Hisonotus acuen, Silva, Gabriel S. C., Roxo, Fabio F. & Oliveira, Claudio, 2014

Silva, Gabriel S. C., Roxo, Fabio F. & Oliveira, Claudio, 2014, Hisonotusacuen, a new and phenotypically variable cascudinho (Siluriformes, Loricariidae, Hypoptopomatinae) from the upper rio Xingu basin, Brazil, ZooKeys 442, pp. 105-125 : 106-112

Taxon classification Animalia Siluriformes Loricariidae

Hisonotus acuen sp. n. Figs 1, 5, 6; Table 1

Holotype.

MZUSP 115350, female, 25.9 mm SL, Brazil, Mato Grosso State, municipality of Querência, affluent of rio Toguro, rio Xingu basin, 13°00'26"S, 52°11'27"W, 01 Aug 2012, coll. C. Oliveira, M. Taylor, G.J.C. Silva & J.M. Henriques.

Paratypes.

All from Brazil, Mato Grosso State, rio Xingu basin. LBP 15755, 16, 19.5-26.0 mm SL, municipality of Ribeirão Cascalheira, affluent of rio Suiá-Missu, 12°55'36"S, 51°53'27"W, 30 July 2012, coll. Oliveira C, Taylor M, Silva GJC, Henriques JM. LBP 16274, 27, 20.2-29.1 mm SL, 2 c&s 23.6−24.2 mm SL, municipality of Gaúcha do Norte, affluent of rio Culuene, 13°27'26"S, 53°09'36"W, 03 Aug 2012, coll. Oliveira C, Taylor M, Silva GJC, Henriques JM. LBP 16275, 29, 16.7-25.2 mm SL, 2 c&s 19.3−20.8 mm SL, municipality of Querência, affluent of rio Feio, 12°33'20"S, 52°16'16"W, 31 Sep 2012, coll. Oliveira C, Taylor M, Silva GJC, Henriques JM. LBP 16276, 9, 20.7-27.9 mm SL, 2 c&s 21.2−21.4 mm SL, munici pality of Ribeirão Cascalheira, affluent of rio Suiá-Missu, 12°53'04"S, 52°02'00"W, 30 Sep 2012, coll. Oliveira C, Taylor M, Silva GJC, Henriques JM. LBP 16277, 10, 18.9-23.3 mm SL, municipality of Querência, affluent of rio Feio, 12°31'55"S, 52°20'29"W, 31 Sep 2012, coll. Oliveira C, Taylor M, Silva GJC, Henriques JM. LBP 16278, 12, 18.8-25.1 mm SL, 2 c&s 26.8−27.1 mm SL, municipality of Primavera do Leste, córrego Xavante, 14°38'24"S, 53°55'38"W, 05 Aug 2012, coll. Oliveira C, Taylor M, Silva GJC, Henriques JM. LBP 16279, 10, 20.8-26.7 mm SL, municipality of Gaúcha do Norte, affluent of rio Culuene, 13°26'32"S, 53°08'45"W, 03 Aug 2012, coll. Oliveira C, Taylor M, Silva GJC, Henriques JM. LBP 16280, 11, 17.4-24.9 mm SL, municipality of Canarana, affluent of rio Culuene, 13°25'30"S, 52°16'47"W, 01 Aug 2012, coll. Oliveira C, Taylor M, Silva GJC, Henriques JM. LBP 16281, 4, 17.5-24.6 mm SL, same collection information as holotype. LBP 16282, 5, 17.5-23.9 mm SL, municipality of Canarana, rio Coronel Vanick, 13°31'34"S, 52°43'52"W, 02 Aug 2012, coll. Oliveira C, Taylor M, Silva GJC, Henriques JM. LBP 16283, 2, 21.3-24.2 mm SL, municipality of Canarana, affluent of rio Toguro, 13°16'52"S, 52°14'42"W, 01 Aug 2012, coll. Oliveira C, Taylor M, Silva GJC, Henriques JM. LBP 16284, 3, 20.2-24.3 mm SL, collected with holotype. LBP 18845, 1, 23.7 mm SL, municipality of Gaúcha do Norte, affluent of rio Culuene, 13°30'57"S, 53°06'39"W, 03 Aug 2012, coll. Oliveira C, Taylor M, Silva GJC, Henriques JM. NUP 16444, 5, 22.2-27.1 mm SL, municipality of Gaúcha do Norte, affluent of rio Culuene, 13°27'26"S, 53°09'36"W, 03 Aug 2012, coll. Oliveira C, Taylor M, Silva GJC, Henriques JM.

Diagnosis.

Hisonotus acuen differs from all congeners except Hisonotus bockmanni , Hisonotus chromodontus , Hisonotus insperatus , Hisonotus luteofrenatus , Hisonotus oliveirai and Hisonotus paresi by having a functional V-shaped spinelet, Fig. 2 a–f (vs. non-functional spinelet, a square ossification, or spinelet absent, Fig. 2 g–h). It differs from Hisonotus insperatus , Hisonotus paresi , Hisonotus luteofrenatus , and Hisonotus oliveirai by having odontodes not forming longitudinally aligned rows on head and trunk (vs. odontodes forming longitudinally aligned rows on head and trunk). Hisonotus acuen differs from Hisonotus insperatus and Hisonotus luteofrenatus by the lower counts of the lateral series of abdominal figs (4−5 vs. 6−8 and 7−8, respectively) and from Hisonotus insperatus by the lower counts of the lateral median figs (22−24 vs. 25−26). The new species can be distinguished from Hisonotus luteofrenatus , Hisonotus oliveirai and Hisonotus paresi by the presence of a single rostral fig at tip of snout (vs. presence of a pair of rostral figs at tip of snout); from Hisonotus bockmanni by the absence of unpaired figlets at typical adipose fin position (vs. presence of the unpaired figlets); from Hisonotus chromodontus by having yellowish-tipped teeth, Fig. 3a (vs. reddish-brown teeth, Fig. 3b), by having the caudal-fin color pattern mostly hyaline, except for dark blotch on origin of rays, and dark brown chromatophores largely concentrated on rays near lower caudal spine, Fig. 3c (vs. caudal-fin mostly dark brown with chromatophores largely concentrated on rays and membranes, and with two hyaline spots on middle of the fin, Fig. 3d); from Hisonotus paresi by the absence of conspicuous dark dorsal saddle and longitudinal stripe on the body (vs. inconspicuous dark saddles and stripe of the body) and from Hisonotus insperatus by the higher number of premaxillary (14−27 vs. 6−12) and dentary teeth (12−23 vs. 5−11).

Description.

Morphometric and meristic data presented in Table 1. Maximum body length 29.0 mm SL. Dorsal profile of head in lateral view convex to straight from upper part of rostrum to posterior margin of nares, slightly curved from eyes to posterior margin of parieto supraoccipital, almost straight to dorsal-fin origin. Dorsal profile of trunk almost straight, descending from base of dorsal-fin origin to caudal peduncle. Ventral profile slightly concave from snout tip to anal-fin origin, slightly convex to caudal peduncle. Greatest body depth at dorsal-fin origin (13.5−22.8% SL). Greatest body width at cleithral region, gradually decreasing towards snout and caudal fin. Cross-section of caudal peduncle almost ellipsoid; rounded laterally and almost flat dorsally and ventrally.

Head rounded in dorsal view. Snout slightly pointed, its tip rounded, elongated (34.2−57.2% HL) and depressed in front of each nostril on dorsal surface. Dorsal and ventral series of odontodes completely covering anterior margin of snout; odontodes of snout similar in size to remaining ones found on head. Snout tip lacking band devoid of odontodes. Odontodes on head and trunk well defined and not forming longitudinal rows. Usually no tufts or crests of odontodes on head, in some juvenile specimens, a tiny tuft of odontodes at posterior tip of supraoccipital. Eyes small (11.2−16.2% HL), dorsolaterally positioned. Lips roundish and papillose; papillae uniformly distributed on base of dentary and premaxilla and slightly decreasing in size distally. Lower lip larger than upper lip; its border fringed. Maxillary barbel present. Teeth slender and bicuspid; mesial cusp larger than lateral cusp. Premaxillary teeth 14−27. Dentary teeth 12−23.

Dorsal-fin ii,7; dorsal-fin spinelet short and V-shaped; dorsal-fin lock functional; its origin slightly posterior to pelvic-fin origin. Tip of adpressed dorsal-fin rays slightly surpassing end of anal-fin base. Pectoral-fin i,6; tip of longest pectoral-fin ray almost reaching half of pelvic-fin length, when depressed. Pectoral axillary slit present be tween pectoral-fin insertion and lateral process of cleithrum. Pectoral spine supporting odontodes anteroventrally. Pelvic-fin i,5; its tip not exceeding anal-fin origin when depressed in both sex. Pelvic-fin unbranched ray with dermal flap along its dorsal surface in males. Anal fin i,5; its tip reaching 7th and 8th fig from its origin. Caudal-fin i,14,i; distal margin forked. Adipose-fin absent. Total vertebrae 27.

Body covered with bony figs except on ventral part of head, around pectoral and pelvic-fin origin and on dorsal-fin base. Cleithrum and coracoid totally exposed. Arrector fossae partially enclosed by ventral lamina of coracoids. Abdomen entirely covered by figs in adults (about 23.0 mm SL); lateral fig series with elongate and large figs, formed by two lateral fig series, similar in size; median figs formed by four to five irregular fig series reaching anal shield (Fig. 4a). Lateral side of body entirely covered by figs; mid-dorsal figs poorly developed, reaching middle of dorsal-fin base; median figs not interrupted in median portion of body, but with 2 or 3 figs not perforated before end of series; mid-ventral figs exceed end of anal-fin base.

Parts of head osteology presented in Fig. 4b. Tip of snout formed by a single almost square rostral fig (r). Nasal (n) almost rectangular, forming anterior medial nostril margin in contact posteriorly with frontals (f), and anterior and lateral margins contacting pre-nasals (pn). Lateral surface of head formed by three posterior rostrum figs (pr1-pr3) similar in size. Complete infraorbital fig series, present just below posterior rostrum series, composed of five figs (io1-io5), fourth infraorbital expanded ventrally, all associated with latero-sensory canal system; first infraorbital (io1) largest and fifth smallest (io5). Preopercle (pop) present just under fifth infraorbital (io5); an elongated bone, covered by latero-sensory canal. Subocular cheek figs (cp1-cp2) present above preopercle fig (pop). Top of head composed of compound pterotic-supracleithrum (cpt), supraoccipital (soc), prefrontal (pf), frontal (f), and sphenotic (sp); cpt covered with fenestrae randomly distributed and with different sizes and shapes.

Color in alcohol.

Large inconspicuous brown lateral stripe extending from tip of snout through inferior orbit to end of caudal peduncle Fig. 5a, e (very weak in some specimens, such as holotype Fig. 5c). Body ground color brown on dorsum, yellowish on ven tral region under lateral stripe. Some specimens with dark saddle on mid-ventral to ventral portion of body (Fig. 5b). Dorsal, pectoral, pelvic and anal fins with brown dots on rays, varying in concentration of chromatophores from one individual to another; inter-radial membranes hyaline. Caudal fin hyaline, except for dark blotch on origin of rays, and dark brown chromatophores largely concentrated on rays near lower caudal spine (Fig. 5d). In some specimens, chromatophores forming two dark bands on middle of rays (Fig. 5b, e).

Color in life.

Similar to pattern described for alcohol individuals, but with ground color light brown (Fig. 6).

Sexual dimorphism.

Males bear a papilla posterior to urogenital opening and present the pelvic-fin unbranched ray with dermal flap along its dorsal surface. Both characters are absent in females.

Distribution.

Hisonotus acuen is known from small to median-sized streams of the upper rio Xingu basin, Mato Grosso State in Brazil (Fig. 7a).

Habitat.

Hisonotus acuen was collected on flat areas in creeks of headwaters of the rio Xingu basin in places of shallow clear waters with low current. The fishes are found associated with vegetation that covers the bottom and the border of the headwaters (Fig. 7b).

Etymology.

The specific name “acuen” is in reference to the Xavante indigenous peoples, who in anthropological literature are known as “acuen”. These people are constituted by the natives inhabiting the east of the Mato Grosso State, living in the margins of the rivers Culuene, Xingu, Mortes and Araguaia.