Comprehensive Description

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Hypostomus interruptus (Miranda-Ribeiro)

(Fig. 5, 6; Table 2)

Plecostomus interruptus Miranda-Ribeiro, 1918 ZBK :632 (type locality: rio Juquiá . Restricted by Britski, 1969:209 to rio Juquiá , Fazenda Poço Grande). Gosline, 1945:81 [reference, distribution]. Fowler, 1954:184 [reference, distribution]. Britski, 1969:209 [catalogue, distribution].

Hypostomus interruptusIsbrücker , 1980:25 [reference, distribution]. Burgess, 1989:431 [reference, distribution]. Isbrücker , 2001:28 [reference]. Weber, 2003:358 [reference, distribution]. Armbruster, 2004:79 [reference].

Hypostomus cf. affinis (Steindachner, 1877) . Bizerril & Lima, 2000:107 [reference].

Hypostomus sp. 1161 Montoya-Burgos, 2003 [biogeography, molecular phylogeny].

Holotype. Brazil. São Paulo: MZUSP 2110, 121.0 mm SL; rio Juquiá , Fazenda Poço Grande, Juquiá ; W. J. Moenkhaus, 1898.

Other material examined. Brazil. São Paulo: - MZUSP 68172, 2, 166.0 - 202.8 mm SL; rio do Queimado, tributary of rio Jacupiranguinha, Parque Estadual do Jacupiranga, approx. 24° 48' 2,2"S, 48° 13' 32,0"W, Cajati; Projeta Biota/Fapesp Ribeira, 9 March 2001. - MZUSP 68192, 4, 32.3-46.6 mm SL; MZUSP 68196, 7, 32.4-55.7 mm SL; same data as above. - MZUSP 75463, 7, 41.8 - 140.0 mm SL; ribeirãoBraço Bonito, tributary of rio Areado, Parque Estadual da Serra do Mar, Núcleo Pedro de Toledo, approx. 24° 14' 59"S, 47° 10' 46"W, Itariri; Projeta Biota/Fapesp Ribeira, 13 September 2001. - MZUSP 75464, 3, 42.7-77.1 mm SL; RibeirãoBraço Bonito, tributary of rio Areado, Parque Estadual da Serra do Mar, Núcleo Pedro de Toledo, approx. 24° 15' 5,0"S, 47° 10' 35,0"W, Itariri; Projeta Biota/Fapesp Ribeira, 13 September 2001. - MZUSP 78706, 1, 33.5 mm SL; Ribeirão Grande creek, Bairro Ribeirão Grande, Parque Estadual da Serra do Mar, Núcleo Pedro de Toledo, approx. 24° 14' 7;0"S, 47° 13' 58,0"W, Pedro de Toledo; Projeta Biota/Fapesp Ribeira, 11 September 2001. - MZUSP 78707, 1, 54.0 mm SL; tributary of rio Itariri, on the road from Manoel da Nóbrega to Santa Rita, approx. 24° 12' 37,0"S, 47° 17' 23,0"W, Pedro de Toledo; Projeta Biota/Fapesp Ribeira, 14 September 2001. - MZUSP 51913, 4 (2), 104.3-108.9 mm SL; rio Saibadela, Saibadela Base Camp of Fazenda Intervales, Sete Barras; S. Buck et al., 4-6 March 1994. - MZUSP 70693, 1, 43.5 mm SL; rio das Criminosas, tributary of rio Catas Altas, Itapirapuã Paulista, approx. 24 º 34' 16,7"S, 48º 10' 22,4"W; Projeto Biota/Fapesp Ribeira, 09 August 2001. - MZUSP 37992, 1, 149.0 mm SL; rio Pardo, tributary of rio Turvo, Água do Padre district, Barra do Turvo; O. T. Oyakawa et al., 22 July 1987. - MZUSP 40003, 4, 83.7-96.5 mm SL; riacho Arataca, tributary of rio Jacupiranga, at road Pariquera - Açu to Iguape, Pariquera-Açu ; O. T. Oyakawa et al., 28 March 1987. - MZUSP 45410, 1, 117.0 mm SL; rio Pilões , tributary of rio Ribeira de Iguape, Eldorado; M. Damato, 7 March 1993. - MZUSP 45457, 1, 202.3 mm SL; rio Ribeira de Iguape, close to rio Batatal, Eldorado; M. Damato, 5 March 1993. - MZUSP 51981, 21 (5), 75.9-169.4 mm SL; rio Betari, Serra district, Iporanga; R. Pardini, 16 February 1995. - MZUSP 52636, 2, 116.5-180.5 mm SL; rio Betari, bellow rio Águas Quentes, Águas Quentes cave, Serra district, Iporanga; S. Buck et al., 26 January1995. - MZUSP 52639, 3, 141.3-178.0 mm SL; rio Betari, Serra district, Iporanga; S. Buck et al., February 1995. - MZUSP 52455, 1, 124.0 mm SL; rio Ribeira de Iguape, close to rio Batatal, Eldorado; M. Damato, 5 March 1993. - MZUSP 46066, 7, 75.9-120.7 mm SL; rio Betari, Iporanga; R. Pardini, 1993. - MZUSP 50715, 3, 118.5-150.0 mm SL; rio Betari, near of rio Ribeira de Iguape, Iporanga; S. Buck, February 1995. - MZUSP 45168, 1, 168.6 mm SL; rio Batatal, tributary of rio Ribeira de Iguape, Eldorado; M. Damato, 3 March 1993. - MZUSP 55486, 1, 192.5 mm SL; rio Pilões , tributary of rio Ribeira de Iguape, Iporanga; M. R. Santos & M. Morato, 19 January 1995. - MZUSP 55217, 3, 206.1-226.8 mm SL; rio Pardo, Barra do Turvo; M. R. Santos & C. E. Espírito Santo, October 1995. - MZUSP 55214, 5, 172.8-197.2 mm SL; rio Catas Altas, Ribeira; M. R. Santos & M. Morato, 23 January 1995. - MZUSP 55487, 2, 156.5-188.8 mm SL; rio Batatal, Eldorado; M. R. Santos & M. Morato, 17 January 1995. - MZUSP 55482, 2, 155.4-189.2 mm SL; rio Pardo, Barra do Turvo; M. R. Santos & M. Morato, 25 January 1995. - MZUSP 55488, 16, 115.1-223.7 mm SL; waterfalls of rio Palmital, 1000 m above mouth into rio Ribeira de Iguape, Apiaí ; M. R. Santos & M. Morato, 22 January 1995. Paraná : - MZUSP 25010, 10, (5), 125.3-180.8 mm SL; Capivari-Cachoeira Dam, Campina Grande do Sul; L. C. Freitas, 26 August 1977. - MZUSP 54581, 236.0 mm SL; rio Pardo, Bairro Água do Padre on the road Iporanga to Barra do Turvo, Barra do Turvo; O. T. Oyakawa, F. Langeani & V. C. Silva, February 1988. - MZUSP 79558, 49, 21.2- 39.1 mm SL, Arroio Taquaral, tributary of rio Açungui , Campo Largo, 25º 24' 50.3" S, 49º 38' 31.8" W; Projeto Biota/Fapesp Ribeira, 19 May 2002. - MZUSP 79559, 9, 30.5-47.5 mm SL; Arroio 3 Barras, tributary of rio Ponta Grossa, 24º 50' 14.8"S, 49º 15' 51.2"W; Cerro Azul; Biota/Fapesp Ribeira, 20 May 2002.

Diagnosis . Hypostomus interruptus is distinguished from its congeners inhabiting rio Ribeira de Iguape basin by its oblique dark bands on flanks (versus absence of such bands), comparatively smaller spots over body and fins, more so over anterior portion of head, and spots on region of trunk posterior to dorsal-fin end more conspicuous in smaller specimens (up to 130.0 mm SL), becoming faded or absent in larger specimens (versus color pattern of trunk relatively homogeneous throughout ontogeny).

FIGURE 6. Dorsal, lateral, and ventral views of Hypostomus interruptus , MZUSP54581, 236.0 mm SL.

Description. Standard length of examined specimens 32.3 to 236.0 mm SL. Counts and proportional measurements presented in Table 2. Dorsal profile gently raising upwards from snout tip to dorsal-fin origin and gently descending from this point to the end of caudal peduncle. Caudal peduncle roughly oval in cross-section, 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 approximately at midlength of pelvic-fin base extension. Plates of mid-dorsal series not aligned, interrupted by first plate of dorsal series (Fig. 1B). Covering of abdomen ontogenetically variable. Plates restricted to central area of abdomen in specimens up to 95.0 mm SL; in larger specimens abdomen usually covered with minute platelets, leaving a naked area just around the pelvic fin.

Plates on dorsal and lateral portion of body relatively smooth in small and median size specimens. Trunk plates of larger specimens with relatively well developed ridges, forming four keels along flanks. Dorsal-most keel located 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 middorsal series of plates on pre-dorsal region of trunk, and not aligned to keel of posterior portion of mid-dorsal series. Keel on median series of plates poorly developed. Keel on three dorsal-most horizontal series of plates usually starting at dorsal-fin origin, except by largest specimens examined that have those keels more conspicuous posterior to the vertical through insertion of sixth branched dorsal-fin ray. Mid-ventral keel well developed, more conspicuous on anterior half of trunk.

Head somewhat triangular, rounded anteriorly. Dorsal and ventral region of head completely covered with dermal ossifications, except for a small oval naked area on snout tip. Outer face of upper lip covered with small platelets, except small specimens that have most of this region naked (smaller than 100.0 mm SL). Ornamentation of pterotic-supracleithrum similar to the remaining surface of head and with odontodes densely distributed. Dorsal margin of orbit slightly elevated, continuing in a low ridge on pterotic-supracleithrum. Larger specimens with a low ridge on supraoccipital, diverging in two weakly developed separated ridges on predorsal plates. Usually two plates, sometimes one, bordering posterior margin of the supraoccipital bone. Space between orbits almost straight or slightly convex. Eyes large.

Mouth wide, rounded. Anterior-most papillae of inner face of lower lip irregular in form, somewhat elongate, followed by roundish papillae decreasing in size posteriorly. Teeth long and bicuspid; medial cusp approximately twice in length of outer cusp and curved inwards. Premaxillary teeth inserted in a relatively straight line; dentary teeth inserted in a concave arch facing mouth cavity; contralateral dentaries forming a relatively wide angle. Maxillary barbels relatively thin, elongated, slightly shorter 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 adpressed last two rays ending on second or third plate anterior to adipose-fin spine. Margin of dorsal fin relatively straight . Adipose-fin spine compressed, moderately strong with posterior-most portion curved ventrally in specimens around 150.0 mm SL and straight in smaller specimens. Distal half of pectoral-fin spine of larger specimens covered dorsally with small odontodes slightly curved forward (larger than 110.0 mm SL). Tip of adpressed pectoral fin beyond origin of pelvic fin. Tip of adpressed pelvic-fin spine reaching origin of anal fin in larger specimens and posterior to origin of the last branched ray in small specimens (up to 180.0 mm SL). Basal lamina of first proximal radial of anal fin covered by skin in the majority of specimens examined, except in a few small specimens. Caudal fin margin concave, lower spine slightly longer than upper.

Color in alcohol. Dorsal and lateral surface of body with light brown or grayish ground coloration. Relatively small black or dark-brown roundish spots scattered all over dorsal and lateral surface of body, becoming gradually smaller towards anterior portion of head. Spots on region of trunk posterior to dorsal-fin end more conspicuous in smaller specimens (up to 130.0 mm SL), becoming faded or absent in larger specimens. Lateroventral portion of body below mid-ventral series of plates without spots on specimens 150.0 mm SL or larger. Four dark brown inconspicuous oblique bands on flanks, more visible in juveniles; dorsal portion of anterior-most band aligned with base of first three branched dorsal-fin rays; anterodorsal margin of second band aligned with insertion of last one or two dorsal-fin rays; third band located immediately posterior to dorsal-fin end and last band over posterior portion of caudal peduncle. Ventral surface of body pale or yellowish, usually clear except in some juveniles that have the ventral surface scattered with spots similar to those on body. Overall ground coloration of all fins pale to yellowish; recently fixed specimens pale orange. Dark brown or black spots larger than those of body sparsely distributed over fin rays and interradial membranes; pattern of distribution usually forming series when fins erected in specimens 180.0 mm SL or smaller. Caudal-fin spots arranged in irregular vertical series. Ground color of living specimens usually darker than alcohol preserved specimens and pattern of the four oblique bands more conspicuous.

Distribution and notes. Hypostomus interruptus is known to occur only in Ribeira de Iguape river basin. Sampling efforts in this region in the last ten years suggests Hypostomus interruptus as the most common Hypostomus ZBK in the area. This conclusion involves the high number of individuals collected, high diversity of environments inhabited, and wide geographical distribution of this species (Fig. 5). Hypostomus interruptus was found in relatively large rivers as exemplified by the rivers Ribeira, Pilões , Catas Altas, Pardo, and also in smaller drainages as Betari, Saibadela, Arataca, a tributary of rio Jacupiranga, and Braço Bonito, a tributary of rio SãoLourenço . The area of occurrence of H. interruptus varies from 165 to 900 m above sea level.


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