Family PILUMNIDAE Samouelle, 1819

<em>Pilumnus kingstoni</em> (half denuded to show carapace detail) [from Rathbun 1923: pl. 30]

Pilumnus kingstoni (half denuded to show carapace detail) [from Rathbun 1923: pl. 30]

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Family PILUMNIDAE Samouelle, 1819

Compiler and date details

May 2012 - Peter Davie, Queensland Museum, Brisbane

Taxonomic Decision for Synonymy

Sakai, T. 1976. Crabs of Japan and the Adjacent Seas. Tokyo : Kodansha 3 vols xxix 773 pp. [English vol.]; 1–16, 251 pls [Plates vol.]; 461 pp. [Japanese vol.].
Serène, R. 1984. Crustacés Décapodes Brachyoures de l'Océan Indien occidental et de la Mer Rouge. Xanthoidea: Xanthidae et Trapeziidae. Avec un addendum par Crosnier, A.: Carpilliidae et Menippidae. Faune Tropicale 24: 1-400 figs A-C, 1-243 pls 1-48
Ng, P.K.L. 1987. The Indo-Pacific Pilumnidae II. A revision of the genus Rhizopa Stimpson, 1858, and the status of the Rhizopinae Stimpson, 1858 (Crustacea, Decapoda, Brachyura). Indo-Malayan Zoology 4: 69-111 figs 1, 2 pl. 1 table 1
Stevcic, Z., Castro, P. & Gore, R.H. 1988. Re-establishment of the family Eumedonidae Dana, 1853 (Crustacea: Brachyura). Journal of Natural History 22: 1301-1324
Ng, P.K.L. & Clark, P.F. 2000. The eumedonid file: a case study of systematic compatibility using larval and adult characters (Crustacea: Decapoda: Brachyura). Invertebrate Reproduction and Development 38(3): 225-252
Ng, P.K.L. & Clark, P.F. 2000. The Indo-Pacific Pilumnidae 12. On the familial placement of Chlorodiella bidentata (Nobili, 1901) and Tanaocheles stenochilus Kropp, 1984 using adult and larval characters with the establishment of a new subfamily, Tanaochelinae (Crustacea: Decapoda: Brachyura). Journal of Natural History 34(2): 207-245

Introduction

Pilumnids are a diverse group of small benthic crabs found in all oceans. Pilumnids mostly live under rocks, in crevices, and amongst coral and epizoic fauna on coral and rocky reefs, but a few live in the low intertidal zones of muddy and rocky shores, or in estuaries, and a number are trawled or dredged from sandy to muddy bottoms. Many are small and covered in long setae which feature has led to their common epithet of `hairy crabs'. A number of species show only subtle morphological differences, and this, combined with their setal covering, makes them notoriously difficult to identify. Members of one aberrant group, the Eumedoninae, live symbiotically on, and sometimes within, echinoderms, with some species having developed bizarre shapes as an adaptation to their hosts. While at first appearing totally different from all other pilumnids, their affinities become obvious when the characteristic pilumnid male first and second gonopods are examined.

No single work is available for identification of pilumnid species. Sakai (1976) remains one of the most useful general works. Papers dealing with Australian species include: Griffin (1970), Griffin & Yaldwyn (1971), Davie (1988, 1989a, 1989b, 1993), Ng & Davie (1991) and Ng (1992). Ng (1987) reviewed the subfamily Rhizopinae and formally moved it from the Goneplacidae into the Pilumnidae. Guinot (1971, 1978) also placed Galene and Halimede in the Pilumnidae, with the names Galeninae Alcock, 1898, and Halimedinae Alcock, 1898, being available to accommodate them, however recent opinion is that the Galenidae should be of family rank, with the Halimedinae as a subfamily under it (see Ng et al. 2008).

The phylogenetic relationships of the Eumedoninae, and thus its appropriate taxonomic rank, have been a matter of uncertainty. For many years it was treated as a subfamily of the Parthenopidae Miers, 1879. However, the most recent comprehensive revision by Stevcic, Castro & Gore (1988) showed clearly that these crabs are closely affiliated with the Pilumnidae Ortmann, 1893. These authors argued, nevertheless, for their placement in a separate family, with two constituent subfamilies—Eumedoninae Dana, 1853, and Ceratocarcininae Stevcic, Castro & Gore, 1988. There is still some doubt over justification for this subfamilial division, with more recent revisionary studies finding that the taxa overlap in most characters previously used to separate them (Castro pers. comm.). Compelling recent opinion is to treat the Eumedoninae as a subfamily of the Pilumnidae (Ng & Clark 2000), and I follow this position in the present work.

The Heteropanopioida Alcock, 1898, has in the recent past been treated as an alliance within the Xanthidae: Pilumninae (Sakai 1976), and more recently as a subfamily, Heteropanopeinae, of the Pilumnidae by Serène (1984). It has been recognised by the following combination of characters: carapace broadly ovate; dorsally convex; smooth or weakly granular; regions not, or only weakly, indicated; anterolateral margins with three broad teeth or lobes (never spinose); posterior margin narrow; chelipeds dissimilar, smooth or weakly granular. The generic composition of the group has varied considerably between authors, including genera as widely divergent as Panopeus H. Milne Edwards, 1834, Glabropilumnus Balss, 1932, and Parapilumnus Kossmann, 1877, all of which we now know to have no close relationship to Heteropanope. The broadly oval, smooth carapaces of species in genera such as Benthopanope Davie, 1989, Eurycarcinus A. Milne Edwards, 1867, Heteropanope Stimpson, 1858, and Pilumnopeus A. Milne Edwards, 1863, have a superficially similar appearance, but there do not seem to be any solid synapomorphic characters that unite them unequivocably, and that can define the Heteropanopeinae. Davie (1989) showed that Benthopanope has a differently shaped thoracic sternum which also belies a close relationship with Heteropanope, in which most Benthopanope species had been included previously. Eurycarcinus is also poorly defined and in need of characters to separate it adequately from Heteropanope. All the 'heteropanopeine' genera are thus restored to the Pilumninae sensu lato until future evidence is found to support alternative arrangements.

Serène (1984) erected two new subfamilies, Heteropilumninae and Planopilumninae. However, the subfamilies were diagnosed only briefly in his key to the Xanthoidea, and were not further discussed. As I consider several of the more long established pilumnid subfamilies still to be poorly defined, I choose not to recognise Serène's Heteropilumninae in this Catalogue, pending future studies of the family. The type-species of Planopilumnus, P. spongiosus (Nobili, 1905) is clearly not a pilumnid at all, because of the very different form of the male gonopods (P.K.L. Ng, pers. comm.). Following Ng et al. (2008) the Planopilumnidae is recognised as a family related to the Pseudoziidae.

Diagnosis

Carapace hexagonal, transversely rectangular or transversely ovate; dorsal surface convex, smooth or granular; frontal margin entire, bilobate or multilobate; anterolateral margins typically 1–4 teeth, lobes, or spines. Endostome with crests defining efferent branchial channels more or less well developed and continued to anterior border of buccal cavity. Claws subequal or markedly unequal, similar or dissimilar in form. Legs stout, short to moderately long. Abdomen of male with seven movable segments; elongate and narrow, covering most of sternite 4; abdomino-sternal locking mechanism present; genital openings coxal or coxo-sternal. Male first gonopod slender, sinuous, tip typically simple, recurved; second gonopod very short and sigmoid.