Psilorhynchus brachyrhynchus, Conway, Kevin W. & Britz, Ralf, 2010

Conway, Kevin W. & Britz, Ralf, 2010, Three new species of Psilorhynchus from the Ayeyarwaddy River drainage, Myanmar (Teleostei: Psilorhynchidae), Zootaxa 2616, pp. 31-47 : 32-38

Psilorhynchus brachyrhynchus new species

( Figure 1 )

Psilorhynchus balitora ( Mukerji 1933: plate I, 2–4).

Holotype. NRM 40935, male, 44.9 mm SL; Myanmar: Kachin State, Putao, Ayeyarwaddy River drainage, Ma Kyaww Wa Chaung and its tributary Nan Hto Chaung, ca 1 mile from 46th regiment, close to rice mill, 27° 19' 44" N, 97° 22' 36" E, 28 March 1998, S. O. Kullander & R. Britz.

Paratypes. NRM 60761, 1, 42.6 mm SL; same data as holotype. NRM 40922, 15 (2c&s), 28.2–51.1 mm SL; same locality as holotype, 27 March 1998, S. O. Kullander & R. Britz. NRM 59658, 1 (c&s), 40.9 mm SL; same locality as holotype, 27 March 1998, S. O. Kullander & R. Britz. NRM 57222, 32.9 mm SL; same locality as holotype, 27 March 1998, S. O. Kullander & R. Britz.

Other material examined. NRM 40630, 3, 40.0– 45.7 mm SL; Myanmar: Kachin State, Putao, 27° 20' 60" N, 97° 23' 60" E, April 1934, Fan Li San.

Diagnosis. A species of Psilorhynchus most similar to P. amplicephalus , P. balitora , P. breviminor , P. gokkyi , P. nepalensis , P. pavimentatus , P. piperatus and P. rahmani in general appearance. Psilorhynchus brachyrhynchus is distinguished from P. amplicephalus , P. balitora , P. breviminor , P. gokkyi , P. nepalensis , P. pavimentatus and P. piperatus by its shorter snout (snout length 43–48% HL vs. 48–56); from amplicephalus , P. balitora , P. nepalensis , P. pavimentatus and P. piperatus by having more principal rays in the upper caudalfin lobe (10 vs. 8–9); from P. amplicephalus , P. balitora and P. nepalensis by the absence (vs. presence) of a dark irregular vertical bar across the distal edge of the caudal fin; from P. balitora and P. nepalensis by the absence (vs. presence) of a broad swath of melanophores across the anterior half of the dorsal fin; from P. breviminor , P. gokkyi , P. pavimentatus , P. piperatus and P. rahmani by the presence (vs. absence) of a large dark blotch at the base of each caudal fin lobe; and from P. breviminor , P. piperata and P. rahmani by the presence (vs. absence) of an irregular vertical bar across the center of the caudal fin. Psilorhynchus brachyrhynchus is further distinguished from the aforementioned species and all remaining congeners by the following combination of characters: 2 branchiostegal rays; ventral surface between paired fins with traingular scale-less patch; presence of a large postepiphysial fontanelle; branched dorsal-fin rays 9; unbranched pectoral-fin rays 5; caudal-fin rays 10+9; lateral-line scales 32–34; lateral sides of body marked with 5–7 indistinct round to squarish dark blotches, arranged in a longitudinal row; caudal fin with a dark, irregular vertical bar across its center.

Description. General body shape as in Figure 1 . Morphometric and meristic data are listed in Table 1 . Body deep, greatest depth at dorsal-fin origin. Dorsal profile arched, ventral profile straight from lower jaw to anal-fin origin, with slight dorsad inclination from anal-fin origin to caudal-fin base.

Head small, eye large. Mouth inferior, snout short, rounded, its ventral surface bordered by a deep longitudinal groove on each side. Rostral cap and upper lip fused, separated by a shallow groove. Lower jaw covered by a thick squarish ‘cushion’ that can be folded backwards, the ‘cushion’ composed of two adnate tissue layers: deeper layer (lower lip), smooth, not continuous with upper lip around corner of mouth; superficial layer densely papilliated, thick, continuous with skin of isthmus, connected with rostral cap by narrow strip of skin around corner of mouth, extended posteriorly, broadened as a ridged, heavily papillated skin fold at posterolateral-most corner of mouth. Upper lip with numerous, horizontally arranged rows of unculi. Pre-epiphysial fontanelle large, rectangular, extending from ethmoid region to epiphysial bar. Postepiphysial fontanelle large, irregularly shaped, extending from epiphysial bar to occipital region. Cranial fontanelle separated by a narrow strut of frontal bone directly dorsal to the epiphysial bar. Five infraorbital bones (IO1-5); IO1-3 platelike; IO4-5 reduced in width, composed of sensory-canal ossification only. Gill membranes joined to isthmus. Fifth ceratobranchial with four needle-like pharyngeal teeth, arranged in a single row. Branchiostegal rays 2; anteriormost branchiostegal articulating with medial face of anterior ceratohyal absent. Anterior swimbladder chamber surrounded by a thick peritoneal tunic, partially enclosed in a bony capsule formed anteriorly by lateral process of 2nd vertebral centrum, laterally by outer arm of os suspensorium. Posterior swimbladder chamber greatly reduced in size.

Dorsal-fin rays iii.9, anal-fin rays ii.6. Principal caudal-fin rays 10+9, dorsal procurrent rays 7(2), ventral procurrent rays 5(1) or 6(1). Pelvic-fin rays ii.6 (4) or ii.7 (13), pectoral-fin rays v.9 (1), v.10 (11) or v.11 (6). Paired fins large, horizontally placed. Pectoral fin reaching vertical through dorsal-fin origin, reaching to one or three scale rows anterior to pelvic-fin origin when adpressed. Pelvic-fin origin posterior to dorsal-fin origin, insertion opposite 2nd branched dorsal-fin ray. Skin on ventral surface of unbranched pectoral- and pelvic-fin rays thickened and covered in a layer of unculi, forming adhesive pads. Dorsal fin high, tip weakly rounded, posterior margin straight to weakly concave. Anal fin short, tip pointed, posterior margin concave, reaching to vertical through caudal-fin base when adpressed.

Anus positioned 2 scale rows posterior to insertion of pelvic fins. Scales large, 32(2), 33(10) or 34(5) along lateral line, plus 1(2), 2(14) or 3(1) on base of caudal fin. 3.5/1/2(8) or 3.5/1/2.5(9) transverse scale rows from dorsal-fin origin to pelvic-fin origin, 10 around caudal peduncle, 10(1), 11(13) or 12(2) predorsal scales, 9(4) or 10(12) scales between anus and anal-fin origin. Ventral surface with a narrow, triangular scaleless patch between paired fins. Total number of vertebrae 35, comprising 17+18(3) or 18+17(1) abdominal and caudal vertebrae.

Small conical tubercles with keratinised tips distributed over entire surface of snout, lateral surface of head, rostral cap and papilliferous skin folds lateral to mouth. Head tuberculation more strongly developed in males. Tubercles on dorsal surface of head arranged as a series of small, irregular longitudinal ridges. Scales on anterior half of body with similar elongate tubercles, forming a series of small parallel ridges across scale surface in both sexes, more strongly developed in males. Posterior edges of scales on dorsal and lateral body surface of males each rimmed with four or five small conical tubercles with keratinized tip. Keratinized tips most greatly developed on tubercles on anterior half of body. Strip of minute conical tubercles, multiple rows thick, present along dorsal surface of unbranched and anteriormost branched pectoral-fin rays in males. Single row of minute conical tubercles present along dorsal surface of unbranched and anteriormost branched pectoral-fin rays in females. Single row of minute conical tubercles present along dorsal surface of unbranched and anteriormost branched pelvic-fin rays and lateral surface of anteriormost dorsal-fin rays of males only.

Coloration. In alcohol body background light cream ( Fig. 1 ). Occiput dark brown. Dorsal surface between occiput and dorsal fin with two faint brown saddles, first saddle situated closer to occiput than to dorsal-fin origin, extending between predorsal scales 4–6, second saddle situated 1–3 scales anterior to dorsal fin origin, extending to base of 1st branched dorsal-fin ray. Dorsal saddles between occiput and dorsal fin most obvious in smaller specimens (below 40 mm SL), becoming increasingly less visible with size due to occlusion by dark markings along posterior margins of predorsal scales. A small, prominent dark brown spot situated at anteriormost point of dorsal fin. Four brown saddles along dorsal surface between mid-dorsal fin and caudal-fin base. First saddle situated between insertions of branched dorsal-fins rays 3–9, second saddle directly between dorsal-fin and anal-fin origin, third saddle directly above anterior half of anal fin, fourth saddle situated anterior to caudal-fin base. Dorsal saddles between mid-dorsal fin and caudal-fin base decreasing in size caudad, extending ventrad 2–3 scale rows on body side, connecting with round to squarish dark-brown blotches arranged in a longitudinal row on flank.

Flank with 5–7 indistinct round to squarish dark-brown blotches, arranged in a longitudinal row. In specimens with 5, first situated posterodorsal to opercle opening, extending beneath lateral-line scales 1–7 or 8, second extending beneath lateral-line scales 10–15, third extending beneath lateral-line scales 17–21, fourth extending beneath lateral-line scales 24–28, fifth situated at base of caudal fin, extending beneath lateral-line scales 30/31 to 32/33/34. Second and or third blotch described above often divided into two small separate dark-brown blotches in specimens with blotch counts of 6 or 7. Scale row situated below lateral-line scale row densely speckled with dark brown melanophores, forming an indistinct, irregular line between pectoral-fin base and pelvic-fin origin, continued posteriorly as an indistinct, frequently interrupted streak, ventrad to dark-brown round to squarish blotches. Scales at pelvic-fin origin darkly pigmented in a number of specimens, forming an indistinct dark brown pre-pelvic spot. Large melanophores, deeply situated in epidermis, forming short stripe between tip of snout and anterior edge of eye; a dark brown blotch-like marking on cheek below ventral margin of eye; another at center of opercle.

Ventral surface largely devoid of pigment except for melanophores on anterior edge of rostral cap; a small patch of melanophores situated beneath scales at anal-fin origin; a short line of melanophores posterior to anus, running along ventral midline beneath 3rd to 5th scale post anus in row between anus and anal-fin origin. Broad swath of small melanophores at base of pectoral fin. Anteriormost pectoral- and pelvic-fin rays lightly speckled with small dark melanophores. Pelvic fin with an indistinct stripe across its center, formed by small aggregations of melanophores around first branching point of branched rays. Dorsal fin intensely marked with a black proximal stripe running along base of rays; a more distal black stripe crossing center of fin, formed by small aggregations of melanophores around first branching point of branched rays. Caudal fin with two large black blotches, one at the base of each lobe; a single irregular black vertical bar across center of fin, formed by small aggregations of melanophores around first branching point of branched rays. Anal fin immaculate.

Distribution. Known to date only from the upper Ayeyarwaddy River drainage, in the vicinity of Putao in northern Myanmar ( Fig. 2 ). The type locality, at the confluence of the Ma Kyaww Wa Chaung and its tributary the Nan Hto Chaung ( Fig. 3 ), is described in detail by Kullander & Britz (2002) and Kullander & Fang (2005).

Etymology. Latinized from the Greek words brachys (βραχυς), short, and rhynchos (ρυγχος), snout, in reference to the short snout of this species. An adjective.

Remarks. Psilorhynchus brachyrhynchus most closely resembles P. breviminor in general appearance and in several meristics characters, including number of principal caudal fin rays (10+9), and unbranched pectoral-fin rays (5). Psilorhynchus brachyrhynchus is easily distinguished from P. breviminor by features of its caudal-fin pigment pattern ( Fig. 4 B), which consists of two large black blotches, one at the base of each lobe, and a single irregular vertical black bar across the center of the fin, traversing both upper and lower lobes. In P. breviminor the caudal fin lacks such distinctive blotches or vertical barring and instead exhibits irregular black markings, which are most prominent along the outer edge of the upper and lower lobes ( Fig. 4 C). Several other species of Psilorhynchus , similar in general appearance to P. brachyrhynchus , also exhibit black vertical barring on the caudal fin, including P. amplicephalus (see Arunachalum et al. 2007), P. balitora and P. nepalensis (see Conway & Mayden 2008b). In each of these species, the proximalmost caudal bar is dumbbell-shaped, being pinched at its center ( Fig. 4 A), and it is likely that the blotches at the base of the caudal fin in P. brachyrhynchus are homologous with the proximalmost bar in P. amplicephalus , P. balitora and P. nepalensis . Similarly, the vertical bar across the center of the caudal fin of P. brachyrhynchus is considered to be homologous with the central caudal-fin bar of P. amplicephalus , P. balitora ( Fig. 4 A) and P. nepalensis . Psilorhynchus brachyrhynchus lacks the distalmost caudal-fin bar present in P. amplicephalus , P. balitora ( Fig. 4 A) and P. nepalensis . Other species of the genus lack vertical barring in the caudal fins (e.g. P. arunachalensis (Nebeshwar, Bagra & Das) , P. gokkyi [ Fig. 4 D], P. gracilis Rainboth , P. homaloptera Hora & Mukerji , P. melissa [ Fig. 4 G], P. microphthalmus Vishwanath & Manojkumar , P. pavimentatus [ Fig. 4 E], P. piperatus [ Fig. 4 F], P. pseudecheneis Menon & Datta , P. robustus Conway & Kottelat [ Fig. 4 H], P. sucatio (Hamilton) and P. tenura Arunachalam & Muralidharan ) or lack caudal-fin pigmentation entirely ( P. rahmani ; Conway & Mayden 2008b). Psilorhynchus brachyrhynchus is further distinguished from similar-looking species, including P. amplicephalus , P. balitora , P. breviminor , P. g o k k y i, P. nepalensis , P. pavimentatus and P. piperatus by its extremely short snout, which is only 43–48% HL (vs. 48–58% in P. amplicephalus , 50–53% in P. balitora , 51–56% in P. breviminor , 51–57% in P. gokkyi , 48–55% in P. nepalensis , 50–55% in P. pavimentatus , and 53–55% in P. p i p e r a t u s).

Psilorhynchus brachyrhynchus is the only member of the genus (and the only member of the order Cypriniformes ; Conway et al. 2010) known to possess two branchiostegal rays (vs. three in all other species in which this character has been examined). The two branchiostegal rays of P. brachyrhynchus each articulate with the lateral face of the hyoid bar (the first at the suture between anterior and posterior ceratohyals and the second with the posterior ceratohyal) and are considered homologous to the two posteriormost branchiostegal rays of other cypriniform fishes. In a number of Psilorhynchus (viz., P. balitora , P. breviminor , P. pavimentatus , P. rahmani and P. s u c a t i o) the anteriomost branchiostegal ray, which articulates with the medial face of the anterior ceratohyal, is composed of the articular head only and is much shorter than the two posterior rays. In P. breviminor the anteriormost branchiostegal ray exhibits asymmetry, being present on the left side only in two out of the three c&s specimens examined. Reduction of the anteriomost branchiostegal ray is clearly a derived character and may be of utility in defining a monophyletic group within Psilorhynchus ( Conway & Kottelat 2010) . The complete absence of this element in P. brachyrhynchus should also be considered within this context.

Mukerji (1933: plate I) illustrated a specimen of Psilorhynchus collected from a tributary stream of the Mali Hka River, northern Myanmar (Myitkyina District) ( Fig. 5 ). He referred this specimen to P. balitora , a species restricted to the Ganges-Brahmaputra drainage of northern India (West Bengal and Assam), eastern Nepal, and northern Bangladesh ( Conway & Mayden 2008b). Based on features of the specimen figured by Mukerji (1933), particularly the absence of scales from the midventral region and the presence of a distinctive stripe across the center of the dorsal fin, Conway & Mayden (2008a) argued that this specimen did not belong to P. balitora or P. breviminor , later suggesting ( Conway & Mayden 2008b) that it likely represented an undescribed species. We tentatively consider the specimen illustrated by Mukerji (1933) to belong to P. brachyrhynchus , until more material becomes available.

Figures

FIGURE 1. Psilorhynchus brachyrhynchus, NRM 40935, male, 44.9 mm SL; Myanmar: Kachin State, Putao.

FIGURE 2. Distribution of Psilorhynchus brachyrhynchus (square), P. piperatus (star) and P. gokkyi (circle).

FIGURE 3. Ma Kyaww Wa Chaung and its tributary Nan Hto Chaung, Putao, Kachin State, Myanmar. Type locality of Psilorhynchus brachyrhynchus. Photograph by S. O. Kullander.

FIGURE 4. Schematic illustration of caudal-fin pigmentation patterns in Myanmar species of Psilorhynchus and in P. balitora. A. Psilorhynchus balitora, KU 29191, 45.5 mm SL. B. Psilorhynchus brachyrhynchus, NRM 40922, paratype, 45.5 mm SL. C. Psilorhynchus breviminor, ZRC 51222, holotype, 35.9 mm SL. D. Psilorhynchus gokkyi, BMNH 2010.4. 14.1, holotype, 50.7 mm SL. E. Psilorhynchus pavimentatus, UMMZ 248831, holotype, 48.7 mm SL. F. Psilorhynchus piperatus, BMNH 2010.4. 14.8, holotype, 47.7 mm SL. G. Psilorhynchus melissa, UMMZ 248829, holotype, 47.6 mm SL. H. Psilorhynchus robustus, ZRC 51111, holotype, 60.3 mm SL. Tips of caudal-fin membranes frayed or torn in majority of specimens.

FIGURE 5. Psilorhynchus brachyrhynchus as illustrated in Mukerji (1933: plate I).

Tables

TABLE 1. Selected morphometric and meristic data for Psilorhynchus brachyrhynchus holotype and 11 paratypes.

	Holotype	Range	Mean	St.Dev.
Standard length (mm)	44.9	28.2–51.1
% of standard length
Body depth	19.4	18.6–21.9	20.0	1.1
Head length	20.9	19.6–23.2	21.0	1.0
Pre-dorsal length	48.5	47.7–53.6	50.0	1.5
Pre-pectoral length	19.6	17.0–20.9	19.1	1.2
Pre-pelvic length	48.7	48.2–52.4	49.8	1.3
Pre-anal length	79.9	78.2–82.4	79.6	1.8
Snout to anus length	57.2	57.2–60.0	58.7	1.1
Anus to anal fin length	21.6	18.5–22.3	20.3	1.1
Caudal-peduncle length	15.1	12.2–15.2	14.4	1.2
Caudal-peduncle depth	9.1	8.0–9.5	8.7	0.5
Caudal-peduncle width	5.3	4.2–5.4	4.8	0.4
Pectoral-fin length	27.2	24.5–27.3	25.9	0.9
Pelvic-fin length	20	17.8–20.8	19.9	0.8
Length of last unbranched anal-fin ray	15.7	15.0–18.2	16.3	1.0
Length of last unbranched dorsal-fin ray	23.4	18.9–23.8	22.6	1.4
% of head length
Head width	70.2	64.3–70.2	67.3	2.6
Head depth	56.4	54.0–61.5	57.3	2.5
Eye diameter	25.5	22.5–28.7	26.4	1.8
Snout Length	44.7	43.1–48.4	45.9	1.6
Interorbital width	44.7	37.7–45.0	40.9	2.7
Mouth width	30.8	28.4–35.2	31.7	2.0
Dorsal-fin rays	iii.9	-
Anal-fin rays	ii.6	-
Principal caudal fin-rays	10+9	-
Pectoral-fin rays	v.10	v.9–10
Pelvic-fin rays	ii.7	ii.6–7
Lateral-line scales	33	32–34
Scales between dorsal and pelvic fins	3.5/1/2	3.5/1/2–2.5
Circumpeduncular-scale rows	10	-
Preanal-scale rows	9	9–10
Predorsal-scale rows	11	10–12
Abdominal vertebrae	-	17–18
Caudal vertebrae	-	17–18
Total vertebrae	-	35