Drombus rubropunctatus Chen & Li, 2024

Drombus rubropunctatus Chen & Li , new species

( Figs. 1–5 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 )

Materials Examined

Holotype. — NTOUP-2023-04-003 , 31.88 mm SL, Estuary of Shih-Ting River , Gongliao County, New Taipei City, Taiwan; coll. H.E. Li, 22 April, 2023 .

Paratypes. — NTOUP-2003-06-003 , 2 specimens (46.74–47.70 mm SL), Kaoping River , Kaoshiung; coll. I-S. Chen, 3 June, 2003 .

NTOU-P2023-04-004 , 3 specimens (32.48–35.99 mm SL), Estuary of Shih-Ting River , Gongliao, New Taipei City, Taiwan; coll. H.E. Li & M. Huang, 23 April, 2023 .

Diagnosis

The new species Drombus rubropunctatus can be distinguished from its congeners from the following unique combination of characters (counts for holotype shown in brackets or marked with asterisk): (1) fin rays: D2 I, 10*; A I, 9*; P 1 modally 17*; (2) squamation: LR 32*–34; TR 12–13*; D-P 6*; Pred 9–10 (10); (3) vertebral count V 10+16=26*; and (4) specific coloration: body colour overall dark brownish, lower half with rows of numerous dark red spots. pectoral fin base with a triangle-shaped spot; D1 dusky with a single dark blotch and transparent, colourless stripe.

Descriptions

Body proportions as shown in Table 1 View TABLE 1 , counts for holotype marked with asterisk. Body subcylindrical anteriorly, laterally compressed posteriorly. Snout moderately pointy in dorsal view. Snout slightly blunt in large individuals (> 40 mm SL). Mouth oblique, lower jaw prominent, posterior end of gape doesn’t reach beyond middle-vertical position of orbit. Anterior nostril openings with short tube, extends to upper lip anteriorly; posterior nostril with simple pore-like opening. Eye dorsolateral, relatively large, orbit margins almost meet at dorsal side of head. Jaws with enlarged canine teeth. Anterior tip of lower jaw with bulged, pad-like formation. Cheeks slightly prominent but extremely bulgy, heave-like in larger adult males (> 40 mm SL). Genital papillae pointy in male (not reaching anal fin) and blunt in female, without any projections or lateral flaps.

Fins. First dorsal fin elements VI* (6); second dorsal fin elements I, 10* (6); anal fin elements I, 9* (6); pectoral fin elements 16 (2) or 17*(4); pelvic fin elements I, 5* (6). First dorsal fin with the third and fourth spinous rays the longest, and for larger adult males (> 40 mm SL) the second, third, and fourth spinous rays with filament-like tips, extending to the first segmented ray of second dorsal fin when compressed. Second dorsal fin base longer than anal fin base in both sexes, the latter two segmented rays of second dorsal fin and anal fin slightly longer than the others. Pectoral fin oval-shaped, posterior tip extending beyond the vertical position of anus and reaching the vertical position of the first segmented ray of anal fin in male individuals; fin without any free, loose fin rays. Pelvic fins fused with well-developed frenum between spinous rays and membrane between the innermost segmented rays, forming a slightly posteriorly elongated, oval-shaped disc, reaching anterior margin of anus while extending beyond anus only in male individuals. Caudal fin oval shaped, slightly vertically compressed and elongated longitudinally in male individuals.

Squamation. LR 32* (4), 33 (1) or 34 (1); TR 12 (2) or 13* (4); D-P 6*; Pred 8 (1), 9* or 10 (1). Body overall covered in ctenoid scales except for predorsal regions, thorax, pectoral fin base (axillary region with ctenoid scales) and abdomen in cycloid scales. All ctenoid scales roughly equal in size and without enlarged or elongated cteni. Predorsal squamation shown in Fig. 1A View FIGURE 1 , scales small in size than body scales, squamation of the median predorsal region extends anteriorly. Both cheeks naked. Coverage of cycloid scales on thorax and abdomen does not reach beyond vertical position of the preopercle anteriorly and the vertical position of the posterior end of first dorsal fin base, respectively. Pectoral fin base with numerous small cycloid scales.

Cephalic lateral line system. Cephalic lateral line systems including oculoscapular canal openings (sensory pores) and sensory papillae row patterns shown in Fig. 1 View FIGURE 1 . Oculoscapular canal pores well-developed, anterior canals with paired pores σ (located beside posterior nostril) and unpaired pores λ and κ (located at interorbital region), posterior edge of orbit with paired pores ω (located dorsally) and α (located laterally), and paired pores β and ρ located above preopercle. Preopercular canals with paired pores γ, δ, and ε. Posterior oculoscapular canals with paired pores θ and τ. Anterior oculoscapular canals separated from posterior canals, with preopercular canals not continuous with oculoscapular canals. All sensory papillae arranged in simple, single rows. Cheek with horizontal rows c and d, separating vertical rows 2–5; rows 2s–5s short, not reaching vertically to row c; row 4i touching row d while row 5i not reaching row d; rows i and e interrupted at around middle point of orbit; row c in loosely arranged single papillae on nasal region and snout. Tip of lower jaw with single row f, arranged transversely. Vertical rows of papillae located transversely along the middle line of body laterally.

Colouration when in life. In natural state, body overall dark brown. Head with greyish white patches and two rows of dark brown stripe present, one locates behind orbit, reaching until upper edge of operculum, another locates below orbit, from upper lip reaching posteriorly but not reaching beyond preopercle. Pectoral fin membrane of male individuals with blueish shade while transparent in females; caudal fin dark brown in male with rows of white specks, while transparent with rows of black spots in females. When under stress or warning state ( Fig. 2–3 View FIGURE 2 View FIGURE 3 ), dorsal side of body greyish white, body with four to five dark brown blotches, caudal fin base with one black spot medially. Head dark brown below orbit with yellowish white blotches.

Colouration when fresh. See Fig. 4 View FIGURE 4 , Body overall brown, slight yellowish in female individuals. Upper half of body spotless, lower half with two to three rows of dark red spots (relatively ambiguous in female). Caudal fin base with a single black blotch. Head with two vague brown stripes, position same with living condition; posterior edge of gape dark brown; cheek and operculum with dark red spots. Ventral side of head, thorax, and abdomen greyish, spotless. For first dorsal fin pigmentation see Fig. 5 View FIGURE 5 , overall dusky brown, spinous rays lined with rows of dark red spots; an oval to round shaped black blotch located at the second to third ray (ambiguous in female); a transparent, colourless stripe located horizontally or slightly oblique medially. Second dorsal fin with two rows of darkish red spot lined near base and a reddish margin; a bright transparent yellow stripe presents only in male individuals near margin. Anal fin spotless, dusky with black margin and an orangish red stripe near margin in both sexes. Pectoral fins dusky with a large black spot and a small triangle-shaped yellow speck present at the upper half of fin base; fin rays lined with whitish yellow specks at upper half, red spots at lower half. Pelvic fin membrane black. Caudal fin slightly dusky while darker on the lower 1/3-part, fin rays lined with rows of red spots in the upper 2/3 part; a bright, transparent yellow smear located at the posterior tip of the fifth to ninth fin rays.

Colouration in preservatives. Body overall greyish white, spotless. Head with a dark stripe below eye. All fins dusky; second dorsal fin with a whitish, transparent margin and rows of dark specks near fin base; anal fin dusky with a black margin, shade darker near fin base; pectoral fins dusky, spotless, fin base with a large black spot and a small triangle-shaped white speck present; caudal fin dusky, fin rays lined with rows of dark spots in the upper 1/3 part; a transparent white smear located at the posterior tip of the fifth to ninth fin rays.

Etymology

The specific name, rubropunctatus , is coined with ruber and punctatus, both in latin meaning “red” and “spotted”, respectively, in allusion to the unique specific feature: rows of red spots on lower half of body.

Distribution and habitat

Drombus rubropunctatus n. sp. has so far known from northeastern and southwestern Taiwan, and a literature record from southern Japan, the Okinawa Isl., Hong Kong, Hainan Island and Singapore based on Akihito et al. in Nakabo (2013). They prefer to inhabit in silty sand flats or muddy plains, burrowing in crevices of dead corals, rocks or shelter in dead mollusc shells. This species is aggressive, territorial and is a fierce, small carnivore.

Remarks

The new species, Drombus rubropunctatus is most similar with the West Pacific species D. triangularis ( Weber, 1909) in certain meristic counts and fin colorations based on the type description, however the former can be distinguished from the latter by lower anal fin ray counts (9 vs. 8) and longitudinal scale counts (32–34 vs. 35–38), first dorsal fin pigmentations (dusky with transparent stripes and single black spot vs. dusky, black pollenated) and body colorations (dark brown with rows of red spots vs. dark brown with blurred dark spots). D. rubropunctatus sp. nov. can also be distinguished from another West Pacific species, also the generic type species, D. palackyii Jordan & Seale, 1905 by higher counts of anal fin segmented rays (9 vs. 8), pectoral fin rays (17 vs. 18), lateral line scale rows (32–34 vs. 31), and transverse scale rows (12–13 vs. 11), also by first dorsal fin pigmentations (dusky with transparent stripes and single black spot vs. dusky with two or three darker blotches) and body colorations (dark brown with rows of red spots vs. brown with indistinct whitish specks). Comparisons of D. rubropuncatus sp. nov. with other congeneric species see Table 2 View TABLE 2 .

The brackish gobies of Taiwan are probably the more understudied gobiid group of them all ( Huang et al. 2015), species often inhabit in severely polluted or high turbidity habitats with deep, soft sediments or often effected by strong tidal activities, increasing collection or investigation difficulties. The new species, D. rubropunctatus was firstly collected and recorded by Chen and Fang (1999) in southern Taiwan over 30 years ago, though collections of this species is considered rare with distributions and sightings of this species scattered and unclear, we can infer to its specific habitat and further locate its occurrence in muddy or silty substrates, and therefore, in future, with more intense and focused investigations upon these habitats facilitated will surely supply its distributional records and let us gain a better knowledge of them. However, it is still possible the species in Taiwan may be same species to several Japanese specimens but need to further examination for them ( Hayashi & Itoh, 1978; Akihito et al. in Masuda et al., 1984; Akihito et al. in Nakabo et al. 2013; Senou et al., 2004, 2021).

Fishes of Drombus are generally small in size and distributes mainly in brackish or marine aquatic biomes of the Indian Ocean and Western Pacific ( Fricke et al. 2023), some individuals were even observed to have taken shelter in burrows of Alpheid snapping shrimps, although it is unclear that they were symbiotic partners of these snapping shrimps like general shrimp gobies ( Amblyeleotris Bleeker, 1874 , Tomiyamichthys Smith, 1959 etc.) does or they were simply taking temporary shelter in these burrows ( Tan & Jaafar 2017). The new Drombus species herein in estuaries were often coupled with Alpheid snapping shrimps with every collection attempt, although diving surveys done by the second author (HEL) has no sighting of Drombus -shrimp pairs in burrow or crevices, but base on the sighting record of Tan and Jaafar (2017), possible symbiotic relationship of the new species is suspected and requires visual census by underwater camera traps or more diving survey to confirm.