Platycephalus chauliodous Knapp, 1991

Imamura, Hisashi, 2015, Taxonomic revision of the flathead fish genus Platycephalus Bloch, 1785 (Teleostei: Platycephalidae) from Australia, with description of a new species, Zootaxa 3904 (2), pp. 151-207 : 174-176

Platycephalus chauliodous Knapp, 1991

Common English name: Bigtooth flathead ( Figs. 16–17 ; Table 6)

Platycephalus chauliodous Knapp, 1991: 24 , figs. 1–3 (type locality: southern WA); Hoese et al., 2006: 941; Imamura, 2006: 304, tab. 1.

Neoplatycephalus sp.: Hutchins & Swainston, 1986: 127, fig. 196.

Platycephalus sp.: Hutchins & Thompson, 1983: 78, fig. 115.

Material examined. Holotype: AMS I.20231-007, 313 mm SL, Cockburn Sound, 0.5 km south of Carnac Island, WA, Australia (32°10’S, 115°40’E), 6–7 m depth, 27 Mar. 1978.

Paratypes (5 specimens, 65.6–460 mm SL, from southwestern Australia): USNM 307398, 75.6 mm SL, off Garden Island, WA (32°12’S, 115°40’E), 10 Apr. 1976; WAM P.24172-001, 460 mm SL, Cockburn Sound, Carnac Island, 3 miles off Freemantle, WA (32°07’S, 115°40’E), ca. 10 m depth, 30 Dec. 1973; WAM P.25798-008, 65.6 mm SL, Eagle Bay, WA (33°33.5’S, 115°04’E), 0–4 m depth, 21 Oct. 1976; WAM P.29879-001, 336 mm SL, WA (31°50’S, 115°44’E), ca. 40 m depth, Dec. 1988; WAM P.29944-001, 398 mm SL, Cowaramup Beach, WA (33°47’S, 115°00’E), ca. 8 m depth, 19 Feb. 1989.

Other specimens (3 specimens, 99.7–426 mm SL, from southwestern Australia): CSIRO CA 696, 424 mm SL, Great Australian Bight, WA (32°30’S, 126°45’E), 36 m depth, 13 Nov. 1996; WAM P.28517-005, 99.7 mm SL, Dunsborough, WA (33°35’S, 115°06’E), 12 Apr. 1985; WAM P.31595-001, 426 mm SL, Straggler’s Reef, off Fremantle, WA, Jan. 1999.

Diagnosis. A species of Platycephalus with the following combination of characters: second dorsal-fin rays usually 14; anal-fin rays usually 13; caudal-fin rays 9–11 (usually 10–11); pored lateral-line scales 59–68; orbital diameter 11.3–21.8% HL; interorbital width 9.3–17.5% HL; postorbital length 50.0–61.1% HL; snout, area anteroventral to eye, interorbit, occipital and lower half of suborbital naked; one or two large caniniform teeth anteromedially on upper jaw; margin of interopercle scalloped; fleshy sensory tubes from suborbitals and preopercle slightly developed, partly covering dorsal and ventral margins of cheek region.

Description. Counts and measurements shown in Table 6. Data for all specimens presented first, followed by holotype condition in parentheses.

Snout, area anteroventral to eye, interorbit, and occipital and lower half of suborbital regions naked. Interorbit narrower than orbital diameter in 99.7 mm SL or smaller specimens, wider in larger specimens (including holotype). Upper iris lappet broad, bilobed; lower weakly convex. Nasal, preorbital, preocular, suborbital and supplemental preopercular spines absent. Lower preopercular spine slightly shorter than upper in 99.7 mm SL or smaller specimens, longer than upper, not reaching opercular margin in larger specimens (including holotype). Interopercular flap absent; margin of interopercle scalloped. Maxilla usually reaching to or slightly beyond anterior margin of pupil in 99.7 mm SL or smaller specimens, to middle of eye in larger specimens [up to 426 mm SL (including holotype)] and to posterior margin of eye in largest (460 mm SL). Upper jaw with one or two (two) large caniniform teeth anteromedially. Palatine teeth in two rows, villiform in outer row, moderate or large caniniform (large caniniform) in inner row. Vomerine teeth usually in one row (including holotype), becoming larger posteriorly; three larger teeth positioned medially to tooth row in 398 mm SL specimen. Fleshy sensory tubes from suborbitals and preopercle slightly developed, partly covering dorsal and ventral margins of cheek region. Posterior tip of pelvic fin reaching from anus to base of third anal-fin ray (base of second anal-fin ray). Posterior margin of caudal fin mostly straight or slightly rounded (mostly straight).

Color in alcohol. Ground color of head and body of holotype ( Fig. 17 ) pale brown above, slightly paler below. Dorsal surface of head and body with many small brown and white spots. First and second dorsal fins with whitish and pale brownish spots along fin rays. Pectoral fin with distinct whitish and pale brownish spots anterodorsally; other portions of pectoral fin with indistinct paler spots tending to form bands. Pelvic fin with moderate pale brown spots. Anal fin pale. Caudal fin with small pale brown spots, small whitish spots basally.

Distribution. Known only from southwestern Australia, from Great Australian Bight (149°16’E), WA to near Perth (31°50’S), infrequently taken on shallow coastal reefs in depths from 4 to ca. 40 m (e.g., Hutchins & Swainston, 1986; Knapp, 1991; Hoese et al., 2006; this study).

Size. Previously known maximum length 46.5 cm ( Hutchins & Swainston, 1986). One specimen examined during the present study measured 460 mm SL (541 mm TL).

TABLE 6. Comparison of counts and proportional measurements of Platycephalus chauliodous . *Usually 10, nine in smallest specimen.

Remarks. As pointed out by Knapp (1991), P. chauliodous has one fewer anal-fin rays (13–14, usually 13) than second dorsal-fin rays (14–15, usually 14), an unusual characteristic in Platycephalus (usually the same number of second dorsal- and anal-fin rays). Also unusual is a scalloped interopercular margin that is found elsewhere only in P. orbitalis among species of Platycephalus .

Apart from the above characters, P. chauliodous resembles P. aurimaculatus , P. conatus and P. richardsoni in having one or two large caniniform teeth anteromedially on the upper jaw (large caniniform teeth absent on upper jaw in other species of Platycephalus ). The first-mentioned can be easily distinguished from the other three species in having 9–11 caudal-fin rays (usually 10–11) (vs. 12 or 13), 59–68 pored lateral-line scales (75–90 in P. aurimaculatus , 70–81 in P. conatus and 65–74 in P. richardsoni ), the occipital region naked (vs. scaled), and fleshy sensory tubes from the suborbitals and preopercle slightly developed, partly covering the dorsal and ventral margins of the cheek region (vs. tubes not covering cheek region). The orbital diameter/ interorbital width relationship is also valuable for separating P. chauliodous from the above three species; viz. P. chauliodous has a narrower orbit and broader interorbit, the former dimension being greater than the latter in smaller specimens but less in 312 mm SL or larger specimens, whereas the orbit diameter is consistently greater than the interorbital width in all examined specimens of the other species (orbital diameter 11.3–21.8% HL and interorbital width 9.3–17.5% HL in P. chauliodous vs. 16.3–22.4% and 7.4–11.7% in P. aurimaculatus , 16.9–22.6% and 7.4–14.1% in P. conatus , and 18.4–24.1% and 10.1–15.7% in P. richardsoni ) ( Fig. 18 A). In addition, P. chauliodous has a greater postorbital length (50.0–61.1% HL vs. 49.1–56.9%, 49.7–56.2% and 49.7–56.2%, respectively) ( Fig. 18 B).

Figures

FIGURE 16. (A) Dorsal and (B) lateral views of Platycephalus chauliodous, WAM P. 29879 - 001, paratype, 336 mm SL, Ian Beaumont, WA.

FIGURE 17. Dorsal view of holotype of Platycephalus chauliodous, AMS I. 20231 - 007, 313 mm SL, Cockburn Sound, WA.

FIGURE 18. Comparison of (A) orbital diameter (solid symbols) and interorbital width (open symbols) versus standard length, and (B) postorbital length versus standard length in Platycephalus chauliodous (circles), P. aurimaculatus (diamonds), P. conatus (triangles) and P. richardsoni (squares). Holotypes labeled by capitalized initial of specific names.