Acantopsis van Hasselt 1823

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 : 161-163

Acantopsis van Hasselt 1823

Acantopsis Van Hasselt, 1823: 133 (type species: Acantopsis dialuzona Van Hasselt, 1823: 133 , by monotypy) Acanthopsis Van Hasselt, 1824: 376 , 377 (incorrect spelling of Acantopsis )

Prostheacanthus Blyth, 1860: 167 (type species: Prostheacanthus spectabilis Blyth, 1860: 167 , by monotypy)

Acantopsis and the type species, Acantopsis dialuzona , were described in a letter from J. C. van Hasselt to C. J. Temminck, director of the Leiden Museum. Temminck published the letter in 1823, making van Hasselt’s name available ( Kottelat 1987). Alfred (1961b) provided an English translation of the original description:

“ Acantopsis distinguishes itself from them [referring to Acantophthalmus , a synonym of Cobitis ] by a very elongate pointed face which in those is blunt and so short that the eyes are situated nearly in a vertical line with the mouth-opening. Owing to this elongation the moveable spines are situated far in front of the eyes and the whole form too divergent (for them) to be combined with each other. I found this animal in the river at Batavia and in my drawing it bears the name Dialuzona Mihi.”

Roberts (1993) provided a previously unpublished but more informative description and a watercolor of A. dialuzona by Valenciennes (fig. 25), a drawing by J. Werner based on RMNH 2707—the type of A. dialuzona (fig. 59), and a vertebral count of 30 abdominal +14 caudal = 44 for the type. The description and illustrations were apparently intended for, but were not included in, the Histoire naturelle des Poissons ( Cuvier and Valenciennes 1846). The description included: "Compressed body and head, more pointed snout than in Cobitis . Eyes on top of head, almost touching, preceded by pointed spines. Very small mouth, very short barbels. Dorsal fin in middle of body. Long, pointed pectoral fin. Reddish back, white belly, silvery stripe along side of body, 8–9 darker gray oblong spots. Greenish-gray caudal fin with black dot at upper base. Dorsal-fin rays 11; pectoral-fin rays 10; pelvic-fin rays 7, anal-fin rays 6, caudal-fin rays 15."

Bleeker (1860) redescribed A. dialuzona based on additional specimens collected from Batavia [Jakarta]. The description was reproduced in English in van Oijen and Loots (2012:76–77, fig. 4), along with an illustration from the Atlas Ichthyologique ( Bleeker 1863 –1864) of the original drawing of the type left in Java by van Hasselt, as noted by Roberts (1993).

Diagnosis. Cobitidae . Distinguished from all other genera by the erectile, bifid ‘suborbital’ spine being far forward, approximately midway between the eye and the tip of the long snout ( Fig. 5 ). In other genera of cobitids, the spine is located under or slightly anterior to the eye, never midway between the eye and the tip of the snout.

The only other cobitid genus in mainland Southeast Asia with a similar body shape and color pattern is Aperioptus Richardson ( Siebert 1991a, Page and Tangjitjaroen 2015), which is distinguished from Acantopsis by having the suborbital spine only slightly anterior to the eye (reaching posteriorly to at least the anterior margin of the eye), 7 branched dorsal-fin rays (8 or more in Acantopsis ), and the dorsal-fin origin over, slightly anterior, or slightly posterior to the pelvic-fin origin (vs. far in front of the pelvic-fin origin in Acantopsis ). Although morphologically similar, molecular data indicate that Kottelatlimia may be more closely related to one of these two genera than Acantopsis and Aperioptus are to each other ( Fig. 4 , Šlechtová et al. 2008, Havird et al. 2010).

Description. Body long and slender, deepest predorsally; straight to slightly arched predorsally, tapering from origin of dorsal fin to narrow caudal peduncle. Venter flat, tapering from origin of pelvic fins, more strongly from origin of anal fin, to caudal peduncle. Dorsal-fin origin far in front of pelvic-fin origin. Head long (22–30% SL); snout long (54–72% HL), pointed, steeply sloped to nape. Suborbital spine bifid, medial point longest ( Fig. 5 ), located near midpoint between eye and tip of snout. Groove containing spine ending below anterior margin of eye; spine ending well before eye. Eye round, subcutaenous, high on rear half of head; interorbital distance less than eye diameter. Window to gas bladder posterior to dorsal limb of cleithrum. Scales absent on head and breast, usually absent along midline of abdomen; rest of body covered with ctenoid scales; scales typically embedded on nape, lower side of body, and often anteriorly on side of body. Caudal fin forked in large individual, emarginated in small individual; lobes subequal. Lateral line complete, extending onto caudal fin for short distance. Branched dorsal rays 8½–11½; branched caudal rays 14, 7 in upper, 7 in lower lobe; branched anal rays 5½; pectoral rays 9–11; pelvic rays 7; 28–35 abdominal plus 10–14 caudal = 39–48 total vertebrae. One pair each of rostral, maxillary, and mandibular barbels; 0–3 pairs of labial barbels. Maximum SL = 212.5 mm, TL = 242.5 mm ( A. spectabilis , NIFI 2456).

Color. Color patterns vary inter- and intraspecifically. Variation within species, and possibly among species, appears to be related to habitat with darker patterns on individuals living on mixed sand and gravel or in clear water, and lighter patterns on those living on sand only or in turbid water. Intraspecific variation in color can be extreme and is probably in large part accountable for the taxonomic confusion that has surrounded this genus.

The most conspicuous aspects of the color pattern of all species are the 1–2 rows of dark-brown to black spots on top of the head, continuing as a row of saddles along the dorsal midline to the origin of the caudal fin, and a row of smaller dark spots or blotches along the midside of the body from the head to the origin of the caudal fin. Spots on top of the head are in one row anterior to the nares and one or two rows posterior to the nares. Dorsal saddles and spots along the side may be faint, and the latter are often obscured by a dusky to dark line along the lateral line. Less well-defined dark spots, blotches, and reticulations may occur on the upper side, and less often on the lower side. Other dark brown to black pigment may include spots on the cheek and opercle, sometimes as 1–2 welldefined rows of large spots with many smaller spots above; large spots or dusky bands on the dorsal, caudal, anal, and paired fins; and a small black spot near the upper margin of the origin of the caudal fin, sometimes developed as an ocellus. The lower side of the head, breast, and belly are white.

In life, large individuals have a faint yellow to reddish brown cast dorsally, are translucent white ventrally, and have a green iridescence on the side of the head. Fins are mostly clear but with dusky bands on some or all fins, black spots in the dorsal and caudal fins, and a faint yellowish cast on the paired and anal fins ( Inger and Chin 1962, pers. obs.). Some species have a reddish-brown streak along the lower caudal-fin margin near the base. Smaller individuals are more translucent and have less contrasting color patterns.

Sexual dimorphism. Males have a longer, ramified first branched pectoral-fin ray as noted by Inger and Chin (1962) and Siebert (1991b, fig. 3), and a distal lobe on the first branched pectoral-fin ray in at least one species ( A. dinema , Fig. 5 ). In some, perhaps all species males reach a smaller adult size. In the largest series of specimens examined, (UF 188116; A. dinema ) males (N = 15) averaged 88.1 mm SL, and females (N = 45) averaged 99.5 mm SL. In at least some species, the medial point of the suborbital spine is longer and more curved in males ( Siebert 1991b). Interspecific and seasonal variation in sexually dimorphic characteristics, perhaps including color, remains mostly unknown in Acantopsis .

Figures

FIGURE 4. Combined (CO 1 + RAG 1) Bayesian phylogenetic reconstruction of Acantopsis. BI posterior probabilities and ML bootstrap support are plotted aboVe and beloW branch lengths, respectiVely. The geographic distribution of each major clade is described using the freshWater ecoregions delimited by Abell et al. (2008).

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.