Phenacostethus Myers, 1928

Parenti, Lynne R., Lumbantobing, Daniel N. & Haryono, 2023, Description of a new species of Phenacostethus (Atheriniformes: Phallostethidae) endemic to Kalimantan Selatan, Indonesian Borneo, reveals deep mtCOI divergence among miniature species, Raffles Bulletin of Zoology 71, pp. 553-571 : 557

Genus Phenacostethus Myers, 1928

Type species. Phenacostethus smithi Myers, 1928 , by original designation and monotypy.

Differential Diagnosis. Phenacostethus differs from the genus Phallostethus in having a lower oral jaw that protrudes beyond the upper jaw and a reduced second ctenactinium (priapial bone) which is prominent and serrated in Phallostethus . Phenacostethus has fewer anal-fin rays (14–15 as opposed to 26–28), second dorsal-fin rays (5–7 as opposed to 8–10) and vertebrae (33–35 as opposed to 40) than in Phallostethus (Parenti, 1986: table 1). Phenacostethus has a first dorsal fin with one unsegmented ray versus first dorsal fin absent in Phallostethus . Phenacostethus and Phallostethus differ from all other phallostethines ( Neostethus and Gulaphallus ) in having a priapium with a prominent, hooked toxactinium and a shield-like pulvinular pad, structures present in other priapiumfishes but not as well-developed.

Composition and distribution. Four species, including the new species described herein ( Table 1): Phenacostethus smithi Myers, 1928 , fresh and brackish waters, Thailand, Cambodia, Sumatra, Peninsular Malaysia, Sarawak, and Brunei; Phe. posthon Roberts, 1971a , fresh and brackish waters, Thailand and Peninsular Malaysia, and Sumatra; Phe. trewavasae Parenti, 1986b , freshwater, Sarawak, Malaysian Borneo, and Brunei; Phe. sikat , new species, freshwater, Kalimantan Selatan, Indonesian Borneo.