Five in situ observations of live oarfish Regalecus glesne (Regalecidae) by remotely operated vehicles in the oceanic waters of the northern Gulf of Mexico

As part of the SERPENT Project, five observations of apparently healthy oarfish Regalecus glesne by remotely operated vehicles are reported from the northern Gulf of Mexico. Regalecus glesne were observed between 2008 and 2011 at depths from within the epipelagic and mesopelagic zones. These observations include the deepest verified record of R. glesne (463–492 m) and the first record of an arthropod ectoparasite (isopod).     

Mitochondrial genome and a nuclear gene indicate a novel phylogenetic position of deep-sea tube-eye fish (Stylephoridae)

The rare, monotypic deep-sea fish family Stylephoridae has long been considered a member of the order Lampridiformes (opahs, velifers, ribbonfishes), and no systematic ichthyologist has questioned its placement within the order for over 80 years. Recently three individuals of Stylephorus chordatus were collected from different oceans, and we sequenced the whole mitochondrial genome and a partial nuclear recombination activating gene 1 (RAG1) gene sequences for each specimen. We aligned these sequences with those available from higher teleosts, including representative lampridiforms, and constructed two separate datasets from the sequences. The resulting trees derived from partitioned Bayesian analyses strongly indicated that S. chordatus is not a lampridiform but is closely related to the order Gadiformes (cod and their relatives). Lampridiformes is diagnosed on the basis of four synapomorphies, three of which are correlated with the rare and possibly unique ability to extend both the maxilla and premaxilla as a unit during feeding. Stylephorus also possesses such unique ability, but lacks two and possibly three of the four synapomorphies, suggesting that further morphological analysis is needed. Considering its unique morphologies with no indication of affinities within Gadiformes (or any other presently recognized order), the present results warrant a recognition of the new order for S. chordatus in fish systematics.     

Cranial morphology of Ateleopus japonicus (Ateleopodidae: Ateleopodiformes), with a discussion on metamorphic mouth migration and lampridiform affinities

The cranial osteology and myology in the ateleopodiform Ateleopus japonicus were studied. Many free bony ossicles constitute the cephalic lateral line canals and are separated from the neurocranial roof by thick gelatinous tissue. The preoperculomandibular canal is unique in having a direct connection with the infraorbital canal owing to strong reduction in the size of the preoperculum. The neurocranium is largely cartilaginous, with 6 chondrocranial and 1 dermal element being absent (or not undergoing ossification). The left and right frontals are separated by a deep groove into which a long, mobile rostral cartilage is deeply inserted. Five pairs of cartilages, including 2 pairs of menisci, are associated with the ethmoid region, allowing premaxillary protrusion without involving maxillary rotation. The levator operculi is well developed and likely generates the primary force for depressing the lower jaw. The large interhyal is tightly attached to the entire ventral margin of the operculum, and the two elements appear to function as a single unit in mouth opening. The oral cavity is large because of the posterior position of the branchial arches [the last (5th) arch is situated below the 3rd vertebra]. In pelagic individuals the head is flat with a terminal mouth and straight parasphenoid shaft, whereas in small, benthopelagic individuals the head is rounded with an inferior mouth and bent parasphenoid shaft. “Bending” of the parasphenoid with a dorsally elevated apex is considered the result of the posterior migration of the mouth during the habitat shift. Ateleopodiform characters are discussed phylogenetically and the deep insertion of the rostral cartilage into an open space in the ethmoid region is suggested as a synapomorphy of the order and Lampridiformes.