rudman, W. B., Gosliner, T. M. (2009). Systematics and preliminary phylogeny of Bornellidae (Mollusca: Nudibranchia: Dendronotina) based on morphological characters with description of four new species. Zootaxa, 1975: 1-57.

– This Species Profile has been modified from a previously published article in Dive Log Magazine’s – Critter ID with NudiNotes Column, Issue: #379 (February 2020): 12 by David A. Mullins.