Osteology-focused redescription and description of the blood-feeding candirus Paracanthopoma parva and Paravandellia alleynei sp.n. (Trichomycteridae: Vandelliinae).

This study resolves a significant impediment to the taxonomy of the Neotropical endemic hematophagous candirus by providing the first high-resolution, CT-based osteological descriptions of type and nontype specimens of Paracanthopoma parva, type species of the genus. We also describe the distinctive new species Paravandellia alleynei based on specimens that were previously misidentified as Parac. parva in the only taxonomic study of that species since its 1935 description. Paracanthopoma parva is distinguished from all nominal congeners by its parietosupraoccipital and caudal skeleton morphology and by various meristics, including numbers of teeth on median premaxilla, vertebrae, and procurrent and principal caudal-fin rays. Paravandellia alleynei differs from both nominal congeners (Paravandellia oxyptera and Paravandellia phaneronema) by the unique morphology of its maxilla, mesethmoid and opercular apparatus, relative position of the pelvic- and anal-fin origins, orientation of the opercular odontodes, and various meristics, including numbers of vertebrae, median premaxillary teeth, medial teeth on premaxilla, branchiostegal rays, opercular and interopercular odontodes, distal claw-like premaxillary teeth, dorsal-fin rays and dentary teeth. This is the first species of Paravandellia recognized from Guyana and the Essequibo River basin. It is currently known only from two type specimens from the lower Essequibo River basin and 43 nontype specimens from the upper Branco River basin. By providing the first skeletal observations for type specimens of the type species Parac. parva and for topotypic specimens of all three nominal species of Paravandellia, we clarify and confirm the diagnosis of Parac. parva and establish a robust foundation for ongoing taxonomic revisions of these two small-sized and species-poor, yet trans-continentally distributed genera, both of which contain considerable unrecognized diversity.