Macrognathus kris, Ng & Tan, 2020

Ng, Heok Hee & Tan, Heok Hui, 2020, A new, uniquely patterned spiny eel (Teleostei: Mastacembelidae) from southern Borneo, Kalimantan Tengah, Indonesia, Zootaxa 4819 (1), pp. 170-178 : 171-174

Macrognathus kris , new species

( Fig. 1 )

Type material. Holotype: MZB 10978, 189.4 mm SL; Borneo: Kalimantan Tengah, Kahayan River drainage, Rungan River , 02°02.016’S 113°47.091’E; H. H. Tan, 22–30 October 2007.

Paratypes: MZB 10979 (2), 115.9–118.1 mm SL ; ZRC 51202 (7), 173.1–276.2 mm SL ; ZRC 51203 (12), 99.8–141.5 mm SL ; ZRC 51204 (4), 331.7–387.6 mm SL; CMK 24244 (5), 111.7–232.8 mm SL; data as for holotype . ZRC 54295 (2), 232.2–240.2 mm SL; Borneo: Kalimantan Tengah, Kahayan River drainage, Tahai area , Rungan River sub-drainage, Sungai Buyot , feeder stream to Danau Sargumang , 2°1’46.6”S 113°47’49.6”E . ZRC 54296 (4), 48.8–67.6 mm SL; CMK 24243 (2); Borneo: Kalimantan Tengah, Kahayan River drainage, Rungan River sub-drainage, Sungai Panta , blackwater river draining into Rungan River and its confluence, connected to Nyaru Menteng , 2°2’1.0”S 113°47’5.5”E; H. H. Tan & M. Kottelat, 5 March 2008 . NSMT-P 111939 (1), 247.0 mm SL ; NSMT-P 112002 (1), 270.0 mm SL; Borneo: Kalimantan Tengah, Kahayan River drainage, Lake Takapan ; A. Doi, 11 July 2000 .

Diagnosis. Macrognathus kris is distinguished from all congeners in having a combination of the following characters: rim of anterior nostril with two fimbriae and two fimbrules; 43–45 rostral tooth plates; 24–25 dorsal spines; 46–55 dorsal-fin rays; 51–59 anal-fin rays; 20–23 principal caudal-fin rays; 76–78 total vertebrae; body depth at anus 11.8–15.9% SL; color pattern consisting of light brown stripe on dorsum and 11–14 large irregular dark brown blotches on side of body.

Description. Morphometric data in Table 1. Body anguilliform, oval in cross section, narrowing posteriorly, becoming strongly compressed posterior to anal-fin origin. Minute scales on body, opercular area and cheek. Vertebrae 34–35 + 42–43 = 76–78 [77].

Head compressed, with snout produced into rostral appendage projecting from upper jaw. Rostral appendage with tubular anterior naris located subdistally, approximately one quarter distance from anterior tip of rostral appendage to its base; appendage supported by 43–45 [43] rostral tooth plates. Rim of anterior nares with two fimbriae and two fimbrules. Posterior nares horizontally elongate, located approximately one fifth distance between anterior rim of eye and tip of rostral appendage. Eye ovoid, horizontal axis longest, subcutaneous; located entirely in dorsal half of head. Preorbital region with single short spine located in groove vertically below posterior naris. Preopercular region lacking spines. Gill openings of moderate size, extending from level of base of first pectoral-fin ray to isthmus. Mouth subterminal. Oral teeth small, villiform, in irregular rows on all tooth-bearing surfaces.

Pectoral fins with 22–23 [22] rays; base of first ray at dorsal corner of gill opening. Pelvic fins absent. Dorsal and anal fins located towards posterior of body, separate from caudal fin. Dorsal fin with 46–55 [51] soft fin rays, preceded by 24–25 [24] spines; spines partially covered by skin, gradually increasing in size posteriorly. First dorsal-fin pterygiophore inserted posterior to 35–36 [35] neural spine; last dorsal-fin pterygiophore inserted posterior to 67–69 [69] neural spine. Anal fin with 51–59 [57] soft fin rays, preceded by three spines. Spines situated in median groove of skin pouch immediately anterior to anal-fin origin; first spine much smaller than second. First anal-fin pterygiophore inserted posterior to hemal spine of 35–37 [36] vertebra. Caudal fin with rounded posterior margin, 20–23 [22] principal rays.

Coloration. In 70% ethanol: Ground color of head and body medium brown, fading to dark yellow on venter. Lighter brown stripe located on dorsum, extending from tip of snout to base of caudal fin, but broken up by dorsal elongation of dark brown blotches at and posterior to anal-fin origin. Flanks posterior to pectoral-fin base with series of 11–14 large irregular dark brown blotches. First 5–8 blotches anterior to anal-fin origin in shape of irregular pentagon with ventrally-directed vertex; ventrally directed vertices frequently with thin prolongation forming 6–9 thin dark brown bands encircling belly. Blotch immediately preceding anal-fin origin and those posterior to this point irregularly shaped, with thin dorsal and ventral prolongations that extend to dorsal- and anal-fin rays, respectively. Posteriormost 2–3 blotches tend to coalesce. Elongate, large irregular dark brown blotches on side of head and body anterior to pectoral-fin base. Ventral edge of blotch irregular, poorly defined, frequently with ventral prolongations forming incomplete thin dark brown bands on ventral surface of head and snout. Pectoral fin with small dark brown spots forming 2–3 subdistal bands. Dorsal and anal fins with numerous dark brown spots irregularly arranged. Caudal fin with dark brown spots forming 2–3 median and subdistal transverse bands.

Distribution. This species is currently known only from the Rungan River sub-drainage of the Kahayan River drainage in Central Kalimantan, Borneo ( Fig. 2 ). We hypothesize that it may occur also in neighboring sub-drainages within the Kahayan River drainage, or even in adjacent river drainages (e.g. the Mentaya River drainage). Further surveys are needed to confirm this.

Habitat. Macrognathus kris inhabits blackwater habitats associated with peat swamp forests. Sungai Panta (where some of the paratypes have been collected) is a blackwater feeder stream flowing into Rungan River, with alluvial forest and flooded forest habitats. Syntopic fish species include: Brevibora cheeya Liao & Tan , Crossocheilus pseudobagarius Duncker , Desmopuntius foerschi (Kottelat) , D. johorensis (Duncker) , D. rhomboocellatus (Koumans) , Eirmotus cf. insignis Tan & Kottelat , Malayochela maassii (Weber & de Beaufort) , Osteochilus pentalineatus Kottelat , O. spilurus (Bleeker) , Striuntius lineatus (Duncker) (Cyprinidae) , Kottelatia brittani (Axelrod) , Pectenocypris korthusae Kottelat , Rasbora calliura Boulenger , R. cephalotaenia (Bleeker) , R. paucisqualis Ahl, in Schreitmüller , Sundadanio retiarius Conway et al. , Trigonopoma gracile (Kottelat) (Danionidae) , Barbucca cf. diabolica Roberts (Barbuccidae) , Neohomaloptera johorensis Herre (Balitoridae) , Kottelatlimia pristes (Roberts) (Cobitidae) , Nemacheilus cf. spiniferus Kottelat (Nemacheilidae) , Hemibagrus capitulum (Popta) , Nanobagrus immaculatus Ng , Leiocassis bekantan Ng & Tan , Pseudomystus funebris Ng (Bagridae) , Silurichthys ligneolus Ng & Tan , S. phaiosoma (Bleeker) (Siluridae) , Parakysis notialis Ng & Kottelat (Akysidae) , Chaca serica Ng & Kottelat (Chacidae) , Xenetodon canciloides (Bleeker) ( Belonidae ), Hemirhamphodon chrysopunctatus Brembach , H. tengah Collette, in Anderson & Collette (Zenarchopteridae) , Chendol lubricus Kottelat & Lim , Nagaichthys sp. ( Chaudhuriidae ), Macrognathus circumcinctus (Hora) , M. tapirus Kottelat & Widjanarti (Mastacembelidae) , Pristolepis grooti (Bleeker) (Pristolepididae) , Nandus nebulosus (Gray) (Nandidae) , Betta anabatoides Bleeker , B. edithae Vierke , Luciocephalus aura Tan & Ng , Parosphromenus filamentosus Vierke , Sphaerichthys acrostoma Vierke , S. selatanensis Vierke , Trichopodus leerii (Bleeker) (Osphronemidae) , Achiroides sp. ( Soleidae ), and Pao palembangensis (Bleeker) (Tetraodontidae) . The inhabitants are a mix of riverine—with mainly swamp forest and peat swamp—taxa.

Etymology. The kris is a wavy-bladed dagger carried and used by local nobility and warriors. The name is used as a noun in apposition, in allusion to the wavy or zigzag pattern on the body of the spiny eel and the general resting posture of the fish when viewed from above.

Figures

FIGURE 1. Macrognathus kris, A. MZB 10978, holotype, 189.4 mm SL; B. ZRC 51203, paratype, 99.8 mm SL; C. ZRC 51202, paratype, 227.3 mm SL; D. ZRC 51204, 370.0 mm SL.

FIGURE 2. Map of Borneo showing type location of Macrognathus kris.