Choerodon typus ( Bleeker, 1856 )

Martin F., Martin F., 2017, A review of the tuskfishes, genus Choerodon (Labridae, Perciformes), with descriptions of three new species, Memoirs of Museum Victoria 76, pp. 1-111 : 62-64

Choerodon typus ( Bleeker, 1856)

Bluetooth Tuskfish

Xiphocheilos typus Bleeker, 1856: 224 , Nias.

Xiphochilus quadrimaculatus Günther, 1880: 45 , pl. XX, fig. c, Arafura Sea.

Diagnosis. Dorsal fin rays XII, 8; anal fin rays III, 10, rarely 9 or 11; pectoral fin rays ii, 14, rarely 12, 13 or 16, dorsalmost ray of moderate length 24.6–33.8% pectoral fin length, ventralmost rays shorter than those above, posterior edge of fin obliquely straight, dorsoposterior corner bluntly pointed, posteroventral corner angular; body shallow, 24.6–31.5% SL, head depth 22.1– 26.9% SL, caudal peduncle depth 12.7–15.2% SL; head blunt, dorsal profile of snout steep, snout snout length 7.9–9.8% SL; predorsal scales approximately 7–10, reaching forward on dorsal midline to or slightly in advance of above centre of eye; cheek covered by large imbricate scales in about 3 nearly vertical rows, posteriormost with about 6 scales to upper extent of free preopercular edge, reaching forward in advance of corner of upper lip crease above mouth, below posterior half of eye, with narrow naked margin posteriorly and ventrally on preopercle; about 5 large scales covering subopercle forward to about anterior end of ventral preopercular margin; each lateral line scale with multiple branching laterosensory canal tube; scales above lateral line about 2 or 2½; cephalic sensory canal pores numerous but confined to lines or short branches associated with major canals; second pair of canines in lower jaw directed anterodorsally and slightly laterally; dorsal and anal fins without basal sheath, 1–3 progressively smaller accessory scales adjacent to fin base; posterior lobe of dorsal and anal fins barely reaching hypural crease at most; caudal fin truncate to slightly rounded, upper corner slightly produced in largest individuals; pelvic fin reaching well short of anus in small individuals, just beyond anus in largest, length 18.5–26.5% SL. (See Table 2 for additional meristic and morphometric ranges.) Olive above, somewhat orange to pink below, with black bar between lateral line and base of middle dorsal fin spine; numerous posteroventrally angled oblique yellow-edged blue lines on side; additional, anteroverntrally angled lines on head.

Reaches small maximum size, largest specimen examined 123 mm SL.

Pigmentation in alcohol. Juvenile patterns unclear. Adults pale, slightly duskier above with dusky horizontal stripe above lateral midline from above pectoral fin base to hypural crease and vertical dusky mark above lateral line below central dorsal fin spines; pectoral fin base dusky darkest along proximal ends of rays dorsally; head with diffuse dusky blotch on opercle and underlying blue bones faintly evident. Dorsal, anal, pectoral and pelvic fins pale, anal with broad dusky distal stripe; caudal fin pale, broadly blue basally and with broad dark dusky marginal band on lower half of fin.

Fresh colours. Olivaceous above, somewhat orange or pink below (fig. 31); broad black short band dorsally on side below about 6th dorsal fin spine; numerous narrow evenly spaced posteroventrally angled, oblique pale blue bands outlined with yellowish orange on side; head with additional bands, first 2 directed anteroventrally from eye, third anoteroventrally from origin of lateral line across cheek to corner of mouth, remaining 1 or 2 on head vertically adjacent to posterior edge of preopercle. Dorsal fin blue with 2 or 3 narrow yellowish orange or pink stripes; anal fin yellowish orange with numerous narrow blue bands basally; caudal fin yellowish orange with about 5–8 narrow blue bands; fin suffused with black centrally. Pectoral fin transparent to orange with blue band edged with black posteriorly on fleshy fin base; pelvic fin yellowish orange with blue leading edge ( Sainsbury & Kailola, 1984: 261, bottom; Kuiter, 2010: 66, figs A–C; Allen & Erdmann, 2012: 726).

Etymology. The name typus is from the Greek typos for “figure or mark”, most likely a reference to the black band dorsally on the side below the central dorsal fin spines.

Distribution. Occurs in the tropical western Pacific Ocean from at least Taiwan to the Gulf of Carpentaria, extending into the north-eastern Indian Ocean westward to about Madras, India (fig. 32). Lives over sand or rubble bottom at depths of 15–60 m, occasionally near reefs ( Allen & Erdmann, 2012).

Comments. Bleeker (1856: 223–224) described his new genus and species X. typus in considerable detail from a 128’’’ (102 mm SL) specimen collected off the island of Nias on the western coast of Sumatra, Indonesia, and now lodged in the Natural History Museum (BMNH 1864.5.15.35). Günther (1880: 45) presented his description of his Xiphochilus quadrimaculatus in much less detail and failed to compare it with previous species referred to the genus. His type specimen (BMNH 1879.5.14.34) from the Arafura Sea is smaller than Bleeker’s type but clearly an example of the same species.

As discussed above, C. typus most closedly resembles slender species of the subgenus Choerodon (Pealopesia) (fig. 1, clade 1a), differing from them in having a longer first pectoral fin ray equal to 24.6–33.8% (versus 2.8–17.5%) of the pectoral fin length, 7–10 predorsal scales reaching forward on the dorsal midline to or slightly in advance of above the centre of the eye, in contrast to 5–8 scales reaching forward no farther than above the posterior extent of the eye and its cheek covered by large imbricate scales rather than small, partially or almost completely embedded scales extending over far less of the cheek. Choerodon typus is recognised here as a monotypic subgenus (fig. 1, clade 1b) based on these considerable morphological differences.

Material examined. 45 specimens, 38.6–123 mm SL; see appendix.