Ancistrus lithurgicus Eigenmann 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 : 27-30

Ancistrus lithurgicus Eigenmann 1912

( Figs. 14–15 )

Ancistrus lithurgicus Eigenmann, 1912: 241 , pl. 25 (fig. 3). Type locality: Crab Falls ; Lower Essequibo, British Guiana. Holotype: FMNH 53091 [approximately 5.403128, -58.820068].

Specimens examined. Guyana, Essequibo River Basin. ANSP 177368 (4, 55.5–66.8 mm SL), Burro Burro River, Water Dog Falls camp, 4.68056, -58.83463, 20-Nov-1997, E. McBirney, W. Prince, D. Jaferally, et al.; ANSP 177369 (4, 49.9–70.5 mm SL), Burro Burro River, Water Dog Falls camp, 4.68056, -58.84833, 20-Nov-1997, E. McBirney; AUM 37941 (1, 40.4 mm SL), Essequibo River at Kurukupari, 4.66149, -58.67519, 17-Nov-2003, M. Sabaj, M. Hardman, N. Lujan, L. de Souza, D. Arjoon; AUM 38150 (1, 85.7 mm SL), Kuyuwini River 60.6 km ENE Kuyuwini Landing, 179 km SE Lethem, 2.19313, -058.70407, 6-Nov-2003, J. Armbruster, M. Sabaj, M. Hardman, D. Arjoon, N. Lujan, L.S. de Souza; AUM 38182 (1, 100.3 mm SL), Kuyuwini River 48.4 km E Kuyuwini Landing, 182 km SE Lethem, 2.06496, -58.80917, 6-Nov-2003, J. Armbruster, M. Sabaj, M. Hardman, D. Arjoon, N. Lujan, L.S. de Souza; AUM 38821 (5, 65.4–92.1 mm SL), 2.09860, -59.24936, Kuyuwini River at Kuyuwini Landing, 14-Nov-2003, J. Armbruster, M. Sabaj, M. Hardman, D. Arjoon, N. Lujan, L.S. de Souza; AUM 45300 (1, 49.6 mm SL), Essequibo River at Pisham-Pisham rapids, 4.43153, -58.48643, 4-Dec-2005, L. de Souza, N. Lujan, D. Taphorn, J. Hartsell, E. Liverpool, S. Lord; FMNH 53091 (1, 68.5 mm SL) (holotype), Essequibo River at Crab Falls, 5.39439, -58.86854, Sep-1908, C. Eigenmann; FMNH 53092 (3, 42.8–63.4 mm SL) (paratypes), Essequibo River at Crab Falls, 5.39439, -58.86854, Sep-1908, C. Eigenmann; USNM 66104 (1, 35.5 mm SL) (paratype), Essequibo River at Crab Falls, 5.39439, -58.86854, Sep-1908, C. Eigenmann. Guyana, East Berbice, Berbice River Basin. ROM 86895 (14, SL unrecorded), Doreen Bank Creek, about 100-200m upstream of mouth in fast to moderate flowing water, 4.93237, -58.22445, 26-Mar-2010, H. López-Fernández, C, Bernard, J. Maldonado, L. Wilson, D. Bloom, D. Taphorn, F. Gonzales, R. Vandenburg, E. Holm; ROM 88561 (3, SL unrecorded), 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; ROM 88607 (1, SL unrecorded), Berbice River, side channel (left side looking downstream) by island, 5.15107, -58.19616, 28- Mar-2010, C. Bernard, J. Maldonado, E. Holm, H. López-Fernández.

Diagnosis. Ancistrus lithurgicus can be separated from all Ancistrus in the region except A. leoni and A. macropthalmus by being very dorsoventrally flattened, having the eyes mostly dorsally placed (vs. mostly laterally placed in other Ancistrus ), and by having the median plate below the posterior edge of the adipose-fin membrane just slightly taller than wide (vs. about twice as wide as tall). Ancistrus lithurgicus can be separated from A. leoni by being black with white to golden dots and no dorsal saddles (vs. brown with white spots), by having the plates along the median line on the snout forming a triangle (vs. a narrow column); from A. macrophthalmus by having posteromedial tentacles forming a V -shape (vs. U -shape) and by having the pelvic fin reaching to nearly the end of the anal fin when both fins are adpressed (vs. to just barely beyond base of pelvic fin); and from A. leoni and A. macrophthalmus by having the eyes not as dorsally located with the medial section of the interorbital space most elevated (vs. the orbital ridge higher than interorbital space). The dark color with small white to golden dots sparsely present on the entire body and fins present in A. lithurgicus separates the species from all other potentially sympatric Ancistrus except A. nudiceps ( A. kellerae has small yellow spots present only on the head and nape and A. leucostictus has large white spots on the body and fins).

Description. Morphometrics given in Table 3. A medium-sized Ancistrus , with a maximum size recorded of 100 mm SL. 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, compressed posteriorly. Dorsal profile of head ascending steeply from snout tip to nares, then ascending in gentle convex arc to dorsal-fin origin. From the dorsal-fin origin descending in a straight line to posterior adipose-fin tip, then ascending slightly to caudal fin. Ventral profile flat, abdomen slightly convex or concave depending on state of preservation or fullness of intestines.

Head wide, interorbital width equal or slightly less than head depth, less than half of head length. Snout rounded with large broad naked margin in males, less wide in females and juveniles. Snout length more than onehalf head length. Eye large in size, interorbital area flat or 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 long with premaxillary tooth rows forming gentle arc and dentaries forming angle of>135°. Dentary and premaxillary tooth rows slightly curved medially, most lateral dentary tooth slightly medial to most lateral premaxillary tooth. Teeth numerous (50–130 per jaw ramus), asymmetrically bifid, medial cusp much larger, longer and spatulate, smaller lateral cusp pointed, equal in worn teeth. Hypertrophied cheek odontodes strongly evertible, eight to 16, stout with tips hooked anteriorly, bases encased in thick fleshy sheaths. Exposed part of opercle small, roughly triangular, covered with odontodes that are stouter near 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 not easily visible.

Ventral surface of head and abdomen naked, no exposed platelets anterior to anal-fin spine. Nuchal plate small and curved posterolaterally. Odontodes at edge of lateral plates larger than rest. Five series of lateral plates anteriorly, three series on caudal peduncle, mid-dorsal and mid-ventral plate series end on caudal peduncle beneath adipose-fin spine. Last plate in median series same size as penultimate plate, and median plate below end of adipose fin just slightly higher than wide. Base of caudal fin with about ten platelets covering bases of caudal-fin rays.

Dorsal-fin origin situated anterior to vertical through pelvic-fin insertion. First dorsal-fin ray not elongate but much longer than snout length; last dorsal-fin ray reaching first preadipose plate when depressed. Adipose-fin spine not embedded, oriented at angle to horizontal axis of body, membrane present, easily visible beneath spine. Pectoral spine moderate in length, when adpressed ventrally reaching beyond the pelvic-fin base, but not to the cloaca. Anal fin small but well developed; base of first anal-fin pterygiophore covered by skin, anal-fin origin 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=22). Mid-ventral plates 16–20, x= ̃18; median plates 21–23, x= ̃22; mid-dorsal plates 16–20, x= ̃ 18; plates bordering dorsal-fin base seven to eight, x= ̃ eight; plates between dorsal and adipose fins four to seven, x= ̃ five; preadipose plates one. Fin-ray formulae invariable: dorsal II,7; pectoral I,6; pelvic i,5; anal i,4; caudal i,14,i. Caudal procurrent spines: dorsal: three to five, x= ̃five; ventral: one to four, x= ̃three.

Sexual dimorphism. Snout tentacles of nuptial males short, largest approximately eye diameter. Posteromedial tentacles diverging in broad V- shape along anteriorly triangular snout plates. Naked areas of snout without tentacles rugose, separated from naris by one narrow plate; 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. 14 ) Base color of all fins, dorsum, sides and ventrum of body brown or gray with tiny white dots; dots often lost in preservative. First dorsal-fin membrane dark black near its base. Lower caudal-fin lobe darker than upper. Abdomen and oral disk lighter than rest of body.

Life colors. ( Fig. 15 ) Black; a few minute white dots on back and fins, more numerous on belly, sometimes quite obscure; all fins black, the dorsal and caudal margined with white sor yellow ( Eigenmann, 1912).

Distribution: Ancistrus lithurgicus is found in the Essequibo and Berbice River Basins in Guyana ( Fig. 7 ).

Figures

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

FIGURE 14. Ancistrus lithurgicus in dorsal, lateral, and ventral views, AUM 38182, 100.3 mm SL. Scale = 1 cm. Photos by J.W. Armbruster.

FIGURE 15. Live coloration of Ancistrus lithurgicus in dorsal and dorsolateral views, AUM 37941, 40.4 mm SL. Scale = 1 cm. Photo by M.H. Sabaj.