Pseudacanthicus major, Chamon & Costa, 2018

Chamon, Carine C. & Costa, Thiago, 2018, Pseudacanthicus major: description of one of the largest known Loricariidae (Hypostominae: Ancistrini), a species from rio Tocantins basin, Brazil, Zootaxa 4387 (3), pp. 499-510 : 500-505

Pseudacanthicus major , new species

( Figs. 1 and 2 ; Table 1 )

Holotype. MNRJ 50822 (ex. UNT 8345 ), 540.0 mm SL, Porto Nacional, rio Areias near to the confluence with rio Tocantins, 1050'30"S 4823'35"W, 21 Jan 2008, B. Pires.

Paratypes. All from Brazil, Tocantins state, rio Tocantins basin: MZUSP 79084 , 1 , 460.0 mm SL, Itaguatins, rio Tocantins, praia do Imbiral , 546'13"S 4728'37"W (aproximated coordinate) 21-23 Dec 1987, J. N. Fontenele. UNT 8344 , 1 , 600.0 mm SL, Paranã, rio Paranã, in Fazenda Traçadal , 1230'35"S 4812'57"W, 21 Jan 2008, Neamb- UFT staff. UNT 8346 , 1 , 490.0 mm SL, same data and collectors as UNT 8344 . UNT 8504 , 1 , 390.0 mm, Porto Nacional , rio Tocantins, 1043'15"S 4825'14"W, 28 Jan 2008, Neamb-UFT staff. Pará state, rio Tocantins basin: INPA 4557 , 1, 120.9 mm SL, Tucuruí, rio Tocantins, downstream to Tucurui Dam , 03°45'58”S, 49°40'21”W, 9 Oct 1984, G. M. Santos. INPA 6309 , 11 , 62.2-116.8 mm SL, same locality of INPA 4557 , 31 Aug 1984, Ictiologia INPA staff. INPA 32234 , 1, 115.1 mm SL, same locality as INPA 4557 , 31 Aug 1984, Ictiologia INPA staff. MNRJ 19346 , 1, 166.6 mm SL, rio Tocantins, near Tucuruí , 345'51"S 4939'39"W, Sep 1984, collectors unknown. MNRJ 27719 , 1, 117.9 mm SL, same locality and collectors as MNRJ 19346 .

Diagnosis. Pseudacanthicus major sp. n. can be diagnosed from its congeners by a dark brown background color lacking spots or blotches and transversal white bands on dorsal and caudal fins (vs. dark gray to dark brown background color with black spots or blotches and dorsal and caudal lacking transversal white bands fins with intensely orange to red coloration in P. leopardus , P. pitanga and P. pirarara ; body and fins with dark background color with white spots in P. serratus and P. fordii , or gray background color with black blotches in P. histrix and P. spinosus ); by the anterior process of compound pterotic with no contacting with the posterior margin of the orbit (vs. small contact with the orbit in its congeners); by the absence of a conspicuous crest on the posterior edge of parieto-supraocciptal ( Figure 3 ) (vs. with a conspicuous V -shaped crest in its congeners) and by the ventral surface, including thorax and abdomen, being covered with small plates, more concentrated at pectoral-fin origin and thorax region, and more conspicuous in large specimens (vs. ventral surface, including thorax and abdomen completely naked). Pseudacanthicus major is further diagnosed from congeners by the following combination of osteological characteristics: 12 to 14 vertebrae from the first neural spine, not including the hypural plate (vs. 8 to 11 vertebrae, except in P. pitanga and P. pirarara ); posterior contact area between cleithrum and coracoid expanded ventrally (vs. straight, except in P. pitanga ); ventral crest of basipterygii straight (vs. rounded or triangular, except in P. pirarara ).

Description. Morphometric and meristic data summarized in Table 1 . Dorsal profile of body slightly convex from tip of snout to vertical through dorsal-fin origin; concave, nearly straight from that point to caudal-fin origin. Ventral profile of body straight from snout tip to caudal-fin origin. Ventral surface from the pectoral girdle to urogenital papilla covered with small plates, more concentrated at pectoral-fin origin and thorax region. Greatest body width at pectoral girdle. Trunk strongly keeled; five rows of longitudinal keels; one keel along each series of body plates. Body depth greatest at dorsal-fin origin, shallowest at caudal peduncle, between adipose fin and first procurrent caudal-fin ray. Head deep, rounded anteriorly; snout and cheek completely covered by numerous small plates, except for small naked area on tip of snout. Snout very pointed in dorsal view. Nasal elongate, L-shaped. Frontal short, broadly contacting nares anteriorly and orbit posteriorly. Anterior margin of frontal short, reaching posterior margin, or half length, of nares. Parieto-supraoccipital not elongate, posterior edge short, without crest formed by conspicuous odontodes. Sphenotic short, contacting sixth infraorbital, and lacking conspicuous odontodes. Orbit dorsolateral, moderate in size (5.2–13.7% HL). Iris with small dorsal flap over pupil. Compound pterotic short with few fenestrae; anterior process not contacting posterior margin of orbit. Posterior area of compound pterotic with one or two small plates. Infraorbital series with eight pores. Fourth infraorbital widely contacting posterior margin of orbit. Sixth infraorbital contributing only to the posteroventral margin of orbit. Lateral-line pores restricted to hypural plate.

Mouth moderate in size, nearly as long as wide. Lips large, covered with papillae; size of papillae decreasing towards posterior margin of lower lip; central buccal papilla absent or weakly developed. Upper lip folded over itself. Maxillary barbel short; base of barbel united to upper and lower lips, tip free. Lower lip not reaching anterior margin of coracoid. Medial end of premaxillary teeth series curved inwards. Premaxillae and dentary narrow and elongate. Dentary strongly curved inwards. Teeth well-developed, slightly thickened with long crown and large lateral cusp; distal edge slightly curved inward. Four to five pairs of well-developed predorsal plates. Cheek plates evertible with hypertrophied odontodes.

Dorsal-fin rays I,8; spinelet V -shaped with locking mechanism. Pectoral and pelvic fins well-developed, medial portion much expanded relative to base; distal margin rounded. Pectoral-fin rays I,6; unbranched ray covered with hypertrophied odontodes. Tip of adpressed pectoral fin almost reaching vertical through medial pelvic-fin spine. Pelvic-fin rays i,5; pelvic-fin spine reaching vertical through anal-fin base when adpressed. Anal-fin rays i,5. Caudal fin i,14,i, truncate; supracaudal plates eight to 10. Usually four procurrent caudal-fin rays, on each dorsal and ventral lobe. Caudal peduncle deep. Total vertebrae 30, precaudal 14. Sixth rib strongly thickened, remaining ribs slender.

Color in life. The living color pattern of Pseudacanthicus major comprises background dark brown to dark gray. Ventral region pale without blotches or spots. Fins dark brown to dark gray with transversal white bars, more conspicuous in the dorsal and caudal fins and in specimens under 120 mm SL ( Figure 2 ).

Color in alcohol. Specimens in alcohol usually exhibit the same color pattern as when alive, but in most cases the white bars on fins are inconspicuous and faint ( Figure 1 ).

Etymology. The specific epithet major , derives from Latin meaning greater than, larger than, in allusion to the large size of the specimens in comparison with others species of the genus. An adjective.

Distribution. Pseudacanhticus major occurs throughout rio Tocantins ( Figure 4 ). It was reported at the upper Tocantins, in Paranã region, and in the medium rio Tocantins, at Porto Nacional and Itaguatins, in Tocantins state. At the lower rio Tocantins, the specimens of the new species were collected at Tucuruí, Pará state.

Ecological notes. Pseudacanthicus major can be found in the main channel of the river, usually in moderate to strong currents, and shallow to deep environments down to 18 m. The habitats where the species was collected usually present many submerged branches and trunks (eg. rio Farinha, Figure 5 ); and the marginal vegetation frequently deforested by anthropic actions. The species presents restricted distribution and low abundace. Water properties at Estreito area: depth 18.0 meters, with transparency of 3.0 meters, pH 7.2 and dissolved oxygen 9.4 (mg/L).

Remarks. Pseudacanthicus major is known and marketed in ornamental fish trade, like others species of the genus. Pseudacanthicus major is recognized in the L number system employed by aquarists as L186 (Schraml & Schaefer, 2004; Stawikowski et al., 2004; Werner et al., 2005). There is no suggestion that the species is consumed as food source by the colonies of fishermen (pers. obs.)

Figures

FIGURE 1. Holotype of Pseudacanthicus major, MNRJ 50822 540.0 mm SL, in dorsal (A), lateral (B) and ventral (C) views.

FIGURE 2. Color in life of Pseudacanthicus major, specimen collected and released during monitoring for route of migratory fish. Image by Wesley Zago (CESTE, Consórcio Estreito Energia Usina Hidrelétrica Estreito).

FIGURE 3. Dorsal profile of the head of (A) Pseudacanthicus major (holotype, 540.0 mm SL), (B) a smaller specimen of P. major (INPA 32234, 115.1 mm SL) and (C) P. pirarara (MZUSP 107172, 246.5 mm SL), showing the parieto-supraocciptal.

FIGURE 4. Distribution map of Pseudacanthicus major, white circle corresponds to the type locality.

FIGURE 5. Rio Farinha, transition area of the Estreito Dam (medium rio Tocantins).