Hypostomus ancistroides (Ihering, 1911)

Osvaldo T. Oyakawa, Alberto Akama & Angela M. Zanata, 2005, Review of the genus Hypostomus Lacépède, 1803 from rio Ribeira de Iguape basin, with description of a new species (Pisces, Siluriformes, Loricariidae)., Zootaxa 921, pp. 1-27 : 10-14

Hypostomus ancistroides (Ihering, 1911)

(Fig. 4, 5; Table 1)

Plecostomus ancistroides Ihering, 1911 :396 (type locality: rio Tatuhy, afluente do lado esquerdo do rio Sorocaba; rio Piracicaba, Estado de São Paulo).

Material examined: Brazil. São Paulo: - MZUSP 51988, 2, 127.0-154.0 mm SL; rio Juquiá, Cachoeira do França waterfall, Juquitiba; M. D. Domingos; May 1997. - MZUSP 78734, 3, 34.1-52.6 mm SL; ribeirão das Laranjeiras, approx. 23° 50' 39.5"S, 47° 3' 13.5"W, São Lourenço; Projeto Biota/Fapesp Ribeira, 23 October 2001. - MZUSP 78435, 14, 25.9-92.3 mm SL; tributary of rio São Lourenço, near Bairro da Serraria, on the road to São Lourenço, approx. 23° 52' 43.2"S, 46° 59' 42.1"W, Juquitiba, Projeto Biota/ Fapesp Ribeira; 23 October 2001. - MZUSP 78436, 71 (19), 25.9-164.0 mm SL; tributary of Ribeirão das Laranjeiras, on the road to São Lourenço, approx. 23° 50' 45.6"S, 47° 4' 58.7"W, Juquitiba; Projeto Biota/Fapesp Ribeira, 23 October 2001. - MZUSP 79000, 1, 95.2 mm SL; Ribeirão da Barrinha, tributary of rio São Lourenço, approx. 23° 52' 23.3"S, 46° 55' 56.5"W, São Lourenço; Projeto Biota/Fapesp Ribeira, 26 June 2002 - MZUSP 79001, 5, 41.6-112.2 mm SL; tributary of Ribeirão do Chiqueiro, near the Fish Farm Araponga, approx. 23° 48' 11.0"S, 46° 55' 46.8"W, São Lourenço; Projeto Biota/ Fapesp Ribeira; 26 June 2002.

Diagnosis. Hypostomus ancistroides can be distinguished from its congeners inhabiting Ribeira de Iguape river basin by the absence of plates on ventral surface of head (versus ventral region of head completely covered with dermal ossifications), exclusive color pattern represented by spots on posterior half of body less conspicuous and more sparsely distributed than on anterior portion of body, and exclusive presence of aligned spots on fins, sometimes forming dark bands.

Description: Standard length of examined specimens 25.9 to 164.0 mm SL. Counts and proportional measurements presented in Table 1. Dorsal profile slightly convex, raising somewhat abruptly upward from snout tip to dorsal-fin origin, and gently descending from this point to the end of caudal peduncle. Caudal peduncle roughly ovoid in cross-section; slightly flattened on ventral portion. Dorsal plates between end of dorsal-fin base and adipose-fin spine flattened. One preadipose plate.

Pre-dorsal region of trunk located between pterotic-supracleithrum and vertical through dorsal-fin origin covered by three horizontal series of plates that extends posteriorly to caudal fin. Median series of plates bearing the lateral-line canal. Mid-dorsal series situated above and mid-ventral series situated below median series. Dorsal series of plates starting at dorsal-fin origin. Ventral series of plates starting after the insertion of the posterior-most pelvic-fin ray. Plates of mid-dorsal series not aligned, interrupted by first plate of dorsal series (Fig. 1B). Covering of abdomen ontogenetically variable; completely naked in specimens around 60.0 mm SL or smaller; usually covered with minute platelets, leaving naked areas around the pelvic fin that extends antero- and posterolaterally in larger specimens.

Body with four keels along flanks. Dorsal-most keel situated over dorsal series of plates. Keel on mid-dorsal series of plates interrupted, following the alignment of plates. Anterior portion of this keel somewhat continuous with ridge on pterotic-supracleithrum, crossing the plates of mid-dorsal series of pre-dorsal region of trunk, becoming somewhat posterodorsally oriented and not aligned to keel on plates of posterior portion of mid-dorsal series. Keel on median series of plates poorly developed. Mid-ventral series with keel more developed on anterior-most six plates.

Head somewhat triangular, rounded anteriorly. Dorsal region of head completely covered with dermal ossifications, except for naked area on snout tip that continues ventrally to reach margin of upper lip. Ornamentation of pterotic-supracleithrum distinct from remaining surface of head and with odontodes more sparsely distributed. Ventral area of head completely naked. Dorsal margin of orbit slightly elevated, continuing in a low ridge on pterotic-supracleithrum. Specimens larger than 63.0 mm SL with a prominent ridge on supraoccipital, diverging in two separated ridges on predorsal plates. One or two plates bordering posterior margin of supraoccipital bone. Space between orbits almost straight or slightly convex. Eyes large.

Mouth rounded. Anterior-most row of papillae on inner face of lower lip roundish and sparsely distributed, followed by patch of smaller, closer papillae, decreasing in size posteriorly. Teeth long and bicuspid; medial cusp approximately twice in length of outer cusp and curved inward. Premaxillary teeth inserted in a relatively straight line; contralateral dentary row of teeth inserted in a relatively acute angle. Maxillary barbels long, slightly larger than eye diameter, and without papillae.

Dorsal-fin origin situated on vertical anterior to pelvic-fin origin, approximately on posterior third of pectoral-fin spine. Dorsal fin relatively small; tips of the adpressed last three rays ending at second plate before the adipose-fin spine. Margin of dorsal fin relatively straight or slightly convex. Adipose-fin spine compressed, somewhat straight. Distal half of pectoral-fin spine of specimens larger than 70.0 mm SL covered dorsally with small odontodes slightly curved forward. Tip of adpressed pectoral fin slightly beyond origin of pelvic fin. Tip of pelvic fin beyond origin of last branched anal-fin ray. Basal lamina of first proximal radial of anal fin covered by skin in the majority of specimens examined. Caudal fin margin concave, lower spine longer than upper.

Color in alcohol. Dorsal and lateral surface of body with light brown ground coloration. Body covered with roundish black or dark brown spots. Spots on portion of body anterior to dorsal-fin insertion relatively small, close together and decreasing in size over snout. Spots on portion of body posterior to dorsal-fin insertion sparsely distributed, comparatively larger (sometimes occupying area beyond the limits of one plate). Some plates of this region without spots. Area below mid-ventral keel commonly with spots. Ventral surface of body yellowish, clear in smaller specimens and usually with scattered well defined large dark spots in specimens around 90.0 mm SL or larger. Ventral portion of caudal peduncle with median horizontal dark stripe continuing posteriorly from anal fin, bordered by clear areas. Overall ground coloration of all fins light brown or pale orange with dark brown spots in spines, rays and interradials membranes. Spots over fins usually similar in size to those distributed over trunk. Spots usually distributed in series on all fins. Some specimens have spots over pelvic, caudal, and more often on dorsal fin merged to each other forming well defined bands.

Distribution and notes. Hypostomus ancistroides is herein reported for the first time to occurs in Ribeira de Iguape river basin. Previously, H. ancistroides was only known to occur in Upper Paraná river basin. Recent collecting efforts, mainly focused on the ongoing project “Fish Diversity of the Headwaters and Streams of the Ribeira de Iguape River”, revealed that the species in the area of interest is restricted to small rivers close to the watershed with the Upper Paraná river basin, at 700 to 800 m above sea level (Fig. 5). Hypostomus ancistroides represents the smallest species of Hypostomus from Ribeira de Iguape basin.