Rediscovery of Hallaxa fuscescens

August 21, 2006
From: Bill Rudman

PHOTOS: Upper right:  Arrawarra Head, Coffs Harbour, nthn New South Wales, Australia. intertidal, on Halisarca. 16 March 1982. Live length 18 mm. AM C115783.  A. Doris fuscescens Pease, 1871: Plate 4, fig.3, 3a-c. B. Kentrodoris nigra Risbec, 1928: Plate 2, fig.6

In Gosliner & Johnson's (1994) review of Hallaxa, a new species Hallaxa atrotuberculata is proposed for a species from Madagascar and the Marshall Islands which is characterised externally by its rounded black tubercles. I have also found this species in Tanzania, Australia and New Caledonia. As I show here, there would appear to be at least two earlier names for this species

Doris fuscescens Pease, 1871b: 14, Pl.4, fig.3, 3a-c.
Kentrodoris nigra Risbec, 1928a: 91, Pl.2, fig.6., Risbec, 1953: 37.
Hallaxa nigra: Pruvot-Fol, 1930: 231.
Hallaxa atrotuberculata Gosliner & Johnson, 1994: 159-163, Figs 1A, 6, 7.

Pease (1871) described Doris fuscescens, from Maiao Is, Society Islands, which is identical in colour and has the typical gill arrangement of this group. The relationship is further confirmed by the description of the head region as `Mouth notched beneath; no distinct head or labial tentacles'. Risbec (1928) described Kentrodoris nigra from New Caledonia. The description is based entirely on the external features. The mantle is translucent gray with rounded black tubercles. The bipinnate gills form a tight circle, and the buccal tentacles are described as `lobiform', which are characteristic of Hallaxa. Pruvot-Fol (1930) in fact placed it in the genus Hallaxa.

This species clearly has a wide Indo-West Pacific distribution, and as I report in a separate message [#17533 ] it feeds on a species of halisarcid sponge.  The appropriate name for this species would appear to be Hallaxa fuscescens.

  • Pease, W.H. (1871) Descriptions of new species of Nudibranchiate Mollusca inhabiting Polynesia. No.2. American Journal of Conchology. 7 (1): 11-19 
  • Pruvot-Fol, A. (1930) Diagnose provisoires (incomplètes) des espèces nouvelles et liste provisoire des mollusques nudibranches recueillis par Mme. A. Pruvot-fol en nouvelle Calédonie (Ile des Pins). Bulletin du Museum National d'Histoire Naturelle Paris, 2: 229-232.
  • Risbec,  J. (1928) Contribution a l'étude des nudibranches Néo-Calédoniens. Faune des Colonies Francaises, 2(1): 328, pls.1-12.     
  • Gosliner, T.M. & Johnson, S. (1994) Review of the genus Hallaxa (Nudibranchia: Actinocyclidae) with descriptions of nine new species. The Veliger, 37(2): 155-191.
Rudman, W.B., 2006 (Aug 21) Rediscovery of Hallaxa fuscescens. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from


Hallaxa fuscescens

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