Glyptothorax porrectus, Ng, Heok Hee & Kottelat, Maurice, 2017

Ng, Heok Hee & Kottelat, Maurice, 2017, The Glyptothorax of the Bolaven Plateau, Laos (Teleostei: Sisoridae): new and endangered, Zootaxa 4238 (3), pp. 406-416 : 410-413

Glyptothorax porrectus new species

( Fig. 4 )

Type material. Holotype. MHNG 2766.055, 88.7 mm SL; Laos: Champasak Province, Pakxong District, Bolaven Plateau, Xe Nam Noy at bridge downstream of Xe Pian–Xe Nam Noy dam site, 15°03’34”N 106°36’08”E, 708 masl; M. Kottelat & T. Phommavong, 22 January 2013.

Paratypes. CMK 23367 (3), 88.7–119.4 mm SL; Laos: Champasak Province, Pakxong District, Bolaven Plateau, Xe Nam Noy near confluence with Houay Nam Tang near Tayiksua , 15°05’03”N 106°35’26”E; M. Kottelat & T. Phommavong, 16 January 2013 . CMK 23420 (10), 35.7–87.9 mm SL; ZRC 55629 (3), 46.2–69.7 mm SL; data as for holotype . CMK 15514 (2), 28.0–35.0 mm SL; same locality as holotype, 15°03'25"N 106°36'11"E; M. Kottelat et al., 19 May 1999 . CMK 23332 (19), 34.4–79.1 mm SL; Laos: Champasak Province, Pakxong District, Bolaven Plateau, Xe Nam Noy , first rapids downstream of Xe Pian–Xe Namnoy dam site, 15°01’38”N 106°36’17”E, 833 masl; M. Kottelat & T. Phommavong, 13 January 2013 . CMK 23345 (1), 44.3 mm SL; Laos: Champasak Province, Pakxong District, Bolaven Plateau, Houay Xoy , a tributary of Xe Nam Noy , 14°52’41”N 106°34’49”E; M. Kottelat & T. Phommavong, 14 January 2013 .

Additional material (non-types). CMK 23427 (4); Laos: Champasak Province, Pakxong District, Bolaven Plateau, Xe Nam Noy at water intake of Xe Pian–Xe Nam Noy hydropower plant, 14°56’50”N 106°37’41”E, 759 masl; M. Kottelat & T. Phommavong, 22 January 2013.

Diagnosis. Glyptothorax porrectus differs from Indochinese congeners except for G. coracinus , G. forabilis , G. interspinalum , G. lanceatus , G. laosensis , G. longinema , G. strabonis , G. trilineatus and G. zanaensis in having a uniformly dark gray body with pale midlateral and mid-dorsal stripes (vs. body with pale or dark bands, patches or spots). It is distinguished from G. coracinus , G. forabilis , G. interspinalum , G. lanceatus , G. laosensis , G. longinema , G. strabonis , G. trilineatus and G. zanaensis in having the following unique combination of characters: eye diameter 8–10% HL; interorbital distance 23–31% HL; head depth 10.6–11.6% SL; thoracic adhesive apparatus with medial pit and without anteromedial striae; body depth at anus 8.7–12.4% SL; post-adipose distance 18.6–24.6% SL; caudal peduncle depth 5.8–6.7% SL; caudal peduncle length 21.7–25.8% SL; and very thin pale midlateral stripe only as wide as a single tubercle.

Description. Morphometric data in Table 2 . Head depressed; body slender, subcylindrical. Dorsal profile rising evenly from tip of snout to origin of dorsal fin, then sloping gently ventrally from origin of dorsal fin to end of caudal peduncle. Ventral profile straight to anal-fin base, then sloping gently dorsally from anal-fin base to end of caudal peduncle. Anus and urogenital openings located at vertical through middle of adpressed pelvic fin. Depth of caudal peduncle 3.2–4.1 times in its length. Skin tuberculate, with tubercles of small and even size on sides of body. Lateral line complete and midlateral. Vertebrae 19+18=37 (4), 18+20=38 (1), 19+19=38* (7), 20+18=38 (2) or 18+21=39 (1). Tips of neural spines distally expanded, not visible as series of low bumps between dorsal and adipose fins.

Head depressed and broad, triangular when viewed laterally. Snout prominent. Anterior and posterior nares large and separated only by base of nasal barbel. Gill opening broad, extending from ventral margin of posttemporal to isthmus. First branchial arch with 3+8 (1) rakers. Bony elements of dorsal surface of head covered with thick, tuberculate skin. Eye ovoid, horizontal axis longest; located entirely in dorsal half of head.

Barbels in four pairs. Maxillary barbel long and slender, extending to middle of pectoral-fin base. Nasal barbel slender, extending to two-thirds distance between its base and anterior orbital margin. Inner mandibular-barbel extending to slightly over midway between its base and that of pectoral spine. Outer mandibular barbel extending to base of pectoral spine.

Mouth inferior, premaxillary tooth band partially (approximately half) exposed when mouth is closed. Oral teeth small and villiform, in irregular rows on all tooth-bearing surfaces. Premaxillary teeth appearing in single broad semilunate band. Dentary teeth in a single crescentic band, consisting of two separate halves tightly bound at midline.

Thoracic adhesive apparatus consisting of keratinized striae in a narrowly ovate field ( Fig. 2 b) extending from isthmus almost to posterior limit of pectoral-fin base; anterolateral edges of adhesive apparatus almost straight. Narrow medial pit devoid of striae on posterior half.

Dorsal fin located above anterior third of body, with I,6 (12) rays; fin margin concave; spine short and straight, smooth on anterior and posterior margins. Adipose fin with anterior margin straight or slightly concave and posterior margin slightly convex. Caudal fin strongly forked, with lower lobe slightly longer than upper lobe and i,7,8,i (12) principal rays. Procurrent rays symmetrical and extending only slightly anterior to fin base. Anal-fin base vertically opposite adipose-fin base. Anal fin with straight anterior and posterior margins; with iii,10 (2), iv,9* (2), iv,9,i (5), iv,10 (2) or iv,10,i (1) rays. Pelvic-fin origin at vertical through posterior limit of dorsal-fin base. Pelvic fin with slightly convex margin and i,5 (12) rays; tip of adpressed fin just reaching anal-fin origin. Pectoral fin with I,9,i (2), I,10* (9) or I,10,i (1) rays; posterior fin margin slightly concave; anterior spine margin smooth, posterior margin with 7–14 (holotype =13) serrations.

Coloration. In 70% ethanol: dorsal and lateral surfaces of head, and body dark gray, fading to beige on ventral surfaces. A faint thin, cream mid-dorsal stripe extending from base of last dorsal-fin ray to origin of adipose fin; stripe very faint in some individuals. Laterosensory pores and tubercles along lateral line rimmed in beige, imparting appearance of a thin pale midlateral line. All fins with dark gray fin rays, and diffuse melanophores on fin membranes. Pectoral and pelvic fins with dark gray on base of fin rays and hyaline posterior margin. Anal fin with dark gray base and hyaline posteroventral corner. Adipose fin dark gray, with hyaline distal margin. Caudal fin dark gray, with tip of lobes hyaline; in juveniles (CMK 15514, 28.0–35.0 mm SL), a white outer margin along lobes. Maxillary and nasal barbels dark gray dorsally, beige ventrally. Mandibular barbels beige. In life: body dark blackish brown, midlateral stripe white.

Habitat. Glyptothorax porrectus is typically found in streams and creeks with stone to rock bottom, in fast current.

Distribution. Glyptothorax porrectus is known from the Xe Nam Noy drainage in the Bolaven Plateau, southern Laos ( Fig. 3 ).

Etymology. The name porrectus (- us, -a, -um) is the adjectival form of the Latin verb porrigo, meaning to stretch out or to extend. The name is used in reference to the elongate, thin body of this species.

Figures

FIGURE 2. Thoracic adhesive apparatus of: a. Glyptothorax forabilis, holotype, MHNG 2766.054, 76.7 mm SL; b. G. porrectus, holotype, MHNG 2766.055, 88.7 mm SL; c. G. laosensis, ZFMK 24237, 81.7 mm SL. Images not to scale.

FIGURE 3. Map showing the Bolaven Plateau (indicated by red dots) and collection localities of Glyptothorax forabilis and G. porrectus. Outlined symbols indicate collection localities of non-type material. Each symbol may represent more than one locality.

FIGURE 4. Glyptothorax porrectus, holotype, MHNG 2766.055, 88.7 mm SL; Laos: Xe Nam Noy. Dorsal, lateral and ventral views.

Tables

TABLE 2. Morphometric data for Glyptothorax porrectus (n = 12).

	Holotype MHNG 2766.055	Range	Mean±SD
Standard length (mm) %SL	76.7	40.1–119.4
Predorsal length Preanal length Prepelvic length	34.8 63.5 46.7	32.0–34.8 61.4–65.7 44.3–49.8	33.8±1.01 64.0±1.35 46.8±1.49
Prepectoral length Length of dorsal-fin base Dorsal-fin spine length	20 10.3 12.1	17.9–20.0 10.3–12.1 12.4–16.2	19.2±1.19 11.2±0.61 14.3±1.42
Length of anal-fin base Pelvic-fin length Pectoral-fin length	15.8 17.4 23.4	13.5–15.8 15.8–19.3 18.9–24.7	15.1±1.01 17.4±1.12 22.4±1.99
Pectoral-fin spine length Caudal-fin length Length of adipose-fin base	16.1 26.5 13.9	13.9–18.9 25.0–30.7 10.8–14.7	16.8±1.75 28.4±1.83 13.2±1.38
Dorsal to adipose distance Post-adipose distance Length of caudal peduncle	26.3 24.6 23.6	22.7–28.1 18.6–24.6 21.7–25.8	24.8±1.60 21.3±1.73 23.0±1.50
Depth of caudal peduncle Body depth at anus Head length	6.7 12.4 24	5.8–6.7 8.7–12.4 21.9–26.4	6.3±0.33 10.8±1.05 24.5±1.60
Head width Head depth %HL	18.5 11.4	15.8–18.5 10.6–11.6	17.2±0.96 11.3±0.43
Snout length Interorbital distance Eye diameter	55 25 10	44–55 23–31 8–10	50±3.0 26±2.3 9±1.2
Nasal barbel length Maxillary barbel length Inner mandibular barbel length	23 105 38	18–25 79–105 25–39	21±2.4 89±8.7 30±5.6
Outer mandibular barbel length	51	37–54	46±5.9