PHYLOGENETIC SYSTEMATICS AND BIOGEOGRAPHY OF PHALLOSTETHID FISHES (ATHERINOMORPHA, PHALLOSTETHIDAE) OF NORTHWESTERN BORNEO, WITH DESCRIPTION OF A NEW SPECIES

Until recently, the distinctive phallostethid genus Phallostethus was known from a single collection made in 1902 from Johor on the Malay Pe ninsula, described in 1913 by Regan as Phallostethus dunckeri. In 1991 and 1993, specimens of Phallostethus were collected from disjunct coa stal localities in sarawak and Brunei, northwestern Borneo. These Born eo specimens differ from Phallostethus dunckeri in morphology of the p riapium (a complex, bilaterally asymmetric, subcephalic copulatory org an), pigmentation, and paradentary bone dentition. They are described herein as Phallostethus lehi, bringing the number of recognized phallo stethid species to 20. Phenacostethus smithi Myers, 1928, previously u nknown from Borneo has been collected from Sarawak, Brunei, and Kalima ntan, bringing the total number of Bornean phallostethid species recog nized currently to six. The phallostethids of Borneo do not form a mon ophyletic group but, instead, have complex, repeated sets of relations hips with species on the Malay Peninsula and in the Philippines. Compo nents of their biogeographic relationships are shared with other membe rs of the stream biota. Composite biotic relationships are consistent with a composite geological origin of modern Borneo.