The Osteological Features of Ipnops agassizii Garman, 1899 (Aulopiformes: Ipnopidae) from Bathyal and Ultra-Abyssal Depths of the Australia–New Zealand Region, with Remarks on the Biogeographical Significance of these Findings

Abstract

The osteological description of the ocular head region and the pectoral girdle (using alizarin-stained preparations) of Ipnops agassizii Garman, 1899 (family Ipnopidae) was made based on material collected from bathyal and ultra-abyssal depths (3020–5410 m). A detailed description of the axial skeleton is provided and features of the fin skeleton are analyzed (using X-ray images). The morphological transformations in the skeleton that occurred as a result of living at great depths are considered. The wide range of functional and morphological specializations, which have an adaptive pattern aimed at adaptation to deep-sea habitats in contact with the bottom, are shown. The fin rays of the unpaired fins and their supporting elements (respectively, interneuralia and interhaemalia) have reinforced bony heads. The pelvic fins are located at the vertical line through the tips of the pectoral fin rays, slightly anteriorly of the mid-body level. The dorsal fin is located far anteriorly of the anal fin. The caudal peduncle is equally flattened both laterally and dorsoventrally.