Platycephalus orbitalis, Imamura, Hisashi & Knapp, Leslie W., 2009

Imamura, Hisashi & Knapp, Leslie W., 2009, Platycephalus orbitalis, a new species of flathead (Teleostei: Platycephalidae) collected from western Australia, Zootaxa 2271, pp. 57-63 : 58-62

Platycephalus orbitalis , sp. nov.

Proposed common name: Western-Australian flathead ( Figures 1 –5)

Platycephalus marmoratus (not Stead, 1908): Hutchins & Thompson, 1983: 78, fig. 112 (Western Australia) (in part); Hutchins & Swainston, 1986: 127, fig. 204 (Western Australia) (in part); Paxton & Hanley, 1989: 469 (Rottnest Islands to Direction Bank, Western Australia) (in part); Knapp, 1991: 29 (off Rottnest Island and Cape Cuvier, Western Australia) (in part); Hutchins, 2001: 28 (Western Australia); Hoese et al., 2006: 943 (Rottnest Island to Direction Bank, Western Australia) (in part).

Holotype: CSIRO H 6349-04, 267.4 mm SL, northwest of Rottnest Island, Western Australia (31°52.56’S, 115°18.30’E – 31°52.60’S, 115°18.49’E), 100–102 m depth, 10 Apr. 2006.

Paratypes: 6 specimens, all from Western Australia. CSIRO H 6350-02, 236.3 mm SL, northwest of Rottnest Island (31°53’S, 115°16’E), 124 m depth, 10 Apr. 2006; CSIRO H 6381-03, 277.9 mm SL, southwest of Shark Bay (27°03.12’S, 113°04.86’E – 27°02.88’S, 113°04.80’E), 106 m depth, 6 Dec. 2005; CSIRO T 615, 304.6 mm SL, south of Cape Leeuwin (34°35’S, 114°53’E), 144 m depth, 23 Feb. 1981; WAM P.22098-001, Cape Cuvier (24°10’S, 113°20’E), 29 July 1972; WAM P.17451-001, 2 specimens, 266.0, 333.4 mm SL, Rottnest Island (32°00’S, 115°30’E), 50 m depth, 30 Dec. 1981.

Diagnosis. A species of Platycephalus with margin of the interopercle scalloped, skinny sensory tubes on infraorbitals and preopercle well developed, mostly covering cheek region, except for anteroventral region, and body and head lacking distinct large spots and bands dorsally.

Description. Counts and proportional measurements are shown in Table 1 .

Body greatly depressed, mostly covered with ctenoid scales, but some cycloid scales on undersurface. Head greatly flattened, length 3.2 (3.1–3.4) in SL; snout and interorbit naked; nape, and occipital, postorbital, and opercular regions mostly scaled. Snout robust, length 3.2 (3.1–3.3) in HL, longer than orbital diameter.

Upper surface of eye without papillae. Iris lappet broad, well expanded and simple dorsally, and small (broad in one paratype), simple, and weakly convex ventrally ( Fig. 2 A). Interorbital width 7.2 (6.9–8.4) in HL, becoming wider with growth, shorter than orbital diameter. Spines and ridges weakly developed on top and side of head ( Fig. 2 B). Nasal lacking spines. Lachrymal with two (or one in five paratypes) antrorse spines. Single preocular spine present. Suborbital ridge entirely smooth. Single postorbital spine present. Frontal ridges lacking spines. Supracleithrum with spine. Preopercle with two spines; lower spine slightly longer than upper one, not reaching posterior margin of opercle; upper lacking supplementary spine. Opercle with two spines, lacking prominent ridge. Interopercular flap absent; margin of interopercle scalloped ( Fig. 3 A). Maxilla reaching beyond anterior margin of pupil, length 2.7 (2.6–2.7) in HL. Teeth in bands on jaws and palatine, and in shallowly V-shaped (or crescent in a paratype) patch on vomer; tooth band on upper jaw lacking distinct notch medially. Upper jaw with several small canine teeth anteriorly; remainder of jaw with small- to moderate-size conical teeth. Lower jaw mostly with two tooth rows, partially arranged in four rows (or partially arranged in three rows in some paratypes); inner row with longer conical teeth; outer row(s) with small-size conical teeth. Palatine with two tooth rows: inner row with longer and stouter conical teeth, outer row with small conical teeth. Vomer with small- to moderate-size canine teeth anteriorly and a few canine teeth posteriorly. Lip margins without papillae. Skinny sensory tubes on infraorbitals and preopercle well developed, mostly covering cheek region, except for anteroventral region ( Fig. 3 A). Pored scales in lateral line each with one exterior opening posteriorly; opening in most pored scales directed posteroventrally, in several scales posterodorsally. First dorsal fin originating posterior to opercular margin. First and second dorsal fin narrowly separated. Pectoral fin rounded posteriorly, length 2.2 (2.0–2.3) in HL. Posterior tip of pelvic fin reaching to third anal fin ray, length 1.2 (1.1–1.3) in HL. Caudal fin slightly rounded (or mostly flat in some paratypes) posteriorly, length 1.8 (1.7–1.9) in HL.

Color in alcohol. Body and head pale brown, lacking distinct large spots and bands dorsally, whitish ventrally. Head densely covered with very small brownish spots. First and second dorsal fins with small brown spots along rays. Pectoral fin pale brown with white lower margin and scattered small darker brown spots. Pelvic fin dark brown with pale brown basal portion and whitish outer margin. Anal fin with brownish pigments along rays; membranes of posterior portion of anal fin dusky. Caudal fin blackish, with pale brownish basal area and white posterior margin; upper margin with several blackish short oblique bands continuous with middle blackish area.

Color when fresh (based on color photographs of holotype): Color mostly similar to that in alcohol. Distribution. Known only from western Australia, ranging from Cape Cuvier (24°S) to south of Cape Leeuwin (34°S) (e.g., Hutchins, 2001; this study).

Pectoral fin rays 19 20 21 22 P. orbitalis (n=7) 1 5* 1

P. marmoratus (n=9) 2 5* 2

Etymology. The specific name of this new species is derived from Latin for “eye”, based on its characteristic feature of a narrower interorbit.

Remarks. Platycephalus orbitalis belongs to the genus Platycephalus in having pored scales in the lateral line more than 60 and a single tooth plate on the vomer ( Imamura, 1996; Knapp, 1999). Platycephalus orbitalis is most similar to P. marmoratus in having a combination of following the characters: 13 second dorsal and anal fin rays; 65–68 pored scales in lateral line, each with one exterior opening posteriorly; snout and interorbit naked; lower opercular spine slightly longer than upper one; interopercular flap absent; no strong canine teeth on jaws, palatine, or vomer; skinny sensory tubes from infraorbitals and preopercle extending cheek region; and caudal fin blackish with white posterior margin. Other members of the genus Platycephalus do not possess this combination of characters ( Knapp, 1991; Imamura, 2006). For example, a naked snout and interorbit are found only in P. marmoratus , P. chauliodous Knapp, 1991 and P. laevigatus Cuvier in Cuvier & Valenciennes, 1829, and the blackish caudal fin with the white posterior margin is only present in P. marmoratus among known members of Platycephalus (e.g., Imamrua, 2006). However, P. orbitalis is easily separable from P. marmoratus in having the margin of the interopercle scalloped (vs. smooth in P. marmoratus ) ( Fig. 3 ). In addition, there is a difference in the degree of the development of the skinny sensory tubes from the infraorbitals and preopercle covering cheek region; they mostly cover the cheek region, except for the anteroventral region in P. orbitalis , whereas they only partially cover it in P. marmoratus ( Fig. 3 ). The coloration is also helpful separating these two species; viz. the body and head lack distinct large spots and bands dorsally in P. orbitalis , while they are marbled with dark brown, brown, and pale irregular bands and spots in P. marmoratus . Platycephalus orbitalis is also distinguished from P. marmoratus in having a larger orbital diameter (17.5–20.3% HL) and narrower interorbit (11.9–14.6% HL), the former larger than the latter in examined material (vs. orbital diameter smaller, 15.2–20.1% HL, and interorbit wider, 13.6–21.4% HL, the former becoming smaller than latter by 270 mm SL in P. marmoratus ) ( Fig. 4 ), although the ranges of the orbital diameter and interorbital width of the two species are partly or mostly overlapping. Finally, the range and mode of the number of the pectoral fin rays differ in P. orbitalis and P. marmoratus , and this difference is statistically significant (Mann-Whitney’s U test; P <0.01), although the ranges of these species also overlap ( Table 2).

Comparative materials. Platycephalus marmoratus (10 specimens, all collected from eastern Australia): AMS I.15279 (471.6 mm SL); AMS I.15260 (holotype, 310.4 mm SL); AMS I.20721-002 (270.9 mm SL); AMS I.20870-001 (178.0 mm SL, dissected by Imamura, 1996); AMS I.22129-004 (309.5 mm SL); AMS I.25663-013 (169.5 mm SL); AMS I.25665-026 (184.6 mm SL); AMS I.27322-006 (173.0 mm SL); QM I.17021 (221.6 mm SL); QM I.2842 (398.8 mm SL).

Figures

FIGURE 1. Dorsal (upper) and lateral (lower) views of Platycephalus orbitalis, sp. nov., CSIRO H 6349 - 04, 267.4 mm SL, holotype, northwest of Rottnest Island, Western Australia.

FIGURE 2. Lateral views of iris lappet (right eye) (A) and dorsal view of head (B) in Platycephalus orbitalis, sp. nov., CSIRO H 6350 - 02, 236.3 mm SL, paratype, northwest of Rottnest Island, Western Australia.

FIGURE 3. Ventrolateral views of head of Platycephalus orbitalis, sp. nov., CSIRO H 6350 - 02, 236.3 mm SL, paratype, northwest of Rottnest Island, Western Australia (A) and Platycephalus marmoratus, AMS I. 25665 - 026, 184.6 mm SL, northeast of Yamba, New South Wales, Australia, showing the interopercle and the skinny sensory tubes arising from the infraorbitals and preopercle.

FIGURE 4. Relationships of orbital diameter (circle) and interorbital width (square) (% head length) versus standard length (mm). Solid symbol, Platycephalus orbitalis, sp. nov.; open symbol, P. marmoratus. “ H ” indicates holotype.

Tables

TABLE 1. Counts and proportional measurements of Platycephalus orbitalis sp. nov.

	Holotype	Paratypes
SL (mm) Counts:	CSIRO H 6349-04 267.4*	6 specimens 236.3–333.4
First dorsal fin rays	I+VIII	I+VIII (4 specimens) or I+VII+I (2)
Second dorsal fin rays	13	13
Anal fin rays Pectoral fin rays (upper, unbr.+middle, br.+lower, unbr.) Pelvic fin rays	13 1+13+6=20 I,5	13 2+11–12+5–7=19–21 I,5
Branched caudal fin rays Pored scales in lateral line (with spine) Scale rows above lateral line slanting	12 67 (1) 108	11 (2 specimens) or 12 (4) 65–68 (0–1) 101–105
downward and backward Scale rows above lateral lineslanting downward and forward	117	104–111
Gill rakers Proportional measurements (% SL):	2+4=6	2+7–8=9 (5 specimens) or 10 (1)
HL Predorsal length Length of first dorsal fin base	31.1 32.8 20.5	29.7–32.1 31.8–34.6 18.4–22.2
Length of second dorsal fin base Length of anal fin base Caudal peduncle length	34.6 37.4 7.8	33.0–35.3 37.3–38.3 7.2–8.3
Caudal peduncle depth Snout length Orbital diameter	3.9 9.6 5.8	3.8–4.2 9.2–9.8 5.3–6.2
Upper jaw Lower jaw Interorbital width Postorbital length	11.6 16.5 4.3 15.9	11.0–12.3 16.0–17.5 3.6–4.6 15.3–17.0
Suborbital width Pectoral fin length Pelvic fin length	2.8 14.4 26.4	2.4–2.9 14.4–15.1 24.3–27.1
Caudal fin length Length of first spine of first dorsal fin Length of second spine of first dorsal fin	17.5 3.6 Broken	16.8–17.6 2.9–3.7 13.9–15.7
Length of first ray of second dorsal fin Length of first anal fin ray Proportional measurements (% HL):	11.0 6.8	8.2–15.0 6.5–7.2
Snout length	31.0	30.5–32.0 contineud next page