Rediagnosis of Lissonanchus Smith 1966, a senior synonym of Briggsia Craig and Randall 2009 (Gobiesocidae), with notes on included species and their osteological characters

Abstract

A detailed morphological investigation, including osteological anatomy based on micro-CT scans, of two poorly known monotypic genera and species of gobiesocids, Lissonanchus lusherae Smith 1966 and Briggsia hastingsi Craig and Randall 2009, revealed that no generic-level differences existed between the two species. Briggsia Craig and Randall 2009, therefore, is a junior synonym of Lissonanchus Smith 1966. Lissonanchus is rediagnosed, having the following characters: 30 or 31 vertebrae; cephalic lateral-line canal pores poorly developed, including 2 nasal, 2 lacrimal and 1 postorbital canal pores; posterodorsal portion of anguloarticular strongly expanded laterally with bifurcated process; gill membranes on each side united ventrally, attached to the isthmus; 4th gill arch without filaments; double type adhesive disc; flattened papillae on disc region A continuous across center; flattened papillae on disc region D arranged along disc edge and continuous with papillae on disc region A; center of anterior disc (= middle area between disc regions A and D) lacking papillae; small fleshy pad on lower part of pectoral-fin base; anterior part of dorsal-fin base lacking a swollen fleshy appearance; general fresh coloration, including brownish-green body, dark brown strip extending from snout tip to posteroventral part of head through eye, and whitish part on lateroventral surface of head (bordered by dark brown strip). In particular, the anguloarticular feature of Lissonanchus is likely unique within the Gobiesocidae and is regarded as a putative autapomorphy for the genus. In contrast, the two species could be distinguished from each other by species-level differences, including counts of pectoral-fin rays, number of teeth on pharyngobranchial 3, jaw lengths, and streak patterns on the body. Accordingly, Lissonanchus is now considered to include two valid species: L. lusherae (type species) and Lissonanchus hastingsi, new combination. Although Lissonanchus was previously included in the subfamily Diademichthyinae, the genus does not share any diagnostic features of that subfamily, and the subfamilial assignment of the genus remains equivocal, like other Indo-Pacific genera considered as incertae sedis within the Gobiesocidae (e.g., Aspasmogaster Waite 1907, Conidens Briggs 1955, and Creocele Briggs 1955).