Author: Donohoo & Gosliner, 2023

Order: Nudibranchia  Family: Discodorididae

Maximum Size: 120 mm

Sightings: Sunshine Coast

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Halgerda labyrinthus Donohoo & Gosliner, 2023

This is a large species of Halgerda. The single specimen we have sighted, was on the Sunshine Coast in December of 2012, and measured 120 mm. 

Halgerda labyrinthus is oval in shape and high in profile. At rest it can appear almost circular in shape. The central notum carries a few large ridges peaking at their intersections while the whole notum bears irregular low yellow ridging. The background colour is white being covered in a maze or labyrinth of fine, alternating, connected black/dark brown and yellow lines (hence its name).Some of these lines reach the mantle margin perpendicularly while others stop short. The mantle margin carries a yellow band and irregularly spaced small but slightly raised yellow tubercles. There are also dark spots submarginally at intervals. The Sunshine Coast specimen also exhibited a submarginal ring of distinctive raised white tubercles at intervals.

The large thick rhinophore stalks are white with vertical dark lines/dashes. The somewhat smaller lamellate clubs are tapered, canted posteriorly on their stalks and covered in dark spots. The rhinophore pockets are rimmed in yellow. The large gill has four tripinnate branches, two anterior and two posterior with each of the posterior further divided into two. They are essentially white and pale yellow and covered in dark spots. The gill pocket has a smooth white rim that receives small yellow ridges from the notum.

Interestingly in the remarks section of the description the authors state that Halgerda labyrinthus is a deep water species found in depths from 27-51 metres. Our Sunshine Coast specimen was found in just 10 metres of water.

Halgerda labyrinthus is a spongivore.

Reported distribution according to the authors of the paper is the Izu Peninsula of Honshu, Japan; the Ryukyu and Kerama Islands of southern Japan and Taiwan, with the type locality in Okinawa. Our find on the Sunshine Coast greatly extends the known distribution and suggests intermediate localities.

– This is the Halgerda willeyi of Nakano, 2004 p.131 Fig.E.
– This is the Halgerda sp. 11 of Debelius & Kuiter, 2007 p. 234. 

Previously known on this website, until the 2023 description, as Halgerda sp. 01. (Changed 24/08/2023)

David A. Mullins – August 2023

References:
– Nakano, R. (2004). Opisthobranchs of Japan Islands. Rutles, Tokyo

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

– Donohoo, S. A., Villalobos, S. G., Hallas, J. M. & Gosliner, T. M. (2023). Hyperdiversity of the genus Halgerda Bergh, 1880 (Nudibranchia: Discodorididae) with descriptions of fourteen new species. Marine Biodiversity. 53(3): 42: 1-60.