Ancistrus alga ( Cope, 1872 )

Provenzano, Francisco & Barriga-Salazar, Ramiro, 2018, Species of Ancistrus (Siluriformes, Loricariidae) from Ecuador, with the description of a new species from the Amazon River Basin, Zootaxa 4527 (2), pp. 211-238 : 217-222

Ancistrus alga ( Cope, 1872)

Tables 2, 5 Figures 2 , 3 , 5

Chaetostomus alga Cope, 1872 . Proceedings of the Academy of Natural Sciences of Philadelphia, v. 23:287, Pl. 15 (fig. 3).

Ambyiacu (Ampiyacu?) River, Peru. Syntypes: ANSP 16461-62 (2). Chaetostomus tectirostris Cope, 1872 . Proceedings of the Academy of Natural Sciences of Philadelphia v. 23:288, Pl. 15 (fig.

2). Ambyiacu (Ampiyacu?) River, Peru. Syntypes: ANSP 8298 (1), 8300 (1). Ancistrus alga Isbrücker, 1980:66 . Ortega & Vari, 1986:16. Burgess, 1989:436. Isbrücker, 2001:25, 26. Isbrücker, 2002:11. Ancistrus tectirostris Isbrücker, 1980:73 . Ortega & Vari, 1986:16. Burgess, 1989:437. Isbrücker, 2001:25, 26. Isbrücker,

2002:12.

Material examined. All from Ecuador. Orellana province: MEPN-460, 1, 110.1 mm SL, Quebrada Cotoyacu, 01°00’31”S 75°26’12”W, R. Barriga & K. Galacatos, 15 June 1996. MEPN-829, 1, 119.0 mm SL, Quebrada

Tambococha, 00°57’34”S 75°26’26”W, R. Barriga & K. Galacatos, 26 February 1996. MEPN-1308, 5, 60.0– 125.8 mm SL, Tributario norteño del río Tiputini , a unas 1.5 horas en canoa motorizada, aguas arriba de la boca en el río Napo, 00°44’53”S 75°47’41”W, D. Stewart, R. Barriga & M. Ibarra, 28 October 1981 . MEPN-2544, 7, 105.4– 148.1 mm SL, Río Gabarón afluente del río Nashiño , pozo OBE, bloque 31, 01°12’04”S 75°48’48”W, R. Barriga, 0 8 March 1998 . MEPN-14853, 1, 115.1 mm SL, Laguna Muyuna, km 12.5 de Chiroisla en el río Tiputini , 00°42’35”S 75°55’54”W, R. Barriga & José Pinargote, 20 June 2006 . Pastaza province: MEPN-10348, 1, 76.9 mm SL, Pavacachi, Río Curaray , 01°34’33”S 76°21’24”W, G. Herrera, March 1963 . Sucumbíos province: MEPN- 2273, 1, 109.9 mm SL, Río Aguarico, tributario norteño del río Yanayacu at Puerto Loja, 00°53’00”S 75°13’42”W, R. Barriga & D. Stewart, 24 May 1998 . MEPN-13896, 1, 131.4 mm SL, Laguna Imuya, junto al río Lagartococha, campamento Transturi , 00°36’07”S 75°14’27”W, R. Barriga & E. Medina, 0 1 May 1993 . MEPN-15169, 2, 112.14– 160.9 mm SL, Canal de la laguna Zancudococha , 00°35’00”S, 75°30’00”W, R. Barriga, 30 October 1994 .

Diagnosis. Ancistrus alga can be distinguished from other species that inhabit Amazonian Andean piedmont rivers, except A. latifrons and A. malacops , by its mandibular ramus length which fits 3.1–4.0 times in the interorbital width. In A. bufonius , A. marcapatae , A. montanus , A. heterorhynchus , A. boliviana , A. megalostomus , A. occloi , A. greeni and A. shuar the mandibular ramus length fits fewer than 3.0 times in the interorbital width. It differs further except from A. latifrons , A. megalostomus and A. shuar by its interorbital width which fits 1.8–2.3 times in head length. In A. bufonius , A. malacops , A. jelskii , A. marcapatae , A. montanus , A. heterorhynchus , A. boliviana , A. occloi and A. greeni , interorbital width fits more than 2.35 times in head length. In A. lineolatus and A. tamboensis , it fits less than 1.7 times in head length. Ancistrus alga can be distinguished from A. latifrons and A. hoplogenys (last one according the image available at ACSI image database) by the color pattern, its body and fins are dark brown or black with very small white dots vs. uniform black, and uniform brown yellowish, respectively. The shape of caudal fin of A. alga is lunate vs. oblique truncate in A. hoplogenys . Among the species caught in eastern Ecuador ( A. malacops and A. shuar ), it is easily recognized by having a massive head and anterior region of the body; cleithral width 34.3%–36.2% SL vs. 27.9–31.8% SL in A. malacops and 30.3%–32.5% SL in A. shuar . Interorbital width 17.5%–20.5% SL vs. 13.4%–16.4% SL in A. malacops and 14.4%–17.0% SL in A. shuar . In males, the values are higher, cleithral width 35.3%–36.2% SL vs. 27.8%–30.2% SL in A. malacops and 30.7%– 32.5% SL in A. shuar . Interorbital width 20.1%–20.5% SL vs. 13.5%–15.7% SL in A. malacops and 15.4%–17.0% SL in A. shuar ( Table 5). Also, the color pattern of A. alga , black or dark brown with very minute white dots on body and fins is distinctive when compared with other species ( Figs. 2 , 5 ).

Description. Morphometric data given in Tables 2 and 5. Body robust, depressed anteriorly and progressively become compressed posteriorly. Caudal peduncle compressed, deep and, robust. Dorsal profile of body from tip of snout through dorsal-fin origin gently convex, then descending in straight line to adipose-fin origin. From this point to caudal-fin origin straight and horizontal. Ventral profile of body flat and straight or slightly concave. Ventral surface of head and belly naked until anal-fin origin. Urogenital papilla is not usually visible, in some mature males opening is partially visible just posterior to anus ( Figs. 2 , 5 ).

Head massive, very wide and depressed. In dorsal and lateral view, this species shows a massive head compared with the other two species. Snout partially naked with or without fleshy cylindrical tentacles branched or not, its contour semicircular. In males, naked area wider but does not reach nares or orbits. Females have only a narrow naked strip on snout border. Nostrils juxtaposed and closer to eyes than tip of snout. Eyes in dorsolateral position, orbits not raised and without odontodes. Interorbital space is broad and flat. Supraoccipital flat without ridges, posterior border straight and truncate. Movable hypertrophied cheek odontodes well developed, specimens can have from eight to twelve. The size of these odontodes also is variable in each specimen, the longest odontode nearly extends to pectoral-fin origin independently of size of specimen. Anteriorly, base of movable hypertrophied odontodes has covering plates. Opercular bone has an exposed surface easily visible externally, its lateral margin carries odontodes ( Figs. 2 , 5 ).

Mouth oval or rounded. Upper lip narrow, usually cover premaxilla and only external surface is visible, edge is almost horizontal and with very minute undulations. The internal surface papillose. Lower lip broad, its border with very minute undulations. Lower lip surface papillose. Papillae smaller near border of lip increasing in size near lower jaws. Papillae of anterior lip have similar size from those near lower jaws. Maxillary barbels evident and free. Upper and lower jaws with similar length. The hemimandibles are straight, placed horizontally or forming a V between them. Teeth numerous and minute. Between 65 to 80 teeth in each hemimandible. Premaxillary and dentary teeth with same size. Teeth incisor type, asymmetrically bifid, medial cusp longer and wider than lateral cusp. Medial cusp rounded or straight truncated, lateral cusp pointed. Tooth apex curved toward interior of mouth. Tooth apex yellowish, stalk whitish. Premaxillary and dentary without posterior papillae or ornamentation.

Lateral line plates 23–24. Post-anal plates 11–12. Six plates between dorsal-fin and adipose-fin, all plates without keels. Origin dorsal-fin is anterior to vertical passing through pelvic-fin origin. Dorsal-fin with one spine, followed by seven branched rays; when depressed reaching adipose-fin origin. Adipose-fin well developed and always present. Spine of adipose-fin wide, and curved. Pectoral-fin with one spine, and six branched rays. When depressed, spine of pectoral-fin reaches half, (females and males) of pelvic-fin spine length. Spine and first branched ray of pectoral-fin with same length. Distal region of pectoral-fin spine with enlarged odontodes, more developed in males, and a small fleshy prominence. Pelvic-fin with one spine and five branched rays; its posterior margin surpassed anal-fin base when depressed. Anal-fin with one flexible spine and four branched rays. Caudalfin rays i,14,i. Posterior border of caudal-fin concave.

Sexual dimorphism. Adult males have a wide naked area on snout, with developed (long) and branched fleshy tentacles. Tentacles are arranged in the following pattern: Along snout edge a row of tentacles, long and conical are present, those at snout tip are longest and branched. Dorsal midline with two or three tentacles very long, branched or not. Anterior the nares, the dorsal midline row of tentacles split in three or two tentacles on each side. The tentacles near midline can show ramifications, while the laterals are just conical. On each side of head, from snout edge to near eyes, another row of three or four, conical tentacles is present, passing in front of cheek odontodes ( Fig. 5 ). Some cataloged lots have adult males with small or very small fleshy tentacles. Females possess a narrow naked anterior stripe on snout, as in females of the other species analyzed. On the naked strip, a single row of small, conical fleshy tentacles is present, from one side to the other side. The two central tentacles a bit longer, and occasionally, conical tentacles have bifid or branched tip ( Figs. 2 , 3 ).

Color. Head, and dorsolateral body surface dark brown to black with very small dots, white or whitish, sometimes faded or difficult to observe. Belly slightly paler than sides of the body; with very small dots, white or whitish, generally more evident. All fins uniform black, with minute white dots spaced on interradial membranes. In juveniles, the dots on dorsal-fin membrane are relatively larger. Dorsal-fin with black spot between bases of spine and the first branched ray ( Figs. 2 , 5 ).

Geographical distribution. The species inhabits the northeastern part of the country, in Sucumbíos and Orellana provinces, in systems that drain to the Napo River. There is one sample (juvenile) that comes from the Curaray River, in Pastaza province; apparently this locality may be the southern limit. On the other hand, there are no samples from the Napo province, these results seems to indicate that the species has a preference for low altitudes in the drainages ( Fig. 8 ).

Figures

FIGURE 2. Females of Ancistrus species, lateral view. From top to bottom: A. shuar, MEPN 17983, 93.9 mm SL. A. alga, MEPN 15169, 160.9 mm SL. A. clementinae, MEPN 5996, 100.1 mm SL. and A. malacops, MEPN 7804, 93.4 mm SL.

FIGURE 3. Ventral view of the head of females to show the presence (arrows) or absence of soft, fleshy tentacles on snout. A) A. clementinae, MEPN 5996, 100.1 mm SL. B) A. malacops, MEPN 7804, 93.4 mm SL. C) A. alga, MEPN 15169, 160.9 mm SL, D) A. shuar, MEPN 17983, 93.9 mm SL.

FIGURE 5. Ancistrus alga, MEPN 14853, 115.1 mm SL, male. From top to bottom, lateral, dorsal, and ventral view.

FIGURE 8. Map of Ecuador showing the geographical distribution of the species. A. shuar, star. A. alga, square. A. clementinae, circle. A. malacops, triangle. Symbols may represent more than one lot.