Family GECARCINUCIDAE Rathbun, 1904

<em>Austrothelphusa transversa</em> [from McCulloch 1917: pl. 42 fig. 1]

Austrothelphusa transversa [from McCulloch 1917: pl. 42 fig. 1]

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Family GECARCINUCIDAE Rathbun, 1904

Compiler and date details

May 2012 - Peter Davie, Queensland Museum, Brisbane

Gecarcinucinae Rathbun, M.J. 1904. Les crabes d'eau douce (Potamonidae). Nouvelles Archives du Muséum National d'Histoire Naturelle, Paris 4 6: 225-311, pls 1-10 [233].
Parathelphusinae Alcock, A.W. 1910. On the classification of the Potamonidae (Thelphusidae). Records of the Indian Museum 5(4): 253-261 [254, 255].
Type genus:
Parathelphusa H. Milne Edwards, 1853.
Spiralothelphusinae Bott, R. 1968. Parathelphusiden aus Hinterindien (Crustacea, Decapoda, Parathelphusidae). Senckenbergiana Biologica 49(5): 403-422 [403].
Type genus:
Spiralthelphusa Bott, 1968.
Somanniathelphusinae Bott, R. 1968. Parathelphusiden aus Hinterindien (Crustacea, Decapoda, Parathelphusidae). Senckenbergiana Biologica 49(5): 403-422 [406].
Type genus:
Somanniathelphusa Bott, 1968.
Ceylonthelphusinae Bott, R. 1969. Flußkrabben aus Asien und ihre Klassifikation (Crustacea: Decapoda). Senckenbergiana Biologica 50(5/6): 359-366 [364].
Type genus:
Ceylonthelphusa Bott, 1969.
Sundathelphusidae Bott, R. 1969. Flußkrabben aus Asien und ihre Klassifikation (Crustacea: Decapoda). Senckenbergiana Biologica 50(5/6): 359-366 [362].
Type genus:
Sundathelphusa Bott, 1969.
Liotelphusinae Bott, R. 1969. Flußkrabben aus Asien und ihre Klassifikation (Crustacea: Decapoda). Senckenbergiana Biologica 50(5/6): 359-366.
Nautilothelphusini Števčić, Z. 2005. The reclassification of Brachyuran Crabs (Crustacea: Decapoda: Brachyura). Natura Croatica 14(1): 1–159.

Taxonomic Decision for Synonymy

Ng, P.K.L. & Sket, B. 1996. The freshwater crab fauna (Crustacea: Brachyura) of the Philippines. IV. On a collection of Parathelphusidae from Bohol. Proceedings of the Biological Society of Washington 109(4): 695-706 [696]

Introduction

The taxonomic treatment of this group adopted here represents a marked departure from the nomenclature that has been most recently accepted. Bott (1969) erected the Sundathelphusidae for a small group of freshwater crabs, represented in Australia by seven species that he placed in his new genus and subgenus Holthuisana (Austrothelphusa) Bott, 1969. Ng (1988: 84) cast doubt upon the validity of the Sundathelphusidae as a separate family, and suggested that the characters that separate it from the Parathelphusidae Alcock, are ambiguous and unreliable. Ng & Sket (1996: 696) later formally placed Sundathelphusa in the Parathelphusidae, thus synonymising the two families. However, there has continued to be considerable interest in the phylogenetic relationsips of the freshwater crabs. In the most recent appraisal using a wide variety of morphological and genetic markers, Klaus et al. (2009) showed conclusively that the current classification of Parathelphusidae and Gecarcinucidae is not parismonious and synonymised the two families. Although there appears to be some structure inside the now enlarged Gecarcinucidae, the authors argued that more genera will need to be analysed to show the real patterns inside the family. This classification is followed here (see also Cumberlidge & Ng, 2009).

The subgenus Holthuisana (Austrothelphusa) differs sufficiently from Holthuisana sensu stricto, to be raised to full generic status. Austrothelphusa differs from Holthuisana most significantly by the shape of the male abdomen which in Austrothelphusa species is comparatively broader and less obviously T-shaped (those of several species appearing almost triangular), and in particular the distal segments are broader and less elongated. Other less obvious features are a more convex and smoother carapace that has the epigastric and postorbital cristae comparatively weaker. Peter K.L Ng (pers. comm.) also believes that the remaining Holthuisana species are polyphyletic, and may need to be further split generically.

Australian species were revised by Riek (1951), and then more comprehensively by Bishop (1963) who recognised six species. Bott (1970) recognised only two of Bishop's species, but made this judgement after examining only limited material from a restricted range of localities. Short (1994), in describing a new species, Holthuisana tigrina, again supported recognition of all six species, a view with which I concur after examination of a large collection held at the Queensland Museum.

Unlike most marine crabs, gecarcinucids do not have a planktonic larval stage, instead having direct development, with the young crabs hatching from the large eggs. Typically, the adults burrow up to about one metre in swampy ground or into the banks of rivers, creeks or waterholes. They can survive several years of drought by plugging their burrows with clay. One species, Austrothelphusa transversa, has proved enormously successful, being widespread from inland north-western Australia across the Northern Territory to the Lake Eyre Basin, the Darling River drainage system in western New South Wales, and into inland and coastal tropical Queensland.

Gecarcinucids have a very wide distribution, however a single genus.Austrothelphusa appears to be confined to Australia. Given the great extent of morphological similarity between most of the Australian species, and the fact that most are found on Cape York, a reasonable hypothesis is that the Australian representatives radiated relatively recently from a New Guinean stock that crossed to Cape York during a period of glacial land-bridge connection.