Parequula elongata, Iwatsuki, Yukio, Pogonoski, John J. & Last, Peter, 2012

Iwatsuki, Yukio, Pogonoski, John J. & Last, Peter, 2012, Revision of the genus Parequula (Pisces: Gerreidae) with a new species from southwestern Australia, Zootaxa 3425, pp. 42-54 : 43-48

Parequula elongata , new species

New English name: Western Silverbelly Fig. 1 A; Table 1

Parequula sp. A; Last et al. 2006:10, 17, and 24, figured as 37 349801 (off Perth). Parequula melbournensis (in part); Gomon et al. 2008:587 (W Coast population).

Holotype. CSIRO H 6344–04, 76 mm SL ( MX), off Rottnest I., Western Australia, Australia (32°08’S, 115°15’E), 132– 133 m.

Paratypes. 42−81 mm SL, n =20, all from Australia. AMS I 18707–004, 69 mm SL ( MX), Great Australian Bight, Western Australia (ca. 32°54’S, 127°36’E), 57–58 m; CSIRO H 6345–03, 67 mm SL ( MX), off Rottnest I., Western Australia; CSIRO H 6349–12, 2 specimens ( MX), 58–71 mm SL ( MX), off Rottnest I., Western Australia (32°10’ S, 115°18’E), 102–104 m; CSIRO H 6349–15, 3 specimens, 57–66 mm SL ( MX), off Rottnest I., Western Australia (31°53’S, 115°18’E), 100–102 m; CSIRO H 6452–06, 71 mm SL (X), off Shark Bay, Western Australia (25°54’S, 112°50’E), 95–100 m; MUFS 32938–32939, 2 specimens, 60–65 mm SL ( MX), off Rottnest I., Western Australia (31°55’S, 115°36’E), 100–102 m; NMV A 29356–005, 3 specimens, 69–78 mm SL ( MX), NMV A 29356–009, 77 mm SL ( MX), NMV A 29356–021, 70 mm SL, same data as holotype; SAMA F 12097, 3 specimens, 63–76 mm SL, Great Australian Bight, South Australia (32°53’S, 133°08’E), 77 m; WAM P 26068–007, 42 mm SL ( MX), Goss Pass, Beacon Island, Houtman Abrolhos Islands, Western Australia (28°29’S, 113°47’E), 40 m; WAM P 27219–034, 81 mm SL ( MX), Hummock Island, Houtman Abrolhos Islands, Western Australia (28°48’S, 114° 03’E), 40– 44 m.

Non-type specimens. 50−70 mm SL, n =17, all from Australia. CSIRO H 6349–17, 2 specimens, 59–69 mm SL (X), off Rottnest I., Western Australia (31°55’S, 115°36’E), 100–102 m; NMV A 29361–008, 5 specimens, 55–66 mm SL (X, poor condition), NMV A 29361–018, 50 mm SL (X, poor condition), NMV A 29361–024, 51 mm SL (X, poor condition), and NMV A 29361–025, 56 mm SL (X, poor condition), off Rottnest I., Western Australia (31°55’S, 115°36’E), 100–102 m; SAMA F 12089, 5 specimens, 54–65 mm SL (X, poor condition), Great Australian Bight, South Australia (32°16’S, 131°25’E), 60 m; WAM P 13274–001, 2 specimens, 58–70 mm SL (X, poor condition), off Rottnest I., Western Australia (ca. 32°00’ S, 115°30’E), depth unknown.

Diagnosis. Distinguished from its congener in having the following combination of characters: slender body (2.7–3.4, mean 3.0 in SL); reddish upper margin of dorsal-fin rays when fresh; soft anal-fin rays 14–15, usually 15; pored lateral-line scales 34–35, mode 34.

Description. Counts and proportional measurements of the holotype and 20 paratypes of Parequula elongata n. sp. are shown in Table 1. Proportional data and counts of 17 non-type specimens of P. elongata n. sp. are excluded from Table 1 because most specimens were damaged or in poor condition. In the description below, data for the holotype are presented first, followed by those of the paratypes in parentheses if different. All vertebral counts in non-type specimens are noted below.

Body oblong, compressed; rostro-occipital (dorsal) profile of head almost straight, but interorbital space slightly convex (slightly convex or flat, sometimes with a shallow groove when skin tightly connected with skull in preserved specimens; a pair of weak protuberances (nasal bones) of dorsal anteriormost snout, observed as naked nasal bones, more obvious when jaws protracted ( Fig. 3 A); predorsal length shorter than body depth (subequal to slightly shorter than body depth); orbit diameter 2.4 (2.3–2.8) in head, almost equal to bony interorbital width (equal to or slightly greater than interorbital width); snout in dorsal view usually flat (flat or with a shallow groove for process of intermaxillary bones, especially in specimens ca. 70–80 mm SL, but groove extends little beyond anterior margin of orbit), its length slightly less than orbit diameter; maxilla almost reaching to vertical at front margin of dermal eye opening, its posterior edge concave; mandibular profile weakly concave; anterior premaxillary bones with a pair of weak, blunt bony protuberances in front in dorsal view; preopercular flange naked, rounded, angle slightly less than 90º; mouth protractile; teeth small, weakly curved, in broad band in jaws, outer row somewhat enlarged.

Dorsal fin usually not notched; length of soft portion slightly exceeding that of spinous portion; length of spinous dorsal-fin base slightly exceeding three quarters base of soft portion of anal fin; dorsal-fin spines moderately strong and gradually increasing in height to penultimate spines; last three spines subequal, their length about half length of head; fin rays subequal in height to posterior spines; anal fin commencing beneath anterior dorsal-fin ray, length of its base one quarter greater than head length (slightly greater than head length in most paratypes), spines much stronger than those of dorsal-fin spines, third longest, subequal to eye diameter; pelvic fins not quite extending to vent, it length ca. 0.6 times head length, while its spine ca. 0.8 times length of adjacent ray, recessible into post-pelvic groove when pelvic fin retracted; origin of pelvic fin beneath (slightly behind in some paratypes) posterior angle of base of pectoral fin; pectoral-fin length less than head length, fin tip reaching to vertical at anus and first anal-fin spine base; caudal fin moderately forked.

Gill rakers short; rakers of upper limb shorter than uppermost rakers on lower limb, and rakers on lower limb gradually becoming shorter anteroventrally; body scales oval and cycloid; interorbital space, snout, and preorbital naked, head and body punctuated by numerous small round pores, barely visible without magnification, most obvious on snout and interorbital region, but also evident on dorsolateral body ( Fig. 3 A–B); posterior nostril twice size of anterior nostril, placed very close to eye, a small skin flap between anterior and posterior nostril; scales of cheek smaller than those of body, extending on to mandible; branchiostegals 6; pseudobranchiae present; 3 supraneural bones (0/0/0+2/), but rarely 0/0+0/2/ (only in MUFS 32938); upper caudal fin rays (dorsal) 18–22, lower caudal fin rays (ventral) 15–18, total caudal fin rays 35–40, upper procurrent rays (dorsal) 9–13, lower procurrent rays (ventral) 7–10, total procurrent rays 17–23; vertebrae 10+15 (same in all non-type specimens).

Coloration. Fresh coloration is based on the holotype (CSIRO H 6344–04, 76 mm SL, photographed by P. Last) and 2 paratypes (CSIRO H 6345–03, 67 mm SL, photographed by P. Last, and CSIRO H 6452–06, 71 mm SL, photographed by L. Conboy): head and body translucent with weak silvery tone both above and just beneath lateral line, silvery white ventrally; pectoral, pelvic and anal fins translucent or whitish; dorsal fins translucent with reddish outer margin; caudal fin pale whitish or translucent with four dotted vertical bands, posteriormost band or margin somewhat yellowish; cheeks and opercles similar to body colour; anterior and posterior iris lighter, remainder golden, darker in upper and lower parts. In preserved specimens: head and body yellowish or dusky brownish, lighter ventrally on abdomen; dotted vertical bands of caudal fin becoming indistinct. Alcohol-fixed specimens yellowish to dusky dorsally and whitish ventrally.

Distribution. Parequula elongata n. sp. is endemic to Australia and currently known only from the following localities: off Shark Bay, the Houtman Abrolhos Islands, Rottnest Island, and in the Great Australian Bight. The distribution of this species is probably limited to southwestern Australia.

Ecological notes. The first known specimens of P. elongata n. sp. were captured by trawls in depths of 100–133 m ( Last et al. 2006). Specimens later detected in museum collections were taken by SCUBA and trawls at depths of ca. 40– 100 m. The species is not known to occur in shallow inshore waters (less than 40 m) like its congener P. melbournensis . Thus, the species appears to be mainly demersal on the mid continental shelf, whereas P. melbournensis is more common in shallow, inner-shelf and coastal environments.

Etymology. The specific name, “ elongata ”, is proposed in reference to the more slender body of this species than its congener.

Remarks. The authors consider Parequula elongata n. sp. to be a member of the genus Parequula (previously monotypic) due to the similarities with P. melbournensis ( Castelnau 1872) , including its dorsal-fin and anal-fin ray counts, and other similar morphological characters (see Table 1). However, it is noted that the overall body shape is subtly different. Parequula elongata n. sp. is more slender than P. melbournensis and all specimens were smaller than 85 mm SL, indicating that it is probably a smaller species than P. melbournensis .

Figures

FIGURE 1. Parequula elongata n. sp. (A) and P. melbournensis (B). A) holotype, CSIRO H 6344 – 04, 76 mm SL, off Rottnest I., Western Australia; B) CSIRO H 6942 – 05, 108 mm SL, Investigator Strait, South Australia.

FIGURE 3. Pores on dorsal head view and dorsolateral view of Parequula elongata n. sp. (A – B, CSIRO H 6344 – 04, holotype, 76 mm SL, off Rottnest I., Western Australia) and P. melbournensis (C, CSIRO CA 52, 157 mm SL, Great Oyster Bay, Tasmania; D [image reversed], CSIRO H 3536 – 06, 159 mm SL, off Disaster Bay, NSW). Arrows show scattered pores, easily observed after body scales are removed.