Ancistrus leoni, De & Taphorn & Armbruster, 2019

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 : 20-23

Ancistrus leoni , new species

( Figs. 11–12 )

Holotype. MCNG 56680 81.6 mm SL, (ex MCNG 53811 ), Venezuela, Amazonas State, Atabapo District, Río Negro , in rapids about 1 km south (downstream) of the mouth of the Casiquiare , 1.987611, -67.120250, 2-Feb- 2005, O. León Mata, K. Redden, R. Williams.

Paratypes. Venezuela, Amazonas State . MCNG 53811 (2) same data as holotype ; AUM 43265 (2, 0), Orinoco River 147 km ESE of San Fernando de Atabapo, 3.30662, -66.603, 4-Mar-2004, N. Lujan, M. Sabaj, M. Arce, T. Wesley ; AUM 42972 (4, 2, 53.6–59.9 mm SL), Orinoco River at Puerto Venado, 4.3 km S of Samariapo, 56.4 km SSW of Puerto Ayacucho , 5.21060, -67.80495, 26-Feb-2005, N. Lujan, D. Werneke, M. Sabaj, M. Arce, R. Betancur, T. Wesley ; AUM 43665 (5, 4, 44.9–49.3 mm SL), Casiquiare River, left bank upstream from mouth of Siapa River , 2.15570, -66.46377, 19–22-Mar-2005, N. Lujan, M. Arce, T. Wesley, G. Santaella ; AUM 53527 (1, 55.0 mm SL), Orinoco River at Pasaganado , 38 km NNW of San Fernando de Atabapo, 4.38418, -67.77473, 27- Mar-2010 N.Lujan, D. Werneke, M. Sabaj, T. Carvalho, V. Meza, O. León Mata . Brazil, Amazonas state : CAS-SU 56890 (2, not measured), rio Negro, São Gabriel rapids, -0.138826, -67.088998, 1-Feb-1925, C. Ternetz .

Diagnosis. Ancistrus leoni can be separated from all other Ancistrus in the region by having the odontodes located medially on the snout in a single, narrow column (vs. a broad triangular, curved, or rectangular area) and by having a color pattern consisting of small white spots and well-developed dorsal saddles (vs. many smaller white or yellow spots packed more closely together or just on head, large white spots, or entirely brown sides and saddles weakly developed if present); and from all except A. macrophthalmus by having the eyes almost completely dorsally located on the head and the orbital rim the most elevated portion of head (vs. eyes slightly dorsally placed in A. lithurgicus and mostly lateral in all other species and with the medial interorbital point more dorsal than the orbital rim). The nuptial male A. leoni is the only Ancistrus we examined with a tentacle located in an area between the posteromedial and cheek sections (all other Ancistrus have the tentacles absent from an area medial to the nasal aperture and the base of the evertible cheek odontodes). Ancistrus leoni also differs from A. macrophthalmus and A.

lithurgicus by having a very light ventral surface (vs. ventral surface only slightly lighter than black sides).

Description. Morphometrics given in Table 2. Size range of examined specimens: 45–60 mm SL. A mediumsized Ancistrus , greatest body width just posterior to opercles, then narrowing progressively to end of caudal peduncle. Head and body flat, very depressed, greatest body depth at level of pectoral-fin insertions. Caudal peduncle of moderate depth, greatly compressed posteriorly. Dorsal profile of head almost straight, ascending in slightly convex arc from snout tip to dorsal-fin origin then in straight line to posterior margin of adipose fin, angled slightly up to caudal fin. Ventral profile flat to pectoral-fin insertions, abdomen slightly concave to pelvic-fin insertions, from there, straight to slightly convex to vertical through dorsal caudal-fin spine, then sloping gently ventrally towards ventral caudal-fin spine, which is offset and posterior to dorsal caudal-fin spine.

Head wide, interorbital width greater than head depth, equal or slightly more than half of head length. Snout long and somewhat pointed, narrowly rounded with moderate naked margin in males, less wide in females and juveniles. Snout very elongate its length much more than half head length. Eye moderate in size, interorbital area flat to slightly concave. Oral disk almost round, only slightly 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 slightly curved medially, lateralmost dentary tooth medial to lateralmost premaxillary tooth. Teeth numerous, but less so than many Ancistrus , (44–58 on dentary, 47–62 on premaxillary), asymmetrically bifid, medial cusp much larger and spatulate, lateral cusp smaller, usually not reaching more than half length of medial cusp, equal in worn teeth. Hypertrophied cheek odontodes strongly evertible, eight to 13, stout with tips hooked anteriorly, bases encased in thick fleshy sheaths. Exposed part of opercle small, roughly triangular with large patch of odontodes.

Head smooth, bones on back of head not carinate; supraoccipital with margins between surrounding bones and plates usually clearly visible. Lateral plates with enlarged odontodes but not carinate, lateral line complete, pores not always readily visible.

Ventral surface of head and abdomen naked, no exposed platelets anterior to anal-fin spine. Nuchal plate small and curved posterolaterally. Enlarged odontodes present forming keel on posterior, ventral plates of caudal peduncle. Five series of lateral plates anteriorly, three series on caudal peduncle, middorsal plate series ending on caudal peduncle beneath preadipose plate just anterior to embedded adipose-fin spine; mid-ventral plate series extending more posteriorly, ends on caudal peduncle beneath anterior part of 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 six or seven smaller platelets covering bases of caudal-fin rays.

Dorsal-fin origin situated slightly anterior to vertical through pelvic-fin insertion. First dorsal-fin ray not elongate, just slightly longer than snout length; last dorsal-fin ray just reaching first preadipose plate when depressed. Adipose-fin spine oriented at 30–40 degree angle to horizontal axis of body, membrane light near spine, dark near body, easily visible. Pectoral spine short, reaching past pelvic-fin insertions but only to anterior third of pelvic fins. Anal fin small but well developed; base of first anal-fin pterygiophore covered by skin, anal-fin origin posterior to vertical posterior edge of dorsal-fin base. Pelvic fins reaching well past anal-fin origin, inserted posterior to vertical through first branched dorsal-fin ray. Caudal fin margin truncate, lower lobe slightly longer than upper, its base at angle to body’s horizontal axis, with upper spine insertion anterior to that of lower.

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=6). Mid-dorsal plates 16–18, x= ̃16; median plates 22–24, x= ̃ 23; mid-ventral plates 17–18 x = ̃ 18; plates bordering dorsal-fin base seven to eight, x= ̃eight; plates between dorsal and adipose fins six to seven, x = six; 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: four to five, x= ̃five; ventral: three to four, x= ̃three.

Sexual dimorphism. Snout tentacles of nuptial males short, largest approximately same length as eye diameter. Posteromedial tentacles diverging in narrow V- shape along anterior single row of snout plates, posteromedial tentacles very short. Naked areas of snout without tentacles rugose, separated from naris by several wide plates; one small tentacle located between posteromedial and cheek sections of tentacles; 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. 11 ) Dorsum of body base color tan with well-separated white spots on plateless area of snout, head and body and five faint, wide brown saddles. White spots relatively larger in smaller specimens. Opercle and sides of head, body and caudal peduncle also tan or light brown with white spots as on dorsum. Spines and rays of fins with alternating light and dark sections, membranes translucent clear or light gray. Oral disk and ventral surfaces of head and abdomen white, lower lip in some smaller specimens with narrow gray edges. Ventrum of caudal peduncle lighter tan than sides, without white spots. Some specimens with pigment pattern mostly faded to varying degrees of brown, with light spots not visible.

Life colors. ( Fig. 12 ) Dorsum brown to olive brown with five darker brown to blackish saddles peppered with white, cream or light greenish to yellowish spots (most about one fifth to one fourth orbit diameter in size, a few larger) on plateless area of snout, top of head and entire length of body. Spots on head more numerous, smaller and closer together on top of head than on dorsum of body. Sides of head and body light brown with white spots; lower half of body posterior to pelvic-fin insertions lighter brown than top half. Ventrum of head and body white. Oral disk and adjacent area on chest white. Fin membranes gray, without light or dark spots, but spines and rays marked with two to five alternating dark and light sections (the longer ones with more). Caudal-fin spine and rays with alternating light and dark sections often aligned to form irregular vertical rows or arcs, with the dark sections much wider than the light.

Distribution. The upper río Negro and río Orinoco in Amazonas state of Venezuela, northernmost Brazil and probably tributaries of the río Negro in adjacent regions of Colombia ( Fig. 7 ).

Etymology: Named to honor our fallen colleague, Ing. RNR Oscar León Mata (1964-2018), who collected the holotype and dedicated much of his too-short life to Venezuelan ichthyology. Oscar collected the type series of this new species and was invaluable during many of the expeditions to Venezuela, which would not have succeeded without him. He is sorely missed by his family and friends.

Figures

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

FIGURE 11. Holotype of Ancistrus leoni in dorsal, lateral, and ventral views, MCNG 53811, 81.6 mm SL. Scale = 1 cm. Photos by J.W. Armbruster.

FIGURE 12. Live coloration of the holotype of Ancistrus leoni in dorsal and lateral views, MCNG 53811, 81.6 mm SL. Scale = 1 cm. Photos by N.K. Lujan.