Observations on ponticocythereis tricristata (Brady, 1880) from the Admiralty Islands, Papua New Guinea and comments on quaternary ostracod evolution within the sw Pacific Ocean

The ostracod species originally described as <i>Cythere tricristata</i> Brady, 1880 from the Admiralty Islands, Papua New Guinea, appears to belong to the SW Pacific and Australasian genus <i>Ponticocythereis</i> McKenzie, 1967 (<i>sensu</i> Warne & Whatley 1996). This interpretation is based on the presence of some posterior pointing scale-like spines on the carapace surface of this species. SEM images of the type material for <i>Ponticocythereis tricristara n</i>. comb., which are presented here for the first time, enable the clear differentiation of this species from the very similar <i>Ponticocythereis ichthyoderma</i> (Brady, 1890), <i>Ponticocythereis quadriserialis</i> (Brady, 1890) and <i>Ponticocythereis laingensis</i> (Wouters, 1981). As a consequence of the subdued manifestation of scale-like or blade-like spines on adult specimens of <i>P. tricristata</i>, this species closely resembles juvenile rather than adult specimens of some other <i>Ponticocythereis</i> species. This ontogenetic/phylogenetic relationship suggests that paedomorphic processes were significant in the Quaternary evolutionary radiation of Ponticocythereis species within tropical SW Pacific and Australasian regions.<br /><br />