Abstract:
Neostethus djajaorum, new species, is described from specimens from the Gowa District near Ujung Pandang, Sulawesi. It is hypothesized to be most closely related to Neostethus robertsi from Luzon I., and Neostethus palawanenis from Palawan and Cuyo Is., the Philippines, with which it shares a distinctive, bifid or claw-shaped second ctenactinial bone in the intromittent organ of males. Neostethus djajaorum is distinguished from its closest relatives by the shape of the claw and extent of a bony projection and fleshy profile on the ventral margin of the first ctenactinium that abuts the claw. It is the first species in the distinctive atherinomorph fish family Phallostethidae known from east of Wallace's Line and from Sulawesi. The inferred ancestral distribution of the new species and its close relatives is coincident, in part, with limits of a now geographically dispersed ancient island-are system, the Sumba block or terrane, that comprises west Mindanao, northern Borneo (plus Palawan), east Kalimantan, the southwestern arm of Sulawesi and part of Java and the lesser Sunda Islands. The coastal and freshwater Phallostethidae and its sister taxon, the marine shorefish Dentatherinidae, have largely complementary (allopatric) distribution patterns that overlap (are sympatric) in northeastern Borneo and the Philippines, including portions of the Sumba terrane.
