Schistura systomos Kottelat, 2017, new species
Creators: name: Kottelat, Maurice
Publisher: name: Zenodo
Year: 2017
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Actinopterygii
Cypriniformes
Nemacheilidae
Schistura
Schistura systomos

description: <i>Schistura systomos</i>, new species (Figs. 1-2) <b>Holotype.</b> MHNG 2767.056 &amp;imath; 35.0 mm SL; Laos: Champasak Province: Bolaven Plateau: Tad Set on Houay Set (Xe Set&amp;imath; tributary of Xe Don)&amp;imath; <b>a b</b> near Ban Nonghinkhao&amp;imath; 15°18'03" N 106°18'23" E; 1136 m asl; M. Kottelat et al. &amp;imath; 19 January 2013. <b>Paratypes.</b> CMK 23401 &amp;imath; 6&amp;imath; 21.7-35.4 mm SL; 2&amp;imath; ethanol-fixed&amp;imath; 28.6-31.6 mm SL; same data as holotype. <b>Diagnosis.</b> <i>Schistura systomos</i> is distinguished from the other species of the genus in Southeast Asia by having a small mouth (gape about 2.9- 3.1 times in maximum head width; Fig. 3 a)&amp;imath; occupying only the median half of head width at its position (vs less than about two times&amp;imath; lateral extremity of lips reaching or almost reaching sides of head in ventral view; Fig. 3 b); a blunt snout (vs. rounded or pointed) resulting in a relatively deep infraorbital area; head about circular in crosssection (vs. depressed)&amp;imath; lower surface flat only in middle (vs. whole surface flat); infraorbital area rounded&amp;imath; not expanded laterally and leaving the eyes partly or almost visible in ventral view (vs. infraorbital area vertical or expanded laterally or swollen&amp;imath; eyes visible only in dorsal view). Additional diagnostic characters&amp;imath; not unique to the species are: small size at maturity (35 mm SL and possibly less); wide interorbital area (interorbital distance about 1.7-2.1 times eye diameter); depth of caudal peduncle 1.5-1.7 times in its length; 8 <b>1</b> / <b>2</b> branched dorsal-fin rays; pelvic-fin origin below or slightly in front of dorsal-fin origin; pelvic axillary lobe varying from rudimentary and fused to small and free; 9 +8 branched caudal-fin rays; no suborbital flap; 14-17 bars (4-6 predorsal&amp;imath; 3-4 subdorsal&amp;imath; 6-9 postdorsal) on body&amp;imath; of regular width and shape&amp;imath; wider than interspaces&amp;imath; continuous over back with contralateral bars under dorsal fin and on caudal peduncle; on predorsal area&amp;imath; bars irregularly shaped and set&amp;imath; dissociated in blotches and short stripes. Pattern at caudal-fin base made of a black vertically elongated blotch occupying median <b>1</b> / <b>3</b> of caudal base&amp;imath; not reaching dorsal and ventral midlines; overimposed to it&amp;imath; a dark brown bar extending ventrally beyond the base of the lower unbranched principal ray&amp;imath; and extending dorsally to base of branched ray 5; and a small blotch from above the base of the upper unbranched principal ray&amp;imath; reaching or not the dorsal midline. <b>Description.</b> See Figures 1-2 for general appearance and Table 1 for morphometric data of holotype and 2 largest paratypes. A moderately elongate nemacheilid with body depth slowly increasing up to slightly in front of dorsal-fin origin. Behind dorsal fin&amp;imath; body depth almost uniform until caudal-fin base. Dorsal profile continuous between head and body. Head about circular in cross section&amp;imath; lower surface flat only in middle; infraorbital area rounded&amp;imath; not expanded laterally. Body slightly compressed anteriorly to compressed posteriorly. Interorbital area arched. Eye dorso-lateral&amp;imath; at edge of cranium and partly or almost visible from below because infraorbital area not expanded laterally; diameter 1.7-2.1 times in interorbital width; in lateral view&amp;imath; eye located lower than profile of head. Cheeks not swollen. Snout rounded&amp;imath; blunt. Depth of caudal peduncle 1.5-1.7 times in its length&amp;imath; uniform; low dorsal keel on posterior fourth of post-dorsal area; no ventral keel. Dorsal keel continuous with upper margin of caudal fin. Largest recorded size 35.4 mm SL. Dorsal fin with 4 unbranched and 8 <b>1</b> / <b>2</b> (7) branched rays; distal margin slightly convex or straight. Second branched ray longest. Pectoral fin with 1 unbranched and 8 (1) or 9 (6*) branched rays&amp;imath; rounded&amp;imath; reaching about halfway of distance to pelvic-fin base. No axillary pectoral lobe. Pelvic fin with 1 unbranched and 7 (7) branched rays&amp;imath; reaching to anus&amp;imath; rounded; posterior margin convex; origin below or slightly in front of dorsalfin origin; axillary lobe from rudimentary and fused to small and free. Anus situated about 1.5 eye diameter in front of anal fin. Anal fin with 3 unbranched and 5 <b>1</b> / <b>2</b> (7) branched rays; distal margin convex. Caudal fin with 9 + 8 (7) branched rays&amp;imath; emarginate&amp;imath; lobes rounded&amp;imath; of equal length. Body covered by embedded scales&amp;imath; except on predorsal area and on belly in front of anus. Lateral line complete&amp;imath; pores difficult to count with accuracy&amp;imath; about 80- 90&amp;imath; anterior most 16-29 conspicuous&amp;imath; remainder indistinct (fixation artefact&amp;imath; pores hidden in midlateral groove resulting from dehydratation by ethanol). In anterior half of body&amp;imath; a small auxiliary pore or papillae above and below some lateral line tubes (usually by pair). Cephalic lateral line system with 6 supraorbital&amp;imath; 4 + 11-12 infraorbital&amp;imath; 8-9 preoperculo-mandibular and 3 supratemporal pores. Anterior nare pierced in front side of a pointed triangular flap-like tube. Posterior nare adjacent to anterior one. Mouth arched&amp;imath; narrow&amp;imath; gape about 2.9-3.1 times in maximum head width&amp;imath; occupying only median half of head width and lateral extremity of lips by far not reaching lateral outline of head in ventral view; gape about two times wider than long (Fig. 3 a). Lips thick. Upper lip with a rounded median notch in which processus dentiformis is visible&amp;imath; with numerous fine and shallow furrows&amp;imath; edge finely crenulated. Processus dentiformis present&amp;imath; well-developed. Lower lip with conspicuous V-shaped median interruption; broad median part with two or three sulci&amp;imath; narrower lateral part&amp;imath; short&amp;imath; with a few fine and shallow furrows. Tip of lower jaw exposed. A shallow median concavity in lower jaw in which processus dentiformis is fitting. Inner rostral barbel not reaching corner of mouth; outer one reaching slightly beyond corner of mouth or vertical of anterior margin of eye. Maxillary barbel reaching below vertical of posterior half of eye. Intestine thin (about 0.3 mm diameter in 35.4 mm SL specimen)&amp;imath; straight&amp;imath; without bend behind stomach (Fig. 4); stomach comparatively small&amp;imath; about 3 mm long&amp;imath; body of stomach wide&amp;imath; swollen. Air bladder without posterior chamber in body cavity. <b>Sexual dimorphism.</b> None observed. No specimen with suborbital flap&amp;imath; groove or slit. No modified pectoral rays&amp;imath; no tubercles&amp;imath; no patches of unculi. Ripe females deeper bodied. <b>Coloration.</b> After three weeks in formalin. Head and body background colour pale yellowish brown&amp;imath; throat and belly whitish to pale yellowish; except otherwise stated&amp;imath; all markings dark brown to blackish. Head without distinct pattern. Body with 14-17 bars (4-6 predorsal&amp;imath; 3-4 subdorsal&amp;imath; 6-9 postdorsal)&amp;imath; reaching downwards to level of pectoral fin&amp;imath; or to ventral midline on caudal peduncle&amp;imath; continuous over back with contralateral bars under dorsal fin and on caudal peduncle&amp;imath; of regular width and shape&amp;imath; wider than interspaces&amp;imath; anterior bars slightly broader than posterior ones. On predorsal area&amp;imath; bars irregularly shaped and set&amp;imath; dissociated in blotches and short stripes and usually not meeting contralaterals. A conspicuous black blotch on caudal-fin base. Black inner pigments forming a vertically elongated blotch occupying median <b>1</b> / <b>3</b> of caudal-fin base&amp;imath; not reaching dorsal and ventral midlines; overimposed&amp;imath; a dark brown bar extending ventrally beyond base of lower unbranched principal ray&amp;imath; dorsally to base of branched ray 5 (from top). A smaller blotch from above base of upper unbranched principal ray&amp;imath; reaching or not dorsal midline. Space between bar on caudal-fin base and preceeding bar paler than rest of body background coloration. A wide inner axial stripe made of chevron-shaped elements present but faintly marked&amp;imath; not visible in front of dorsal fin. Dorsal fin hyaline&amp;imath; with a small black blotch at base of simple and first branched rays&amp;imath; followed by two or three blackish blotches on or near base of following rays&amp;imath; space between blotches hyaline; on median third of rays (near branching in branched rays)&amp;imath; black pigments along edge of rays and between segments. Caudal fin hyaline&amp;imath; on proximal two thirds of principal rays&amp;imath; black pigments along edge of rays and between segments. Anal fin hyaline&amp;imath; with black blotch on base of simple rays; on median third of rays (near branching in branched rays)&amp;imath; black pigments along edge of rays and between segments. Pelvic and pectoral fins hyaline; on median third of rays (near branching in branched rays)&amp;imath; black pigments along edge of rays and between segments. In smallest specimen (21.7 mm SL; Fig. 2 b)&amp;imath; body greyish&amp;imath; bars more faintly marked&amp;imath; more irregularly shaped. <b>Notes on biology.</b> A dissected female (35.4 mm SL) had one ripe ovary with 14 yellow ova about 1.2-1.4 mm diameter and about 31 whitish oocytes. Its stomach and intestine contained remains of unidentified insect larvae. <b>Distribution.</b> <i>Schistura systomos</i> is presently known only from the type locality&amp;imath; a waterfall on Xe Set&amp;imath; a tributary of Xe Done&amp;imath; near edge of Bolaven Plateau (Fig. 5). It was collected between stones and blocks&amp;imath; in about 50-100 cm depth (dry season) below the waterfall. <b>a Etymology.</b> From the classical Greek σύστοµο&amp;sigmav; (systomos)&amp;imath; meaning with a narrow mouth. An adjective&amp;imath; indeclinable. <b>Remarks.</b> <i>Schistura systomos</i> has the smallest mouth in the genus <i>Schistura</i> and possibly among loaches of the family Nemacheilidae. The mouth occupies only the median half of head width at its location (Fig. 3 a)&amp;imath; while in the other species it occupies most of head width&amp;imath; with the lips&amp;imath; when seen in ventral view&amp;imath; extending to or almost to the lateral outline of the head (Fig. 3 b). As mentioned earlier&amp;imath; the genus <i>Schistura</i> is very diverse and&amp;imath; as presently understood&amp;imath; polyphyletic. A number of species group can be distinguished by morphological characters and by colour pattern&amp;imath; most of which will likely be recognised as distinct genera. Two species of small size (<i>S. geisleri</i> &amp;imath; <i>S. isostigma</i>) have the mouth somewhat narrower than other <i>Schistura</i> (not quantified) but they are distinguished by the pale yellow background and the colour pattern made of a midlateral row of dark brown to black blotches and a row of saddles along dorsal midline (Kottelat&amp;imath; 1990&amp;imath; 1998). They also have a suborbital flap in male that is lacking in <i>S. systomos</i>. Similarly&amp;imath; two species of <i>Physoschistura</i> (<i>P. brunneana</i> &amp;imath; <i>P. pseudobrunneana</i>) also have the mouth somewhat narrower than species of <i>Schistura</i> (not quantified)&amp;imath; slightly compressed and deep body and head&amp;imath; and the eyes partly or almost visible in ventral view; <i>S. systomos</i> is distinguished by the absence of a posterior chamber of the air bladder in the body cavity (vs. presence)&amp;imath; the absence of a suborbital flap in male (vs. presence)&amp;imath; the arched mouth (vs. U-shaped)&amp;imath; and the lower lip with V-shaped median interruption&amp;imath; the median part with two or three sulci&amp;imath; the lateral part short&amp;imath; with a few shallow furrows (vs. with wide median interruption forming two lateral triangular pads with deep sulci). <i>Physoschistura</i> is another genus to which a number of species have been added in recent years (Chen et al. &amp;imath; 2011; Lokeshwor &amp; Vishwanath&amp;imath; 2012 a- b; Suvarnaraksha&amp;imath; 2013) that do not seem related to the type species (<i>P. brunneana</i>) and seem to represent one or more distinct genera. A number of species placed in <i>Schistura</i> are apparently also related to these <i>‘Physoschistura’</i> &amp;imath; for example <i>S. geisleri</i> &amp;imath; <i>S. isostigma</i> &amp;imath; <i>S. maepaiensis</i> and <i>S. shuangjiangensis</i>. There is no character suggesting that <i>S. systomos</i> could be more closely related to any of these <i>‘Physoschistura’</i> rather than to <i>‘Schistura’</i>. In fact&amp;imath; <i>S. systomos</i> likely represents a genus of its own. It relationships will be addressed in a forthcoming review of the genera of Southeast Asian Nemacheilidae. Compared to other nemacheilids&amp;imath; the stomach of <i>S. systomos</i> appears proportionally smaller (not quantified) and the intestine is very thin and straight. In the great majority of nemacheilids&amp;imath; the intestine has at least one conspicuous bend&amp;imath; a loop or a complex coiling. The stomach and intestine of the two dissected specimens contained remains of insect larvae that could not be identified.
description: Published as part of <i>Maurice Kottelat, 2017, Schistura systomos ı a new species of loach from southern Laos (Teleostei: Nemacheilidae), pp. 9-16 in Ichthyol. Explor. Freshwaters 28 (1)</i> on pages 10-15, DOI: 10.5281/zenodo.886698
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