Pariolius pax, Faustino-Fuster & López-Castaño & Quiñones & Meza-Vargas, 2024

Faustino-Fuster, Dario R., López-Castaño, Jeisson A., Quiñones, Jhonatan M. & Meza-Vargas, Vanessa, 2024, Increasing the species diversity of the monotypic genus Pariolius Cope 1872 (Siluriformes: Heptapteridae) after more than 150 years, Zootaxa 5433 (3), pp. 389-403 : 391-396

Pariolius pax new species

urn:lsid:zoobank.org:act:DBC8415C-88B5-4EAE-BAC9-62CDE8E2FAE2

(Figs. 1 a–c, Tables 1–2 )

Holotype. MHNU-I, 3258 , 38.8 mm SL, Colombia, Meta, Mapiripán Municipality, vereda San Jorge, Caño Ovejas , tributary of the Guaviare River , 03°5’26.82’’N; 72°42’33.14’’W, 28 February 2021, J. M. Vásquez-Ramos, M. A. Cortés-Hernández, J. M. Quiñones-Montiel, Y. A. Rojas-Molina, J. A. López-Castaño.

Paratypes. Thirty-one specimens, all from Colombia, Orinoco basin , IavH-P 11228 , 4, 25.8–27.3 mm SL (1C&S), Puerto Gaitán municipality, vereda Alto Neblinas, Finca Unillanos , Caño La Insula , 4°18’59.8” N; 72°03’57.6” W, 5 March 2008, E. Aya-Baquero, Rincón M. Meta: MPUJ 10047 , 5 (2 C&S), 26.9–36.7 mm SL, Mapiripán Municipality, Caño Claro, tributary of the Guaviare River , 03°7’5.1’’N; 72°30’14.8’’W, 16 September 2013, J. E. Zamudio. MPUJ 10048 , 3 (1 C&S), 24.5–29.1 mm SL, Mapiripán Municipality, Caño La División , 3°7’26.60” N; 72°32’18.50” W, 17 September 2013, J. E. Zamudio. MPUJ 10790 , 2, 36.1–37.0 mm SL, Vista Hermosa municipality, Sardinata River , 3°1’7.10” N; 73°50’27.40” W, 25 January 2014, J. E. Zamudio. MPUJ 11256 , 2, 31.8–32.6 mm SL, Mapiripán Municipality , 3°5’19.86” N; 72°35’2.31” W, 6 June 2011, J. E. Zamudio. MHNU-I 3256 , 6, 27.2–33.4 mm SL, same data as holotype . MHNU-I 3337 , 5, 17.2–34.8 mm SL, Puerto Gaitán municipality, 11 March 2021. MHNU-I 3325 , 4, 20.8–25.6 mm SL, Puerto Gaitán Municipality, 24 March 2021. MUSM 71201 , 2, 27.– 33.1mm SL, same data as holotype .

Genseq-2 coI. GenBank accession number. Obtained from paratypes MUSM 71201 ( PP057713 and PP057714 ).

Diagnosis. Pariolius pax is distinguished from all congeners by having very faint cream bar (collar) or homogeneus coloration of the nuchal region (vs. well-defined white nuchal collar present), six branched caudal-fin rays on dorsal lobe (vs. 4–5 in P. maldonadoi sp. nov. and five in P. armillatus ) and light brown in life (vs. 4–5 in P. maldonadoi sp. nov. and five in P. armillatus ) and light rosy in life (vs. dark grey in life). Additionally, it is further distinguished from P. maldonadoi vs. by having deeper body (13.3–17.0% SL vs. 9.5–13.2% SL), deeper head at supraoccipital (48.0–51.5% SL vs. 35.7–41.6% SL) and deeper head at interorbital (34.5–43.5% SL vs. 26.3–29.9% SL). It is further distinguished from P. armillatus by having shorter preadipose distance (70.2–73.3% SL vs. 74.0–76.7% SL), deeper adipose fin (3.1–4.6% SL vs. 2.1–2.2% SL), larger eye (8.5–11.5% SL vs. 6.8–7.3% SL), and wider internostril distance (9.5–11.5% SL vs. 6.3–9.0% SL).

Description. Morphometric data present in Table 1 . Body cylindrical, moderately elongated. Oval in cross section at dorsal-fin origin and compressed on caudal peduncle. Dorsal body profile nearly straight from snout tip to supraoccipital, slightly convex from supraoccipital to dorsal-fin origin, straight from dorsal-fin origin to adipose-fin origin, slightly convex from adipose-fin origin to posterior base of adipose-fin, straight from posterior adipose-fin base to caudal-fin origin. Ventral profile of head slightly convex from snout tip to pectoral-fin origin, nearly convex from pectoral-fin origin to pelvic-fin origin, straight descending from pelvic-fin to anal-fin origin, and slightly convex from anal-fin origin to caudal-fin origin. Anus pore located at level of one third of pelvic fin length; urogenital papilla close to anus pore (approximately eye diameter).

Head small, depressed ascending to supraoccipital, and trapezoidal in dorsal view (Figure 1). Mouth wide and subterminal. Snout short and rounded in dorsal view. Barbels shorts, slender, flatted. Maxillary barbel longest; inserted dorsal to upper lip, lateral and nearly posterior to anterior nostrils; anterior portion extending in superficial groove under anterior- and posterior-nostril region; tip of maxillary barbel surpassing pectoral-fin origin (one third pectoral-fin length). Mental barbels inserted midway between the anterior border of lower jaw and gular fold. Inner mental barbel shorter than outer barbel, inserted approximately posterior to third pore of preoperculomandibular laterosensory canal (pm3); tip of inner mental barbel surpassing the inner margin of branchiostegal membrane. Outer mental barbel inserted posterior to fourth pore of preoperculomandibular laterosensory canal (pm4); tip of outer mental barbel surpassing the pectoral-fin origin. Eye small, elliptical horizontally, slightly dorsal, and anterior to midpoint of head length. Orbital margin not free and pupil rounded. Nostrils arranged as in vertices of squared, anterior internostril distance similar to posterior internostril distance. Anterior nostril tubular, closer to upper lip than posterior nostril. Posterior nostril closer to anterior margin of eye than anterior nostril, anterior margin with flap.

Pectoral fin rays i + 7 (14), distal margin rounded; unbranched pectoral-fin ray soft and short (0.8–0.9 times length of pectoral-fin length); second pectoral-fin ray (first branched rays) as long as third ray (second branched ray); last branched rays short and decreasing gradually; tip of pectoral fin not reaching pelvic-fin origin. Pelvic fin rays i + 5 (14), distal margin rounded; unbranched pelvic-fin rays soft and shorter than branched pelvic-fin rays; second pelvic-fin ray (first unbranched ray) shorter than third ray (second branched rays); third pelvic-fin ray (second branched ray) as long as and fourth ray (third branched ray); last two branched rays short and decreasing gradually; pelvic-fin origin anterior to midpoint body (excluding caudal fin), anterior to vertical through dorsal-fin origin; tip of pelvic fin surpassing the urogenital papilla (one half its length). Insertion of first pelvic-fin ray on basipterygium at vertical through between centra 13–14.

Dorsal fin rays i + 6 (14), distally rounded in lateral profile, unbranched dorsal fin soft and short (0.7–0.8 times length of longest dorsal-fin rays) followed by six branched rays decreasing gradually in length; dorsal fin origin anterior to vertical through pelvic-fin origin. First dorsal-fin pterygiophore inserted on bifid neural spine of vertebra 13 (2). Last dorsal-fin pterygiophore inserted between space of neural spine of vertebrae 15–16 (1) or 16–17 (1). Anal-fin rays iv + 8 (1), v + 7 (4), iii + 8 (3), iii +9 (5), v + 9 (1). Anal fin convex and short (0.2 times its standard length). Anal-fin origin anterior to vertical through adipose-fin origin, last anal-fin ray slightly posterior to half adipose-fin base length. First anal-fin pterygiophore inserted between hemal spines of vertebrae 22–23 (2); last anal-fin pterygiophore inserted between hemal spines of vertebrae 29–30(1) or 30–31 (1); anal fin with 11 (1) or 12 (1) pterygiophores. Adipose fin short (0.2–0.3 times of standard length), rectangular and gently convex in lateral profile (Figure 1a); adipose-fin base longer than dorsal to adipose fin distance (1.2–1.9 times its length) and anal-fin base (1.2–1.5 times its length). Adipose-fin origin posterior of anal-fin origin and posteriorly not continuous with dorsal procurrent caudal-fin rays. Insertion of adipose fin at vertical through vertebrae centra 27–28; terminus of adipose fin at vertebrae 38–39.

Caudal fin gently emarginate with rounded border, dorsal lobe slightly longer than ventral lobe; dorsal caudal lobe with six (14) branched rays; ventral lobe with five (8) or six (6) branched rays. Total caudal-fin rays 40 (2) or 42 (1); with 20 (1) or 21(2) rays on the dorsal lobe and 19 (1), 20 (1) or 21(1) rays on ventral lobe. Five hypural series: hi1, hi2, hi3, hi4, and hi5. Ventral caudal plate (hi1 and hi2) free from parhypural, dorsal caudal plate hi3, hi4 separated from hi5 or fused (Figure 2A).

Canals of laterosensory system with simple pores and arrangement according to figure 3. Supraorbital canal with four branches: s1, s2, s3 and s8; each supraorbital laterosensory opening into a single pore, except branch s2 fused with antorbital branch (s2+i2). Infraorbital canals with six branches: i1, i2, i3, i4, i5 and i6; all opening into its own, except branch i2 fused with s2 opening into a single pore (s2+i2). Preoperculomandibular canal with 11 branches: pm1, pm2, pm3, pm4, pm5, pm6, pm7, pm8, pm9, pm10 and pm11; all opening into its own pore except branch pm11, fused with branch po1 (pm11+po1). Postotic canal with three branches: po1, po2 and po3; all opening into its own pore except branch po1 fused with pm11 opening into a single pore (pm11+po1). Lateral line incomplete, last pore approximately at vertical through the end of anal-fin base.

Total vertebrae 40 (1) or 41 (2). 14 (2) or 15 (1) vertebrae with incomplete hemal spine on vertebrae. 26 (2) or 27 (1) vertebrae with complete hemal spine. Six (3) pair ribs.

Osteology. Cranial skeleton (Figure 4) not ornamented; dorsal surface straight or slightly convex without crests; orbital region well defined dorsally; slightly concave, limited by lateral ethmoid anteriorly, frontal laterally, and sphenotic posteriorly; interorbital approximately half its length; two cranial fontanels separated by epiphyseal bar; posterior and anterior fontanels similar width; posterior fontanel longer than anterior in length; anterior and posterior region of anterior fontanel rounded; anterior region of posterior fontanel triangular and posterior region rounded; epiphyseal bar located to midpoint of frontal length. Mesethmoid with dorsal and ventral horizontal plane; anterolateral mesethmoid in dorsal horizontal plane, anterolateral mesethmoid ramus shorter, thicker, and more blunt-tipped than posterolateral mesethmoid, and anterolaterally directed; posterolateral mesethmoid anterolaterally projected forming a conspicuous cornu; region between posterior border of posterolateral mesethmoid and anterior border of lateral ethmoid filled by ethmoidean cartilage. Vomer arrow-shaped, posterior portion longer than lateral arms, anterior margin of vomer anterior of posterolateral mesethmoid cornu. Lateral ethmoid slightly quadrangular; posterior and anterior face straight and lateral face concave; posterior portion longer than anterior portion; posterolateral angle more pointed than anterolateral angle. Premaxilla rectangular, size three times its width, anterior margin continuous and without process, posterolateral angle not pronounced; six or seven irregular rows of villiform teeth. Maxilla small and trapezoidal (distal margin longer than proximal margin), distal region forming bony tubule attached to maxillary barbel.Autopalatine rod-like, shorter than orbital region; small cartilages at extremities, anterior cartilage longer than posterior one. Nasal bone poorly ossified, shorter and narrower than autopalatine. Antorbital poorly ossified triangular, and shorter than autopalatine. Frontal smooth and lacking any process; anteriorly limited by lateral ethmoid, posterolaterally limited by sphenotic and posteriorly limited by supraoccipital; posterior portion slightly wider than anterior portion; orbital face straight. Sphenotic longer and gently narrower than pterotic length; anterior portion with anterior and lateral process. Pterotic shorter and wider than sphenotic; anterior and posterior portion with similar width. Supraoccipital limited laterally by posterior portion of sphenoid and the pterotic; supraoccipital process thin and not reaching the anterior region of complex centra (in dorsal view).

Complex anterior vertebra (Figure 5A). Composed of first five vertebrae; vertebra 1 disc-like element and attached to complex vertebra with tissues ventrally; complex vertebra (vertebrae 2 to 4) attached to vertebra 5 with suture ventrally; neural spine of vertebra 4 not covering neural spine of vertebra 5. Transverse process of vertebra 4 divided in anterior and posterior branches. Anterior branch of transverse process of vertebra 4 wide, laminar, and expanded laterally; proximal portion wider than distal portion. Posterior branch of transverse process of vertebra 4 arborescent; proximal region wider than distal region; distal region divided in anterior and posterior portion; anterior portion laminar, rectangular, notched and joined to distal region of the posterior portion; posterior portion triangular. Transverse process of vertebra 5 is expanded and not branched.

Suspensory (Figure 6A). Entopterygoid small and slightly triangular; posterior edge concave and attached to anterior margin of metapterygoid.Metapterygoid quadrangular, smooth, and approximately three times entopterygoid size; dorsal margin convex; posteroventral and medial margin of metapterygoid attached with dentate suture and cartilaginous bar to dorsal margin of quadrate; and ventral margin joint with anterodorsal process of quadrate. Quadrate approximately quadrangular and slightly shorter than hyomandibula; anterior and posterior portion separates; anterior margin of quadrate with long anterodorsal process covering ventrolateral margin of metapterygoid; dorsal margin gently concaves along its free dorsal margin; posterior and ventral margin join to hyomandibula with denticulate suture and cartilaginous bar; anteroventral portion of quadrate with robust quadrangular process to articulate to angulo- retroarticular. Hyomandibula quadrangular; mostly smooth; anterodorsal margin slightly concave; posterodorsal hyomandibular process slightly rectangular with posterior margin gently pointed. Opercle triangular and two times interopercle length; anterior and posterior margins convex, ventral-posterior margin slightly convex, and dorsal margin straight; Interopercle triangular; anterior, posterior, and dorsal margin pointed; ventral margin slightly convex, anterodorsal and posterodorsal region concave.

Branchial arches(Figure7A).Three basibranchial series:bb2, bb3,and bb4(basibranchial1absent).Basibranchial 2 anteroposteriorly elongate, largely ossified, size is three times bb3 length, anterior portion wider than posterior portion. Basibranchial 4 completely cartilaginous, quadrangular shape; bordered by cartilaginous heads of hb3 anteriorly, cb5 posteriorly and cb4 laterally. Three hypobranchial series: hb1, hb2, hb3. Hypobranchial 1 laterally elongate, largely ossified, size more than three times its greatest width, cartilage in extremities, anterior portion with uncinate process. Hypobranchial 2 slightly elongate, L -shape, anterior portion ossified and posterior portion cartilaginous with similar size. Hypobranchial 3 completely cartilaginous, rectangular, elongate anterolaterally. Five ceratobranchial series: cb1, cb2, cb3, cb4, cb5; fully ossified with cartilage only at their distal and proximal extremities; ceratobranchial 1, 2 and 3 similar size and longer than ceratobranchial 4 and 5. Ceratobranchial 1 to 4 with similar width along its length. Ceratobranchial 5 expanded anteromedially to support patch of conical teeth, teeth with similar size and covering more than two-thirds of cb5 length. Four epibranchial series plus accessory element of ceratobranchial 4: eb1, eb2, eb3, eb4, and aecb4; first four rod-shaped, anteromedial narrower than posterolateral portion; eb1, eb2, eb3 and eb4 mostly ossified; aecb4 cartilaginous; epibranchial 1 and 2 similar size and longer than epibranchial 3 and 4. Epibranchial 3 with triangular posterior uncinate process close to epibranchial 4. Epibranchial 4 expanded at anterior and posterior portion. Two pharyngobranchial series: pb3 and pb4; pharyngobranchial 1 and 2 absent. Pharyngobranchial 3 rod-like, ossified, anterior portion narrower than posterior portion; posterior margin mostly expanded. Pharyngobranchial 4 ossified; quadrangular and anteroposteriorly elongate.

Color. Dorsal and lateral surface of body cream covered by brown marbled melanophores in preserved specimens and light rosy in life (Figure 8A). Ventral surface of head cream. Upper portion of head covered by brown pigment; cheeks with brown scattered melanophores fading ventrally. Dorsal surface of head between eyes and supraoccipital with dark brown quadrate spot.Very faint cream bar (collar) above pectoral fins contacting each other dorsally.Region between posterior margin of eye and maxillary barbel insertion with dark brown bar. Maxillary barbel pigmented with dark brown dorsally (until one half its length) and ventrally unpigmented. Outer mental barbel pigmented with dark brown dorsally (until one half its length) and ventrally unpigmented. Inner mental barbel unpigmented (some brown melanophores at base). At least seventeen brown chevron-shape lines marking the myosepta, progressively narrower, more angled, and intense posteriorly. Dorsal, anal, caudal, pectoral, and pelvic fins with dispersal brown melanophores along rays and inter-radial membranes devoid of melanophores. Base of caudal fin with dark brown semilunar spot. Base of dorsal and anal fins with concentration of dark brown melanophores. Adipose fin with concentration of brown melanophores (half its height) and distal region unpigmented. Lateral line with dark brown and narrow stripe, nearly convex above pectoral fin and straight along midbody from that point to caudal-fin base and more intense anteriorly (Figure 2), lateral stripe more intense in life (Figure 8A).

Geographic distribution. Pariolius pax is distributed in small tributaries to the Guaviare River and Meta River in the Orinoco River basin, Meta State, Colombia (Figure 9).

Etymology. The specific epithet is the Latin noun pax , which means peace and is in honor of the Colombian peace process signed in 2012. Peace allowed for access to territories that were previously not possible due to the armed conflict, such as Mapiripán, Meta; this species was recorded in this place, and it was a municipality where a massacre occurred in 1997. Treated as a noun in apposition.