Ancistrus leucostictus ( Günther 1864 )

De, Lesley S., Taphorn, Donald C. & Armbruster, Jonathan W., 2019, Review of Ancistrus (Siluriformes: Loricariidae) from the northwestern Guiana Shield, Orinoco Andes, and adjacent basins with description of six new species, Zootaxa 4552 (1), pp. 1-67 : 24-27

Ancistrus leucostictus ( Günther 1864)

( Fig. 13 )

Chaetostomus leucostictus Günther, 1864: 248 . Type locality: Essequibo [ Guyana]. Possible holotype: BMNH 1864.1.21.85 (type designation questioned by Muller, 1989 and Fisch-Muller, 2003).

Specimens examined. Guyana, Essequibo/ Rupununi River drainage. AUM 35629 (2, 45.3–50.9 mm SL), Rupununi River 4.6 km NW Massara, 3.92603, -59.28037, 26-Oct-2002, J. Armbruster, M. Sabaj, D. Werneke, L Allison, M. Thomas, C. Chin, D. Arjoon, M. James; AUM 35630 (1, 57.9 mm SL), Simoni River , 4 sites from 6.6 km SE to 3.2 km W Karanambo, 3.71917, -59.26121, 29-Oct-2002, J. Armbruster, M. Sabaj, L. Allison, M. Thomas; AUM 37910 (2, 54.5–55.0 mm SL), Kuyuwini River at Parabara , just downstream of Kuyuwini Landing , 155 km SSE Lethem, 2.09585, -59.24116, 4-Nov-2003, J. Armbruster, M. Sabaj, M. Hardman, D. Arjoon, N. Lujan, L. de Souza; AUM 38094 (2, 42.8–43.8 mm SL), Madkauwau Creek , tributary of Kuyuwini River between Kuyuwini Landing and Parabara, 155 km SSE Lethem, 2.09672, -59.24346, 4-Nov-2003, J. Armbruster, M. Sabaj, M. Hardman, D. Arjoon, N. Lujan, L. de Souza; AUM 38820 (2, 40.0– 63.8 mm SL), Kuyuwini River at Kuyuwini Landing, 2.09860, -59.24936, 14-Nov-2003, J. Armbruster, M. Sabaj, M. Hardman, D. Arjoon, N. Lujan, L. de Souza; AUM 48162 (6, 64.0– 87.8 mm SL), Burro Burro River at Surama, 4.18256, -59.06375, 23-Nov-2007, L. de Souza, D. Taphorn, J. Baskin, T. Geerinckx, J. Hwan . Guyana, Berbice River Drainage : ROM 88561 (3, not measured) , Berbice River about 1 km downstream of Cat Creek. 4.96558, -58.24321, 27-Mar-2010, D. Bloom, D. Taphorn, C. Bernard, H. López-Fernández, J. Maldonado, L. Wilson, R. Vandenburg .

Diagnosis. Ancistrus leucostictus differs from all other Ancistrus in the region except A. brevifilis (endemic to the Tuy River Basin in Venezuela), A. saudades (from Amazon River tributaries in southern Guyana, and Guyana Shield rivers of the Orinoco Basin in Venezuela), and A. triradiatus (from Orinoco River Basin in Venezuela) by having light, large spots on the caudal fin, abdomen, dorsum of head and body and sides (these can be obscured in preserved specimens, but spots generally remain on the fins, vs. body and fins all dark color with very small white spots, spots may be absent in preserved specimens) in all other Ancistrus in the region. Ancistrus leucostictus can be separated from A. saudades by having the adpressed dorsal fin reaching to at least the middle of the adipose-fin spine (vs. to middle of preadipose plate), by having the pectoral-fin spine when adpressed ventral to the pelvic fin reaching the base of the cloacal tube (vs. short of the cloacal papilla), and by having relatively larger light spots and narrower dark interspaces on the anterolateral plates and posterodorsal head bones with the interspaces much less than half the width of the spots and at least some spots always visible in this area on preserved specimens (vs. interspaces half or greater the diameter of the spots and the spots often obscured in this region in preserved specimens; the difference in spots vs. interspaces generally works on the abdomen as well); from A. brevifilis by having round spots on the caudal fin (vs. oval spots), and from A. brevifilis and A. triradiatus by having spots on the abdomen in life (vs. spots absent).

Description. Morphometrics given in Table 3. A large-sized Ancistrus , body broadest anteriorly, greatest body width just posterior to opercles, then narrowing progressively to end of caudal peduncle. Head and body depressed, greatest body depth between level of pectoral-fin insertions and dorsal-fin origin. Caudal peduncle deep, robust, compressed posteriorly. Dorsal profile of head ascending steeply in convex arc from tip of snout to just posterior of orbits, ascending in straight line to posterior tip of supraoccipital, then descending to dorsal-fin origin. From the dorsal-fin origin descending in a slight convex arc to just posterior of dorsal-fin base, then straight to caudal fin. Ventral profile flat to slightly convex from tip of snout to pelvic-fin insertions. Abdomen flat to slightly concave to pelvic-fin insertions, from there, straight to slightly convex and sloping gently ventrally towards caudal fin.

Head wide, interorbital width equal or slightly less than head depth, slightly less than half of head length. Snout rounded with large broad naked margin in males, less wide in females and juveniles. Snout length about onehalf head length. Eye moderate in size, interorbital area slightly convex. Oral disk ovate, wider than long. Lips covered with minute papillae, larger near mouth. Lower lip moderate in size, not reaching gill aperture, its border covered with very small papillae. Maxillary barbel very short, its length less than orbit diameter. Jaws moderate with premaxillary tooth rows forming strong arc and dentary tooth rows forming angle of>135°. Dentary and premaxillary tooth rows strongly curved medially, lateralmost dentary tooth medial to lateralmost premaxillary tooth. Teeth numerous (36–62 per jaw ramus), asymmetrically bifid, medial cusp much larger and spatulate, lateral cusp minute and pointed, usually not reaching more than half length of medial cusp, equal in worn teeth. Hypertrophied cheek odontodes strongly evertible, eight to 17, stout with tips hooked anteriorly, bases encased in thick fleshy sheaths. Exposed part of opercle small, roughly triangular with larger odontodes along free edge. Head smooth, bones on back of head not carinate; supraoccipital with margins between surrounding bones and plates usually clearly visible. Lateral plates not carinate, lateral line pores distinctly visible, horizontally elongate.

Ventral surface of head and abdomen naked, no exposed platelets anterior to anal-fin spine. Nuchal plate small and curved posterolaterally. No enlarged odontodes at edge of lateral plates. Five series of lateral plates anteriorly, three series on caudal peduncle, mid-dorsal and mid-ventral plate series end on caudal peduncle beneath adiposefin spine. Last plate in median series slightly smaller than penultimate plate, and median plate below end of adipose fin about twice as high as wide. Base of caudal fin with six platelets covering bases of caudal-fin rays.

Dorsal-fin origin situated anterior to vertical through pelvic-fin insertion. First dorsal-fin ray not elongate, just slightly longer than snout length; last dorsal-fin ray reaching first preadipose plate when depressed. Adipose-fin spine not embedded, oriented at an angle to horizontal axis of body, membrane present, easily visible beneath spine. Pectoral spine long and stout, when adpressed ventrally it reaches to the cloaca, which we categorize as maximum length (long). Anal fin small but well developed; base of first anal-fin pterygiophore covered by skin, its origin below or posterior to vertical through base of last dorsal-fin ray. Pelvic fins reaching well past anal-fin origin, inserted posterior to vertical through first branched dorsal-fin ray. Caudal fin truncate, lower lobe longer than upper. Tiny odontodes present on body plates, largest on posterior margins of plates. All fin spines with small odontodes, more developed in pectoral-fin spine of males. All fin rays with tiny odontodes on rays.

Meristics (N=15), mid-ventral plates 16–18, x= ̃17; median plates 22–24, x= ̃23; mid-dorsal plates 16–19, x= ̃ 17; plates bordering dorsal-fin base seven to eight, x= ̃seven; plates between dorsal and adipose fins four to seven, x= ̃five; preadipose plates one. Fin-ray formulae invariable (N=15): dorsal II,6–8, x= ̃II,7; pectoral I,6; pelvic i,5; anal i,4; caudal i,14,i. Caudal procurrent spines: dorsal: three to five, x= ̃four; ventral: two to four, x= ̃three.

Sexual dimorphism. snout tentacles of nuptial males longer than in females, largest over twice eye diameter. Posteromedial tentacles diverging in V- shape along anteriorly triangular snout plates. Naked areas of snout without tentacles rugose, separated from naris by several wide plates; naked area wide, distance from anteromedial plate to snout greater than or equal to distance from anteromedial plate to line formed between anterior edges of nasal apertures.

Color in alcohol. ( Fig. 13 ) Base color light brown with medium light spots concentrated on head and snout, sometimes looking netlike, especially in juveniles. Plateless area of snout and tentacles also light brown with light spots. All fins with alternating dark and light spots. Ventral surface of head and abdomen tan to yellowish tan, oral disk yellowish, plates of ventral surface of caudal peduncle with posterior margins darker brown, forming alternating light and dark pattern. Medium white spots on ventral surface of head and abdomen. Dark interspaces on the head, anterior body, and abdomen usually less than half the width of the spots.

Life colors. Base color brown and gray with medium white irregularly-shaped spots concentrated on the head and snout. Body posterior to dorsal-fin origin equally spotted. Preadipose plate and vestiges of adipose-fin spine outlined in yellow. Sides with irregular light and dark spots. Ventrum of body with light brown base color and medium irregularly-shaped white spots. Oral disk and adjacent area on chest pink to whitish. Fin membranes lightly pigmented, grayish. Spines and rays brown in color with spots on all fins. Dark interspaces on the head, anterior body, and abdomen usually less than half the width of the spots.

Distribution. Found throughout the middle and upper Essequibo River system of Guyana ( Fig. 7 ). Probably present in the Cuyuni River drainage in Venezuela.

Figures

FIGURE 7. Distribution of species of Ancistrus from the northwestern Guiana Shield and neighboring regions.

FIGURE 13. Ancistrus leucostictus in dorsal, lateral, and ventral views, AUM 48162, 185.3 mm SL. Scale = 1 cm. Photos by J.W. Armbruster.