Galapagos Ghostshark

materials_examined

- 1 specimen. CAS 86558, juvenile female, 381 mm TL, 274 mm PCL, 211 mm BDL, southeast of San Cristobal Island, Galapagos (01 ° 5.981 ’ S, 89 ° 12.235 ’ W), 396.24 m, collected by J. E. McCosker (CAS), R. Grant Gilmore (HBOI) and Bruce Robison (MBARI), 17 Nov. 1995 (JSL dive 3934)

A new species of chimaeroid, Hydrolagus alphus sp. nov. (Chimaeriformes: Chimaeridae) from the Galapagos Islands.

biology_ecology

Individuals were found alone or in groups along steep slopes, within a few meters of the seafloor. Habitat was composed of igneous boulders, cobbles, and pebbles. The observed bathymetric range is shallow compared to many other Hydrolagus, and may reflect incomplete deep-water sampling in the region. However, the two most similar congeners in morphology and distribution, H. novaezealandiae and H. colliei, are also found in relatively shallow depths (Eschmeyer et al. 1983; Anderson et al. 1998), suggesting that the observed depth distribution of H. mccoskeri may accurately represent its true bathymetric range.

Hydrolagus mccoskeri sp. nov., a new species of chimaeroid fish from the Galápagos Islands (Holocephali: Chimaeriformes: Chimaeridae).

description

Description. Holotype and paratype morphometric measurements are presented in Table 1. Head small (HDL 31 - 32 % BDL), with rounded, short snout and large eyes (EYL 9 - 13 % BDL). Body depth (dorso-ventral height of body at a given distance from snout tip) remains similar from head to origin of pelvic fins, from which point it rapidly tapers distally to pelvic fin tips (when depressed posteriorly), subsequently transitioning into a whiplike tail. Skin firm and robust, not deciduous as in some other Hydrolagus (Didier 2002). Post-anal pad present, but inconspicuous in the juvenile type specimens. Tooth plates light yellow in preserved specimens, with white tritors. Vomerine tooth plates small and incisor-like with 5 tritors visible on the right and 5 - 6 on the left. Palatine tooth plates with 2 - 3 tritors along the oral surface originating at the posterior edge and terminating prior to the anterior edge. Small protrusions are present along the anterior labial edge. Mandibular tooth plates incisor-like and large (three times wider than vomerine tooth plates), with 5 tritors per side. Lateral line canals on head are open grooves with especially wide dilation of canals on the snout.

Hydrolagus mccoskeri sp. nov., a new species of chimaeroid fish from the Galápagos Islands (Holocephali: Chimaeriformes: Chimaeridae).

diagnosis

Diagnosis. A species of Hydrolagus distinguished from congeners by the following combination of characters: head small with short, blunt snout; second dorsal fin only slightly indented along its length; preopercular and oral lateral line canals branching from the same node off the infraorbital canal and sharing a short common branch; dorsum medium brown with numerous narrow, sharply delineated irregular circular and elongate white blotches; ventrum white to tan with extremely fine brown mottling.

Hydrolagus mccoskeri sp. nov., a new species of chimaeroid fish from the Galápagos Islands (Holocephali: Chimaeriformes: Chimaeridae).