Xenisthmus eirospilus, Gill & Hoese, 2004

Gill, A. C. & Hoese, D. F., 2004, Three New Australian Species of the Fish Genus Xenisthmus (Gobioidei: Xenisthmidae), Records of the Australian Museum 56, pp. 241-246 : 243-245

Xenisthmus eirospilus n.sp.

Fig. 2

Xenisthmus n.sp. —Gill & Reader, 1992: 224 (Elizabeth and Middleton Reefs, Tasman Sea).

Type material. HOLOTYPE: AMS I.27149-041, 19.3 mm, female, Australia, Tasman Sea, NE slope of Elizabeth Reef , 29°54'S 159°02'48"E, 5–10 m, sand around base of coral patch reef, rotenone, A.C. Gill et al., 10 December 1987 . PARATYPES: AMS I.27134-034, 2: 16.0 mm, male, 21.2 mm, ♀, Australia, Tasman Sea, Middleton Reef , 29°27'12"S 159°06'48"E, 6–9 m, reef front, rotenone, A.C. Gill et al., 4 December 1987 ; AMS I.33739-081, 2: 12.5–15.2 mm, juveniles, Australia, Coral Sea, NE side of Ashmore Reef, front reef slope, 6–9 m , FNQII party, 25 January 1993 ; BMNH 2003.1 .22.9, 1: 14.1 mm, juvenile, collected with AMS I.33739-081 ; BPBM 39134 , 12.0 mm, juvenile, American Samoa, north shore of Tutuila, west side of Tapisi Point , rocky shore with surge, vertical dropoff to 6 m, rotenone, J.E. Randall et al., 9 May 1974 ; ROM 73524, 1 : 14.5 mm, juvenile, 1: 19.5 mm, ♀, Fiji, Great Astrolabe Reef , 3.7 km east of Yanu-Yanu-i-Sau I., area on reef top around prominent “rock” just south of south side of Herald Pass , R. Winterbottom et al., 5 April 1983 ; USNM 283132 , 17.7 mm, juvenile, Fiji, south coast of Rotuma , east of Sumi , c. 12°30'S 177°05'E, 0–9 m , V.G. Springer et al., 9 May 1986 ; USNM 338561 , 4 : 16.8–21.0 mm, ♀♀, Tonga, Vava'u Group, Hunga Island , eastern shore at small undercut cave in shore, 18°40'55"S 174°06'05"W, surge zone at rocky undercut, coral and rock bottom along surge channels, 0–5 m, J . T. Williams et al., 25 October 1995 ; USNM 352587 , 1 : 18.2 mm, male, Solomon Islands, Santa Cruz Islands, Reef Islands, Lomlom Island , steep vertical wall at Nialo Point on east side of Forrest Passage , 10°16'S 166°18'30"E, vertical reef wall and rocky surge channels at surface, 0–35 m, rotenone and dipnets, J . T. Williams et al., 18 September 1998 .

Diagnosis. A species of Xenisthmus with the following combination of characters: second dorsal-fin rays I,12–13, usually I,12; anal-fin rays I,11–12, usually I,11; vertebrae 10 + 17; tongue indented; posterior naris with welldeveloped flap on anterior rim; upper sides of body with 12 large, closely spaced spots, which usually do not extend to dorsal edge of body; and predorsal area broadly scaled to about vertical through posterior edge of preopercle.

Description. Dorsal-fin rays VI + I,13 (I,12 f14); first dorsalfin formula 3–22110; anal-fin rays I,11 (I,11 f13; I,12 f1); pectoral-fin rays 15/15 (15 f4; 16 f23; 17 f1), upper 1/1 (1– 2) and lower 0/0 (0–3) rays unbranched; pelvic-fin rays I,5, inner ray unbranched; segmented caudal-fin rays 9 + 8; branched caudal-fin rays 8 + 7 (7–8 + 6–7 = 13–15); upper unsegmented caudal-fin rays 7 (5 f1; 7 f10; 8 f3); lower unsegmented caudal-fin rays 7 (5 f1; 6 f8; 7 f4; 8 f1); total caudal-fin rays 31 (27 f1; 30 f8; 31 f2; 32 f2; 33 f1); scales in lateral series 54/57 (50 f1; 51 f3; 52 f5; 53 f6; 54 f2; 55 f5; 56 f2; 57 f2; 58 f2); scales in forward transverse series 18/20 (17 f1; 18 f8; 19 f4; 20 f11; 21 f3; 22 f1); scales in backward transverse series 20/20 (16 f1; 17 f4; 18 f8; 19 f7; 20 f6; 21 f2); circumpeduncular scales 25 (24 f3; 25 f3; 26 f3; 27 f3; 28 f1); predorsal scales 17 (12 f1; 13 f4; 14 f5; 15 f3; 17 f1); cheek scales 3 (1–4); gill-rakers 2 + 8 (1–3 + 7–11 = 8–13); pseudobranch filaments 3 (3 f8; 4 f1); vertebrae 10 + 17; epurals 2.

As thousandths of SL (based on holotype and six paratypes, 15.2–21.0 mm): head length 249 (233–257); predorsal length 342 (324–355); prepelvic length 233 (224– 241); preanal length 565 (531–566); first dorsal-fin origin to second dorsal-fin origin 192 (171–195); second dorsalfin base length 332 (309–333); anal-fin base length 280 (274–303); pectoral-fin base depth 67 (62–75); first dorsalfin origin to pelvic-fin origin 166 (152–178); second dorsalfin origin to anal-fin origin 135 (126–143); snout length 41 (40–53); orbit diameter 62 (62–72); head width 124 (115– 138); body width 109 (92–125); bony interorbital width 16 (14–20); snout tip to retroarticular tip 98 (90–105); caudalpeduncle length 171 (151–174); caudal-peduncle depth 104

(97–118); length of first spine of first dorsal fin 73 (69– 95); length of third spine of first dorsal fin 88 (79–101); length of sixth spine of first dorsal fin 57 (52–71); length of spine of second dorsal fin 83 (72–101); length of first segmented ray of second dorsal fin 98 (87–107); length of last segmented ray of second dorsal fin? (broken in holotype, 87–126); anal-fin spine length 62 (57–77); length of first segmented anal-fin ray 83 (86–92); length of last segmented anal-fin ray 130 (79–131); pectoral-fin length 212 (174– 217); fourth segmented pelvic-fin ray length 161 (154–185); caudal-fin length 218 (190–217).

Body covered with small scales; scales cycloid on anterior body, usually ctenoid on mid-side (more or less posterior to oblique line extending from posterior third of anal-fin base to anterior third of second dorsal-fin base) and caudal peduncle, although sometimes with mostly cycloid scales present and only few ctenoid scales on posterior body (mostly on caudal peduncle); ventral body contour fully scaled, except for narrow area beneath branchiostegal membranes; predorsal area broadly scaled to about vertical through posterior edge of preopercle; cheeks and upper part of operculum scaled; scales present on pectoral-fin base; narrow band of mostly ctenoid scales on fleshy portion of caudal-fin base; no scales on dorsal- or anal-fin bases.

Head pores A'BC D(S)EFHIJK' M'NOPQ' (head pores incompletely developed in 12.0 mm paratype); lower lip fleshy and protruding, with uninterrupted, free ventral margin; anterior naris in short tube; posterior naris with raised rim, with prominent membranous flap anteriorly; tongue indented anteriorly; gill opening extending anteriorly to about midway between verticals through posterior edge of preopercle and posterior edge of eye.

Upper jaw with 2–3 (anteriorly) or 2 (posteriorly) rows of small, conical teeth, outer-row teeth largest and slightly curved; lower jaw with 2–4 (anteriorly) or 2 (posteriorly) rows of small, conical teeth, outer-row teeth largest and slightly curved; vomer, palatines and tongue edentate.

Preserved coloration. Head and body beige to pale brown; short, narrow, dark grey-brown stripe extending from midanterior orbital rim to mid-side of upper lip; second dark grey-brown stripe extending from mid-posterior orbital rim to shoulder, overlapping upper part of pectoral-fin base; sides of body with 12 large (almost as large as eye diameter), dark brown to dark grey-brown spots, some of which may coalesce in some specimens (particularly final two on caudal peduncle); first spot just behind pectoral-fin base, second below first dorsal-fin origin, third below middle of first dorsal-fin base, fourth beneath and between dorsal fins, next six equally spaced beneath second dorsal-fin base, final two on caudal peduncle; posterior few spots on body and caudal peduncle sometimes connected to dorsal mid-line by short bars, or with irregular dorsal extensions to form saddles over caudal peduncle; first dorsal fin hyaline, usually with series of dark brown to dark grey-brown spots (one per fin ray) on distal third of fin; second dorsal fin hyaline with series of dark brown to dark grey-brown spots (one per fin ray) on distal third of fin, often with additional series of dark grey-brown spots on fin-ray bases; caudal fin hyaline with short dusky brown bar lining hypural edge near middle few caudal-fin rays; behind bar, a dark grey to grey-brown spot between lower three rays on upper hypural plate and upper ray on lower hypural plate; broad dusky brown to dark brown stripe extending from caudal-fin spot on to distal part of fin, often to distal tip of fin; remainder of caudal fin with several narrow wavy bars, usually best developed on upper part of fin; anal fin hyaline, sometimes with series of dark brown to grey-brown spots (one per fin ray) along distal third of fin; pectoral and pelvic fins hyaline to beige.

Live coloration. Not recorded in detail, although field notes (by J.E. Randall) accompanying BPBM 39134 say “white with a mid-lateral row of blackish dots”.

Comparisons. Xenisthmus eirospilus belongs to a species complex characterized by the following combination of characters: upper sides of body with a series of large dark spots; second dorsal-fin rays usually I,12; anal-fin rays usually I,11; tongue indented; posterior naris with welldeveloped anterior flap; and vertebrae 10 + 17. Xenisthmus semicinctus is the only other described species in the complex. It differs from X. eirospilus in the following: predorsal scales with median series extending to near pore D (versus predorsal area broadly scaled to about vertical through posterior edge of preopercle); a median spot or short bar on the upper nape, just anterior to the vertical through the pectoral-fin base (versus nape without dark markings); no dark stripe extending from the bar or spot on the caudalfin base (versus stripe present); and dark bands extending dorsally from the body blotches to the dorsal edge of the body (versus mostly without bands extending from dark blotches, although such bands occasionally present beneath posterior part of second dorsal fin). Additional, undescribed species in this complex are known from southern Japan, the Philippines and the Caroline Islands.

Remarks. The specific epithet is a noun in apposition derived from the Greek eiro, to join in lines or string together, and spilos, spot or fleck, and alludes to the prominent pattern of closely spaced dark spots on the mid-side.