Neostethus djajaorum, new species, from Sulawesi, Indonesia, the first phallostethid fish (Teleostei : Atherinomorpha) known from east of Wallace's line

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 1. , 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 cla~. 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-arc 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. Complexity of the biota of the Indo-Australian archipelago was recognized by Alfred Russel Wallace (1869) who identified an Asian biota on the western portion of the archipelago and an Australian biota on the eastern portion. One imaginary line drawn vertically between islands, known as Wallace's Line, separates the two regions (Fig. 1). Early renditions of the line passed to the west of Sulawesi (formerly the Celebes); later renditions to the east. Other lines, such as Weber's Line, Lydekker's Line, or Huxley's modification of Wallace's Line (Fig. 1), were drawn as it became clear that not all taxa followed Wallace's Line precisely (viz. Simpson, 1977: fig. 1). Interpretations of the geology of the entire region explicitly within a plate tectonic framework, first by Hamilton (1979, 1988) and subsequently by others, such as Audley-Charles (1987), Daly et al. (1991), and Metcalfe (1991), demonstrated its extreme complexity, including that modem, large islands, such as Borneo, Sulawesi and New Guinea, are geological composites. Corresponding developments in the theory of historical biogeography support Fig. 1. Distribution of Neostethus djajaorum (circle, Sulawesi), N. robertsi (triangle, Luzon) and N. palawanensis (squares, Palawan). Wallace's Line (dotted and dashed), Huxley's Line (dashed) after Simpson (1977:fig. 1). Hatched lines represent approximate limits of some suture and fault lines delimiting Sumba block or terrane, the major portions of which are shaded, following Rangin et al. (1990), Michaux (1996), and herein. the idea that distributions of plants and animals are explained best by the extent to which they conform to a generalized pattern, rather than by individual episodes of long-distance dispersal (viz. Croizat, 1958; Nelson & Platnick, 1981) and, further, that these generalized patterns may be explained by concordance with complex geological or climatic patterns. Evaluations of the biogeography of Sulawesi within a cladistic or vicariance biogeographic framework (e.g., water striders, Polhemus & Polhemus, 1990; butterflies, Vane-Wright, 1991) have confirmed that the biota of Sulawesi is composite, that is, neither wholly Asian nor wholly Australian, although the ratio of Asian to Australian taxa varies from group to group. In a summary of the cladistic relationships among mirid insects, Schuh & Stonedahl (1986:fig. 11) depicted Sulawesi in an unresolved position between western (or Asian) and eastern areas. An imaginary line could pass through the islands rather than between them to reflect their geological and biological complexity (viz. Parenti, 1991). Phallostethids are small, transparent to opaque, surface-feeding, schooling fishes readily distinguished from all other bony fishes by a complex intromittent organ in males, called the priapium (Regan, 1913, 1916). The family Phallostethidae sensu Parenti (1984), comprising twenty-one species including the new species described herein, was known previously to be distributed broadly throughout coastal and freshwater habitats in Southeast Asia entirely west of Wallace's Line, including Thailand, peninsular Malaysia, Singapore, Borneo, the Philippines and Sumatra (see Parenti, 1989, 1996; Kottelat et aI., 1993). The marine shorefish silverside genus Dentatherina Patten & Ivantsoff (1983), was recognized as the closest living relative of phallostethids by Parenti (1984) and placed in its own family, the Dentatherinidae, sister to the Phallostethidae in the atherinomorph superfamily Phallostethoidea. This sistergroup relationship was corroborated by Dyer & Chernoff (1996) who classified Dentatherina in the Phallostethidae. Dentatherina is broadly distributed throughout coral reef habitats from off Java, northeastern Borneo, the Philippines, the Moluccas and across the IndoAustralian archipelago to eastern New Guinea, northeastern Australia and Fiji (Patten & Ivantsoff, 1983; Fig. 2). Our discovery in 1995 of a phallostethid species in southwestern Sulawesi, described herein as new, has prompted reinterpretation of some aspects of phallostethid biogeography as well as a search for distribution patterns of other taxa that may conform to that of phallostethids and their close relatives (Fig. 2).