Gonostomatidae

Family Gonostomatidae View in CoL View at ENA

Examination of whole preserved Gonostoma elongatum Gunther, 1878 revealed enclosed lateral line canals. Thin, needle-like bones and partially ossified canals were revealed in µCT reconstructions, and a fully ossified canal was also present in the supracleithrum ( Table 1). A bifurcated bony longitudinal ridge is found in the frontal bone rostral to the orbit, which merges into a single ridge at the level of the anterior edge of the orbit ( Fig. 3D View Figure 3 ). The enclosed, but partially ossified SO canal starts rostral to the orbit at the level of the anterior naris and medial to the longitudinal ridge. Caudal to the orbit, epithelial canal pores are found lateral to the ridge suggesting that the canal extends laterally through it. The presence of a trough in the preoperculum and epithelial canal pores in the opercular region indicates that the PO canal is enclosed, but only partially ossified. Epithelial canal pores are not present in the mandible indicating the absence of an MD canal. Three epithelial canal pores ventral to the orbit suggest the presence of an IO canal, but IO bones could not be resolved in µCT images suggesting that the IO canal is unossified or weakly ossified. Epithelial canal pores at the posterior margin of the skull indicate the presence of OT, PT and ST canals, which appear to be incompletely ossified based on µCT data and a fully ossified canal is present in the supracleithrum.

Cleared and stained specimens of Cyclothone ( C. acclinidens Garman, 1899 , C. alba Brauer, 1906 , C. pseudopallida Mukhacheva, 1964 , C. signata Garman, 1899 ) and µCT reconstruction of C. microdon (Gunter,

are bilaterally symmetrical (here, in dorsal view), but are described with reference to the ridge(s) on one side of the head. A, ridge absent in Cyclothone , Bathophilus , Malacosteus and Neonesthes . B, one longitudinal ridge extends dorsally from the frontal bone. The longitudinal ridge extends medially, meeting the ridge on the other side of the head medial to the orbits without fusing, in Argyropelecus and Ichthyococcus . C, one longitudinal ridge is present, but does not meet with or fuse with the ridge on the other side of the head in Aristostomias , Idiacanthus , Flagellostomias , Pachystomias and Tactostoma . D, one longitudinal ridge is present in the frontal bone, but bifurcates rostral to the orbit, in Gonostoma , Echiostoma and Eustomias . E, two longitudinal bony ridges extend from the frontal bone, but they never meet or fuse with the ridges on the other side of the head in Astronesthes and Opostomias . 1878) revealed thin, needle-like cranial bones. In contrast to Gonostoma and other stomiiforms (see below), all lateral line canals (and troughs indicating the presence of partially ossified canals) are absent, and there is no evidence of a bony longitudinal ridge on the dorsal surface of the frontal bone ( Figs 1F, G View Figure 1 , 3A View Figure 3 ; Table 1). Examination of whole preserved specimens ( C. acclinidens , C. alba , C. braueri Jespersen and Taning, 1926 , C. microdon , C. parapallida Badcock, 1982 , C. pallida Brauer, 1902 , C. pseudopallida , C. signata ) showed no evidence of epithelial canal pores that would suggest the presence of incompletely ossified canals. Histology ( C. microdon ) confirmed the absence of either soft tissue canals or ossified cranial lateral line canals.