Chaudhuria ritvae, Britz, Ralf, 2010

Britz, Ralf, 2010, A new earthworm eel of the genus Chaudhuria from the Ayeyarwaddy River Drainage, Myanmar (Teleostei: Synbranchiformes: Chaudhuriidae), Zootaxa 2571, pp. 62-68 : 63-66

Chaudhuria ritvae new species

( Figures 1a,c ,d,e; 2a; 3a,b)

Holotype. BMNH 2010.7.21.1, 39.3 mm SL; Myanmar: Ayeyarwaddy Division: Hmoain pool, 7.5 miles southwest from Einme, Ayeyarwaddy River Drainage, 16° 47' 51" N, 95° 04' 4" E, 15 March 2003, R. Britz & R. Roesler.

Paratypes. BMNH 2010.7.21.2-9, 8, 33.2–40.0 mm SL; same data as holotype. BMNH 2010.7.21.68-71, 4 (c&s), 33.0– 39.8 mm SL; same data as holotype. USNM 398655, 4, 34.8-37.4 mm SL; same data as holotype.

Diagnosis. Chaudhuria ritvae differs from C. caudata by possessing a greater number of caudal vertebrae (46–49 vs. 42–45), a smaller mouth with the posterior angle of the lips situated in front of vertical through anterior margin of posterior nostril (vs. reaching vertical through anterior margin of eye), broad and large ribs (vs. narrow and small), neural arches of vertebrae without fenestration (vs. with fenestration), absence of spots associated with base of dorsal and anal fin rays (vs. presence), body pigmentation sparse, consisting of only minute widely separated melanophores (vs. body pigmentation well-developed consisting of numerous densely distributed melanophores that form lines or blotches), and absence of pigmentation along pectoral-fin rays (vs. rows of melanophores lining pectoral-fin rays). It differs from its only other congener, C. fusipinnis , by having the dorsal and anal fins separate from the caudal fin (vs. confluent with caudal fin), by a smaller number of dorsal- (40-43 vs 44-48) and anal-fin rays (40-43 vs. 44-48), by a greater number of caudal-fin rays (4+4 vs. 3+3) and by the presence of teeth on hypobranchial 3 (vs. teeth absent).

Description. General body shape as in Figure 1a . Selected morphometric data are listed in Table 1.

Holotype Range Mean St. Dev. SL in mm 39.3 33.2–40.0 36.3 2.1

in percent of SL

Body depth at anal fin origin 5.3 5.3–6.0 5.6 0.3 Head length (HL) 12.7 12.1–12.8 12.5 0.3

in percent of HL

Eye diameter 10.0 9.6–11.6 10.6 0.8 Snout Length 22.0 21.3–23.3 22.2 0.8 Body elongate, eel-like ( Fig. 1a ), greatest depth at dorsal-fin origin, 16.6 to 20.0 times in SL. Dorsal and ventral profile more or less straight in abdominal and anterior caudal region, after which body tapers towards tail. Body anteriorly round in cross section, laterally compressed in caudal region. Head elongate, cylindrical, 7.6 to 8.3 times in SL; eye small, situated dorsolaterally in anterior third of head, covered by skin ( Fig. 1c –d, 2a); mouth terminal, snout short, rounded, its length contained 4.3 to 4.7 times in head length; tube of anterior nostril short, situated at tip of snout, projecting slightly from it ( Fig. 1c –d, 2a). Lips fleshy, well-developed on upper and lower jaws; posterior corner where lips join situated in front of vertical through anterior margin of posterior nostril ( Fig. 2 a). Postorbital part of head elongate, with 6 long branchiostegal rays supporting prominent gill membrane covering base of pectoral fin. Scales and lateral line canals absent, therefore myomeres and myosepta along body visible ( Fig. 1 e).

Dorsal and anal fins long, separate from caudal fin. Dorsal-fin rays 40 (1), 42 (1) or 43 (2). Anal-fin rays 40 (1), 42 (2) or 43 (1). Caudal-fin rays 4+4 (4). Pectoral-fin rays 7(2), 8 (1) or 10(1). Pelvic fin absent. Total number of vertebrae 74 (2), 75 (1), or 76 (1), comprising 27 (3) or 28 (1) abdominal and 46 (1), 47 (1), 48 (1) or 49 (1) caudal vertebrae.

Head skeleton very similar to that described for C. caudata from Thailand in detail in Britz & Kottelat (2003). Jaws with two to three rows of small, pointed, conical, recurving teeth ( Fig. 3 a). Posterior end of maxilla in front of vertical through lateral ethmoid. Exoccipitals separated in the dorsal midline by supraoccipital. Small epicentral on both sides of vertebra 1 (2), on left side only (1), or absent (1). Neural arches of vertebrae without any fenestration, but rather showing small round depressions or openings ( Fig. 3 b). Abdominal vertebrae with median triangular process of membrane bone coming off roof of neural arch. Well-developed stout ribs ( Fig. 3 b) on vertebrae 4-26 (1), 4-27 (1) or 4-28 (2). First dorsal-fin pterygiophore inserted behind neural spine of vertebra 25 (1) or 26 (3), last dorsal-fin pterygiophore inserted behind neural spine of vertebra 66 (2), 67 (1) or 68 (1). Anal-fin pterygiophores in front of first haemal spine 2 (1) or 3 (3). Last anal-fin pterygiophore inserted behind haemal spine of vertebra 67 (3) or 68(1).

Colouration. In alcohol body light cream with numerous minute black spots on head and sparsely scattered minute spots along rest of body ( Figs. 1a, 1c –e, 2a). All median fins and pectoral fins, unpigmented, translucent.

Distribution. The type series was collected from Hmoain pool near Einme in the Ayeyarwaddy delta region ( Fig. 4), although the species can be expected to occur in other areas of the river delta. Etymology. Named after my wife Ritva Roesler, who helped collect the species, honouring her continuing support of my work on Myanmar freshwater fishes.

Habitat. At the time of collection Hmoain pool was ca 20 m long, up to 1 m deep and 4 m wide, with very dense aquatic vegetation consisting of Nelumbo and Eichhornia ( Fig. 5 ). The water was clear, with a temperature of 29°C and a pH of 7.1 and the bottom was muddy. This pool is located in the Ayeyarwaddy delta floodplain at about 15 m above sea level. It is also the type locality of Parasphaerichthys lineatus , the exact location of which was not known at the time of description ( Britz & Kottelat 2002). Among the other fish species in the pool were also Dario hysginon and Indostomus paradoxus , which have so far only been recorded from the Myitkina and Indawgyi area, with the exception of a single locality for D. hysginon east of Mandalay ( Kullander & Britz 2002). Their occurrence in southern Myanmar thus extends their distribution considerably. The effect on the type locality of the cyclone Nargis, which hit the Ayeyarwaddy delta on 2 May 2008, is unknown, but expected to be considerable.

Figures

FIGURE 2. Close-up of head in lateral view. a, Chaudhuria ritvae, BMNH 2010.7. 21.1, holotype, 39.3 mm SL. b, Chaudhuria caudata, BMNH 2010.7.21.10 - 67, 39.0 mm SL.

FIGURE 3. Head skeleton and anterior vertebrae and abdominal vertebrae 19 – 21 of cleared and stained specimens in lateral view. a, b, Chaudhuria ritvae, BMNH 2010.7.21.68 - 71, paratype, 39.3 mm SL; c, d, Chaudhuria caudata, BMNH 2010.7.21.72 - 81, 39.0 mm SL. Arrows point to ribs in a and b and to the fenestration of neural arches in d.

FIGURE 5. Hmoain pool, 7.5 miles southwest of Einme, Ayeyarwaddy Division, Myanmar. Type locality of Chaudhuria ritvae.

FIGURE 1. a, c, d, e Chaudhuria ritvae, BMNH 2010.7. 21.1, holotype, 39.3 mm SL; Myanmar: Ayeyarwaddy Division, Einme. b, f, g, h Chaudhuria caudata, BMNH 2010.7.21.10 - 67, 39.0 mm SL; Myanmar: Shan State, Inle Lake.