On a new terrestrial genus and species of Scottiinae (Crustacea, Ostracoda) from Australia, with a discussion on the phylogeny and the zoogeography of the subfamily

Abstract

The Scottiinae, thus far comprising the genera Scottia and Mesocypris, form an important lineage of (semi-) terrestrial ostracods within the family Cyprididae. Scottia has a mainly Holarctic distribution, while Mesocypris was thus far known from Australia (including Tasmania) and Africa (including Madagascar). Detailed description of a new species from Australia and subsequent cladistic analysis of the Scottiinae as a whole, based on morphological characteristics, showed that the two geographically separated clusters of Mesocypris s.l. actually belong in two genera. The most derived Australian clade requires the erection of a new genus. Austromesocypris n.gen., and its type species, A. berentsae n.sp. are here described. Austromesocypris n.gen. and Mesocypris s.s. are lodged in the tribe Mesocypridini, previously a subfamily synonymised with Scottiinae, but here re-instated with a change of rank, while Scottia is in the nominate tribe Scottiini. Various morphological transformation series are present in the Mesocypridini, i.e. progressive loss of natatory setae on A2 and fusion of segments on A1. The latter transformation is a reversal to aspects of juvenile morphologies through heterochronic processes. Analysis of all aspects of the A1 chaetotaxy, by comparison to an ontogenetic sequence of another cypridinid, shows that evolution of different characters (e.g. segment fusion and number and position of setae) has occurred independently. The distribution of the Scottiinae in the southern Hemisphere is briefly discussed in light of past continental distributions.