Family RHYSODIDAE

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Family RHYSODIDAE

Compiler and date details

2002 - Updated by Andrew A. Calder, CSIRO Entomology, Canberra, Australia

1987 - B.P. Moore, T.A. Weir & J.E. Pyke

Introduction

This small and relatively uniform, but cosmopolitan, group is generally accorded the status of a separate family within the Adephaga. The presence of certain adult morphological features, however, such as tactile setae and an advanced form of antenna cleaner, together with the structures of the pygidial defensive system (Forsyth 1972) and of the male genitalia, all point to a close relationship with the Carabidae. This led Bell & Bell (1962) to suggest that the Rhysodidae represent merely a specialised offshoot of Carabidae and that they should be placed in that family as a tribe, Rhysodini, next to the Scaritini. Such a placement, though plausible, would imply a significant secondary change in feeding habits for rhysodines, together with substantial re-adaptation of adult and larval characters, for which there is little direct evidence. The traditional view would relate the fundamental similarities between Rhysodidae and Carabidae with common ancestry and interpret the superficial resemblance between the former and the Scaritini as being due to convergence. However, Beutel's (1990, 1992) phylogenetic analysis of the external metathoracic structures, musculature and larval head capsule of Omoglymmius hamatus (LeConte) failed to support the hypothesis of the Rhysodini (or Rhysodidae) being a first offshoot of the adephagan phyletic tree but supported a position of the Rhysodini within a monophyletic group comprising Geadephaga excluding Trachypachini as well as suggesting a closer relationship between Scaratini and Rhysodini (see also Bell & Bell 1962 and Baehr 1979). Our present knowledge does not permit clarification of the postion of Rhysodini within Adephaga, but must await further more inclusive and comprehensive studies of the Adephaga.

Recent revisional studies (Bell & Bell 1978, 1979, 1982, 1985, 1993) have greatly augmented the known world fauna of this family, which at present stands at 19 genera and some 340 species. The Australian fauna currently comprises five genera and 13 species, but additional undescribed species exist in collections. Bell & Bell (1991) revised the Australian species giving keys to tribes and genera and discussed the zoogeography of the group. The following tribes (corresponding to subtribes of Bell & Bell 1978, 1991) are represented: Leoglymmiini (Leoglymmius), Sloanoglymmiini (Sloanoglymmius), Rhysodini (Kaveinga), Clinidiini (Rhyzodiastes) and Omoglymmini (Omoglymmius ).

Adult rhysodids are elongate, slow-moving insects, with heavily sclerotized and characteristically sculptured cuticle. Their short, stout legs enable them to force their way through soft and very rotten wood where they are believed to feed upon slime-mould plasmodia. The grooves present on the head, pronotum, and sometimes also the elytra, accumulate these plasmodia and may serve to transport an inoculum from one site to another. The larvae are elongate, fusiform and fleshy, with short, widely separated legs, but lacking urogomphi. They occur in the same situations as the adults and have similar feeding habits. The larval differences between genera appear to be minor, but the following genera have been described: Clinidium Kirby (Böving & Craighead 1931), Omoglymmius Ganglbauer (Grandi 1955), Rhysodes Dalman (Burakowski 1975) and Rhyzodiastes Fairmaire (Vanin & Costa 1978). Burakowski's paper also includes useful information on the biology of Rhysodes sulcatus F. in Poland, but there are no published data concerning the early stages of the Australian species.