Paracanthopoma saci, Dagosta & Pinna, 2021

Dagosta, Fernando Cesar Paiva & Pinna, Mário de, 2021, Two new catfish species of typically Amazonian lineages in the Upper Rio Paraguay (Aspredinidae: Hoplomyzontinae and Trichomycteridae: Vandelliinae), with a biogeographic discussion, Papéis Avulsos de Zoologia (Pap. Avulsos Zool., S. Paulo) 61, pp. 1-23 : 4-6

Paracanthopoma saci sp. nov.

http://zoobank.org/ 6536E8CD-A751-4CEF-AD74-FAA3669F99D6 ( Figs. 1-2 )

Holotype: MZUSP 125624 , 19.1 mm SL, Brazil, Mato Grosso do Sul, Alcinópolis, Rio Taquarizinho (tributary to Rio Taquari , Rio Paraguay drainage) (18°12′14.8″S, 53°34′11.3″W), elev. 363 m, col. F. Dagosta, A. Ferreira, R. Zanon, 18 Sep 2019.

Paratypes: MZUSP 125626, 13 ex (2 c&s), 14.5-21.8 mm SL, collected with holotype. MZUSP 125622, 2 ex, 19.5-19.9 mm SL, same locality and col- lectors as holotype, 17 Sep 2019. MZUSP 115585, 1 ex, 19.3 mm SL, Brazil, Mato Grosso do Sul, Alcinópolis, stream tributary to Rio Taquari (Rio Paraguay drainage) at dirt road between Alcinópolis and road MS-217 (18°12′16.5″S, 53°34′13.5″W), col. O. T. Oyakawa, P. Camelier, M. Marinho, F. Dagosta, 26 Aug 2013. MNRJ 53559, 2 ex, 14.6- 16,8 mm SL, from MZUSP 125626.

Diagnosis

Distinguished from the only other species of Paracanthopoma , P.parva , by: 1) short and anteriorly-displaced opercular patch of odontodes, which leaves a large posterior free area of integument continuous with the rest of the head integument around it (as a consequence of that morphology, in dorsal view the posterior tips of the opercular odontodes do not reach the base of the pectoral fin); 2) pelvic fin with three rays (vs. five); 3) opercle lacking an ascending process (vs. ascending process present); 4) caudal peduncle spatulate by hypertrophied series of 22-29 (upper) and 20-29 (lower) procurrent caudal-fin rays (vs. caudal peduncle narrow, with 15 to 19 upper and 14 to 18 lower rays); 5) median premaxillary dentition feeble, with three delicate teeth (vs. median premaxillary dentition robust, with nine large strong teeth); 6) supraorbital canals opening as two separate s6 pores (vs. canals fused at midline and opening as single median s6 pore); 7) caudal fin slightly convex or truncate, with round edges ( Fig. 2 ; in Fig. 1 the apparent emarginated margin is a preservation artifact) (vs. bilobed or emarginate, concave); 8) supraoccipital lacking anterior median process (vs. supraoccipital with produced anterior process); 9) origins of dorsal and anal fins approximately at same vertical (vs. origin of dorsal fin clearly anterior to vertical through origin of anal fin). The three former characters also distinguish P. saci from all undescribed species of the genus known to the authors at this time.

Description

Morphometric data provided in Table 2. Body elongate. Cross-section of body as broad as deep at pectoral-fin insertion and increasingly compressed posterior to that point, tapering to caudal fin. Dorsal profile of body in broad gentle arc,nearly straight,from head to origin of dorsal fin ( Figs. 1-2 ). Dorsal midline with transparent fin fold anterior to dorsal fin. Dorsal and ventral profiles of caudal peduncle straight immediately posterior to ends of dorsal and anal fins, then expanded by dorsal and ventral procurrent caudal-fin rays resulting in symmetrically spatulate caudal peduncle. Ventral profile of body nearly straight until pelvic-fin origin, but greatly distend- ed in some specimens due to gut contents. Myotomes and longitudinal skeletogenous septum clearly visible through thin integument along whole body. Axillary gland large, elongate, positioned dorsal to pectoral-fin base and extending posteriorly approximately to midlength of adpressed pectoral fin, its large round or oval pore located at its posterior terminus. Some specimens preserved with large amount coagulated secretion still attached to pore.

Dorsal profile of head continuous with that of dorsum. Head longer than broad, snout very broad, semicircular with a continuous round anterior margin. Head muscles not entering skull roof. Head depressed (head depth approximately 50% of head width) with dorsal profile mostly continuous from nape to tip of snout.Ventral profile of head straight, flattened, though externally irregular due to integument folds. Eye size slightly less than one-third of snout length, without free orbital rim, located dorsally on head and directed dorsolaterally. Integument over eyes thin and transparent. Center of eyes located slightly anterior to middle of HL, interorbital width equal to, or slightly larger than,longitudinal diameter of eye. Eye lens unconstricted by iris,entirely exposed on external aspect of eye. Anterior nostril small, surrounded by short tubule of integument produced posteriorly into small and pointed flap. Anterior internarial width slightly narrower than interorbital. Posterior nares slightly larger than anterior ones, oval (longer than broad) in shape, located close to anteromesial margin of eyes. Center of posterior nares slightly anterior to transverse line through anterior margin of eyes. Posterior internarial width slender than interorbital and approximately twice as wide as anteroposterior length of nostril.

Opercular patch of odontodes tiny, dorsolaterally located on head, on dorsal half of head depth in lateral view, anterodorsally to pectoral-fin base. Opercular odontodes six,disposed in two irregular rows.Odontodes with distal portions curved medially. Opercular fold of integument vestigial or absent, instead continuous with large well-delimited roundish area of thickened integument resembling a vastly hypertrophied opercular fold. Interopercular patch of odontodes miniscule, nearly invisible on surface of head, located ventrolaterally on head, horizontally aligned with origin of pectoral fin. Interopercular odontodes four. Interopercular patch of odontodes closer to opercular patch than to eye. Interopercular flap of integument absent or vestigial.

Mouth ventral and small, strongly flattened ventrally, delineated anteriorly and laterally by vast crescent-shaped upper lip and posteriorly by small lower lip. Each premaxilla with a single claw-like tooth attached to its distal tip, and one additional tooth socket with partly-formed tooth in parallel.Claw-like tooth deeply hidden in labial tissue and difficult to expose in preserved specimens without damaging soft tissue. Conical teeth absent on premaxilla. Upper lip very broad but poorly-differentiated, continuous with ventral surface of snout. Median premaxilla miniscule, with three closely-set tiny teeth. Dermal pad of median premaxilla semicircular. Lower jaw narrow, its anterior profile M-shaped and composed mostly of produced dentary lobes, continuous with mental region posteriorly. Jaw cleft short, strongly directed posteriorly, but curved laterally at posterior end. Dentary diastema as deep median concavity between dentary lobes. Dentary teeth four on each side, large but difficult to visualize in alcoholic specimens, concentrated at mesial end of dentary and directed anteromesially,arranged in two ventral and two dorsal ones, not aligned. Dentary teeth long, their axis anteriorly-directed at base, but curved dorsally or dorsolaterally at distal half. Median tooth of ventral row longer than others.

Branchiostegal membrane continuous posteriorly with large, continuous, posteriorly concave, free branchiostegal velum across whole of ishtmus region. Dorsal portion of branchiostegal velum reaching and slightly overlapping anterior margin of pectoral-fin base. Branchial opening small, located anteriorly to pectoral-fin base, approximately equal to space between opercular and interopercular patches of odontodes. Maxillary barbel ranging from extremely short to vestigial, extending maximally for one-third distance between its base and base of interopercular patch of odontodes. Posterior point of its base slightly anterior to vertical through anterior margin of eye in lateral view. Rictal barbel vestigial, reduced to small knob mesially to base of maxillary one, absent in some specimens. Nasal barbel vestigially represented by posterior elongated portion of fold around anterior naris described above.

Lateral line short, approximately half of pectoral-fin length, and straight, extending alongside dorsal margin of anterior portion of axillary gland. Terminal lateral-line pore immediately dorsal to axillary gland opening. Short secondary branch splitting off ventrally from proximal portion of main canal, with corresponding pore opening anteriorly to midlength of main canal. Single lateral-line tubule poorly calcified, extending over part of main canal immediately posterior to bifurcation.

Pectoral fin small, approximately 60% of HL, with i+4 rays in all specimens (except i+ 3 in one side of one specimen). Pectoral-fin morphology with pronounced variation, with most specimens (n = 9, including holotype) having triangular pointed shape with first ray slightly longer than others. Some specimens (n = 5) with all rays equally long, resulting in truncate fin margin. Two exceptional specimens in MZUSP 125626 (14.5 and 15.0 mm SL) with hypertrophied first pectoral-fin ray forming long filament. First ray corresponding to 36% SL in smaller specimen and 26% SL in larger specimen, with filamentous portion approximately 2 and 1.5 times length of rest of fin, respectively (see Remarks below). Pelvic fins minute, closely set together at base, with i+2 rays (with all three rays unbranched in small specimens; one specimen with vestigial additional ray posteriorly). Pelvic splint present in single of three c&s specimens. Origin of pelvic fin close to origin of anal fin, well anterior to vertical through origin of dorsal fin, extending posteriorly well beyond anus and urogenital papilla and slightly beyond origin of anal fin. Posterior margin of pelvic fin gently convex. Dorsal fin elongate, roughly triangular with roundish edge and gently convex, sinusoidal or straight distal margin. Dorsal-fin rays v-viii*+I*-II+5-6*. Anal fin similar in shape to dorsal fin, with v-ix(viii*)+I+5 rays. Origin of anal fin at or slightly posterior to vertical through origin of dorsal-fin.Caudal fin roughly rectangular in preserved position.. Margin of caudal fin truncate with round edges and gently convex margin (in Fig. 1 the apparent emarginated margin is an artifact of the preservation position of middle rays). Principal caudal-fin rays 5+5* or 4+5. Procurrent caudal-fin rays 22-29 dorsally and 20-29 ventrally.

Vertebrae (exclusive of Weberian complex) 40 (n = 2), 41 (n = 3), 42* (n = 4), 43 (n = 3). First dorsal-fin pterygiophore positioned subsequent to neural spine of vertebra 22 (n = 3). First anal-fin pterygiophore positioned subsequent to hemal spine of vertebra 22 (n = 1) or 23 (n = 2). Dorsal- and anal-fin pterygiophores six, poorly calcified or entirely cartilaginous, clearly visible only in c&s preparations. Branchiostegal rays three. Ribs one pair.

Figures

Figure 1.Paracanthopoma saci, MZUSP 125624,holotype,19.1 mm SL.Brazil,Mato Grosso do Sul,Alcinópolis,RioTaquarizinho.(a) Lateral view,(b) Dorsal view of head,(c)Ventral view of head.Photos byV.Reis.

Figure 2.Live coloration of Paracanthopoma saci.Lateral view of MZUSP 125622,19.9 mm SL.