Zu elongatus Heemstra & Kannemeyer 1984

Martin, Jennifer M. & Hilton, Eric J., 2021, A taxonomic review of the family Trachipteridae (Acanthomorpha: Lampridiformes), with an emphasis on taxa distributed in the western Pacific Ocean, Zootaxa 5039 (3), pp. 301-351 : 335-336

Zu elongatus Heemstra & Kannemeyer 1984

Figure 19

Holotype. SAM 24707. 1166 mm SL. Trawled SW of Cape Province, 411m bottom depth.

Material Examined. CSIRO H 6325-01 (1142 mm SL, Pacific, Tasman Sea, Lord Howe Rise); CSIRO H 5915-01 (Photographs only, 1325 mm SL, Indian, Madagascar Ridge); NMNZ P.5681 (426 mm SL, Pacific, New Zealand, South Island, Nelson); NMNZ P.000834 (129.75 SVL (≈ 420 mm SL), Pacific, New Zealand, South Island, Marlborough); QVM 1972.5.511 (405 mm SL, Pacific, northwest Tasmania, Stanley).

Diagnosis. Dorsal-fin rays 138–147 total, in juveniles first six more robust and elongate than remaining; pectoral-fin rays 11–13, first element short and stout; pelvic-fin rays 7–9, elongate in juveniles, bony base only in adults; caudal-fin rays 17, dorsal lobe with 12–13 rays, ventral lobe with 4–5 rays. Gill rakers 2–3 + 7–9. Lateral-line plates 125–143. Vertebrae: 84–88 total, 29–32 precaudal, 37–40 preanal. SVL 31–42 % SL; body depth 14.5–20.4 % SL; eye diameter 9.0–12.9 % SV, eye diameter 1.5–2.0 in length of lower jaw. Premaxilla with 9–21 teeth, 6–9 on dentary; vomer with two teeth in the adult, juveniles with three vomerine teeth; palatine teeth variably present.

Remarks. In juveniles, the three fleshy tabs are present on the ventral midline between the pelvic-fin base and the anus and are much more angular in appearance ( Fig. 19 ) when compared to the smoother, lobe-shaped scalloping of Z. cristatus . The post-anal ventral constriction is not as abrupt as in juveniles of Z. cristatus , but rather tapers more gradually. In both juveniles and adults of Z. elongatus , the lateral line originates against the uppermost portion of the operculum and gradually slopes toward the ventral mid-line until the vent is reached. In comparison, the lateral line of Z. cristatus runs straight from its origin to the point of ventral constriction just posterior to the anus, upon which it joins the ventral midline.

Meristic and morphometric information presented here includes data from specimens collected from previously unreported geographic locations (waters off of Australia, New Zealand and western Indian Ocean-Madagascar Ridge) and larger size classes (> 1142 mm SL). Incorporation of these data provide a broader geographic and ontogenetic description than previously reported for Z. elongatus from the Atlantic waters of South Africa.

Distribution. Known from the Atlantic Ocean off South Africa, Pacific Ocean and Tasman Sea ( New Zealand and Tasmania), and the western Indian Ocean (off Madagascar Ridge). Shirke et al (2017) reported the first record of Z. elongatus from the southeast Bay of Bengal, represented by a 1280 mm SL specimen collected from a depth of 408 m on longline in Andaman and Nicobar Islands waters. However, the specimen photographed ( Shirke et al 2017: fig. 2) lacks the zigzag series of lateral-line plates, which is a diagnostic character of the genus Zu. Additionally, the specimen has tubercles along the mid-ventral line that project beyond the body wall and flattened tubercles along the dorsal fin pterygiophores, both are characters that are absent in Zu and present in Trachipterus . The meristic counts provided also fall within the range for the genus Trachipterus . As the specimen is Trachipterus sp. , the presence of Z. elongatus in the southeast Bay of Bengal is not confirmed.

Previously known from Atlantic waters of South Africa, off northwestern Cape Province (collected by trawlers, bottom depths range from 411–580 m) and from New Zealand waters ( Heemstra & Kannemeyer 1984). New Zealand specimens have been collected mostly by bottom or midwater trawls and at bottom depths ranging from 480–1133 m, with sizes ranging from about 200 to 1330 mm SL. Some smaller specimens (in the 250–400 mm SL range) have been recorded as washed up on beaches. Specimens smaller than 240 mm SL have yet to be reported.

Examination of material in the Australian National Collection at CSIRO and at the QVM confirms the presence of Z. elongatus in Australian waters. The CSIRO specimen, an adult (CSIRO H6325-01, 1142 mm SL), was collect- ed by demersal trawl at 1000 m near Lord Howe Rise in the Tasman Sea. The QVM specimen, a juvenile (damaged, about 405 mm SL, QVM 1972/5/511), was washed ashore at East Inlet, Stanley on the northwest coast of Tasmania. Both specimens fall within the meristic ranges given for Z. elongatus , and the juvenile specimen possesses angular scallops and 7 postanal vertical bars. This species was not found in any mainland Australian collections examined. A specimen collected from the western Indian Ocean, off the Madagascar Ridge (CSIRO H5915-01, 1325 mm SL,) extends the range of the species to the southern Indian Ocean.

Geographic variability. Heemstra & Kannemeyer (1984) reported data on five South African specimens and two New Zealand specimens; data from the New Zealand specimens were not included in the diagnosis or description of Z. elongatus . Upon comparison of these reported values and additional specimens examined it appears that some differences are present in Z. elongatus specimens from South Africa (n= 5), New Zealand and Tasmania (n=5), and a single specimen collected from the southwestern Indian Ocean. Vertebral counts for the New Zealand specimens were different from South African specimens: 1) total vertebrae, 88 vs. 84–87; 2) pre-anal, 37, 39 vs. 38–40; 3) precaudal, 30, 32 vs. 29–31. The eye diameters for New Zealand and Tasmanian specimens are also larger, relative to snout-vent length (11.5–12.9%) than for the South African specimens (9–10%) and for the Indian Ocean specimen (10.7%). Although some differences among specimens collected at different locations are present, so few specimens are available that it is unclear if these differences represent true geographic variation, ontogenetic variation, or artifacts of the small sample size. More specimens of similar sizes are needed for comparison.

Figures

FIGURE 19. Zu elongatus Heemstra & Kannemeyer 1984. NMNZ P.5681; 426 mm SL