Tridentiger radiatus, Cui & Pan & Yang & Wang, 2013

Cui, Rongfeng, Pan, Yashu, Yang, Xinming & Wang, Yingyong, 2013, A new barbeled goby from south China (Teleostei: Gobiidae), Zootaxa 3670 (2), pp. 177-192 : 179-188

Tridentiger radiatus sp. nov.

Materials examined: Holotype: SYSZ0030838 male, fresh SL 64.2 mm, specimen SL 60.6 mm, mangrove of Qi’ao island , Zhuhai, China [22° 23’N, 113° 38’E], depth at high tide circ. 2 m.

Male Paratypes: Standard length listed after the specimen code. SYSZ0030821 60.6mm, SYSZ0030823 60.8mm, SYSZ0030824 63.2 mm, SYSZ0030828 59.7 mm, SYSZ0030832 68.3mm, SYSZ0030833 63.3mm, SYSZ0030834 58.1mm, SYSZ0030835 72.8mm, SYSZ0030836 70.9mm, SYSZ0030839 66.8mm, SYSZ0030841 61.6mm, SYSZ0030843 52.2mm, SYSZ0030845 65.3mm, SYSZ0030846 61.2mm, SYSZ0030847 69.6mm, SYSZ0030848 58.9mm, SYSZ0030850 69.5mm. Data as for holotype .

Female Paratypes: SYSZ0030822 61.3mm , SYSZ0030825 62.8mm , SYSZ0030829 60.9mm , SYSZ0030830 56.7mm , SYSZ0030831 61.3mm , SYSZ0030837 70.0mm , SYSZ0030840 66.2mm , SYSZ0030842 44.52mm , SYSZ0030844 57.6mm , SYSZ0030849 56.8mm , SYSZ0030851 54.64mm. Data as for holotype .

Non-type comparative materials: T. barbatus: SYSZ 0030810 82.6mm, SYSZ0030811 75.0mm, SYSZ0030812 69.5mm, SYSZ0030827 75.3mm. Data as for the T. radiatus types.

Diagnosis. This species can be diagnosed with a combination of the following characters. Exterior row of teeth on both jaws tricuspid. First branched ray of pectoral fin free. Longitudinal scale count exceeding 40, typically> 42; high forward and backward transverse scale counts at origin of anal fin (TRF> 24 and TRB> 17). Barbels present on cheek, preoperculum and lower jaw; barbels reduced, centremost pair of chin barbels not exceeding front edge of chin by more than 1/3 of their length. Transverse opercular papillae line (line ot) normal, not as barbels; barbel line at preopercular edge ending at pore O’.

Description. Fin formulae, scale counts and proportions are given in Table 2.

Scales ctenoid; anterior scales more crowded and smaller, absent from cheek, operculum and majority of nape, except for a narrow area of predorsal scales ending at a vertical at gill opening. Dorsal lateral scales slightly passing gill openings, forming a retuse “W” with predorsal scales from dorsal view.

Gill rakers moderate, ~ 6 on lower limb of the first arch, lowest raker rudimentary; 4 on upper limb, inner 2 rudimentary. Gill membrane broadly connected at isthmus. Branchiostegal rays 5, innermost pair rudimentary.

Vertebrae 11+16, prehaemal pterygiophores 3, spinous dorsal pterygiophore insertion formula 3-221101.

Robust, medium sized goby; anterior cylindrical, posterior increasingly compressed. Head depressed, muscular cheek protruding, head width nearly equal to head length. Occiput slightly humped, depth increasingly equal to anterior body depth. Snout blunt and wide; gape wide, oblique. Jaws about equal in length, joint at a vertical of anterior margin of eye. Eyes large, dorsal; orbital length about 1/7 head length. Interorbital wide, about twice the orbital length. Short, laterally oriented tubules present on anterior nasal pores, extending beyond the skinfold above upper lip. Posterior naris large, about half the diameter of pupil, close to eye, completely covered by a rounded fleshy flap. Tongue rounded, tip free. Approximately 4 series of teeth present on both jaws. Teeth of outermost series tricuspid, erective and distributed in two proximate rows alternating in position. Wide gap present between outermost and second row on lower jaw. Teeth of second row acute and recurved towards oral cavity. Third and fourth series irregular, with diminutive and sparsely distributed teeth.

Pectoral fin wide, tip extending to a vertical of anus, posterior margin rounded; uppermost ray free. Pelvic fin connected to form an oval disk; frenum present, with two fleshy lobes; tip of fin not reaching anus. Pelvic fin length contained 1.3 times in distance from pelvic insertion to anus. First and second dorsal fins about equal in height, close together, 1–3 scales present from insertion of first dorsal fin to origin of second dorsal. Elongated spines absent from both fins in both sexes. Insertion of anal fin slightly behind a vertical of insertion of second dorsal. Caudal fin rounded, length about 75% of head length.

Genital papilla of male coniform, pointed, and slightly bifurcated at tip; in larger specimens often reaching or passing first anal fin spine. Genital papilla of female obtuse.

Cephalic sensory pores, papillae and barbels

Oculoscapular canal pores as illustrated in Figure 2 and Figure 4 . Interorbital canals terminating at a pair of pores (Pore A) beside anterior nares, another pair (Pore B) adjacent to posterior nares covered by rounded flaps. Interorbital canals separate, anterior interorbital (C) and interorbital (D) pores absent. Postocular pore F present and covered by triangular fleshy flap; post-oculoscapular pores H and K fused and covered by elongated fleshy flap. M’, N’ and O’ present, O’ situated at base of the uppermost preopercular barbel, N’ and O’ rounded to slitlike, M’ rounded and small. Other pores absent. Anterior oculoscapular canal (AOC) joins posterior oculoscapular canal (POC) at pore H. Pores F and H+K slit-like, other pores somewhat rounded.

Facial skin-fold above upper lip, extending posteriorly to suborbital area. Edge of fold slightly serrated, with obtuse barbels (line c) along suborbital region. Short barbel series (line d) continuing inferior to suborbital fold, ending approximately at a vertical of posterior margin of eyes. Suborbital and preopercular barbels sometimes fused at their base, forming bicuspid to tricuspid flap-like structures. Two rows of short barbels continuing at external margins of mandible; barbels of interior row (line i) ending at approximately 2/3 of lower jaw and followed by normal sensory papillae along preopercular edge; exterior row (line e) extending to preopercular edge with last barbel situated just above pore O’. Inferior-most preopercular barbel enlarged, upper preopercular barbels fused at base. Centremost pair of chin barbels (CM) short and close at base, with tips just reaching edge of chin without exceeding significantly ( Figure 4 ).

Facial papillae series c, d and mandibular papillae series e, i developed into barbels, transverse opercular line ot, superior longitudinal line os and inferior longitudinal line oi normal, consisted of normal or slightly enlarged papillae ( Figure 4 ) but never barbels.

Colouration. Dorsal brown to blackish brown, ventral pale brown. No prominent spots or speckles on trunk and fins. Colouration variable when alive, 6 saddle-like dark dorsal bands may be present in living individuals ( Figure 1 E ). If present, first band on nape, second above pectoral fin, third from insertion of first dorsal spine to midline of first dorsal fin, fourth from end of first dorsal fin to about ray 2 of second dorsal fin, fifth from ray 5 of second dorsal to ray 8 and last from end of second dorsal to insertion of caudal fin.

Three to four dusky bands emerging suborbitally: first extremely short, extending anteriorly, ending immediately before cheek fold edge, may be invisible in some individuals; second and third subocular bands extending posteriorly and ventrally to preoperculum; fourth band slender, stretching ventrally then curving upward, ending near pore H.

Colouration of fins uniform, pale brown and somewhat transparent, ventral fins almost white. Margins of anal fin and caudal fin may be blackish in some specimens. Dorsal fins and anal fin often tinted with orange.

Formalin-preserved specimens similar in colouration, except for obscured opercular bands and faded orange colour on fins.

Distribution and habitat. The new species is currently only known from the type locality: Zhuhai, China. Inhabits mud flats in mangrove areas of estuary.

Etymology. The specific name radiatus is a Latin adjective standing in nominative singular, meaning radiate, referring to the radiate arrangement of the infraorbital bands.

Length-weight regression. Our linear model revealed an overall lower body weight in T. bifasciatus compared to the two barbeled congeners ( Table 3; Figure 5 ). The three species differ in their length-weight coefficient with T. barbatus being intermediate between the slightly more robust T. radiatus and the more slender T. bifasciatus ( Table 3; Figure 5 ).

Comparisons of two barbeled Tridentiger . T. barbatus and T. radiatus did not differ significantly in most measured variables, except longitudinal scales, TRF, TRB (Table 2) and colouration. There was no difference in vertebrae number, pterygiophore insertion patterns (3-22110) or number of prehaemal pterygiophores (3). Large individuals differed slightly in body weight (See below; Table 3; Figure 5 ).

We found no distinction between the configurations of cephalic canal pores of T. radiatus and T. barbatus . Both species lack pores C and D and possess fused H+K. However, barbels of T. barbatus are more developed than T. radiatus : the former possesses longer barbels; preopercular barbels extending above pore N’, compared to T. radiatus ending at pore O’; transverse opercular papillae row(ot) develops into barbels in T. barbatus compared to the normal papillae in T. radiatus . The short centremost chin barbels are also diagnostic of T. radiatus .

The overall colouration of T. barbatus is more yellowish and mottled than that of T. radiatus , the pectoral fins are often highly mottled in the former and uniform in the latter.

Comparisons of barbeled and unbarbeled Tridentiger species. Tricuspid teeth found in the outermost rows on both jaws are a synapomorphy of Tridentiger , distinguishing the genus from other gobionellines.

The longitudinal scale count and the dorsal fin ray count are higher in the T. trigonocephalus complex (LS 54– 60, D VI, I-12–13) compared to those of other congeners (LS 34–50, D VI, I-9–12), among which T. radiatus has the highest value (LS 40–50). Scales are absent from the operculum and most of the head in all Tridentiger , while in T. nudicervicus the unscaled area extends to the predorsal and ventral areas. The head is more depressed and cheeks are more protruding in T. radiatus and T. barbatus than other congeners. Sexual dimorphism was not noted in T. radiatus or T. barbatus except for the difference in genital papilla shape. Males of the T. trigonocephalus group and T. obscurus group exhibit intensive dark nuptial colouration ( Akihito et al. 1993). Unlike some congeneric males with filamentous spines on the first dorsal fin (e.g., T. obscurus ), the first dorsal fin rays of T. radiatus and T. barbatus are normal in both sexes. Uppermost ray of pectoral fin free in the two barbeled species, T. trigonocephalus and T. nudicervicus , but constrained in T. bifasciatus and the T. obscurus complex. Longitudinal stripes are present in many Tridentiger , including the T. trigonocephalus complex and the T. obscurus complex, while in T. radiatus the stripes terminate at preopercular area. In T. barbatus , stripes are not apparent.

Configuration of cephalic canal pores in both barbeled Tridentiger spp. differ from other congeners in that pores C, D and E are absent, pore F’ is triangular and fully covered by a triangular fleshy flap, and pores H’ and K’ are fused and completely covered by a horizontally elongated fleshy flap.

Sensory papillae are expressed as a small protrusion from the skin surface in unbarbeled species, but in T. radiatus and T. barbatus lines c, d, i and e have evolved into barbel lines. Barbels are treated as homologs of papillae due to their similar spatial arrangement and potentially similar functions. Homology is also supported by the fact that the barbel line ot of T. barbatus remains as papillae in T. radiatus .

Figures

FIGURE 1. Photographs of fresh Tridentiger radiatus sp. nov. and T. barbatus specimens. A. Lateral view of T. radiatus (Holotype, SYSZ0030838, Male, SL=64.2 mm); B. Lateral view of T. barbatus (SYSZ0030812 Male, SL=73.7 mm); C. Ventral view of the same specimen of T. radiatus, arrow showing less developed chin barbels; D. Ventral view of the same specimen of T. barbatus, arrow referring to the highly developed chin barbels; E. Dorsal view of T. radiatus (Paratype, SYSZ0030836, Male, SL=77.8 mm) showing a banded colouration.

FIGURE 2. Cephalic canal system and sensory pores of Tridentiger radiatus. AN: Anterior nasal pore, PN: Posterior nasal pore, AOC: Anterior oculoscapular canal, POC: Posterior oculoscapular canal, PC: Preopercular canal. Nomenclature of sensory pores follows (Akihito et al. 1988), canals are marked by dotted lines.

FIGURE 4. Lateral view of T. radiatus displaying facial barbel and papilla pattern. Nomenclature of sensory canal pores same as Figure 2. Sanzo, 1911 is adopted for the nomenclature of papillae and barbels rows. Pore A’ blocked by anterior nasal tubule from this angle, not shown.

FIGURE 5. Linear regressions of standard length and natural log-transformed wet body weight for T. radiatus (n=191), T. bifasciatus (n=137) and T. barbatus (n=511). Grey regions depict 95% CI of the least-square regression line. See Table 3 for parameter estimates.