Psilorhynchus magnaoculus, Shangningam & Kosygin, 2021

Shangningam, Bungdon & Kosygin, Laishram, 2021, Psilorhynchus magnaoculus, a new species of torrent minnow (Teleostei: Psilorhynchidae) from Myanmar, Records of the Zoological Survey of India 121 (3), pp. 319-324 : 319-322

Psilorhynchus magnaoculus sp. nov. ( Figures 1 a-c, 2)

urn:lsid:zoobank.org:act:A7429508-AD0F-4CFD-8D43-C88B4417C3CD

Type material: Holotype: Myanmar, Sagaing region, Tamu District, Yu River at Tamu ( Chindwin River basin), 24°13’37’’N 94°19’06’’E, 28-xii-2018, collector? Shangningam (ZSI FF 8211) . Paratypes: 3 specimens,

32.0– 40.3 mm SL, same locality and label data as holotype (ZSI FF 8212). The specimens bear a red printed label: “ Psilorhynchus magnaoculus sp. nov., Holotype or Paratype, Bungdon Shangningam* & Laishram Kosygin, Det. 2021.

Type depository: The type specimens are deposited in the Zoological Survey of India (ZSI) , Kolkata, India.

Description (Holotype): Biometric data of holotype and paratypes as in Table 1. Body elongate, deep, greatest depth at dorsal-fin origin. Dorsal profile arched, rising gradually to dorsal-fin origin, sloping gently towards caudal peduncle. Ventral profile straight from lower jaw to anal-fin origin dorsally inclined from anal-fin origin to caudal-fin base.

Head large. Mouth inferior, relatively wide. Eye large, contributing to 42.6–43.6 percent of head length, dorsolateral located its diameter almost equal to snout length. Snout squarish anteriorly with a notch situated at the level of the ethmoid region anterior to nares, ventral surface bordered by deep longitudinal groove on each side. Rostral cap fused with upper lip, separated by shallow groove. Lower jaw covered by thick squarish cushion that can be folded backwards, cushion composed of two adnate tissue layers: anteriorly located deeper layer, lower lip, smooth, not continuous with upper lip around corner of mouth; and posteriorly located superficial layer densely papillated, thick, continuous with skin of isthmus. Superficial layer connected with rostral cap by narrow strip of skin around corner of mouth, extended posteriorly, broadened as ridged, slightly papillated skin fold at posterolateral-most corner of mouth.

Dorsal fin with ii.9 rays, high, tip rounded, posterior edge weakly concave. Anal fin with ii.6 rays, long, posterior edge concave, reaching base of caudal fin. Caudal fin weakly forked, upper lobe slightly longer than lower. Principal caudal-fin rays 10+9, procurrent rays 4 dorsally and 3 ventrally. Pelvic-fin rays ii.7. Pelvic-fin origin posterior to dorsal-fin origin, opposite to 3rd branched dorsal-fin ray. Pectoral with fin v, 10(1) or vi, 11(3) rays. Pectoral fin reaching horizontal through dorsal-fin origin, reaching to two scale rows anterior to pelvic-fin origin when depressed. Skin on ventral surface of unbranched pectoral and pelvic-fin rays thickened.

Scales cycloid, fairly large, thin and more or less regularly arranged on body. Scales along lateral line 31(1) or 32(3), plus 2(4) on base of caudal fin. Transverse scale rows from dorsal-fin origin to pelvic-fin origin 3.5/1/2, scale rows around caudal peduncle 10, predorsal scales 11(3)–12(1). Anus close to pelvic fin, position 2(1)–3(3) scales posterior to pelvic-fin origin. Scales between anus and anal-fin origin 9(1) or 10(3). Scales absent from midventral region between pectoral fins. Total number of vertebrae 33, comprised of 22 abdominal and 11 caudal ( Figure 2 ).

Colouration: In 70% ethanol, body background greyish brown dorsally extends up to3/4 th laterally, then pale white ventrally. Dorsum of head brown, five brown saddles, first, 3–4 scales broad posterior to occiput and extending up to pectoral-fin base, second, 4 scales wide, between 3–9 branched dorsal-fin rays, extending oblique up to anterior of pelvic-fin base; third and fourth respectively between dorsal-fin origin and caudal-fin base, and fifth, 2 scale wide, around caudal-fin base. Squarish to rectangular black patches on lateral line, patches obscured by the background pigmentation in region between lateral-line origin and middle of dorsal-fin base, posterior four Psilorhynchus magnaoculus , a new species of torrent minnow (Teleostei: Psilorhynchidae ) from Myanmar patches, last smallest one on caudal-fin base. Dorsal-fin rays with two rows of spots, one on base and another in middle of the fin. Anal fin immaculate. Paired fin rays with thin melanophores from middle to distal margin. Caudal fin with two black bars, one complete bar in middle, and another incomplete near base of caudal fin.

Diagnosis: Psilorhynchus magnaoculus sp. nov. belongs to the P. balitora species group (sensu Conway, 2011). The new species is notable from all the congeners in having a squarish snout a larger eye, contributing 42.6–43.6 percent of head length, almost equal to the length of snout; a notch on the ethmoid region and caudal fin with two bars.

Etymology: The species is named after the large eye (Latin), ‘magnaoculus’, noun in apposition.

Distribution: Psilorhynchus magnaoculus sp. nov. is presently known only from the Yu River, Chindwin basin in Myanmar ( Figure 3 ).

Figures

Figure 1. P. magnaoculus sp. nov., holotype, ZSI FF 8211, 47.5 mm SL; a. dorsal b. lateral c. ventral view.

Figure 2. Radiograph of P. magnaoculus sp. nov.

Figure 3. Map showing the type locality of P. magnaoculus sp. nov. (▲).