Choerodon Bleeker, 1847

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 : 2-7

Choerodon Bleeker, 1847

Figure 1 ; table 1

The generic synonymy is a sum of the subgeneric synonymies.

Description. Dorsal fin rays XII or XIII (rarely XI or XIV), 7 or 8 (rarely 6 or 9), total rays 20 (rarely 19); anal fin rays III, 9 or 10 (rarely 11); caudal fin rays 7–10 + 12 + 7–9 (rarely 6); pectoral fin rays ii, 13–17 (rarely 12); vertebrae 10 or 11 + 16 or 17 = 27; pleural ribs ending on 10th or 11th vertebra; epipleural ribs ending on 10th–14th vertebra; lateral line scales 27 (rarely 26) + 2; scales above lateral line 2½–5; scales below lateral line approximately 8½–11; predorsal scales approximately 4–15; total gill rakers 13–18.

Body moderately slender to deep; caudal peduncle moderately slender to very slender; head of moderate depth to very deep; snout usually rather short; head broadly pointed to bluntly rounded; dorsal outline of forehead and snout convexly curved to nearly straight in lateral aspect, nape convexly curved, strongly curved in some species; interorbital moderately broad; jaws not attenuate.

Dorsal and anal fins usually without obvious scaly basal sheaths, usually one much smaller scale or 1–3 progressively smaller scales at both ends of at least some oblique scale rows adjacent to fin bases, sheath when present rarely reaching well onto proximal parts of fins. Predorsal scales reaching forward on dorsal midline of head, barely in advance of above centre of eye, not quite to above dorsal end of preopercle or somewhere between. Cheek only partially covered by scales, scales imbricate to embedded, reaching forward to corner of mouth, barely below lower edge of orbit or somewhere between, moderately broad to broad naked margin posteriorly and ventrally on preopercle; subopercle partially scaled to mostly naked, scales confined to 1–3 rows adjacent to ventral edge of preopercle; rows extending forward at most to just short of below anterior extent of ventral preopercular edge, confined to dorsoposterior corner of subopercle at the least; scales in longest row numbering approximately 1–13; lower jaw naked. Lateral line scales each with an unbranched or branched laterosensory canal tube, tube extremely dentritic with irregularly curved branches in some species, best developed in large individuals; centre of second penultimate lateral line scale usually lateral to posterior endge of hypural. Cephalic sensory canal pores numerous but confined to lines or short branches associated with major canals, or extremely numerous covering much of dorsal side of head and snout, often extending onto anterodorsal portion of cheek. Posterior edge of preopercle serrate to smooth. Mouth mostly horizontal, posterior corner situated below point just anterior to forward extent of orbit, positioned slightly posterior to centre of eye, or somewhere between; lower lip rather narrow, often mostly obscured by skin flap on upper side of mouth when jaws occluded; upper lip similarly narrow and obscured by skin flap except at anterior end of jaw; posterior end of maxilla never exposed; crease at corner of mouth curved downward. Gill rakers on first arch simple to arborescent.

Upper jaw with 2 prominent anterior canines; a third very small canine often present mesial to first prominent canine and adjacent to symphysis of jaw; first prominent canine nearly equal to or longer than second, almost four times the length of second in some species; both canines directed mostly ventrally, first occasionally slightly mesially or slightly laterally, second often slightly laterally, occasionally recurved slightly posteriorly; dental ridge smooth to rough with numerous minute teeth along edge; posterior canine present or absent, usually rather small when present and directed mostly ventrally. Lower jaw with 2 prominent anterior canines; first canine approximately 1/3 to twice the length of second; first canine directed anterodorsally to dorsally and slightly mesially, second canine directed anterodorsally or dorsally to dorsolaterally or curved dorsolaterally to laterally and posteriorly; dental ridge entirely smooth to rough with numerous minute teeth along edge, or mostly smooth or rough edged on the anterior 1/4–2/3 of jaw with approximately 1–10 small to moderately sized caniniform teeth posteriorly; teeth when present in one or two series of a single row; anteriormost teeth usually small, becoming progressively larger posteriorly; second series, when present, uniformly short, 2–4 in number. Vomerine teeth absent.

Dorsal fin continuous, spines subequal, pungent; posterior tips of dorsal and anal fins broadly to narrowly rounded, posterior rays not filamentous; posterior tips of fins reaching short of posterior edge of hypurals, almost midway between hypural edge and posterior edge of scaly caudal fin base, or somewhere between. Posterior edge of caudal fin rounded, slightly pointed midposteriorly, truncate, slightly forked or double emarginate, upper and lower lobes only slightly produced at most. Pectoral fin with upper rays distinctly longer than lower, dorsoposterior corner slightly pointed in some, posterior edge often obliquely straight, lower portion sometimes broadly rounded, but some species with ventralmost rays markedly longer than those above forming a falcate posterior margin of fin, lower arm of crescent distinctly shorter than upper. Pelvic fin short to long; posterior tip of fin reaching distinctly short of anus to centre of anal fin base, or somewhere between.

Species of this genus are rather variable in size, reaching a small (106 mm SL) to large maximum size, largest specimen examined 530 mm SL, although the same species is reported to reach one metre.

Pigmentation in alcohol. Juveniles often pale dusky with narrow to broad ill-defined darker bands crossing side; prominent often ocellated dark spot frequently present on posterior half of dorsal fin, as well as on other fins in some species; species otherwise variously pigmented.

Initial phase adults often mostly pale or pale dusky, with or without some combination of dusky to dark or distinctly pale spots, blotches, bands or stripes on body and fins.

Terminal phase adults often with distinctive pigmentation differing from that of initial phase adults.

Colour in life. Extremely variable ontogenetically and interspecifically in most.

Distribution. Species of the genus are confined to the Indo-west Pacific, all but one not occurring east of Guam, Palau, the Solomon Islands, Vanuatu and New Caledonia; the sole exception, Choerodon jordani , is recorded from Tonga, Fiji and American Samoa. Of the 27 species of Choerodon , well over half are present on the Australian plate, with two-thirds of that complement essentially confined to it, while only four are distributed in the western Indian Ocean. Practically all species occur at rather shallow depths, with none known to range below 100 m. Ecologically, most, if not all, prefer back or coral reef areas, or are associated with substrates having similarly low relief.

Etymology. Choerodon is derived from a combination of the masculine Greek nouns choiros, “pig”, and odon, “tooth”, in reference to the prominent anterior canines present in species of this genus.

Comments. The 27 species of the genus Choerodon are distinguishable from those of all other hypsigenyine genera in having XII, 8 or XIII, 7 dorsal fin rays (XI, 9–11, XII, 9–11, XIII, 9 or XIV–XXVII, 9–11 = 23–44 in others) and 27 total vertebrae (versus 28, 27 in Anchichoerops and rarely in Semicossyphus , and 14–33 + 14–22 = 31–54 in “odacids”). The rather low number of lateral line scales (26–28 + 2) present in all species is found elsewhere in the subfamily only in the genus Decodon . Choerodon differs from that genus by dorsal fin formula (XI, 9–10 in Decodon ), in having fewer vertebrae and in having predorsal scales reaching forward only to above centre of eyes at most (at least to anterior nostril in Decodon ). Although Gomon (1989) recognised Xiphocheilus as a monotypic genus distinct from Choerodon, Puckridge et al. (2015) recovered it within Choerodon , clustering as a sister group with the six species of the subgenus Peaolopesia they examined. The recognition of Xiphocheilus as a distinct genus appears to have been based on autapomorphic features without valid synapomorphies supporting the monophyly of the remaining species of Choerodon examined.

In their study of the interrelationships of 20 species of the genus Choerodon, Puckeridge et al. (2015) recovered five major clades, with Choerodon typus representing a clade sister to the largest clade of species within the genus. On the basis of the same morphological features that supported it as a monotypic genus, the clade is regarded here as a major clade within Choerodon , albeit a monotypic one. To further test interrelationships of Choerodon species, sequences of an additional 15 individuals, including the two species C. gymnogenys and C. zosterophorus not previously represented in the analysis, as well as sequences for western Indian Ocean specimens of Choerodon robustus , were obtained and together with sequences featuring in the original study reanalysed by L. Teasdale using the methodology employed by Puckridge et al. (2015). It was deemed important to include material from the true C. gymnogenys because the name had been mistakenly applied over the years to a number of species of similar form distributed in the western Pacific. The outcome supported the confinement of that species to the western Indian Ocean and a sister relationship of it with a terminal clade comprising Choerodon gomoni and C. margaritiferus . Choerodon zosterophorus was recovered as a close sister to C. jordani within the larger clade (fig. 1, clade 1a) that includes C. gymnogenys . The conspecificity of specimens of C. robustus sourced in the western Indian Ocean with those collected in Japan and Indonesia was verified without significant genetic separation between sequences obtained from specimens collected in the widely separated localities. Figure 1 of Puckridge et al. (2015) has been redrawn to incorporate these observations (fig. 1) with the newly incorporated taxa in red.

The 27 species of the genus are here referred to six subgeneric clades with the monophyly of each supported by both genetic and morphological evidence. To his credit, Kuiter (2010) foresaw some of this taxonomic arrangement in his image rich treatment of the Labridae . Five subgenera take available group names, with only the monotypic branch comprising Choerodon vitta requiring a new epithet.

A number of species of this genus are only poorly represented in collections, especially at juvenile and terminal adult stage sizes. Consequently, ontogenetic changes in colour patterns may not be known for those species. Furthermore, among those species in which juvenile colour patterns are known, a number have rather similar dusky banded pigmentations. The following key, therefore, may be somewhat inadequate for individuals of extreme sizes where only colour characters are utilised in key couplets.

Figures

Figure 1. Redrafted “Fig. 1” of Puckridge et al. (2015) with two additional species of Choerodon (red) inserted following a reassessment of the original data set plus 17 new sequences, employing the methodology of the authors. The composition of clades is the same as hypothesised by Puckridge et al. (2015) with two clades subdivided to reflect divergence inherent in the morphology of component species.