503 Accepted by D. Gieger: 16 Apr. 2004; published: 4 May 2004 1 ZOOTAXA ISSN 1175-5326 (print edition) ISSN 1175-5334 (online edition) Copyright © 2004 Magnolia Press Zootaxa 503: 1–13 (2004) www.mapress.com/zootaxa/ An unusual dendrodorid: redescription of the tropical nudibranch Dendrodoris atromaculata (Alder & Hancock, 1864) (Anthobranchia: Doridoidea: Dendrodorididae) GILIANNE D. BRODIE School of Marine Biology & Aquaculture, James Cook University, Queensland, Australia 4811 gilianne.brodie@jcu.edu.au ABTRACT Dendrodoris atromaculata (Alder & Hancock, 1864) is a large, tropical nudibranch mollusc living in the Indo-west Pacific Ocean. A detailed description of the external morphology of the living ani- mal and an investigation of internal anatomy are presented for the first time. In addition the micro- structure of certain organs (i.e., notal tissue and the vestibular gland associated with the reproductive system) are compared with other Dendrodoris species. Dendrodoris atromaculata is unique among currently described species of Dendrodoris in three respects, the gill structure is “cross-like”, the notum possesses prominent spicules and the notum is covered in finger-like pro- cesses. These findings necessitate a reassessment of previously documented generic features of Dendrodoris and reveal a need for changes to future phylogenetic analyses of both porostome and cryptobranch dorids. Key words: nudibranch, Dendrodoris, Dendrodorididae, histology, radula-less INTRODUCTION Indo-Pacific members of the genus Dendrodoris are in need of taxonomic review (Rud- man 1998; Valdés & Gosliner 1999). At least twelve members of the genus are found in Australian waters (Brodie 2002). Several of these species, i.e., Dendrodoris maugeana Burn, 1962 and D. carbunculosa (Kelaart, 1858), are relatively rare and this has hindered interspecific comparison. An investigation of another such rare species follows; it provides new information of the morphological and anatomical characteristics of D. atromaculata (Alder & Hancock, 1864) a large tropical nudibranch first described from the south-east- ern coast of India, and barely mentioned in the literature since (see Eliot 1906a; Willan & Coleman 1984).