Author: Rudman, 1987

Order: Nudibranchia  Family: Goniodorididae

Maximum Size: 10 mm

Sightings: Sunshine Coast

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Trapania aurata  Rudman, 1987

Fifteen years ago while on a shallow shore-entry dive off the Mooloolaba Beach against the Mooloolah River rock training walls on the Sunshine Coast, Qld, I photographed a small white nudibranch with orange tips to some of its appendages. At the time I identified it as Trapania aurata and based on the taxonomy at that time it was a correct identification. However, just over two years later, in early 2008, an extensive review of the Trapania genus was published by Terry Gosliner and Shireen Fahey, wherein sixteen new species of the Trapania genus were described and named. Among these was a Trapania aurata lookalike – Trapania vitta. This newly described species matched the one I had recorded so a name change was required for the species I had found.

Fast forward to November 2019 and another shallow shore dive, this time at La Balsa Park towards the mouth of the Mooloolah River. Under a small overhang upon a cream coloured sponge was another white Trapania this time with all the appendages coloured orange. We had finally found the true Trapania aurata this time, here in our backyard. Interesting to note, is that earlier in the month several specimens of Trapania vitta were also recorded by us in the same area. The Mooloolah River has produced, to the Sunshine Coast Sea Slug Survey Team’s searching, nine species of Trapania over the past six years.

Just a cursory look will not separate these two species on external features. Differences in radula and reproductive morphology though, confirm the distinctness of the two species. The main external differences are that Trapania aurata has orange (sometimes referred to as golden-yellow) colouration to the comparatively large tentacular anterior foot (propodial) corners and also on the extra-rhinophoral and extra-branchial processes. That orange colouration on those particular processes is lacking in Trapania vitta. Additionally it also bears the orange colouration to the oral tentacles, rhinophores, gills and as a stripe located dorso-posteriorly on the midline of the body, as also borne by Trapania vitta.

The Trapania are true nudibranchs. They are grouped with the phanerobranchs whereby the gill is non-retractile, lacking a protective pocket below the mantle surface into which it could be withdrawn. Instead, they possess extra-branchial processes that serve as a form of protection beside the gill. They also possess similar appendages for the protection of the non-retractile rhinophores – extra-rhinophoral processes, and quite well-developed oral and propodial tentacles believed to act in a combined chemical and tactile sensory function. The body is small, narrow, elongate and is lacking a distinct mantle rim. The foot is narrow.

Trapania gibbera is also similar in appearance to the previously mentioned pair and is another of the species first described in the review by Gosliner & Fahey. It too is solid white and exhibits orange colouration to the gills, rhinophores and oral tentacles but may be differentiated by the possession of a distinct dark bar located transversely across the anterior of the head between, and joining, the oral tentacles. There are at least another twenty undescribed species of Trapania still awaiting the attention of taxonomists in the Indo-Pacific region alone.

Species of Trapania are most often found upon sponges but it is believed they are feeding, not on the sponge tissue, but instead on the tiny colonial entoprocts that grow in association with the sponge.

The specific epithet of aurata is a reference to the “golden” markings carried by this species – aurata: derived from the Latin for gilded or golden.

David A. Mullins – December 2020

References:

– Rudman, W. (1987). The genus Trapania (Nudibranchia: Goniodorididae) in the Indo-West Pacific. Journal of Molluscan Studies, 53, 189–212.

– Rudman, W. B., (1998 November 17). Trapania aurata Rudman, 1987. [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/factsheet/trapaura and associated messages.

– Gosliner, T. M. & Fahey, S. J. (2008). Systematics of Trapania (Mollusca: Nudibranchia: Goniodorididae) with descriptions of 16 new species. Systematics and Biodiversity 6 (1): 53–98.

– Rudman, W. B., (2008 March 10). Trapania vitta Gosliner & Fahey, 2008. [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/factsheet/trapvitt and associated messages.

– This Species Profile has been modified from a previously published article in Dive Log Magazine’s – Critter ID with NudiNotes Column, Issue: #378 (January 2020): 18 by David A. Mullins.