Lestidium longilucifer, Ho & Graham & Russell, 2020

Ho, Hsuan-Ching, Graham, Ken & Russell, Barry, 2020, Three new species of the barracudina genus Lestidium (Aulopiformes: Paralepididae) from the Indo-West Pacific, Zootaxa 4767 (1), pp. 71-88 : 72-78

Lestidium longilucifer sp. nov.

urn:lsid:zoobank.org:act:2F042E11-D699-435A-9BFA-E0D36D895473

Long light-organ barracudina

Figs. 1 A–C, 2A–E; Tables 1–3

Lestidium atlanticum (not of Borodin): Paxton et al., 1989:247. Hutchins, 2001:21. Paxton et al., 2006:492. Larson et al., 2013:48.

Holotype. AMS I.22821-063 , 260 mm SL, 18°16’S, 118°12’E, 190 km northwest of Port Hedland , North West Shelf, Western Australia, Australia, demersal trawl, 298–320 m, RV Soela, 10–11 Apr. 1982, coll. J. Paxton & M. McGrouther.

Paratypes. Twenty-one specimens, 183–292 mm SL. AMS I.22809-045 (2 specimens, 214–242 mm SL), 18°40’S, 116°42’E, North West Shelf, 250 km NW of Port Headland, Western Australia, 600 m, 4 Apr. 1982. AMS I.22817-022 (2, 279–292), 18°06’S, 117°45’E, North West Shelf, Western Australia, 500 m, FRV Soela, demersal trawl, 8 Apr. 1982. AMS I.22821-023 (6, 231–259), collected with holotype. AMS 31175-002 (1, 219), 26°57’S, 112°22’E, off Shark Bay, Western Australia, demersal trawl 666–688 m, RV Southern Surveyor, 31 Jan. 1991, coll. J. Paxton. CSIRO H2094-01 (1, 258), 16°59’S, 120°15’E, NE of Mermaid Reef, Rowley Shoals, Western Australia, prawn/demersal trawl, 395 m, 14 Apr. 1989. CSIRO H3040-05 (1, 225), 26°59’S, 112°38’E, SW of Shark Bay, Western Australia, demersal trawl, 435 m, 28 Dec. 1989. CSIRO H3154-36 (1, 231), CSIRO H3154-37 (3, 246–265), 18°07’S, 118°08’E, SW of Imperieuse Reef, Western Australia, demersal trawl, 400 m, 8 Mar. 1992. NMMB-P 25561 (1, 183), 20 Jan. 2017; NMMB-P 26017 (1, 205), 15 Apr. 2017. NMMB-P 27928 (1, 194), 16 Jul. 2017; all from off Dong-gang, Pingtung, Southwestern Taiwan. NTM 12607-007 (1, 243), 17°51’S, 118°30’E, off Rowley Shoals, Northwest Shelf, 410 m, FV Comac Endeavour, 6 Nov. 1985.

Non-type. AMS I.42182-009 (1, 50) 11°01’S, 149°59’E, Coral Sea, S of Alotau, Papua New Guinea, MIDOC plankton trawl, 12 m, RV Southern Surveyor, 16 May 1997. AMS I.42209-017 (2, 52–85), AMS I.42209-056 (2, 62–90), 11°19’S, 149°40’E, Coral Sea, SW of Alotau, Papua New Guinea, MIDOC plankton trawl, 12 m, RV Southern Surveyor, 16 May 1997. AMS I.42310-001 (1, 80), 10°21’S, 147°35’E, Coral Sea, S of Port Moresby, Papua New Guinea, MIDOC plankton trawl, 12 m, RV Southern Surveyor, 21 May 1997. AMS I.42344-010 (1, 48), 9°23’S, 145°23’E, Coral Sea, W of Port Moresby, Papua New Guinea, MIDOC plankton trawl, 12 m, RV Southern Surveyor, 23 May 1997. AMS I.22808-006 (3, 237–250), 17°59’S, 118°17’E, North West Shelf, Western Australia, 410 m, RV Soela, 3 Apr. 1982, coll. J. Paxton and M. McGrouther. AMS I.22825-002 (3, 252–260), 18°59’S, 117°10’E, North West Shelf, Western Australia, 315 m, RV Soela, 13 Apr. 1982, coll. J. Paxton and M. McGrouther. AMS I.23424-012 (2, 255–268, slightly damaged), 18°43’S, 117°12’E, North West Shelf, Western Australia, 370 m, RV Soela, 1 Aug. 1982. CSIRO H5638-01 (2, 247; 1 broken), Northwest Shelf, Western Australia, RV Soela, 1 Aug. 1982. NSMT-P 122098 (2, 232–235), West coast of Australia, Eastern Indian Ocean, no date. NSMT-P 122128 (1, 235), 24°1.2’S, 112°30.6’E, West coast of Australia, 420 m, 6 Nov. 1975. NSMT-P 122129 (1, 254), West coast of Australia, Eastern Indian Ocean, no date.

Diagnosis. Lestidium longilucifer sp. nov. is one of three species recognized in the Lestidium atlanticum species complex with a luminescent duct extending beyond the anterior margin of the eye. It can be distinguished from its two congeners L. atlanticum and L. orientale in having prehaema vertebrae 41–43; predorsal vertebrae 38–40; prepelvic vertebrae 37–39; preanal vertebrae 56–59; total vertebrae 85–88; total lateral-line scales 126–146; and relatively short jaws.

Description. Dorsal-fin rays 10; pectoral-fin rays 13 (14 in 2 paratypes); pelvic-fin rays 9; anal-fin rays 30 (28–30 in paratypes, except for 1 with 26). Lateral-line scales: prepelvic 38 (37–39); predorsal 39 (38–39); preanal 55 (55–57); and total 132 (126–146). Vertebrae: prehaemal 41 (41–43); caudal 47 (43–47); prepelvic 38 (37–55 (55–57); and total 132 (126–146). Vertebrae: prehaemal 41 (41–43); caudal 47 (43–47); prepelvic 38 (37–39); pre- dorsal 39 (38–40); preanal 58 (56–59); and total 88 (85–88).

Body moderately elongate, robust, and relatively thick; belly nearly straight in profile; greatest depth at approximately anterior third of body; depth at pectoral fin 15 (13–15) times in SL. Caudal-peduncle length about 1.5 times eye diameter. Dorsal adipose fin small. A moderately constricted abdominal ridge between head and pelvic fins. Ventral adipose fins weakly developed along abdominal ridge and margin between anus and AFO. Anus above about tip of adpressed pelvic fin, about same vertical through posterior end of dorsal-fin base.

DFO well behind midpoint of SL ( Figs. 1 A–C), slightly behind VFO in most individuals ( Fig. 2D ) or nearly at same vertical in some, predorsal length 1.6 (1.5–1.6). Pectoral fin level with vertical of posterior margin of gill cover, its upper base about level with lower margin of eye. A small pocket behind pectoral-fin base. VFO slightly behind midpoint of SL, prepelvic length 1.6 (1.6–1.7) in SL, with a small axial scale behind pelvic fin base. Anal fin originating at posterior fourth of body, preanal length 1.3 (1.2–1.3). Anal-fin base 6.5 (6.4–7.9) in SL. Adipose fin above rear portion of anal-fin base.

Head moderately long, slightly wider at opercle than body, its length 4.6 (4.5–5.1) in SL. Snout long and blunt, its length 1.9 (1.9–2.1) in HL. Postorbital length slightly less than one-third of HL. Mouth terminal, its gape extend- ing to under anterior half of eye posteriorly; lower jaw upturned distally, with a small fleshy tissue on its tip. Eye diameter 6.4 (5.6–7.5) in HL. No light organ in front of eye ( Fig. 2A ) and no luminescent duct at lower margin of orbit.

Interorbital space narrow, its width 10.7 (9.7–11.5) in HL; some straight ridges on top of head and snout. Upper jaw length 2.2 (2.1–2.3 in HL), posterior end of maxilla terminating at about half of eye diameter before a vertical through anterior margin of orbit. Two nostrils close together, both well in front of posterior end of maxilla, about one eye diameter before the eye. Sensory canals on snout, check, operculum, and jaws; numerous sensory pores on dorsal surface of snout and lower surface of lower jaw.

Opercle thin, with posterior margin bluntly pointed, its lower margin notched around the base of pectoral fin. Gill membranes joined anterior to a vertical from middle of eye, free from isthmus. Four gill arches, all with filaments; the fourth arch fully connected to the gill wall by membrane. Pseudobranchs present, inside a deep pocket above first gill arch.

Two or 3 small fangs at tip of upper jaw, followed by single row of small retrorse teeth along upper jaw, teeth becoming gradually smaller on posterior portion. Three depressible or fixed fangs at front of lower jaw, followed by two rows of fangs on the lower jaw forming 5–9 tooth pairs, those in inner row long, with a knife-like tip, and depressible; those in outer row much shorter, curved back and fixed.Vomerine teeth absent. Two rows of fangs on each palatine, anterior 3–4 teeth forming widely-spaced tooth pairs, those in the inner row depressible and long, and in outer row small and fixed; posterior portion with single row of small fixed teeth. One row of small, straight teeth on each side of tongue.

Gill rakers well-developed on epibranchial, ceratobanchial and hypobanchial of first gill arch; the rakers shield shaped, each with 4–7 small teeth and a narrow base. Rakers on epibranchial of first arch 15 (14–15), ceratobranchial with 19 (16–19), hypobranchial with 18 (17–20), and in total 50 (48–53). Teeth on pharyngeal arch slender, forming an oval patch with about 5 rows at middle/centre. Single row of small teeth on fifth ceratobranchial.

Body devoid of scales, except for a single row of lateral-line scales 132 (126-146) originating at upper corner of pectoral girdle and extending to caudal-fin base ( Fig. 2E ). Anterior 66 (62–66) scales of lateral line extending to about midway along the anal-fin base clearly larger in size than the remaining and almost square in shape with slightly concave upper and lower margins; these scales gradually become smaller and narrower posteriorly. Posterior 66 (63–83) scales of lateral line distinctly smaller. The large scales have a row of 3 (rarely 4) pores on each margin, the first pore larger than the rest; one pore on upper and lower end of these distinctly smaller scales.

A well-developed, unbranched, elongate luminescent duct along mid-line of ventral margin, extending forward from anus to well beyond eye (including those specimens smaller than 50 mm SL).

Coloration. Color when fresh ( Figs. 1 B–C), body slightly translucent, dorsal fourth greyish; dorsal surface of head and lower lips blackish; posterior portion above anal-fin base and behind silvery white; through the skin, upper abdominal cavity black with all peritoneal sections fused, the rest slivery white; all fins clear, except for the caudal fin slightly blackish. Preserved specimens ( Figs. 1A , 2 ) light brown dorsally, with melanophores extending downwards from mid-line about two-thirds the distance to the lateral-line; ventrally the body is uniformly pale. Dense melanophores cover top of head, snout, lips, under surface of lower jaw; the pectoral, dorsal, pelvic and anal fins are covered with scattered melanophores. Adipose and caudal fins densely covered with melanophores; gill chamber with large blackish patches; peritoneal membrane black, all peritoneal sections fused in adults.

Size. The largest specimen examined was 292 mm SL.

Etymology. The specific name longilucifer is derived from the combination of Latin longus and lucifer, referring to the long luminescent duct that extends well forward of the eye.

Distribution. The species is currently known only from the type series collected from northwestern Australia and southern Taiwan.

Remarks. Lestidium longilucifer and its congeners L. orientale and L. atlanticum form a group possessing a luminescent duct extending forward to in front of the eyes, and VFO at about same vertical through DFO; in contrast the luminescent duct extending between the anus to just below the opercle and the DFO is well behind VFO in the rest of congeners. All these species differ from L. bigelowi in lacking light organs on the lateral and ventral surfaces of the body.

Lestidium longilucifer can be separated from L. atlanticum and L. orientale by having predorsal vertebrae 38–40 (vs. 33–35 in L. atlanticum and 33–36 in L. orientale , respectively); prepelvic vertebrae 37–39 (vs. 34–36 and 34–37 [mainly 35–36]); prehaemal vertebrae 41–43 (vs. 36–38 and 37–40); preanal vertebrae 56–59 (vs. 52–53 and 51–54); total vertebrae 85–88 (vs. 81–82 and 79–83); total lateral-line scales 126–146 (vs. 115–123 and 109–126); predorsal length 60.9–64.8% SL (vs. 58.7–60.4% SL and 57.7–59.9% SL); jaws slightly shorter with upper jaw 9.2–10.5% SL (vs. 9.9–11.3% SL in L. atlanticum ; overlapped with L. orientale ) and lower jaw 12.5–14.1% SL (vs. 13.5–14.8% SL in L. atlanticum ; overlapped with L. orientale ). Moreover, the maximum adult size is clearly greater (up to 292 mm SL) in L. longilucifer , whereas the largest known specimen of L. atlanticum is 177 mm SL (USNM 11727; Rofen, 1966) and 177 mm SL (NMMB-P25557) for that of L. orientale .

Ege (1957) recognized Lestidium atlanticum as a widespread species in tropical and subtropical regions (between 40°N and 30°S) of the Atlantic, Indian and Pacific oceans. However, he reported adults only from the western Atlantic Ocean, and only young stages from elsewhere, including just one specimen from each of western and eastern Australia.

The meristic data provided by Ege (1957) were divided into several geographic regions and encompassed broad ranges, i.e. 75–87 total vertebrae and 35–41 prehaemal vertebrae. However, his data for Atlantic specimens are 80–83 total vertebrae (n=44) and 36–38 prehaemal vertebrae (n=22), which agree well with our examination.

Ege’s data for specimens taken from the Indo-west Pacific can be further divided into a high vertebral population (83–87 total vertebrae), moderately high vertebral population (79–83 total vertebrae) and low vertebral population (75–80 total vertebrae).As few adult specimens were available to this study from the Indo-west Pacific other than from Taiwan and Australia (HCH, pers. data), we are not able to make judgement on all these populations. However, Ege’s specimens taken from the western Indian Ocean and Indonesia show similar vertebral counts to L. longilucifer .

Moreover, the northwestern Pacific Ocean population (e.g. from Taiwan, Japan and the Philippines) is now recognised as a distinct species ( Ho et al., 2019a), representing Ege’s moderately high vertebral number population. Specimens of the low vertebral number population are needed for further study.

Rofen (1966) cited Ege’s (1957) data to define Lestodium atlanticum and provided data for three additional specimens collected from the Atlantic Ocean. These specimens have 121 lateral-line scales; 9–10 dorsal-fin rays; 29–30 anal-fin rays 12–13 pectoral-fin rays; 38 prehaemal vertebrae and 80–83 total vertebrae, consistent with our separation of L. longilucifer from the Atlantic population of L. atlanticum .

The smallest specimen of L. longilucifer examined was 48 mm SL (AMS I.42344-010) but even at this small size, it exhibited a well-developed luminescent duct inside the abdominal cavity that extended forward to beyond the eye.Another example is the holotype of Paralepis thermophilus (= Lestidium atlanticum ), a 43.5 mm SL juvenile, also show clearly a luminescent duct extending forward before the eye.

Figures

FIGURE 1. Lestidium longilucifer sp. nov. A. Holotype, AMS I.22821-063, 260 mm SL, preserved. B. Paratype,AMS I.31175- 002, 219 mm SL, fresh, arrow points the VFO. C. Paratype, NMMB-P26017, 205 mm SL, fresh.

FIGURE 2. Lestidium longilucifer sp. nov., from the holotype. A. Lateral view of head. B. Ventral view of head, arrow points the anterior end of luminescent duct. C. Middle region of trunk. D. posterior trunk region, arrows indicate DFO (dorsal), VFO (ventral left) and AFO (ventral right). E. Caudal region, arrow indicates posterior end of lateral line.