Osteology and relationships of Pseudotrichonotus altivelis (Teleostei:Aulopiformes:Pseudotrichonotidae)

Abstract

The osteology of the rare Japanese fish Pseudotrichonotus altivelis is described based on several specimens collected off the Izu Peninsula. Relationships of Pseudotrichonotus are discussed based on osteological comparisons with other neoteleosts. The placement of Pseudotrichonotus among iniomous fishes has been questioned because of its lower numbers of caudal-fin, pelvic-fin, and branchiostegal rays. Our investigation supports an iniomous affinity for Pseudotrichonotus, specifically as a member of the Aulopiformes. Within that group, Pseudotrichonotus belongs in a new suborder diagnosed herein, the Synodontoidei, which also includes the Aulopidae (Aulopus), Synodontidae (Synodus and Trachinocephalus), and Harpadontidae (Harpadon and Saurida). A synodontoid affinity for Aulopus has never been suggested, but numerous osteological features support the monophyly of this clade. Synodontoids have a peculiar proximal segmentation of most principal caudal-fin rays, expanded neural and haemal spines on posterior vertebrae, cartilage extending along the ventral margin of the anterior ceratohyal, ventral displacement of the first one to three epineurals, supraneurals with large laminar expansions and six or more branchiostegals on the posterior ceratohyal. They lack median caudal cartilages. Among synodontoids, Pseudotrichonotus is the sister group of the Synodontidae plus Harpadontidae, with which it shares paired peritoneal pigment spots, an abrupt transition between the epipleurals in and beneath the horizontal septum, and absence of the fourth pharyngobranchial toothplate. Our study does not support a previously proposed relationship between Bathysaurus and synodontids.