A new species of the rare deep-sea genus Sciadonus Garman, 1899 (Teleostei, Bythitidae) from off Brazil, with a discussion of the evolution of troglomorphism and miniaturization in the aphyonid clade

• Published in: Deep-sea research. Part I, Oceanographic research papers Oceanographic research papers, 2022-02, Vol.180, p.103684, Article 103684
• Main Authors: de Melo, Marcelo Roberto Souto, Gomes, Amanda Alves, Møller, Peter Rask, Nielsen, Jørgen G.
• Format: Article
• Language: English
• Subjects: Aphyonid clade; Continental slope; R/V Alpha Crucis; Western South Atlantic
• ISSN: 0967-0637; 1879-0119; 1879-0119
• DOI: 10.1016/j.dsr.2021.103684

A new species of the rare, deep-sea genus Sciadonus Garman, 1899 (Bythitidae) is described based on two specimens obtained by the Brazilian R/V Alpha Crucis on the continental slope off São Paulo State, Southeastern Brazil, western South Atlantic. It differs from its congeners by the combination of the following characters: body pale lacking dark pigmentation except for on female claspers; a pair of dermal tissue flaps anteriorly on lower jaw; pelvic-fin rays present; precaudal vertebrae 39 or 40 and total vertebrae 74 or 75. The key to the species of Sciadonus is updated. A discussion of the presence and differentiation between troglomorphic and miniature characteristics among the species in the aphyonid clade is provided and compared with other bythitids. •A new species of the rare genus Sciadonus is discovered from Brazilian waters.•Highly specialized reproductive apparatus enables internal fertilization and viviparity in a deep-sea fish.•The depletion of sunlight resulted on convergent evolution of troglomorphic traits in deep-sea fishes and cave fishes.•Human activities of oil and natural gas exploration, fisheries and littering may be impacting rare deep-sea species.