Ancistrus macrophthalmus Pellegrin (1912)

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 : 31-35

Ancistrus macrophthalmus Pellegrin (1912)

( Figs. 16–17 )

Xenocara macrophthalma Pellegrin, 1912: 271 , fig. 1. Type locality: l’Orénoque [ Venezuela]. Holotype: MNHN 1887-0650 .

Specimens examined. Colombia: IAvHP 7001 (1, 62.6 mm SL), Departament of Vichada, Cumaripo Municipality, Tomo River , 5.379390, -68.059257, 2-May-2004 . Venezuela: Amazonas state: ANSP 162171 (1, 70.1 mm SL), Ventuari River ca 12 km from its confluence with the Orinoco , backwater and rocky pools, 4.058312, -66.932861, 25-Mar-1987 , B. Chernoff, W. Saul, J. Fernandez, M. Antonio, M. Gutierrez; ANSP 162402 (2, 54.1–54.5 mm SL) Orinoco River backwater behind sand beach, 1/2 hour upstream from Isla Temblador, 3.089606, -66.443982, 10-Mar-1987 , B. Chernoff, W. Saul, H. Lopez, J. Fernandez, O. Castillo, M. Antonio, J. Moreno; ANSP 185312 (1, 76.8 mm SL), Orinoco River at Pasaganado , 38 km N San Fernando de Atabapo, 4.399609, -67.776152, 1-Mar-2005 , M.H. Sabaj, N. Lujan, D. Werneke, et al.; ANSP 185327 (2, 79.3– 79.3 mm SL), Ventuari River ca 20 air miles ENE of confluence w Orinoco , 4.07556, -66.89278, 3-Apr-2005 , N. Lujan, M. Arce, et al.; AUM 42096 (1, 60.6 mm SL), Orinoco River , beach and bedrock outcropping 50 km E of San Fernando de Atabapo, 3.97029, -067.25506, 2-Mar-2005 , N. Lujan, D. Werneke, M. Sabaj, M. Arce, R. Betancur, T. Wesley; AUM 42105 (3, 67.3–77.2 mm SL), Orinoco River 50 km E of San Fernando de Atabapo; 3.96731 -067.25347, 3-Mar-2005 , N. Lujan, D. Werneke, M. Sabaj, M. Arce; AUM 42133 (2, 76.7–80.6 mm SL), Orinoco River at Pasaganado , 38 km N of San Fernando de Atabapo, 4.399609, -67.776152, 1-Mar-2005 , N. Lujan, D. Werneke, M. Sabaj, M. Arce, T. Wesley; AUM 42203 (6, 64.1–88.9 mm SL), Ventuari River , near ornamental fish market on the river, 4.07565, -66.89285, 3-Apr-2005 , N. Lujan, M. Arce, T. Wesley, et al.; AUM 42217 (1, 74.0 mm SL), Orinoco River near Puerto Ayacucho on a beach called Playa Bagre , 5.65642, -67.63103, 13-Apr-2005 , N. Lujan, M. Arce, T. Wesley; AUM 43264 (1, 67.8 mm SL), Orinoco River 147 ESE of San Fernando de Atabapo, 3.30662, -66.60342, 4-Mar-2005 , N. Lujan, M. Sabaj, M. Arce, T. Wesley; FMNH 101046 (3, 52.7–91.0 mm SL), Orinoco River at Cupaven , rocks and rapids, 4.01180, -67.65121, 29-Jan-1991 , A. Machado-Allison, B. Chernoff, D. Machado-Aranda, J. Wheeler; MCNG 12361 (1, 58.3 mm SL), Negro River district, Casiquiare River, Raudal Cabarua , approximately 5 Km. al N. of the confluencia of Siapa River , 2.11667, - 66.46667, 18-Apr-1985 . Venezuela, Apure state: FMNH 69930 (1, 76.0 mm SL), lower Cinaruco River at confluence of Madre Vieja, about 60 miles south of San Fernando de Apure, 6.55142, -67.50643, Feb-1967 , W. Braker et al.

Diagnosis. Ancistrus macrophthalmus differs from all other Ancistrus from the study region except A. leoni by having the raised medial orbital ridges the most elevated point on the head (vs. the medial interorbital space highest point on head), by the tentacles forming a wide U-shape on the central portion of the snout with lines of the tentacles running from the snout tip to the eye margin (vs. running in a transverse line along the middle of the snout or in a V -shape in most Ancistrus , a very narrow V in A. lithurgicus , or almost parallel in A. patronus ), by having the eyes almost completely dorsally placed (vs. almost lateral in all except A. leoni , which has the eyes in the same position and A. lithurgicus where the eyes are about midway between the condition of most Ancistrus and A. macrophthalmus ); and from all Ancistrus except A. leoni and A. lithurgicus by having the median plate below the end of the adipose-fin membrane being just slightly taller than wide (vs. being almost twice as tall as wide). Outside of the region, Ancistrus macrophthalmus is most similar to the Brazilian A. ranunculus , which shares a wide head and widely diverging rows of median snout tentacles; however, the diverging rows of tentacles in A. ranunculus are much closer to the end of the snout (only slightly separated from the margin row of tentacles), and the naked area of the snout does not reach the eyes (vs. reaching the eyes in A. macrophthalmus ). Additionally, A. macrophthalmus can be separated from A. ranunculus by being narrower, having the median plate below the posterior edge of the adipose-fin membrane just slightly taller than wide (vs. about twice as tall as wide), and having the pectoral-fin spine nearly reaching the cloaca when adpressed ventral to the pelvic fin (vs. reaching just slightly beyond base of pelvic fin).

Description. Morphometrics given in Table 4. Size range of specimens examined 52.7–90.9 mm SL. 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 extremely 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 slightly 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 compressed to the posterior of dorsal-fin base, then straight to caudal fin. Ventral profile flat from tip of snout to pelvic-fin insertions. Abdomen flat to slightly concave to pelvic-fin insertions, from there, straight, flat 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 large in size, interorbital area flat. 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 long with premaxillary and dentary tooth rows forming almost straight lines (slightly <180°). Dentary and premaxillary tooth rows slightly curved medially, lateralmost dentary tooth medial to lateralmost premaxillary tooth. Teeth numerous (45–104 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 15, stout with tips hooked anteriorly, bases encased in thick fleshy sheaths. Exposed part of opercle small, roughly triangular with few odontodes. 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 ending on caudal peduncle beneath preadipose plate just anterior to embedded adipose-fin spine. Last plate in median series slightly smaller than penultimate plate, and median plate below end of adipose fin just slightly higher than 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 elongate, just slightly longer than snout length; last dorsal-fin ray reaching first preadipose plate when depressed. Adipose-fin spine (if present) embedded, oriented parallel to horizontal axis of body, membrane present, visible beneath spine. Pectoral spine short and stout, when adpressed ventrally reaching to slightly posterior to insertion of the pelvic fin, which we categorize as medium distance (medium). 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 past anal-fin origin, inserted posterior to vertical through first branched dorsal-fin ray. Caudal fin truncate, lower lobe slightly 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=26). Mid-ventral plates 15–17, x= ̃17; median plates 21–24, x= ̃22; mid-dorsal plates 16–19, x= ̃ 18; plates bordering dorsal-fin base six to eight, x= ̃seven; plates between dorsal and adipose fins three to seven, x = five; preadipose plates one. Fin-ray formulae: dorsal II,7; pectoral I,6; pelvic i,5; anal i,3–4, xĩ,4; caudal i,14,i. Caudal procurrent spines: dorsal three to five, x= ̃four; ventral: one to three, x= ̃two.

Sexual dimorphism. Snout tentacles of nuptial males long, largest approximately 1.5 times eye diameter. Posteromedial tentacles diverging in a broad U- shape along anteriorly triangular snout plates. Naked areas of snout without tentacles rugose, separated from naris by several, wide plates; naked area narrow, distance from anteromedial plate to snout less than distance from anteromedial plate to line formed between anterior edges of nasal apertures.

Color in alcohol. ( Fig. 16 ) Dorsum of body base color dark brown with well-separated small white dots on the plateless area of snout, head and body. Opercle and sides of head, body and caudal peduncle also dark brown with white dots as on dorsum. Spines and rays of fins dark brown, membranes translucent clear or light gray. Oral disk and ventral surfaces of head and abdomen yellowish, lower lip in some smaller specimens with narrow gray edges. Ventrum of caudal peduncle lighter than sides, with small white dots. Some specimens with pigment pattern mostly faded to varying degrees of brown, with light dots not visible.

Life colors. ( Fig. 17 ) Dorsum dark gray, small cream to yellowish dots on plateless area of snout, top of head, tentacles and entire length of body. Dots on head more numerous, smaller and closer together on top of head than on dorsum of body. Sides of head of body dark gray with white dots to caudal fin. Ventrum of head and body white. Oral disk and adjacent area on chest light. Spines, rays and fin membranes gray with white dots. Caudal-fin spine, rays and fin membrane light gray with no dots.

Distribution. Found in the upper Orinoco River system from the río Cinaruco and further upstream to the río Casiquiare ( Fig. 7 ).

Figures

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

FIGURE 16. Ancistrus macropthalmus in dorsal, lateral, and ventral views, AUM 53526, 87.3 mm SL. Scale = 1 cm. Photos by J.W. Armbruster.

FIGURE 17. Live coloration of Ancistrus macropthalmus in dorsal and lateral views, AUM 43264, 67.8 mm SL. Scale = 1 cm. Photo by M.H. Sabaj.