Ancistrus kellerae, 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 : 16-19

Ancistrus kellerae new species

( Figs. 9–10 ).

Holotype. CSBD F 1721 (1, 69.9 mm SL) Guyana, Region 8 (Potaro/Siparuni), Potaro River drainage, Kuribrong River, in rapids at Grass Shoals, 5.40791, -59.53179, 12-Mar-2014 J. Armbruster, D. Werneke, E. Liverpool, D. Fernandes, and D. Taphorn.

Paratypes. AUM 62849 (1, 55.0 mm SL) collected with holotype; FMNH 135052 (1, 50.1 mm SL) collected with holotype .

Diagnosis. Ancistrus kellerae can be separated from all species in the region except A. patronus by having a naked area posteromedial to the medial row of tentacles extending to anterior margin of nasal apertures (area is triangular in A. kellerae , rectangular in A. patronus , and absent in all other species), and by having only a small plate surrounded by flesh between the nasal aperture and the posteriormost odontodes (vs several plates that abut one another); from A. patronus by having a short dentaries (11.6–12.5% vs. 20.3–29.1% HL); and from the most similar species, A. nudiceps , by usually having a broad golden edge of the end caudal fin (vs. a narrow line maximally), by having gold spots only on the head (vs. all over), by having a dark lateral stripe (vs. entirely black), by being darker dorsally along sides than ventrally (vs. uniform color), and by having faint dark spots along the pectoral-fin spine (vs. black with small gold to white spots).

Description. Morphometrics in Table 2. A small-sized Ancistrus ; size range of examined specimens 50.1–69.9 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, 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 short 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 most lateral premaxillary tooth. Teeth numerous, but fewer than in many Ancistrus (36–44 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, 12–17, 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 readily visible anteriorly, but not posteriorly.

Ventral surface of head and abdomen naked, no exposed platelets anterior to anal-fin spine. Nuchal plate small and curved posterolaterally. Odontodes enlarged along edges 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 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 horizontal to axis of body, membrane visible beneath spine. Pectoral spine short and stout, when adpressed ventrally reaching to the insertion of the pelvic fin, which we categorize as minimum distance (short). 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 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=3). mid-ventral plates 16–17, x= ̃ 17; median plates 22–23, x= ̃ 22; mid-dorsal plates 15; plates bordering dorsal-fin base six; plates between dorsal and adipose fins five; preadipose plates one. Fin-ray formulae (N=3): dorsal II,7; pectoral I,6; pelvic i,5; anal i,3–4, x= ̃i,4; caudal i,14,i. Caudal procurrent spines: dorsal: four to five, x= ̃five; ventral: three to four, x= ̃four.

Sexual dimorphism. Snout tentacles of nuptial males long, largest over twice eye diameter. Posteromedial tentacles diverging in V- shape along anteriorly triangular snout plates, but anterior plates covered by thick flesh. Naked areas of snout without tentacles rugose, separated from naris by single, thin plate; naked area wide, distance from anteromedial plate to snout greater than distance from anteromedial plate to line formed between anterior edges of nasal apertures.

Color in alcohol. ( Fig. 9 ) Dorsal and lateral base color dark gray or brown mottled with light brown spots on top of head and body. Dark line present along midline, body darker above than below. Plateless area of snout and tentacles also dark with irregular lighter spots. Pectoral and pelvic fins with at least faint alternating dark and light spots. Dorsal and caudal fins uniform dark brown color. Pale whitish band on the tip of the caudal fin. 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.

Life colors. ( Fig. 10 ) Dorsum mottled dark and light brown with small yellowish spots concentrated on plateless area of snout, tentacles and top of head. Body posterior to dorsal-fin origin with fewer spots, and base color is dark and light brown. Preadipose plate and adipose-fin spine outlined in yellow. Sides with irregular light and dark spots. Body posterior of insertion of dorsal and pelvic fin coloration dorsally is dark brown and lighter brown ventrally, appearing to have a dark median horizontal line along the middle of body to caudal fin. Ventrum of body lighter than sides, and mottled (from what can be viewed in Fig. 10 ). Oral disk and adjacent area on chest cream. Fin membranes lightly pigmented, grayish, but spines and rays tan in color with spots on pectoral and pelvic fins. Caudal-fin spine and rays uniform in color except for a white band vertically along the tip.

Distribution. Known only from the type locality in the Kuribrong River, Potaro River - Essequibo River drainage ( Fig. 7 ). The locality is below Amaila Falls.

Etymology. Named in honor of Connie Keller and in gratitude for her leadership as Chair of the Board of Trustees for the Field Museum, where her unparalleled support of research and conservation work has led to the protection of more than 8 million hectares of South America forests and rivers. Lead author is personally inspired and honored to share a love of fly-fishing, the outdoors and conservation with Connie.

Comments. The Kuribrong River is under dramatic pressure from gold and diamond mining, and Hardman et al. (2002) noted a decrease in loricariids in the mainstem Potaro River compared to what Eigenmann (1912) found likely due to the mining there in 1998. Grass Shoals is the last rapids upstream before the base of Amaila Falls. It is a clear-flowing section of stream with ample rooted vegetation. Little mining was present this far up in the drainage at time of collection, but a recently completed road to the base of Amaila Falls will likely lead to increasing mining pressure from Grass Shoals to above the escarpment.

Figures

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

FIGURE 9. Holotype of Ancistrus kellerae in dorsal, lateral, and ventral views, CSBD F 1721, 69.9 mm SL. Scale = 1 cm. Photos by J.W. Armbruster.

FIGURE 10. Live coloration of the holotype of Ancistrus kellerae in dorsal and lateral views, CSBD F 1721, 69.9 mm SL. Scale = 1 cm. Photos by J.W. Armbruster.