Troglobitic millipedes (Diplopoda: Paradoxosomatidae) from semi-arid Cape Range, Western Australia: systematics and biology

Abstract

Paradoxosomatid millipedes are an important component of the rich troglobitic fauna of the semi-arid tropical Cape Range, Western Australia. They are found in at least 55 of the 282 caves known from Cape Range covering >500 km2. The millipedes occur in dense populations only in areas of high relative humidity and organic carbon content. They appear to be opportunistic and are able to grow and breed rapidly on the intermittently available patches of organic matter washed into the caves by unpredictable rainfall. A new genus of paradoxosomatid millipedes (Stygiochiropus, gen. nov.), comprising three species (S. communis, sp. nov., S. sympatricus, sp. nov., and S. isolatus, sp. nov.) is described from the caves. A key is provided for males, but females cannot be identified. The only widespread species (S. communis) separates into three provinces between which there are many fixed allelic differences, as determined by allozyme electrophoresis. Although these genetic provinces are separated by deep gorges that cut through the cavernous limestone into the underlying non-cavernous strata, the millipede populations cannot be separated using morphological criteria. The affinities of the millipedes are unknown, but they are part of a rich community of troglobites (>26 species) of which many species have affinities with the northern wet tropical forest fauna, rather than with the current semi-arid fauna.