Ancistrus, Kner, 1854

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 : 8-9

Key to the species of Ancistrus from the northwestern Guiana Shield, Orinoco Andes, and adjacent basins

1. No well-defined dark spots on fin spines, fin rays or fin membranes alternating with lighter spots; tiny (the largest usually less than 1/2 the diameter of the pupil of eye) white, yellow or greenish dots on abdomen, sides, dorsum or fins when alive, usually lost after some time in preservative in which case they may appear entirely dark................................... 2

1’. Spines, rays or membranes of fins with alternating dark and light spots, often arranged in rows; body and/or fins usually (but not always visible in preserved material) with larger white spots or blotches, some of which are larger than diameter of pupil of eye................................................................................................. 7

2. Body dorsoventrally flattened. Eyes placed dorsally or slightly dorsolaterally. Last plate in median series below adipose fin just slightly taller than wide............................................................................. 3

2’. Body deep. Eyes placed mostly laterally. Last plate in median series below adipose fin about twice as tall as wide......... 4

3. Medial section of the interorbital space higher than orbital ridge. Plated area of the snout of nuptial males pointed medially. Pelvic fin reaching to nearly the end of the anal fin when both fins are adpressed.......... A. lithurgicus Eigenmann, 1912

3’. Orbital ridge higher than medial section of interorbital space. Anterior border of plated area of the snout of nuptial males almost straight transversely). Pelvic fin reaching to just barely beyond base of pelvic fin… A. macropthalmus ( Pellegrin, 1912)

4. Least interorbital width divided by dentary length less than 2.................................. A. yutajae new species

4’. Least interorbital width divided by dentary length greater than 2.25.............................................. 5

5. Spots only present on head and nape. Edge of caudal fin often broad, gold band. Dark lateral stripe along sides of body with area above darker than below. Pectoral-fin spine with faint, dark spots. In nuptial males, naked area present posteromedially to the medial row of tentacles extending to anterior margin of nasal apertures and only a small plate surrounded by flesh between the nasal aperture and the posteriormost odontodes......................................... A. kellerae new species

5’. Spots present over the entire body or fins (may be completely absent in preserved specimens). Edge of caudal fin without broad, gold band. Sides uniformly dark, without lateral stripe. Pectoral-fin spine uniformly dark or with small, gold spots. In nuptial males, no naked area present posteromedially to the medial row of tentacles and several plates that abut one another between posterior tentacle and nasal aperture................................................................ 6 6. Maximum size 138 mm SL. Snout relatively long and spatulate ( Fig. 5a ), best visualized in nuptial males where the plated region of the snout forms a long, rounded triangle such that the distance between the plates and the tip of the snout (turqoise line in Fig. 5a ) is much smaller than the distance between the tip of the plated area and a line drawn between the anterior margins of the orbits (yellow line in Fig. 5a ). Tentacles of the snout bifurcating at the start of the snout plates in a V................................................................................. A. nudiceps ( Müller & Troschel,1849)

6’. Maximum size 86 mm SL. Snout relatively short and rounded ( Fig. 5b ), best visualized in nuptial males where the plated region of the snout forms a broad arc and the distance from the plates to the tip of snout (turqoise line in Fig. 5b ) is approximately equal to the distance from the tip of the plates to a line drawn between the anterior margin of the orbits (turqoise line in Fig. 5b ), and tentacles of the snout bifurcating at the start of the snout plates in a U.............. A. patronus new species

7. Body dorsoventrally flattened. Eyes placed dorsally or slightly dorsolaterally. Last plate in median series below adipose fin just slightly taller than wide. Tentacles on medial portion of the snout in nuptial males in a single column. Few white spots organized in lines down body. Dorsal saddles prominent........................................ A. leoni new species

7’. Body deep. Eyes placed mostly laterally. Last plate in median series below adipose fin about twice as tall as wide. Odontodes on medial portion of the snout in nuptial males either transversally straight anteriorly or forming a broad triangle. Spots either absent, few and randomly scattered, or numerous and scattered. Dorsal saddles absent or not very visible................ 8

8. Abdomen without spots................................................................................. 9

8’. Abdomen with white spots............................................................................. 11

9. Spots on caudal fin not organized, often combining across rows to form very elongate spots, sometimes almost half the length of the caudal fin and more than twice as long as wide.................................. A. brevifilis Eigenmann, 1920

9’. Spots on the caudal fin organized into rows, never combining across rows and never more than twice as long as wide..... 10

10. Males with tentacles that are no greater than eye diameter. Dentary length/cleithral width 23.8–28.4% in specimens greater than 69 mm SL. Minimal interorbital width divided by dentary length less than 2.1................. A. amaris new species

10’. Males with tentacles much greater than eye diameter. Dentary length/cleithral width 14.4–24.6% in specimens greater than 6 9 mm SL. Minimal interorbital width divided by dentary length usually greater than 2.1. (The only specimens that overlap with A. amaris do so because of smaller interorbital and cleithral widths, not longer jaws)... A. triradiatus Eigenmann 1918 (part)

11. Spots on dorsal fin small and confined to fin rays and not present on membranes (alternating dark and light spots)........................................................................................ A. trinitatis ( Günther, 1864)

11’. Large white spots on dorsal fin centered on membranes separated by smaller dark interspaces........................ 12

12. Adpressed dorsal fin reaching to at least the middle of the adipose-fin spine. Pectoral-fin spine when adpressed ventral to the pelvic fin reaching the base of the cloacal tube in adults. 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 (difference generally works on the abdomen as well).................................................................................... A. leucostictus ( Günther, 1864)

12’. Adpressed dorsal fin reaching maximally to middle of preadipose plate. Pectoral-fin spine when adpressed ventral to the pelvic fin not reaching the base of the cloacal tube in adults. Relatively smaller light spots and larger dark interspaces on the anterolateral plates and posterodorsal head bones with the interspaces half or greater than the diameter of the spots and the spots often obscured in this region in preserved specimens (difference generally works on the abdomen as well).............. 13

13. Spots on head and abdomen small, more than 15 across abdomen in region posterior to pectoral girdle, spots on snouts of males less than half widths of tentacle bases............................................. A. saudades new species

13’. Spots on head and abdomen large, fewer than 12 across abdomen in region posterior to pectoral girdle, spots on snouts of males almost to greater than widths of tentacle bases............................. A. triradiatus Eigenmann, 1918 (part)

Figures

FIGURE 5. Heads, dorsal view, of A. Ancistrus nudiceps AUM 35623, 140.2 mm SL and B. A. patronus, holotype, AUM 39876, 83.6 mm SL demonstrating differences in head shape and tentacle pattern. Ancistrus nudiceps has a longer, more spatulate snout with the point from the edge of medial snout plates to the end of the snout (turquoise line) much shorter than the distance from the edge of the medial snout plates to a line through the anterior margins of the orbits (yellow line, dashed line is the line that demarks the anterior borders of the orbits) while the two lengths are approximately equal in A. patronus. In addition, the anterior margin of the snout plates form a rough V in A. nudiceps and a U in A. patronus (solid white line). Scale = 1 cm. Photos by J.W. Armbruster.