Xenisthmus oligoporus , Gill, Anthony C., Bogorodsky, Sergey V. & Mal, Ahmad O., 2017
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: 205-209
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Xenisthmus oligoporus new species
Holotype. SMF 34908View Materials (field number KAU13-20), 18.0 mm SL male, Red Sea, Saudi Arabia, Duba , unnamed island, fringing reef (27°04’N 35°46’E), 10–12 m, S.V. Bogorodsky, 19 March 2013.GoogleMaps
Paratypes. BPBM 27446, 1: 25.0 mm SL female, Red Sea, Sudan, Towartit Reef , 10–13 m, J.E. Randall, 13 January 1980 ; KAUMM 0 0 6 (tissue sample KAU13-578), 1: 17.7 mm SL female, Red Sea, Saudi Arabia, Duba (26°57’N 35°57’E), small bay with reef wall with many small caves, 12 m, S.V. Bogorodsky, 20 June 2013GoogleMaps ; AMS I.47270-001 (field number F39), 1: 23.0 mm SL male (subsequently cleared and stained), Red Sea, Saudi Arabia, Farasan Archipelago (16°50' N 42°02' E), sand flat with coral patches, 6–8 m, S.V. Bogorodsky & T.J. Alpermann, 21 February 2012GoogleMaps .
Diagnosis. Xenisthmus oligoporus is distinguished from congeners in having a reduced number of cephalic sensory pores (lacking pores A, I, J, K, P and Q) and in having 14–15 segmented rays in the second dorsal fin.
Description. Dorsal-fin rays VI + I,15 (I,14 f1; I,15 f2), all (all or all but first 2) segmented rays branched; first dorsal-fin pterygiophore formula 3-13110; anal-fin rays I,13 (I,13 f2; I,14 f1), all (all or all but first) segmented rays branched; pectoral-fin rays 17/17 (17 f3; 18 f2), upper 2/1 (1–2) and lower 2 rays unbranched; pelvic-fin rays I,5, inner ray unbranched; segmented caudal-fin rays 9 + 8; branched caudal-fin rays 7 + 6 (7); upper unsegmented caudal-fin rays 8 (7 f2; 8 f1); lower unsegmented caudal-fin rays 7 (6 f2; 7 f1); total caudal-fin rays 32 (30 f2; 32 f1); scales in lateral series 61/59 (58 f1; 59 f1; 61 f1; 63 f2; 64 f1); scales in transverse series counted anterodorsally from anal-fin origin 19/21 (18 f2; 19 f1; 20 f1; 21 f1; 22 f1); scales in transverse series counted posterodorsally from anal-fin origin 19/19 (18 f1; 19 f2; 20 f2; 22 f1); circumpeduncular scales 28 (29 f2; 30 f1); predorsal scales 17 (16 f1; 20 f1); gill rakers not determined for holotype (3 + 9 f1; 3 + 10 f1), rakers short, slender and fully ossified; pseudobranch filaments not determined for holotype (4 f1; 5 f1); vertebrae 10 + 16; epurals 2.
Morphometric data are summarised in Table 1.
Body covered with small, cycloid scales, except for caudal peduncle where scales mostly ctenoid; ventral contour of body fully scaled, except sometimes for narrow area beneath branchiostegal membranes; predorsal scales extending anteriorly to or slightly posterior to vertical through posterior edge of preopercle; cheeks partially (anteriorly only) to fully scaled; upper part of operculum scaled; cycloid scales present on pectoral-fin base; single row of ctenoid scales on fleshy portion of caudal-fin base; no scales on dorsal- or anal-fin bases.
Cephalic sensory pores B’C D(S)E’F’H’ M’NO’ ( Figure 2View FIGURE 2); lower lip fleshy and protruding, with uninterrupted, free ventral margin; anterior nostril in short tube overhanging upper lip; posterior nostril with raised rim, but no membranous flap anteriorly; tongue indented anteriorly; gill opening extending anteriorly to point varying from about midway between verticals through posterior edge of preopercle and posterior edge of eye, to vertical through posterior edge of eye.
SMF 34908View Materials (holotype) KAUMM 0 0 6 AMS I.47270-001 Arabian Gulf (n = 9) Ređ Sea (n = 11) Ređ Sea (n = 7)
(mm) 18.0 17.7 23.0 18.0131.0 19.0127.7 14.6122.1 Segmenteđ D2 rays Segmenteđ A rays Pectoral rays* Circumpeđuncular scales Scales in lateral series* Scales in transverse series anterođorsally from A origin* Scales in transverse series posterođorsally from A origin* Upper jaw with three to four (anteriorly) or two (posteriorly) rows of small, conical teeth, the outer-row teeth largest and slightly curved; lower jaw with three to four (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 the holotype and a paratype when freshly dead; Figure 1View FIGURE 1): head and body pale yellow to pale yellowish grey; short brown stripe extending from middle of upper lip through eye to above opercle, breaking into spots posteriorly; front of lower lip brown; upper part of operculum with small yellowish grey spots; iris yellowish brown to white above brown head stripe; upper part of pectoral-fin base narrowly yellowish grey to brown; sides and upper part of body with irregular dark yellow spots in four irregular longitudinal rows (each spot contains tiny dark brown spots), which form about twelve irregular X-shaped markings; first dorsal fin hyaline with a indistinct to distinct punctate brown spot on middle (anteriorly) to distal third (posteriorly) of each spine; second dorsal fin hyaline with brown spot on middle of each ray and anteriorly on adjacent fin membrane, and series of larger brown spots on or near the base of fin, these spaces about 2 to 3 rays apart and variably on ray bases or on membranes between rays; caudal fin hyaline with three curved bars of small brown to orange spots; caudal fin with a short black bar over middle few rays, the bar edged posteriorly with brown; second from lowermost ray on upper hypural plate with small black spot near base; anal, pelvic and pectoral fins hyaline.
Preserved coloration: similar to live coloration; brown and grey markings remain, but become less distinct.
Etymology. The specific epithet is from the Greek oligos (few) and poros (hole) and alludes to the relatively low number of sensory pores on the head. To be treated as a noun in apposition.
Habitat and distribution. Known from sandy areas adjacent to reefs in 6–13 m. The species is currently known from Duba, Saudi Arabia, south to the Farasan Archipelago ( Figure 3View FIGURE 3).
Remarks. Xenisthmus oligoporus resembles X. balius and X. chi in having relatively high numbers of dorsal- and anal-fin rays, a similar colour pattern (body with reticulated mottling forming x-shaped markings on the body, caudal fin with a short dark basal bar and small dark spot on the fin) and in lacking a well-developed flap on the posterior nostril. It differs from each of these species in having reduced head pores (lacking pores A, I, J, K, P and Q), in having more segmented rays in the second dorsal fin (15 versus 13–14, usually 13 in X. balius , and 12 in X. chi ) and in having more segmented anal-fin rays (13–14 versus 12–13, usually 12 in X. balius , and 11 in X. chi ). It further differs from X. chi in having the predorsal scales extend anteriorly only to the vertical through the preopercle (versus with median series extending anteriorly to near pore D) and less extensive coverage of ctenoid scales (restricted to caudal peduncle versus covering body behind mid abdomen). In addition, it differs from X. balius in having fewer circumpeduncular scales (28–30 versus 30–37).
Xenisthmus oligoporus might be confused with X. chapmani , known only from the holotype from Vanuatu, but differs in having more pectoral fin rays (17-18 versus 15), no well-developed flap on the posterior nostril (versus flap present), fewer vertebrae (10 + 16 versus 10 + 17) and a different first dorsal-fin pterygiophore formula (3- 13110 versus 3-12210).
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