Abstract

The tropical and subtropical genus of viviparous cusk-eels Diplacanthopoma (Teleostei: Bythitidae) is differentiated from other bythitids in having a naked head, a fleshy flap bearing a large sensory pore above the opercle, and a large sensory pore on the cheek. The sensory pore on the cheek (i.e., “Diplacanthopoma” pore) is only known from two genera of ophidiiforms, Diplacanthopoma and Hephthocara. Diplacanthopoma includes eight nominal species, with seven in the Indian or Pacific Oceans, and one, D. brachysoma, from the western Atlantic. Recently, blackwater SCUBA divers collected two elongate larval fishes off West Palm Beach, Florida. Fin-ray and vertebral/myomere counts and DNA sequence data support the identification of one of the larvae as D. brachysoma; the first time the larval form for this genus of fishes has been identified. The second larva has higher numbers of medial-fin rays (184 dorsal-fin rays, 140 anal-fin rays) than D. brachysoma (125–164 dorsal-fin rays and 88–127 anal-fin rays), and mitochondrial cytochrome c oxidase subunit 1 barcode divergence of >9%, indicating the presence of a second undescribed species of Diplacanthopoma from the western Atlantic Ocean. We found three specimens (one from southern Brazil and two from the Bay of Campeche) in the Leibniz Institute for the Analysis of Biodiversity Change and the Smithsonian Institution’s National Museum of Natural History fish collections that overlap in fin-ray and vertebral/myomere counts with the larval specimen from Florida. We describe this new species of Diplacanthopoma based on larval and adult characters. We also highlight intraspecific variation in counts and measurements for D. brachysoma, emphasizing further study is needed to understand the taxonomic diversity of this genus of the Bythitidae.