Ancistrus caucanus Fowler 1943
Creators: name: Taphorn, Donald C.
name: Armbruster, Jonathan W.
name: Villa-Navarro, Francisco
name: Ray, C. Keith
Publisher: name: Zenodo
Year: 2013
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Actinopterygii
Siluriformes
Loricariidae
Ancistrus
Ancistrus caucanus

description: Ancistrus caucanus Fowler 1943
(Figs. 1 and 2)
Ancistrus caucanus, Fowler 1943: 253, figs. 40–43. Type locality: Sonsón, Cauca River basin, Colombia (see comments below). Holotype: ANSP 70516. Böhlke 1984:122 Type catalog Isbrücker 1980; Burgess 1989; Isbrücker 2001; Isbrücker 2002; Fisch-Muller 2003 (list); Maldonado-Ocampo et al 2005 (species account based on Fowler’s original description); Ferraris 2007 (list).
Diagnosis. Ancistrus caucanus can be diagnosed from the other species in the Magdalena drainage (A. tolima n. sp. and A. vericaucanus n. sp.) by having: the pectoral fin tip extending to posterior half of pelvic-fin base when depressed ventral to pelvic fin (vs. maximally reaching to pelvic-fin spine); usually just one preadipose plate (vs. usually two to three in A. vericaucanus and 3–5 in A. tolima); the depressed dorsal fin usually reaching to the preadipose plate just anterior to adipose-fin spine (vs. not reaching); by having a pectoral spine length to predorsal length ratio of 58.6–70.4 (vs. 47.5–58.8 in A. vericaucanus) and 46.9–57.3 in A. tolima; Fig. 3 A); and from A. vericaucanus by having a dentary tooth cup length to SL ratio of 5.9–7.7% (vs. 4.7–5.3%; Fig. 3 B). Ancistrus caucanus can further be separated from A. chagresi by having no well-defined white spots on the caudal fin (vs. well-defined white spots present); from A. centrolepis by lacking one to three rows of enlarged odontodes on the lateral plates and no odontodes on lateral plates longer than half the width of the supporting plate (vs. rows of odontodes present with some odontodes almost as long as the supporting plate is wide); from A. galani by having fully developed eyes and pigment (vs. eyes reduced and pigment absent or reduced); and from A. martini by having a snout length to head length ratio of 45.9–54.9% (vs. 55.5–65.3%), a head-eye length to snout length ratio of 72.9– 88.0% (vs. 53.9–73.9; Fig. 3 C), irregular dark spots on the fins relatively large, separated by lighter spaces, forming what appear a four to five irregular bands on the caudal fin (specimens are in a poor state of preservation; vs. six to nine irregular bands) and four to six spots along the pectoral-fin spine (vs. seven to nine spots).
Description. N=18. Morphometrics given in Table 2. Size range this study: 47–66 mm SL.
A relatively small Ancistrus, body broadest anteriorly, greatest body width near opercles, then narrowing progressively to end of caudal peduncle. Head and body depressed, greatest body depth between level of pectoralfin insertions and dorsal-fin origin. Caudal peduncle deep, robust, compressed posteriorly. Dorsal profile of head and body ascending steeply in convex arc from tip of snout tip to dorsal-fin origin, from there, descending in straight line or gently convex arc sloping gradually down to just posterior to tip of adipose-fin spine, then angled dorsally 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 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 about one-half 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. Dentary tooth row straight, about same size as premaxillary tooth row. Teeth numerous (49–80 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, but equal in worn teeth. Hypertrophied cheek odontodes strongly evertible, 10–25, stout with tips hooked anteriorly, bases encased in thick fleshy sheaths. Exposed part of opercle roughly an elongate triangle with few short stout 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.
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, middorsal and mid-ventral plate series end on caudal peduncle beneath adipose fin. Last plate in median series slightly smaller than penultimate plate, base of caudal fin with vertical column of about four small platelets after main series, and about eight roughly triangular 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. Dorsal-fin base length about equal to dorsal-adipose distance. Adipose fin stout, angled up from body, membrane visible beneath spine. Pectoral spine short, stout, 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, 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.
Mid-dorsal plates 14(3), 15(6), 16(4), 17(1), 18(2), 19(2); median plates 22(6), 23(10), 24(1), 25(1); midventral plates 16(2)17(8), 18(8); plates bordering dorsal-fin base 7(14), 8(4); plates between dorsal and adipose fins 3(2), 4(6), 5(3), 7(6), 8(1); preadipose plates 1(9), 2(5), 3(2),4(2). Fin-ray formulae (N=18): dorsal i,7; pectoral i,6; pelvic i,5; anal i,3(4) i,4 (14); caudal i,14,i. Caudal procurrent spines dorsal: 4(2), 5(16), ventral: 3(18).
Color in alcohol. (Fig. 1) Base color of body brown or gray, with darker brown and lighter spots, especially noticeable dorsally on snout and top of head in freshly preserved material (spots fade with time). Ventrum brown or tan with traces of large, irregular light spots in freshly preserved specimens. All fins have dark spots separated by lighter areas present on spine and branched rays that align to form curved, transverse bands on the dorsal, caudal, pelvic and pectoral fins. Ventral surface of head and abdomen whitish tan.
Life Colors. (Fig. 2) Dorsum dark greenish brown with light green spots concentrated on soft nose and top of head. Body posterior to dorsal-fin base with patch of three-four light brown plates; upper margin of posterior caudal peduncle (adjacent to caudal fin) light brown. Tentacles and soft nose dark olive green with lighter green spots. Ventrum dark olive green with light (whitish or light green) irregular spots and vermiculations, abdomen and chest darker green than ventral portion of caudal peduncle behind anal-fin origin. Oral disk whitish. Fin membranes transparent, but spines and rays marked with three-four alternating dark olive green and whitish or light green sections. Caudal peduncle with light vertical bar adjacent to caudal fin. Caudal-fin spine and rays with alternating light and dark sections often aligned to form three-four vertical bars, distal margin of fin hyaline. Ridges of lateral body plates light, in contrast with dark olive green to blackish base color, forming pattern of oblique dark bars along sides.
Distribution. Magdalena River drainage, Colombia (Fig. 4).
Remarks. For many years, this species was known only from the holotype, but recent collecting reveals that it is still present in the Magdalena River drainage. Because the holotype and several other specimens collected with it grouped in our morphological analyses with specimens collected from the Magdalena River drainage but not with any specimens collected from near the type locality in the adjacent Cauca River drainage, this suggests that the type locality is in error. The holotype was collected by Brother Niceforo Maria, reportedly from Sonsón, Colombia in the Cauca River basin; however, it is known that some of the localities of Niceforo Maria are in error. In loricariids, one of us (JWA, pers. obs.) has identified Plecostomus argus as being a member of the trans-Andean Hemiancistrus annectens group, but whose type locality is given as Villavicencio in the Meta drainage, and clearly this is not possible. The town of Sonsón is situated near the watershed divide between the upper Cauca and Magdalena river drainages, and it is feasible that collectors based there could have collected in tributaries of either river without venturing far from town. Our data indicate that the holotype and USNM specimens mentioned here were most likely collected in the Magdalena basin. Because this species is named for the Cauca River (which flows for most of its length independent of the Magdalena River), but apparently does not occur there, this now creates a very confusing situation.
description: Published as part of Taphorn, Donald C., Armbruster, Jonathan W., Villa-Navarro, Francisco & Ray, C. Keith, 2013, Trans-Andean Ancistrus (Siluriformes: Loricariidae), pp. 343-370 in Zootaxa 3641 (4) on pages 346-350, DOI: 10.11646/zootaxa.3641.4.2, http://zenodo.org/record/219655