Acantopsis dinema, Boyd & Nithirojpakdee & Deein & Vidthayanon & Grudpan & Tangjitjaroen & Pfeiffer & Randall & Srisombat & Page, 2017

Boyd, David A., Nithirojpakdee, Patchara, Deein, Gridsada, Vidthayanon, Chavalit, Grudpan, Chaiwut, Tangjitjaroen, Weerapongse, Pfeiffer, John M., Randall, Zachary S., Srisombat, Tippamas & Page, Lawrence M., 2017, Revision of the horseface loaches (Cobitidae, Acantopsis), with descriptions of three new species from Southeast Asia, Zootaxa 4341 (2), pp. 151-192 : 177-179

Acantopsis dinema new species, Boyd and Page

Peppered Horseface Loach

( Fig. 17 )

Holotype. THNHM F0013611, 100.7 mm SL female (ex. UF 188225), Thailand, Mekong River drainage, Ubon Ratchathani Province, Pho Sai District, Ta Wang River on Rt. 2112, 4 km S of Rt. 2337, 15.793N, 105.376E, 1 February 2016, Randall, Z. et al.

Paratypes. Thailand: Mekong River drainage: UF 188225 (3, 72.4–97.9 mm SL), same locality and date as holotype . UF 185131 (9, 71.5–94.3 mm SL), same locality as holotype, 3 January 2013, Singer , R. et al. ANSP 200533 (2, 89.5–90.9 mm SL), ex . UF 185131. NIFI 5104 (2, 81.0– 86.9 mm SL), ex. UF 185131. UF 188116 (56, 68.1–117.7 mm SL), Sakon Nakhon Province, Akat Amnuai District, Songkhram River at confluence with Yam River , 17.709N, 104.076E, 8 January 2015, Boyd, D. et al . ZRC 55598 (3, 94.6–105.5 mm SL), ex. UF 188116. INHS 110606 (3, 75.8–107.7 mm SL), ex. UF 188116.

Diagnosis. Acantopsis dinema differs from all other species of Acantopsis ( Table 4) by combination of no large spots on side of head, many black specks beneath midlateral row of black spots from head to caudal fin, 2 pairs of labial barbels, no distinct small black spot on upper margin of caudal-fin base, no large black spots on dorsal or caudal fins, usually 10½ branched dorsal rays and 10 pectoral rays, 8–17 dark saddles along dorsal midline, 6–12 black spots along side of body, 41–42 total vertebrae, body depth 12.0–14.5% SL, body width 8.0–10.3% SL, caudal-peduncle length 12.1–14.3% SL.

Comparisons. Acantopsis dinema is distinguished from all other species of Acantopsis by having a row of black specks beneath midlateral row of black spots (specks rarely present in A. dialuzona and A. rungthipae ; absent in other species of Acantopsis ), and from all species except A. octoactinotos by having no dark spots on side of head (vs. usually conspicuous dark spots or specks on side of head). It further differs from A. rungthipae and A. ioa by having 2 (vs. 0) pairs of labial barbels, usually 10½ (vs. 9½) branched dorsal rays; from A. rungthipae by lacking distinct small black spot on upper margin of caudal-fin base; and from A. ioa in having 6–12 (vs. 13–21) black spots along side of body, 41–42 (vs. 46–48) total vertebrae ( Fig. 15 ), a wider body (8.0–10.3 vs. 5.2–7.9% SL). It further differs from A. octoactinotos in having usually 10½ (vs. 8½) branched dorsal rays, usually 10 (vs. 9) pectoral rays, no small black spot on upper margin of caudal-fin base, a shorter caudal peduncle (12.1–14.3 vs. 16.1–17.2% SL). It further differs from A. spectabilis and A. thiemmedhi in lacking conspicuous black spots, blotches, or bands on caudal, anal, and paired fins; from A. spectabilis in having usually 10½ (vs. 9½) branched dorsal rays; and from A. thiemmedhi in having 2 (vs. 1) pairs of labial barbels, no large black blotch on tip of anterior rays of dorsal fin. It further differs from A. dialuzona in having 2 (vs. 3) pairs of labial barbels, no well developed ocellus on upper margin of caudal-fin base. It differs from A. dialuzona , A. spectabilis , A. octoactinotos , and A. ioa by having a deeper body (12.0–14.5 vs. 8.9–11.9, 9.0–11.6, 9.6–11.2, and 8.5–11.0% SL, respectively).

Description. As in description of genus; Tables 1, 2, 4. Head long (24.1–26.9% SL); snout long (58.8–65.9% HL); 2, rarely 3, pairs of labial barbels; 10½, rarely 11½, branched dorsal rays; 10, less often 9 or 11, pectoral rays; 29–31 abdominal + 10–13 caudal = 41–42 total vertebrae. Maximum SL = 116.7 mm, TL = 139.1 mm (UF 188116).

Color. Dark spots in 1 or 2 rows on top of head; no or few scattered small spots on side of head; none large. Black line from eye to tip of snout. Eight–17 dark saddles along dorsal midline to origin of caudal fin; 6–12 large dark spots or blotches along lateral line from head to caudal fin; many small dark spots or specks on upper side of body and on lower side of body just below midlateral row of dark spots from head to caudal fin. Fins usually without obvious bands; 2–3 faint bands on dorsal fin of large individuals. Dark upper and lower margins of caudal fin. No small bold black spot or ocellus near upper or lower margins of caudal-fin origin. Live individuals yellowish brown dorsally, white below, with large black blotches dorsally and laterally on body; iridescent yellow on side of head and lower fins.

Sexual dimorphism. Males have a longer first branched pectoral-fin ray, ramified and with a distinctive lateral lobe on the distal end ( Fig. 5 ). As far as is known, other species of Acantopsis do not develop the distinctive distal expansion of the first branched pectoral-fin ray. In the largest series of A. dinema examined, (UF 188116) males (N = 15) averaged 88.1 mm SL, and females (N = 45) averaged 99.5 mm SL.

Etymology. The epithet dinema , from Latin, di meaning two, and nema, for thread, refers to the usual presence of two pairs of labial barbels in this species.

Distribution. Acantopsis dinema is widespread and common in the tributaries of the Mekong River draining the Khorat Plateau and Mekong Delta ecoregions ( Abell et al. 2008) in Thailand, Laos, and Cambodia ( Fig. 18 ), from the Songkhram River in eastern Thailand to the Prek Thnot River south of Phnom Penh, Cambodia.

Figures

FIGURE 5. (A) Dorsal VieW of erectile, bifid ‘ suborbital’ spine (highlighted) on snout of A. rungthipae, UF 188112, 70.0 mm SL. Pectoral fins of A. dinema, (B) UF 185131, 90.3 mm SL male, and (C) UF 188116, paratype, 108.9 mm SL female; and A. rungthipae (D) UF 235976, paratype, 94.5 mm SL male, and (E) THNHM F 0013610, holotype, 107.4 mm SL female.

FIGURE 15. CT-scans of (A) Acantopsis rungthipae, THNHM F 0013610, holotype, 107.4 mm SL. (B) A. dinema, THNHM F 0013611, holotype, 100.7 mm SL. (C) A. ioa, UF 188136, 95.5 mm SL. CT-scans proVided by E. L. Stanley (UF).

FIGURE 17. Acantopsis dinema. A) Lateral and dorsal VieWs, UF 188116, paratype, Songkhram RiVer, 118.3 mm SL. LiVe VieWs of (B) UF 188116, paratype, Songkhram RiVer, 111.8 mm SL, (C) UF 188225, paratype, Ta Wang RiVer, 72.8 m SL, and (D) UF 188111, Mun RiVer, 89.7 mm SL.

FIGURE 18. Localities of specimens examined of Acantopsis dinema.