Leiocassis rudicula, Ng & Hadiaty, 2019

Ng, Heok Hee & Hadiaty, Renny K., 2019, Leiocassis rudicula (Teleostei: Siluriformes: Bagridae), a new catfish from eastern Borneo, Zootaxa 4651 (1), pp. 191-200 : 192-197

Leiocassis rudicula , new species

( Figs. 1 , 2a )

Holotype. MZB 16529, 102.8 mm SL; Borneo: Kalimantan Timur, Kabupaten Kutai Kartanegara, Kecamatan Tabang , Sungai Petung Kanan , 0°32′6′′N 116°10′54′′E; R.K. Hadiaty, A. Mun′im & D. Wowor, 6 June 2008.

Paratypes. MZB 16476 (1), 52.0 mm SL; Borneo: Kalimantan Timur, Kabupaten Kutai Kartanegara, Kecamatan Tabang , Mahakam River drainage, Sungai Senget Kiri , a tributary of Sungai Pinoon , itself a tributary of Sungai Belayan , 0°32′3′′N 116°12′22′′E; R.K. Hadiaty, A. Mun′im & D. Wowor, 6 June 2008 . MZB 17480 (2), 43.8–51.0 mm SL; data as for MZB 16476; R.K. Hadiaty, S. Sauri & D. Wowor, 21–22 April 2009 . MZB 17500 (1), 83.7 mm SL; Borneo: Kalimantan Timur, Kabupaten Kutai Kartanegara, Kecamatan Tabang , Sungai Senget Kanan , 0°31′8′′N 116°13′35′′E; R.K. Hadiaty, S. Sauri & D. Wowor, 22 April 2009 . MZB 19210 (3), 62.6–118.0 mm SL; Borneo: Kalimantan Timur, Kabupaten Kutai Kartanegara, Kecamatan Tabang , Sungai Mejuk at Desa Uma Diam , 0°34′50′′N 16°7′16′′E; R.K. Hadiaty, Mulyadi & D. Wowor, 18 July 2010 . MZB 19264 (1), 106.1 mm SL; Borneo: Kalimantan Timur, Kabupaten Kutai Kartanegara, Kecamatan Tabang , second right tributary of a branch of Sungai Tahap at Desa Ritan Baru , in Batu Pek area ; 0°24′43′′N 116°3′56′′E; R.K. Hadiaty, Mulyadi & D. Wowor, 20 July 2010 . MZB 20147 (2), 53.7–85.8 mm SL; Borneo: Kalimantan Timur, Kabupaten Kutai Timur, Kecamatan Muara Ancalong, Sungai Senyiur in the vicinity of Desa Senyiur , 0°30′15′′N 116°23′17′′E; R.K. Hadiaty, S. Sauri & D. Wowor, 6 August 2011 . MZB 20168 (1), 82.3 mm SL; Borneo: Kalimantan Timur, Kabupaten Kutai Timur, Kecamatan Muara Ancalong, Sungai Senyiur in the vicinity of Desa Senyiur , 0°31′55′′N 116°22′8′′E; R.K. Hadiaty, S. Sauri & D. Wowor, 7 August 2011 . MZB 20233 (1), 48.7 mm SL ; MZB 20278 (1), 98.1 mm SL; Borneo: Kalimantan Timur, Kabupaten Kutai Timur, Kecamatan Muara Ancalong, Sungai Loa Katong in the vicinity of Desa Senyiur , 0°18′9′′N 116°36′39′′E; R.K. Hadiaty, S. Sauri & D. Wowor, 9 August 2011 . MZB 20296 (3), 39.2–104.2 mm SL; Borneo: Kalimantan Timur, Kabupaten Kutai Timur, Kecamatan Muara Ancalong, Loa Ranam Hitam in the vicinity of Desa Senyiur , 0°27′56′′N 116°32′59′′E; R.K. Hadiaty, S. Sauri & D. Wowor, 10 August 2011 . MZB 21004 (3), 64.8–98.6 mm SL; Borneo: Kalimantan Timur, Kabupaten Kutai Timur, Kecamatan Muara Ancalong, Sungai Salai in the vicinity of Desa Senyiur , 0°24′37′′N 116°32′59′′E; R.K. Hadiaty, S. Sauri & D. Wowor, 10 August 2011 . MZB 21099 (2), 56.3–79.2 mm SL; Borneo: Kalimantan Timur, Kabupaten Kutai Timur, Kecamatan Muara Ancalong, lower stretch of Sungai Senyiur in the vicinity of Desa Senyiur , 0°28′21′′N 116°23′27′′E;. K. Hadiaty, S. Sauri & D. Wowor, 6 August 2012 .

Diagnosis. Leiocassis rudicula can be distinguished from congeners by the following unique combination of characters: distinct concavity at level of orbit in dorsolateral profile of head ( Fig. 2 ); tip of supraoccipital spine not reaching anterior nuchal plate element; smooth posterior margin of dorsal spine; presence of an irregular pale band on sides of body between dorsal and adipose fins; anal fin with narrow brown band across middle third of fin; narrow caudal-fin lobes with nearly straight posterior margins; snout length 36–40% HL; eye diameter 14–20% HL; head depth 17.6–20.0% SL; length of dorsal-fin spine 14.1–18.5% SL; length of pectoral-fin spine 15.1–17.7 %SL; dorsal-to-adipose distance 10.9–14.3% SL; body depth at anus 16.4–19.5% SL; length of adipose-fin base 18.9–24.1% SL; length of anal-fin base 18.8–22.6% SL; and caudal peduncle depth 9.1–10.9% SL.

Description. Morphometric data as in Table 1 . Head and body somewhat compressed, body moderately deep; dorsal profile sloping almost evenly, with distinct concavity above orbit; ventral profile almost straight. Dorsal profile rising evenly and steeply from tip of snout to origin of dorsal fin and sloping gently ventrally from origin of dorsal fin to posterior insertion of adipose fin. Ventral profile slightly convex to anal-fin base, then sloping slightly dorsally to end of caudal peduncle. Skin smooth. Lateral line complete and midlateral in position. Vertebrae 19+21=40 (1).

Bony elements of dorsal surface of head covered with thick skin. Midline of cranium with elongate fossa extending from behind snout to base of supraoccipital spine. Supraoccipital spine very short and narrow, reaching well short of nuchal plate. Eye ovoid, horizontal axis longest, with free margin; located entirely in dorsal half of head. Gill openings wide, extending from posttemporal to isthmus. First gill arch with 12 (6), 13* (2) or 15 (1) rakers.

Mouth inferior, snout strongly projecting. Oral teeth small and viliform, in irregular rows on all tooth-bearing surfaces. Premaxillary tooth band rounded, of equal width throughout. Dentary tooth band much narrower than premaxillary tooth band at symphysis, tapering laterally. Vomerine tooth band unpaired, continuous across midline; smoothly arched along anterior margin, tapering laterally to point extending posteriorly well past level of premaxillary band; band width broader than premaxillary band at midline, and tapering posterolaterally.

Barbels slender, short and in four pairs. Nasal barbel extending just beyond posterior orbital margin. Maxillary barbel extending to approximately two-fifths of distance between barbel base and base of pectoral-fin spine. Inner mandibular-barbel origin closer to midline, extending to one-third of distance between barbel base and isthmus. Outer mandibular barbel originating posterolateral of inner mandibular barbel, extending to vertical through anterior orbital margin.

Dorsal fin with spinelet, spine, and 7* (7) or 8 (2) rays. Dorsal fin margin convex, usually with anterior branch of fin rays longer than other branches. Dorsal fin spine moderately long, straight and slender, posterior edge smooth, without serrations. Nuchal plate narrow, tapering to pointed tip anteriorly.

Pectoral fin with stout spine, sharply pointed at tip, and 7* (4), 8 (4) or 9 (1) rays. Anterior spine margin smooth; posterior spine margin with 14–16 large serrations along entire length (serrations fewer in smaller specimens). Pectoral fin margin straight anteriorly, convex posteriorly.

Pelvic-fin origin at vertical through posterior end of dorsal-fin base, with i,5 (9) rays and slightly convex margin; tip of adpressed fin reaching anal-fin origin. Anus and urogenital openings located at vertical through middle of pelvic fin. Males with elongate genital papilla reaching to base of second or third anal-fin ray.

Adipose fin with convex margin for entire length and with deeply-incised posterior portion; length of base approximately equal to length of anal-fin base. Anal-fin base roughly in line with adipose fin, with iv,12 (9) rays and curved posterior margin.

Caudal peduncle moderately slender. Caudal fin deeply forked, with i,7,8,i (9) principal rays; lobes slender and pointed, with upper lobe slightly longer than lower. Procurrent rays extend only slightly anterior to fin base.

Coloration. In 70% ethanol: dorsal and lateral surfaces of head and body chocolate brown, with thin, diffuse irregular yellow band encircling dorsal half of body at nape. Ventral surfaces of head and body yellow, fading to lighter cream ventrally. Lateral line visible as thin pale midaxial stripe running along sides of body. Diffuse ovoid yellow patch present on lateral surfaces of body between nape and base of dorsal-fin spine. Lateral surfaces of body with irregular yellow band at region between dorsal and adipose fins and a pair of horizontally elongate cream patches located dorsal and ventral to midaxial stripe at caudal peduncle. Nasal and maxillary barbels chocolate brown dorsally, cream ventrally; mandibular barbels cream. Dorsal spine mostly chocolate brown in some individuals and mostly yellow in others; dorsal fin hyaline, with chocolate brown band on distal third to distal half of fin. Pectoral spine chocolate brown; pectoral fin with thin irregular chocolate brown band on proximal third of fin, and thicker chocolate brown band subdistally. Adipose fin chocolate brown, with three horizontally elongate ovoid yellow patches along distal margin: first at dorsally-sloping region of fin, second along apex of fin and third at incised posterior insertion of fin. Pelvic and anal fins with diffuse brown base and thin irregular chocolate brown band along middle third. Horizontally elongate ovoid yellow patch on dorsal and ventral procurrent caudal-fin rays. Caudal fin hyaline, with irregular chocolate brown markings on middle of each lobe and thin, subdistal W-shaped chocolate brown band along posterior edge. Color in life similar, but with strong yellowish hue.

Distribution. Known from the Mahakam River drainage in eastern Borneo ( Fig. 3 ).

Habitat. Leiocassis rudicula is known from streams with a moderate or fast current with clear, and sometimes tannin-stained, water. The substrate in habitats it has been collected in typically consist of gravel or sand.

Etymology. The specific epithet is the Latin diminutive for a wooden spoon. The name alludes to the distinct concavity on the dorsolateral profile of the head, which is reminiscent of a spoon.

Figures

FIGURE 1. Leiocassis rudicula, MZB 16529, holotype, 102.8 mm SL; Borneo: Kalimantan Timur, Sungai Petung Kanan.

FIGURE 2. Lateral views of heads of: a. Leiocassis rudicula, holotype, MZB 16529, 102.8 mm SL; b. other congeners (L. micropogon, ZRC 41846, 143.5 mm SL illustrated). Arrow indicates concavity above orbit. Images not to scale.

FIGURE 3. Map showing collection localities of Leiocassis rudicula. Each symbol may represent more than a single locality.

Tables

TABLE 1. Morphometric data for the type series of Leiocassis rudicula (n=9).

	Holotype	Range	Mean±SD
	MZB 16529	(type series)	(type series)
Standard length (mm)	102.8	43.8–118.0
Percent of standard length
Predorsal length	45.3	43.1–46.8	44.8±1.11
Preanal length	68.8	67.1–69.7	68.2±0.98
Prepelvic length	55.3	53.0–58.7	55.1±1.69
Prepectoral length	28.1	27.9–32.2	29.5±1.58
Length of dorsal-fin base	12.4	11.5–15.3	13.0±1.26
Dorsal-spine length	16.8	14.1–18.5	16.7±1.41
Anal-fin length	19.1	18.8–22.6	20.0±1.24
Pelvic-fin length	13.5	12.8–14.8	13.8±0.59
Pectoral-fin length	20.1	18.2–20.5	19.6±0.70
Pectoral-spine length	17.7	15.1–17.7	16.1±0.83
Caudal-fin length	25.8	23.8–27.0	25.6±1.08
Length of adipose-fin base	22.2	18.9–24.1	21.9±1.86
Dorsal to adipose distance	14.3	10.9–14.3	13.0±1.33
Post-adipose distance	15.7	12.3–16.9	15.2±1.56
Caudal peduncle length	16.8	15.4–18.6	17.1±1.09
Caudal peduncle depth	9.6	9.1–10.9	9.5±0.56
Body depth at anus	18.7	16.4–19.5	18.3±1.24
Head length	30.9	29.3–33.2	30.7±1.23
Head width	18.0	17.6–20.0	18.5±0.87
Head depth	17.2	17.2–20.5	18.5±1.05
Percent of head length
Snout length	38	36–40	38±1.6
Interorbital distance	22	21–28	24±2.2
Eye diameter	15	14–20	16±2.1
Nasal barbel length	26	13–26	17±4.5
Maxillary barbel length	42	23–42	32±6.8
Inner mandibular barbel length	15	14–20	17±2.0
Outer mandibular barbel length	24	20–30	24±2.8