Currently, between one-third and two-thirds of marine species may be undescribed, and previous estimates of there being well over one million marine species appear highly unlikely. More species than ever before are being described annually by an increasing number of authors. If the current trend continues, most species will be discovered this century.

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A revision of the genus Pachygrapsus Randall, 1840 (Crustacea: Decapoda: Brachyura, Grapsidae), with special reference to the Southwest Pacific species (Zootaxa 1015) 66 pp.; 30 cm.

The shovel-nosed lobster genus Thenus Leach, 1815, long considered to contain only Thenus orientalis (Lund, 1793), is revised and five species recognised. Thenus indicus Leach, 1815, which had been relegated to the synonymy of T. orientalis, is reinstated and a lectotype designated. Three new species T. australiensis, T. unimaculatus and T. parindicus are diagnosed. Specimens of Thenus were collected from various locations throughout the Indo-West Pacific Oceans. Samples were analysed using a concordance approach involving three techniques: morphometrics/morphology, starch gel isozyme electrophoresis, and mitochondrial DNA sequencing of 16S and COI genes. All three investigations supported the recognition of five species. Despite significant genetic divergence, several sympatric species are morphologically similar and identification can be difficult; a key using a combination of live colour patterns and morphometric ratios is presented as an aid to species discrimination.