Hymenocephalus Giglioli, 1884

Schwarzhans, Werner, 2014, Head and otolith morphology of the genera Hymenocephalus, Hymenogadus and Spicomacrurus (Macrouridae), with the description of three new species, Zootaxa 3888 (1), pp. 1-73 : 26-27

Hymenocephalus Giglioli, 1884

Hymenocephalus Giglioli, 1884: 228 , type species by original designation Hymenocephalus italicus Giglioli, 1884 .

Mystaconurus Günther, 1887: 124 , as a subgenus of Macrurus (correct Macrourus ) Bloch, 1786, type species by original designation Macrurus (Mystaconurus) longibarbis Günther, 1887 .

Papyrocephalus Gilbert & Hubbs, 1920: 539, as a subgenus of Hymenocephalus Giglioli, 1884 , type species by original designation Hymenocephalus aterrimus Gilbert, 1905 .

Diagnosis. Modified from Cohen et al. (1990): Leading spine of dorsal fin not serrated. Ventral striae consisting of fine parallel lines of dark, alternating with silvery pigment associated with a light-producing function on abdominal wall, parts of chest, and shoulder girdle, and joining at median line behind pelvic fin bases. Head cavernous with thin, membraneous skin cover. Median and lateral processes of snout variably pointed or blunt, weak, often flexible. Gill rakers 15–29. Additional diagnostic features from axial skeleton and head morphology are: 10 precaudal vertebrae (based on radiographs); well-developed infranasal, infraorbital and preopercular supporters; snout broad, usually projecting, with soft tip. Additional diagnostic features from otolith morphology are: large, high-bodied, compressed otoliths (OL:OH=0.75–1.3); large to very large, massive predorsal lobe; ventral sulcus margin at collum convex; pseudocolliculum distinct, long to very long, extending forward and backward below colliculi.

Comparison. Hymenocephalus resembles Hymenogadus in many aspects, and it appears as if several of its morphological features have been taken to the extremes, particularly when concerning head and otolith morphology. Differences are ( Hymenocephalus first) wide head canal system with thin integument cover which is rarely preserved (vs head canal system less widened and covered by thin, but usually sufficiently robust skin to be preserved), well-developed infranasal, infraorbital and preopercular supporters (vs incipient development), ventral striae joined behind the pelvic fin bases (vs not joined), otoliths compressed (OL:OH = 0.75–1.3 vs 1.25–1.55), with convex ventral sulcus margin at collum (vs indented) and long to very long pseudocolliculum (TCL:PCL = 1.15–2.8 vs 7.0–10.0). I consider Hymenocephalus as derived from near Hymenogadus with the latter representing a plesiomorphic sister group to Hymenocephalus , while Spicomacrurus in this concept would represent a different lineage of specialization distinct from the other two genera.

Species. Including the three new species described in the following, the synonymization of H. longiceps with H. longibarbis and the upgrading of former subspecies of H. striatissimus to species rank as proposed here, the genus now contains 24 species considered valid. There are, however, indications of at least two further undescribed species to be expected in the genus subject to more material becoming available and also subject to statistical reviews or application of other methods such as DNA-analyses. The species considered valid herein are, in alphabetical order: H. aeger , H. antraeus , H. aterrimus , H. barbatulus , H. billsam , H. grimaldii , H.hachijoensis , H. heterolepis , H. italicus , H. iwamotoi n.sp., H. lethonemus , H. longibarbis , H. longipes , H. megalops , H. nascens , H. neglectissimus , H. nesaeae , H. papyraceus , H. punt n.sp., H. sazonovi n.sp., H. semipellucidus , H. striatissimus , H. striatulus and H. torvus .

See ‘Species Groups’ above for distinction and definition of the various species groups, in which the species of Hymenocephalus have been provisionally placed.