Hymenocephalus iwamotoi, Schwarzhans, 2014

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 : 30-33

Hymenocephalus iwamotoi n.sp.

Figs. 10A–B , 11A–I , 12

Material examined (30 specimens, (58+) 74–103 mm TL). Holotype WAM P.25401-003, 86+ mm TL, off northwestern Australia, vicinity of Browse Island , 13°47’S, 123°18’E, 242 m, 23 December 1969, identified as Hymenocephalus sp. by Iwamoto, 2003 ; Paratypes: WAM P.25401-020, 29 specimens, (58+) 74–103 mm, same data as holotype. 69 further specimens from the same location not investigated in detail and not characterized as type-specimens , WAM P.25401-021.

Diagnosis. A small species, not exceeding 105 mm TL. Pelvic fin rays 8 (7–9); pectoral 12–13; first dorsal II + 6–7; gill rakers 17–20. Barbel long 40–46% HL, reaching vertical through rear end of orbit. Orbit 35–38% HL. Snout rounded, barely protruding, short 15–19% HL. Posterior luminescent lens round; ventral striae extending to near periproct. Otolith compressed (OL:OH = 0.95); colliculi separated, small; pseudocolliculum small (TCL:PCL = 1.8–2.0).

Comparison. Hymenocephalus iwamotoi is readily recognized by the combination of the characters given in the diagnosis, which represent a mixture of assumed plesiomorphic characters, such as the otolith with the separated colliculi and the short pseudocolliculum, the low number of gill rakers, and the long infraorbital supporter, and perceived apomorphic characters such as the blunt head profile, the large orbit and the low number of fin rays in the first dorsal. It shows the longest barbel of any Hymenocephalus species together with H. longibarbis . Because of its unique combination of characters, I propose a species group of its own for H. iwamotoi .

Description. Counts (from 31 specimens): 1D. II,7 (II,6–7); P. 12 (12–13, one specimen 14); V. 8 (7–9, predominantly 8); gill rakers on first arch, inner side 18 (17–20); gill rakers second arch, outer side 18 (18–20).

Measurements (from holotype and two best-preserved paratypes): head length 13.7–15.0 mm, about 18–20% TL; head height 78–82% HL; head width 55% HL (holotype only); barbel 40–46% HL; snout 15–19% HL; orbit 35–38% HL; postorbital 43–49%HL; interorbital 35% HL / 63% HW (holotype only); upper jaw length 56–59% HL; pre-anal about 150% HL; pre-dorsal to 1D about 100% HL; pre-dorsal to 2D about 230% HL; distance base 1D to 2D about 130% HL; 1st dorsal fin length 70–80% HL; pectoral fin length 70% HL; ventral fin length, 1 st ray 110% HL, 2 nd ray 50% HL; supraorbital canal width 12.0–14.5% HL; infraorbital width 14.5–17% HL; minimal infraorbital canal width 7.0–7.5% HL.

The following description is based on the holotype ( Fig. 10A ). Body slender, highest and widest at rear part of head just behind orbit, tapering rather regularly behind first dorsal into the usual whip-like tail. Origin of first dorsal, pectoral and ventral fins about on same vertical. First ray of ventral more than twice the length of subsequent rays. Second dorsal rudimentary; anal well developed.

Teeth all small, on narrow bands of both jaws.

Luminescent striae ( Fig. 11E ) silvery, extending as a narrow band along both sides of isthmus below gill covers, reaching up to bases of pectoral fins and behind ventral fin bases, where they join along medial line, and expanding almost to periproct region. Some dark striae on gular region. Anterior lens of ventral luminescent organ small, pale; posterior lens ( Fig. 11I ) before periproct about three times as large, round, surrounded by thin dark tissue.

Axial skeleton (based on radiographs). Number of precaudal vertebrae 10; vertebrae 1 to 3 much shorter than subsequent vertebrae. Neural spines of vertebrae 1 and 2 nearly twice as long as vertebra 3; neural spines 3 to 9 depressed and with blunt tips; neural spines 3 to 7 short and of equal length, spines 8 to 9 increasing in length. Bases of neural spines 4 to 8 enlarged. Parapophyses on vertebrae 7 to 10. Pleural ribs on vertebrae 5 to 8. First fin ray of 1D supported by two pterygiophores both inserted behind neural spine 2. Last pterygiophore of 1D inserted behind neural spine 7 or 8. First pterygiophore of 2D above vertebra 18 to 20. First pterygiophore of anal fin slightly prolonged, inserted in front of first haemal spine on first caudal vertebrae (11).

Head morphology ( Figs. 10B , 11A–D ): Head stout, with rounded anterior profile, snout barely protruding beyond mouth and nasal flap. Bones thin and fragile; eyes large; barbel long, reaching vertical through rear end of orbit. Head canals well developed, covered with very thin, mostly fragmented integument. Infraorbital, supraorbital and preopercular canal widths 10–17% HL, supraorbital canal with 4 segments, supratemporal canal not identified, postorbital-preopercular interspace 7–10% HL. Infranasal supporter small; infraorbital supporter broad, constantly widened below entire stretch of orbit, 70–90% OD; preopercular supporter narrow, with straight rear margin, long (7–11% HL); mandibular hook small.

Otolith morphology ( Fig. 11F–H ): Otolith high bodied; OL:OH = 0.95; OL:OT about 3. Predorsal lobe massive, slightly anteriorly inclined, terminating posteriorly in a marked incision above middle of otolith. Anterior rim irregular, nearly vertical; posterior tip moderately pointed at or slightly above level of sulcus. Ventral rim deep, smooth and regularly curved, deepest anterior of middle. Inner face slightly convex along horizontal axis, with narrow, median sulcus. Ostial and caudal colliculi small, the latter often distinctly narrower than the ostial colliculum; pseudocolliculum moderately enlarged. CCL:OCL = 1.1–1.2; TCL:PCL = 1.8–2.0. Dorsal depression wide; ventral furrow distinct, close to ventral rim.

Coloration (in alcohol): Very light, yellowish on tail and dorsum; silvery and light yellow colors on head; area of ventral striae silvery, very little dark pigments; some small, indistinct darker pigments on tail below bases of fin rays of 2 nd dorsal.

Distribution. Known only from the type location off Browse Island, probably endemic to the northwest Australian shelf edge.

Etymology. The new species is named in honor of Tomio Iwamoto (San Francisco, U.S.A.) in recognition of his outstanding contribution to the knowledge of the family Macrouridae . He was also the first ichthyologist to see the specimens, then identified as Hymenocephalus sp.

Figures

FIGURE 10. Hymenocephalus iwamotoi: A—Holotype, WAM P.25401-003, TL 86+ mm (photo M. Krag). B—Paratype, WAM 25401-020, TL 90+ mm, head close-up (photo M. Krag).

FIGURE 11. Hymenocephalus iwamotoi: A—Holotype, WAM P.25401-003, TL 86+ mm, lateral view of head. B—Paratype, WAM P.25401-020, TL 90+ mm, lateral view of head. C—Paratype, WAM P.25401-020, TL 58+ mm. lateral view of head. D—Holotype, dorsal view of head. E—Holotype, ventral view of head and trunk. F–H—Non-types, WAM P.25401-020, F, H—inner faces, G—ventral view. I—Holotype, detail view of posterior lens of ventral luminescent organ.

FIGURE 12. Geographical distribution of Hymenocephalus longibarbis, H. longipes and H. iwamotoi.