Xenisthmus balius Gill & Randall, 1994

Gill, Anthony C., Bogorodsky, Sergey V. & Mal, Ahmad O., 2017, Review of Red Sea Xenisthmus Snyder (Teleostei: Gobioidei: Xenisthmidae), with description of a new species, Zootaxa 4286 (2), pp. 203-214 : 209-211

Xenisthmus balius Gill & Randall, 1994

Freckled wriggler

Figures 3–4 ; Tables 1–2

Xenisthmus balius Gill & Randall 1994: 446 , figs 1–3 (type locality, northeast side of Jana Island, Saudia Arabia, Arabian Gulf; holotype BPBM 30458); Randall 1995: 345 (compilation; colour fig.); Carpenter et al. 1997: 215 (compilation; illustration).

Diagnosis. A species of Xenisthmus with the following combination of characters: dorsal-fin rays VI + I,13 (rarely I,14); anterior rim of posterior nostril raised, without well-developed flap; scales of body mainly cycloid; head and body pale, with reticulate mottling dorsally.

Description (data for Red Sea specimens given first, followed where different by Arabian Gulf specimens in parentheses). Dorsal-fin rays VI + I,13–14 (I,13), all or all but first segmented rays branched; first dorsal-fin pterygiophore formula 3-22110; anal-fin rays I,12–13, all but first 1–2 segmented rays branched; pectoral-fin rays 16–18 (16–17), upper 1–2 and lower 1–2 rays unbranched; pelvic-fin rays I,5, inner ray unbranched; segmented caudal-fin rays 9 + 8; branched caudal-fin rays 7–8 + 6–7 (6–8 + 6–7); upper unsegmented caudal-fin rays 7–9; lower unsegmented caudal-fin rays 6–8 (7–9); total caudal-fin rays 30–34 (31–35); scales in lateral series 59–75 (60–70); scales in transverse series counted anterodorsally from anal-fin origin 18–22 (20–22); scales in transverse series counted posterodorsally from anal-fin origin 18–23 (20–22); circumpeduncular scales 30–37 (35–37); predorsal scales 12–20 (16–20); gill rakers 3–4 + 8–12 = 11–16; pseudobranch filaments 4–5; vertebrae 10 + 16; epurals 2.

Morphometric data are given in Table 1.

Body covered with small, cycloid scales, except for caudal peduncle, with either no or a few, irregularly distributed ctenoid scales (Arabian Gulf specimens) or mostly ctenoid scales (Red Sea specimens); ventral contour of body fully scaled, except for narrow area beneath branchiostegal membranes; predorsal scales extending anteriorly to or slightly posterior to vertical through posterior edge of preopercle; usually no scales on operculum or cheek (only one Red Sea specimen with a few imbedded scales on cheek); cycloid scales present on pectoral-fin base; narrow band of scales on fleshy portion of caudal-fin base, these usually cycloid, but sometimes with several, irregularly distributed ctenoid scales; no scales on dorsal- or anal-fin bases.

Head pores A’BC D(S)EFHIJK’ M’NOPQ’ (see Gill & Randall 1994, fig. 2; two Red Sea specimens have additional pore in J position on one side only); lower lip fleshy and protruding, with uninterrupted, free ventral margin; anterior nostril in short tube; posterior nostril with raised rim, without prominent membranous flap anteriorly, though sometimes with small irregular flap; tongue weakly indented anteriorly; gill opening extending anteriorly to about midway between verticals through posterior edge of preopercle and posterior edge of eye.

Upper jaw with two or three (anteriorly) or two (posteriorly) rows of small, conical teeth, the outer-row teeth largest and slightly curved; lower jaw with three (anteriorly) or two (posteriorly) rows of small, conical teeth, the outer-row teeth largest and slightly curved; vomer, palatines and tongue edentate.

Live coloration (based on photographs of specimens from the Arabian Gulf and the Red Sea; Figure 4 ): head and body pale pinkish brown to pale grey, paler ventrally, with irregular, reticulate, brown to black mottling, this darkest on mid-side, forming about 10–12 spots or x-shaped markings laterally; four short, brown to dark grey bars extending from eye, one from mid-anterior part of orbital rim to mid-side of upper lip, one from below mid-ventral part of orbital rim to behind posterior edge of maxilla, one from midposterior part of orbital rim to upper part of preopercle, and one from behind eye to upper part of pectoral-fin base; mid-side of lower lip and adjacent inner part of lower jaw brown to dark brown to dark grey; iris silvery to bluish white or orange-brown, with a dark reddish brown spot at 12, 3, 6 and 9 0’clock positions; upper part of pectoral-fin base with irregular brown to dark grey spot beneath and immediately behind operculum, sometimes with additional spot on ventral part of fin, and moreposterior, smaller spot near bases of upper few rays; interspaces between mottling and spots on head and body sometimes with irregular patches of bright white; short dark brown to black bar on caudal-fin base; first dorsal fin hyaline with brown to dark grey spots on middle of all or most spines, sometimes with additional spots distally; second dorsal fin hyaline with dark grey spots between bases of each ray, a dark grey spot on middle of each ray, and an additional one or two rows of spots on each ray (spots often displaced onto fin membranes); anal fin hyaline, sometimes with dark grey spots between ray bases and on middle of each ray; caudal fin hyaline usually with one (rarely two), irregular, dark grey-brown to black spots on bases of lowermost two rays on upper hypural plate, little posterior to bar at level of its upper half; area between spot(s) and dark bar on caudal-fin base white to yellowish white; caudal fin with a few small dark grey spots arranged in slightly concave or reticulate columns on remainder of fin; pectoral fins hyaline, with irregular dark grey spot basally on upper half of fin, sometimes with additional cluster on ventral half of fin; pelvic fins hyaline.

Preserved coloration: similar to live coloration; dark markings remain, becoming pale greyish brown to dark grey-brown.

Habitat and distribution. Xenisthmus balius was previously known only from Jana Island, Saudi Arabia, in the Arabian Gulf. We newly record this species from the Red Sea on the basis of 13 specimens collected in Eritrea, Egypt and Saudi Arabia ( Figure 3 ). It has been collected from sandy areas adjacent to coral rubble and reefs in 1.5– 17 m.

Remarks. The Red Sea specimens agree in all salient details with the nine type specimens from the Arabian Gulf, but extend our understanding of variation in the following meristic characters (see Description above and Table 2): second dorsal-fin rays; pectoral-fin rays; lower unsegmented caudal-fin rays; scales in lateral series; scales in transverse series counted anterodorsally from anal-fin origin; scales in transverse series counted posterodorsally from anal-fin origin; circumpeduncular scales; and predorsal scales. The new specimens also extend known variation in the following morphometric characters ( Table 1): head length; predorsal length; preanal length; second dorsal-fin base length; anal-fin base length; first dorsal-fin origin to pelvic-fin origin; second dorsalfin origin to anal-fin origin; snout length; orbit diameter; head width; body width; bony interorbital width; snout tip to retroarticular tip; caudal peduncle length; caudal peduncle depth; length of third spine of first dorsal fin; length of spine of second dorsal fin; length of first segmented ray of second dorsal fin; length of last segmented ray of second dorsal fin; anal-fin spine length; length of last segmented anal-fin ray; pelvic–fin spine length; fourth segmented pelvic-fin ray length; caudal-fin length.

Gill & Randall (1994) noted that ctenoid scales were present in only a few of the Arabian Gulf specimens, where they were just a few irregularly distributed ctenoid scales on the caudal peduncle and caudal-fin base. Ctenoid scales are present in all of the Red Sea specimens, and tend to be more widely distributed on the caudal peduncle. Gill & Randall also noted that the type specimens lack cheek scales, whereas one of the Red Sea specimens has a few imbedded scales on the anterior part of the cheek.

Material examined. RED SEA . Egypt: USNM 270676, 1 : 27.7 mm SL male, Gulf of Suez, El Tor , 0–9 m, rotenone, V.G. Springer et al., 27 September 1969 ; USNM 270673, 4 : 19.0– 24.6 mm SL males, 4: 21.1–22.8 mm SL females, Gulf of Aqaba, just N of Ras Burqa , to 1.8 m (stated depth to 6 feet), rotenone, V.G. Springer, 5 September 1969 (field number VGS 69–21) . Eritrea: USNM 270672, 2 : 23.0– 24.2 mm SL females, S shore of Difnein Island (16°36’N 39°20’E), 0–4 m, V.G. Springer et al., 15 August 1969 (field number VGS 69–15) . Saudi Arabia: SMF 35837 (tissue sample KAU11-225), 1: 22.0 mm SL female, Al Lith , fringing reef, 10 m, S.V. Bogorodsky, 29 March 2011 ; KAUMM 417, 1 : 17.6 mm SL female, Saudi Arabia, Al Lith , fringing reef, 6–8 m, S.V. Bogorodsky & T.J. Alpermann, 7 March 2012 (field number AL3) . ARABIAN GULF. Saudi Arabia: BPBM 30458, 1 : 25.5 mm SL female (holotype), NE side of Jana Island , base of dropoff in 15 m, J.E. Randall, A.B. Tarr & J.E. Burfhard, 15 June 1984 ; BPBM 33308, 1 : 26.4 mm SL male (paratype), 1: 29.0 mm SL female (paratype), W side of Jana Island, reef flat, sand and rubble with small patches of mostly dead coral, 1.5 m, J.E. Randall, L.J. McCarthy, B.E. Stanaland & A.B. Tarr, 13 September 1985 ; AMNH 97301, 1: 29.4 mm SL female (paratype), AMS I.34236-001, 1: 23.2 mm SL male (paratype), BMNH 1993.9.25:1, 1: 19.1 mm SL male (paratype), BPBM 33353, 3: 18.0–31.0 mm SL females (paratypes), USNM 326758, 1 : 26.1 mm SL male (paratype; subsequently cleared and stained), SE side of Jana Island, base of drop-off in 17 m, J.E. Randall, L.J. McCarthy, B.E. Stanaland & A.B. Tarr, 13 September 1985 .

Figures

FIGURE 3. Distribution records for Xenisthmus oligoporus (closed circles), X. balius (open circles) and Red Sea X. polyzonatus (triangles).

FIGURE 4. Xenisthmus balius, SMF 35837, 22.0 mm SL female, Al Lith, Saudi Arabia. Photograph by S. V. Bogorodsky.