Author: Rudman, 1987

Order: Nudibranchia  Family: Goniodorididae

Maximum Size: 10 mm

Sightings: Sunshine Coast

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Trapania reticulata Rudman, 1987

Species of Trapania are phanerobranch dorid nudibranchs, being unable to retract their gills into a pocket below the surface of the mantle. Neither do the rhinophores have pockets for retraction. Trapania are usually small species with a consistently uniform body plan across the genus. The mantle skirt is very much reduced to just a pair of protective processes lying each side of the rhinophores and gill.

Trapania reticulata was described and named from a single specimen, collected from the Swains Reef complex of the Great Barrier Reef, Queensland, Australia, in Rudman’s 1987 review of the genus. It has been rarely sighted.

The body is slender and elongate. The most noticeable features are the sizeable extrarhinophoral and extrabranchial appendages that curve around laterally to protect the vital rhinophores and gill respectively. These arise from the lateral edge of the mantle and are considered the only vestiges of the mantle skirt, even a telltale ridge or a distinct edge being absent. The anterior corners of the foot are formed laterally into substantial propodial tentacles. The oral tentacles, carried at the most anterior position on the head, are well developed. The clavi of the rhinophores are bulbous and lamellate and have a small knob on the apex. The tail behind the gill is almost as long as the body and tends to flatten out and terminate bluntly.

The colour is translucent with a fine reticulate pattern of thin dark brown lines that have opaque to translucent yellow infills. This pattern is found almost uniformly all over the animal; on the mantle, head, oral tentacles, propodial tentacles, sides of the body, tail and the extrarhinophoral and extrabranchial processes. The rhinophores are translucent brown, the stalks being spotted with yellow and the lamellae of the clavi carrying dark brown pigment to their edge. The small knob on the apex is yellow. The gills too are translucent with brown edging and yellow spots. The sole of the foot is translucent with brown spotting, the greatest concentration being along the midline. Overall there are no stand-out markings, thus making its appearance quite cryptic upon the substrate.

The spawn is cream in colour laid as spiral, on the substrate, of at least two whorls.

The diet of Trapania reticulata is unknown. Most goniodorids feed upon ascidians or bryzoans however several Trapania species have been recorded upon sponges, not feeding on the sponge tissue but rather on the small entoprocts, also known as kamptozoans, (Phylum Entoprocta) that live in association with the sponge.

As previously mentioned sightings are sparse and reported distribution thus far is limited to: west coast of Thailand in the Andaman Sea (1); east coast of Bali in Indonesia (1); Great Barrier Reef (2) and Sunshine Coast (2) of Queensland, Australia.

Gosliner & Fahey’s 2008 examination of the phylogenetic relationships within Trapania whilst including Trapania reticulata in their data matrix excludes this species from analysis and the phylogenetic tree produced therefrom. This is due to a lack of knowledge of its reproductive characteristics, no doubt as a result of its rarity and therefore a paucity of specimens for examination.

David A. Mullins – January 2021

References:

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

– Rudman, W. B. (2000 May 21). Trapania reticulata Rudman, 1987. [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/factsheet/trapreti and associated messages.

– Fahey, S. J. (2004). A new species of Trapania (Nudibranchia: Gonodorididae) from Western Australia with comparisons to other Indo-West Pacific Trapania. Zootaxa 514, 1–12.

– Rudman, W. B. (2006 December 21). Kamptozoa (Entoprocta). [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/factsheet/kamptozoa

– 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.

– Behrens, D., image by Michlmayer, F. (2010). Opisthobranch of the Week, Week: 676. Mike Miller’s Slug Site. Available at: http://slugsite.us/bow2007/nudwk676.htm

– Gosliner, T. M., Valde ́s, A ́. & Behrens, D. W. (2018). Nudibranch & Sea Slug Identification – Indo-Pacific, 2nd Edition. New World Publications, Jacksonville, Florida, USA.