Hymenocephalus maculicaudus Mcmillan & Iwamoto, 2014, sp. n.

Hymenocephalus maculicaudus sp. n.

Spottytail membranehead

(Figures 4–7; Table 2)

Hymenocephalus megalops (not of Iwamoto & Merrett 1997). Clark & Roberts, 2008: Appendix 4 (listed).

Diagnosis. Pelvic fin rays 8 (rarely 7 or 9), gill rakers first arch (outer/inner) 10–16/16–20, chin barbel length 7–16 % HL, orbit diameter 33–48 % HL, snout length 20–28 % HL, orbit to preopercular length 34–45 % HL. Scattered melanophores ventrally on trunk and distinctive mid-lateral line of melanophores on tail that extends about a head length posterior to anal fin origin.

Specimens examined. Holotype. AMS I 42737 -003 (23.9 mm HL, 161 mm TL), Tasman Sea, Lord Howe Plateau, 34º 01.95' S, 162º 35.96' E, 780–818 m, 25 May 2003, Tangaroa, NORFANZ stn. TAN0308-081, wing trawl.

Paratypes (50: 12.9–26 mm HL, 63–163 mm TL). AMS I 42740 -002 (2: 19.8–21.9 mm HL, 116–142 mm TL), Tasman Sea, Lord Howe Plateau, 34º 11.04' S, 162º 39.11' E, 430–740 m, 26 May 2003, Tangaroa, NORFANZ stn. TAN0308-086. AMS I 42742 -003 (6: 24.6–25.5 mm HL, 85+– 163 mm TL), Tasman Sea, Lord Howe Plateau, 34º 12.18' S, 162º 41.18' E, 748–772 m, 26 May 2003, Tangaroa, NORFANZ stn. TAN0308-089. CSIRO H 6044-16 (8: 18.5–24 mm HL, 88+– 160 mm TL), Tasman Sea, Lord Howe Plateau, 34º 01.95' S, 162º 35.96' E, 780–818 m, 25 May 2003, Tangaroa, NORFANZ stn. TAN0308-081. NMNZ P. 0 13068 (12: 18.3–22.2 mm HL, 81+– 149 mm TL), New Zealand, off Poor Knights Islands, 35º 30' S, 174º 44' E, 558–622 m, Marine Dept. Prawn Survey station 22, prawn trawl, 11 Nov 1962. NMNZ P. 013074 (7: 20.5–25.9 mm HL, 144+– 156 mm TL), New Zealand, 22 miles north of Cape Brett; 34º 51' S, 174º 20' E, 732 m, Marine Dept. Prawn Survey station 30, prawn trawl, 22 Nov 1962. NMNZ P. 0 13080 (21 mm HL, 122+ mm TL), New Zealand, 8 miles east of White Island, 37º 31' S, 177º 26.5' E, 549–629 m, Dept. Prawn Survey station 14, prawn trawl, 30 Sep 1962. NMNZ P. 0 13083 (16.8 mm HL, 92+ mm TL), New Zealand, 8 km north of Mayor Island, 37º 13 S, 176º 20' E, 366 m, Marine Dept. Prawn Survey station 10, prawn trawl, 28 Sep 1962. NMNZ P. 0 23474 (26 mm HL, 100 mm TL), New Zealand, off 90 Mile Beach, 34º 55.1' S, 172º 9' E, 657–661 m, RV James Cook, JCO8106/059, bottom trawl, 24 Apr 1981. NMNZ P. 0 34478 (15.9 mm HL, 107 mm TL), New Zealand, NE of Cavalli Islands, 34º 45.4' S, 174º 4.1' E, 530 m, NZOI station I0353, 0 9 Nov 1977. NMNZ P. 0 34484 (12.9 mm HL, 63+ mm TL), off Cape Karikari, 34º 40.6' S, 173º 50.5' E, unknown depth, NZOI station I0351, 0 9 Nov 1977. NMNZ P. 0 38916 (15.5 mm HL, 93+ mm TL), South Reinga Ridge, New Zealand EEZ, 34º 9.7' S, 171º 27' E, 544–584 m, RV Tangaroa, NORFANZ TAN0308/002, rough bottom trawl, 11 May 2003. NMNZ P. 0 38950 (2: 15–18 mm HL, 63+–72+ mm TL), Reinga Ridge, New Zealand EEZ, 34º 9.9' S, 171º 27' E, 558–573 m, RV Tangaroa, NORFANZ TAN0308/ 0 0 8, Sherman sled, 12 May 2003. NMNZ P. 0 39386, (18.8 mm HL, 109+ mm TL), Reinga Ridge, New Zealand EEZ, 33º 23.3' S, 170º 9.8' E, 605–622 m, RV Tangaroa, NORFANZ TAN0308/125, Sherman sled, 31 May 2003. NMNZ P. 0 39399 (15.8 mm HL, 105 mm TL), Reinga Ridge, New Zealand EEZ, 33º 24.2' S, 170º 10.3' E, 627–662 m, RV Tangaroa, NORFANZ TAN0308/128, rough bottom trawl, 31 May 2003. NMNZ P. 0 39657 (13.8 mm HL, 73 mm TL), West Norfolk Ridge, New Zealand EEZ, 35º 10' S, 169º 29.1' E, 867–869 m, RV Tangaroa, NORFANZ TAN0308/158, beam trawl, 0 4 Jun 2003. NMV A25145-001 (4: 20–26 mm HL, 110+– 135 mm TL), Tasman Sea, Lord Howe Plateau, 34º 01.95' S, 162º 35.96' E, 780–818 m, 25 May 2003, Tangaroa, NORFANZ stn. TAN0308-081.

Description (Counts and proportional measurements are presented in Table 2). Head bones thin, delicate dorsally and around snout and orbit, but head ridges low, lacking large projections. Snout short, not protruding beyond anterior of jaws. Orbits large, diameter about one-third HL, about equal to orbit-to-preopercular length. Mouth large, upper jaw extends posteriorly to about mid-point of orbit. Teeth in both jaws small, curved, sharply pointed. Teeth in upper jaw in a band (4–5 rows wide) with outer teeth not markedly enlarged. Lower jaw teeth in a narrow band with an inner row of slightly enlarged teeth and an outer row of smaller teeth. Chin barbel small, thin. Origin of first dorsal, pectoral and pelvic fins about on same vertical. Interspace between dorsal fins large, about twice length of first dorsal fin base. Light organ with ventral striae luminous tissue on isthmus and on abdomen extending up to about level of pectoral fin base, and posteriorly to near anus. Anterior dermal window slightly smaller than posterior window.

Colour. Prominent dark area on dorsum extending from nape posteriorly to about vertical line through anal fin origin, sharply demarcated along ventral margin of area, and not reaching mid-lateral line. Dark operculum, but preoperculum and ventral surface of head including lower jaw overlain laterally with silver-grey pigment in lessdamaged specimens. Small melanophores scattered on ventral surface of trunk and mid-laterally onto tail, extending about one head length posterior to anal fin origin. Tail translucent with melanophores at base of anterior rays of anal fin, and internally around vertebrae (readily visible through translucent flesh). Mouth cavity and tongue pale, interior side of gill cover pale or dusky distally, blackish proximally.

Size. To about 26 mm HL and 163 mm TL.

Etymology. From the Latin maculis meaning spot and cauda meaning tail, describing the distinctive line of melanophores along the mid-lateral line anteriorly on the tail.

Distribution (Figure 7). Known from the Tasman Sea including southern Lord Howe Rise, southern Norfolk Ridge, and northern New Zealand, at latitudes of approximately 33º 23′– 37º 31′ S.

Comparisons and remarks (Table 2). This is another member of the species group related to Hymenocephalus striatissimus Jordan & Gilbert 1904, which all possess a dark saddle-like mark dorsally on the trunk above the mid-lateral line, silvery lateral aspects of head and trunk, relatively large orbits, usually 8 pelvic fin rays, and a short slender barbel. The most recently described species in this group is Hymenocephalus megalops Iwamoto & Merrett 1997 (Figure 7), which has small scattered melanophores ventrally on the trunk but lacks a mid-lateral line of melanophores on the anterior portion of the tail (described by Iwamoto & Merrett 1997 as having an “immaculate” tail region), a broad band (4–5 rows) of very small uniform-sized teeth in lower jaw, more gill rakers on first arch (outer/inner) 12–19/20–24, and a large orbit diameter (40–48 % HL) than Hymenocephalus maculicaudus. Hymenocephalus megalops was recorded from more northern waters, approximately 11º 53′S to 24º 40′ S (Iwamoto & Merrett, 1997), including Marion Plateau (northeast Australia), Wallis and Futuna Islands, Chesterfield Plateau, and the New Caledonia region. Iwamoto & Merrett (1997:523), made extensive comparisons between Hymenocephalus megalops and two species from the southeast Pacific, H. neglectissimus Sazonov & Iwamoto 1992, and H. semipellucidus Sazonov & Iwamoto 1992, summarised in Table 2. In comparison with H. maculicaudus, H. neglectissimus has a larger orbit diameter (44–55% HL) and longer barbel (18–28 % HL), and H. semipellucidus has a longer barbel (13–22 % HL) and more pectoral fin rays (14–19).