Author: Carlson & Hoff, 2000

Order: Nudibranchia  Family: Discodorididae

Maximum Size: 40 mm

Sightings: Whitsundays, Lembeh Indonesia, Anilao Philippines

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Halgerda batangas Carlson & Hoff, 2000

Halgerda batangas is oval in shape, high in profile and recorded in size up to 40 mm. The notum carries ridges and large tubercles are present at their junctions. Additional smaller tubercles occur along the ridges, randomly on the notum and around mantle margin. The surface of the notum is otherwise smooth. The body is translucent white with a network of fine red or orange lines covering the entire dorsum. There is a degree of variation, with some specimens exhibiting a genuine network whilst others present just with fine lines without or minimal crossover. The aforementioned tubercles are tipped in red/orange that is surrounded by a circle of white. The low tubercles on the mantle margin lack this white circle. The translucent white foot and tail carry a thin orange marginal band.

The rhinophores have long bases and long clubs with the clubs canted somewhat posteriorly. The clubs are lamellate and taper to a point. Both bases and clubs are translucent white with random dark brown spots. In many specimens there is a small tubercle situated posterior-laterally on the otherwise smooth low rhinophore sheaths. There are four main gill branches with some sparse secondary branching evident. They form a circle around the anus. The gills also, are translucent white with dark brown spots. The gill pocket is low with a smooth edge. The oral tentacles carry an orange tip. When mating the swollen connected gonopores display the same dark brown spotting as the gill and rhinophores.  

Halgerda batangas is a spongivore.

Distribution is broadly the western and central Pacific Ocean including: Philippines; Malaysia; Indonesia; PNG; Solomon Islands; New Caledonia; Fiji & tropical Queensland, Australia.

The specific epithet of batangas is derived from a popular diving locality in the Philippines where the species is commonly sighted and specimens were collected to aid in its description.

This species is the Halgerda sp. of Willan & Coleman, 1984, Fig. 117; the Halgerda aff. carlsoni of Marshall & Willan, 1999, Fig. 131.

David A. Mullins – August 2023

References:
– Willan, R. C. & Coleman, N. (1984). Nudibranchs of Australia, Neville Coleman, AMPI: 28-29.

– 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.

– Carlson, C. H. & Hoff, P. J. (2000). Three new Pacific species of Halgerda (Opisthobranchia: Nudibranchia: Doridoidea). The Veliger 43(2):154–163.

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

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

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