Macrognathus aureus, Britz, Ralf, 2010

Britz, Ralf, 2010, Macrognathus aureus, a new spiny eel of the M. aculeatus species group from the Upper Ayeyarwaddy River Drainage, Myanmar (Teleostei: Synbranchiformes: Mastacembelidae), Zootaxa 2514, pp. 55-60 : 56-58

Macrognathus aureus new species

( Figure 1 )

Holotype. BMNH 2010.5.24.26, 194.5 mm SL; Myanmar: Kachin State: small hill stream near Sa Mow, 14 miles on road from Mogaung to Taung Ni; Ayeyarwaddy drainage; Aung Myint, Oct. 2009.

Paratypes. BMNH 2010.5.24.27, 216 mm SL; same data as holotype. NRM 40688, 212 mm SL; Myanmar: Kachin State: Lonton Village market on Lake Indawgyi (25°6'0''N 96°16'59''E); S. O. Kullander & R. Britz, 31 Mar. to 2 Apr. 1998.

Diagnosis. Macrognathus aureus is a member of the M. aculeatus species group. It differs from all other members of this species group by the following combination of characters: rostral tooth plates 8–10, dorsalfin spines 21–22, and a unique colour pattern consisting of a series of large white rimmed dark-brown to black blotches along the dorsal fin and even larger black blotches along the lateral line, of which some are confluent with the dorsal series. In particular it differs from M. aral , M. lineatomaculatus , M. pentophthalmo s, M. siamensis , M. tapirus , and M. aculeatus in having fewer rostral toothplates (8–10 vs 11–55), from M. pavo , M. morehensis , M siamensis , M. meklongensis , and M. pentophthalmos in having a greater number of dorsal-fin spines (21–22 vs 4–18). The only species of the M. aculeatus group with a similar range in the number of rostral tooth-plates and dorsal-fin spines is M. obscurus , from which the new species differs in its colour pattern (large white rimmed dark brown to black blotches along the dorsal fin and the lateral line, of which some are confluent with the dorsal series, vs minute or absent dorsal fin spots and absence of lateral line blotches).

Description. For general appearance see Figure 1 . Morphometric data and vertebral and dorsal-fin spine counts are presented in Table 1 .

Body elongate, oval in cross section, but strongly laterally compressed in its caudal portion. Depth 7.4– 8.3 times in SL, body width 1.8–2.4 times in its depth. Head pointed, with median fleshy rostral tentacle projecting from upper jaw; tentacle with anterior naris at end of nasal tube originating at its subdistal tip, rim of anterior naris with six fimbriae; lips fleshy; jaws with numerous small, pointed teeth; gill membrane connected to isthmus; opercular opening large ventrally but extending dorsally only to level of horizontal through upper third of pectoral-fin base. Preopercular region without any spines. Minute scales on body, opercular area and cheek; a narrow band of scales extending from above eye to posterior naris.

Fin-ray counts as in Table 1 . Dorsal, caudal, and anal fins separated. First dorsal-fin pterygiophore inserted behind 12th to 14th neural spine, pterygiophore of last dorsal-fin spine inserted behind 34th to 36th neural spine. First anal-fin pterygiophore inserted behind haemal spine of 32nd to 33rd vertebra.

Anal-fin spines covered and concealed by thick skin, second spine longest. Penultimate dorsal-fin spine longest, followed by shorter last spine, completely concealed by thick skin, difficult to detect externally.

Lateral line extending from shoulder girdle in a longitudinal line, higher on body in abdominal region descending to middle of body in caudal region and ending some distance in front of caudal fin.

Vertebral counts as in Table 1 .

Standard length/body depth at 1st anal-fin spine 8.1 8.3 7.4

Number of rostral toothplates 8 10 9 Coloration. In alcohol. Based on holotype ( Fig. 1 ). Background colour dark brown, whitish on ventrum. A series of around 20 irregular-shaped black blotches along dorsum from nape to caudal-fin base extending anteriorly as a black stripe to vertical through eye. Blotches along soft dorsal-fin base ocellus-like with a light rim. Lateral series of more than a dozen dark blotches, elongate anteriorly and more roundish posteriorly, present along lateral line, extending anteriorly as a horizontal dark line beyond the eye up to posterior nostril. Both line and blotches rimmed dorsally by whitish line, which rims posterior blotches almost completely and creates an ocellus-like appearance. Some posterior blotches of lateral line series confluent with some blotches of dorsal series. A series of faint irregular dark marks, surrounded by tiny light spots, developed along border between brown colouration of sides of body and whitish colouration of belly. Head with a dark snout and rostral tentacle, a dark band from lower rim of eye extending anteroventrally. Lower opercular area brown with a marbling of light-brown lines. Soft dorsal-fin membrane with a series of more than 12 more or less regular, parallel, oblique, brown striations. Caudal fin with several dark spots arranged in vertical parallel lines. Anal fin brown with numerous small light-brown spots, forming irregular lines posteriorly, with whitish margin. Pectoral fins whitish except for an elongate dark-brown spot at the base and a few lines comprised of darkbrown spots more distally.

In life ( Fig. 2 ). Background colour golden brown with a yellowish golden belly. Dark markings as above, but dorsal and middle series of dark-brown blotches conspicuously set off against golden-brown background colour.

Distribution. Known from Lake Indawgyi and an unnamed small hill stream south of Mogaung, Kachin State, northern Myanmar ( Fig. 3).

Etymology. The Latin word aureus , -a, -um, is an adjective meaning golden, given here in reference to its golden-brown colouration.

Figures

FIGURE 1. Macrognathus areus, BMNH 2010.5. 24.26, holotype, 194.5 mm SL; Myanmar: Kachin State, Mogaung.

FIGURE 2. Colouration in life of Macrognathus aureus, BMNH 2010. 5.24. 26, holotype, 194.5 mm SL; Myanmar: Kachin State, Mogaung.

Tables

TABLE 1. Selected morphometric and meristic data for Macrognathus aureus holotype and paratypes. Holotype Paratype Paratype BMNH 2010.5. 24.26 NRM 40688 BMNH 2010.5. 24.27

Standard length (SL) in mm	194.5	212	216
In percent of standard length
Head length (HL)	18.3	17.1	16.9
Predorsal length of spinous dorsal fin	33.0	33.1	33.8
Predorsal length of soft dorsal fin	65.4	66.1	66.1
Preanal length	60.8	59.8	59.0
Pectoral fin length	7.1	5.3	6.4
Body depth at pectoral fin	7.3	8.0	7.7
Body depth at 1st anal-fin spine	12.4	12.0	13.5
Body width at 1st anal-fin spine	5.9	5.0	7.5
In percent of head length
Snout length	36.1	37.0	34.8
Eye diameter	10.1	9.4	9.6
Ratios
Depth/width of body	2.1	2.4	1.8
Standard length/Head lenth	5.5	5.9	5.9