Pimelodella guato, Pierre & Slobodian, 2024

Pierre, Veida & Slobodian, Veronica, 2024, A new species of Pimelodella (Siluriformes: Heptapteridae) from the Paraguai basin, Brazil, with a discussion regarding its distribution, Neotropical Ichthyology (e 230110) 22 (1), pp. 1-25 : 5-13

Pimelodella guato , new species urn:lsid:zoobank.org:act:E9B6CDE4-ACE0-466B-B97D-A6BB29C8238F

( Figs. 1 , 2A , 3A ; Tab. 1)

Pimelodella serrata non Eigenmann, 1917. —Slobodian et al., 2022:340 (rio Taquari, rio Paraguai basin; geographic distribution).

Holotype. ZUFMS-PIS 8515 , xr, 78.5 mm SL, Brazil, Mato Grosso do Sul, Corumbá municipality, rio Paraguai basin, rio Miranda, sandy beaches at Passo do Lontra region , 19°34’37”S 57°00’42”W, 31 Oct 1991, J. C. Louzan & V. M. F. Jesus.

Paratypes. All from Brazil, rio Paraguai basin. CIUnB 1772, 7, 3 xr, 79.1–99.9 mm SL, 1 c&s, 91.2 mm SL, Mato Grosso do Sul , Corumbá municipality, rio Miranda, sandy beaches at Passo do Lontra region , 19°34’37”S 57°00’42”W, 17 Sep 1993, O. Froehlich. MZUEL 11088 , 1, 103.7 mm SL, Mato Grosso do Sul , Corumbá municipality, corixo, fifth bridge after the entrance to Passo do Lontra, Estrada Parque , 19°38’S 57°02’W, 3 Sep 2002, O. A. Shibatta et al. MZUEL 16829 , 1 , 79.6 mm SL, Mato Grosso do Sul , Corumbá municipality, rio Miranda, BEP/ UFMS (Base de Estudos do Pantanal) , 19°34’36”S 57°1’5”W, 22 Aug 2016, O. A. Shibatta et al. NUP 14295, 1, 72.3 mm SL, Mato Grosso , Cáceres municipality, baía de Cáceres, tributary of rio Paraguai , 16°04’02”S 57°41’38”W, 28 Mar 2012, Nupelia. NUP 19919, 3, 64.8–83.2 mm SL, Mato Grosso do Sul , Coxim municipality, rio Coxim, tributary of rio Taquari , 18°33’32”S 54°44’37”W, 8 Oct 2017, Nupelia. ZUFMS-PIS 647 , 5 , xr, 37.1–94.3 mm SL, Mato Grosso do Sul , Corumbá municipality, rio Miranda, Passo do Lontra, across from the BEP , 19°34’37”S 57°00’42”W, 6 Sep 1990, O. Froehlich. ZUFMS-PIS 676 , 15 , 62.3–107.4 mm SL, Mato Grosso do Sul , Corumbá municipality, rio Miranda, sandy beaches at Passo do Lontra region , 19°34’37”S 57°00’42”W, 17 Sep 1993, O. Froehlich. ZUFMS-PIS 4843 , 2 , xr, 64.6–65.4 mm SL, Mato Grosso do Sul , Corumbá municipality, rio Miranda, across from the BEP , 19°34’37”S 57°00’42”W, 5 Sep 2008, O. Froehlich. ZUFMS-PIS 6370 , 2 , xr, 98.6–127.9 mm SL, Mato Grosso do Sul , Coxim municipality, rio Taquari , 18°31’32”S 54°44’30”W, 16 Dec 2019, H. Gimenes-Jr, M. B. Mendonça, P. Camelier, M. Kaluza, F. Severo-Neto, R. Rech , F. Vasconcelos & R. Mochi. ZUFMS-PIS 8516 , 4 , xr, 49.7–109.0 mm SL, same data as holotype .

Diagnosis. Pimelodella guato differs from all Pimelodella species except P. boliviana , P. chaparae , P. cristata , P. cruxenti , P. dorseyi , P. geryi , P. gracilis , P. howesi , P. humeralis , P. laurenti , P. longibarbata , P. longipinnis , P. martinezi , P. megalops , P. mucosa , P. notomelas , P. odynea , P. ophthalmica , P. parnahybae , P. serrata , P. steindachneri , P. taeniophora , P. tapatapae , P. wesselii , and P. witmeri by the long maxillary barbel, reaching at least the anal-fin terminus when parallel to main body axis (vs. reaching at best posterior limit of anal-fin base). It differs from P. longipinnis and P. tapatapae by having the supraoccipital process reaching the anterior nuchal plate (vs. not reaching, gap between distal terminus of supraoccipital process and anterior nuchal plate ca. 20–25% of supraoccipital process length). It differs from P. boliviana , P. cruxenti , P. geryi , P. laurenti , P. martinezi , P. megalops , P. notomelas , P. odynea , and P. taeniophora by having a robust dorsal-fin spine, bearing small, straight spinules along three-fourths of its posterior margin (vs. dorsal-fin spine not particularly robust, with posterior margin spinules inconspicuous or absent). It differs from P. cristata , P. dorseyi , P. gracilis , P. howesi , P. humeralis , P. ophthalmica , P. parnahybae , P. steindachneri , P. wesselii , and P. witmeri by usually having 41–42 (rarely 43 or 44) total vertebrae (vs. always 43–44 in P. howesi ; 46 or more in the remaining species). It further differs from P. howesi by having the dorsolateral region of body slightly darkened (vs. not darkened), dorsal fin with light brown stripe near its origin, followed by a hyaline stripe, and distal half dark (vs. basal half of dorsal fin hyaline, and distal half dark), and by the dorsal lamina of the Weberian apparatus reaching the ventral margin of the supraoccipital process only at its first third (vs. dorsal lamina reaching the supraoccipital process along all its extension). It differs from P. mucosa and P. longibarbata by the preoperculomandibular laterosensory canal openings at dentary not particularly large (vs. large openings). It differs from P. chaparae , P. longibarbata , and P. serrata by the wide midlateral stripe (vs. narrow) and by the dorsal lamina of the Weberian apparatus reaching the ventral margin of the supraoccipital process only at its first third (vs. first half in P. longibarbata ; and almost its entire extension in P. chaparae and P. serrata ) ( Figs. 2A, D ).

Furthermore, P. guato can be diagnosed from all congeners by the following exclusive character combination: dorsal profile straight from snout to dorsal fin; maxillary barbel reaching at least the anal-fin terminus when parallel to main body axis; supraoccipital process reaching anterior nuchal plate; dorsal-fin spine robust, bearing small, straight spinules along three-fourths of its posterior margin; posterior margin of pectoral-fin spine bearing 13–23 large, retrorse blades along basal two-thirds ( Fig. 3A ); adipose fin 2.5 to 3.0 times in SL; usually 41–42 (rarely 43 or 44) total vertebrae; epiphyseal branch of supraorbital canal on the head (S6) emerging as a single pore; brown midlateral stripe wide, not well delimited, extending from snout to caudal-fin origin.

Description. Morphometric data are summarized in Tab. 1. Body moderately depressed, depth at dorsal-fin origin 5.0 to 6.5 times in SL; and moderately compressed; body width at dorsal-fin origin 7.0 to 9.0 times in SL ( Fig. 1 ). Greatest body depth at dorsal-fin origin. Dorsal profile straight from snout to dorsal-fin origin, concave from dorsal fin to adipose fin, slightly convex along adipose fin, and concave along caudal peduncle. Ventral profile of body slightly convex from snout to branchiostegal membrane, convex between pectoral and pelvic fins, slightly convex from pelvic fin to anal-fin origin, and concave from this point along the caudal peduncle.

Pseudotympanum externally visible, large, oval, dorsal to posterior process of cleithrum and reaching vertical line of sixth (16) vertebrae. Posterior process of cleithrum triangular, long, its dorsal border slightly concave. Anus and urogenital papilla adjacent.

Urogenital papilla tubular, triangular, short. Anus between verticals through half and last third of adpressed pelvic fin; urogenital papilla between verticals through second third and terminus of adpressed pelvic fin. Some specimens might present enlarged urogenital papillae (see Discussion).

Head moderately depressed, depth at supraoccipital-process base 1.5 to 2.5 times in HL. Mouth sub-terminal. Eyes elliptical, 4.0 to more than 5.5 times in HL. Bony interorbital distance roughly equal to eye diameter. Barbels thin, slightly depressed, elliptical in cross-section. Maxillary barbel reaching at least the anal-fin terminus when parallel to main body axis. Outer mental barbel, when parallel to main body axis, reaching between second third of adpressed pectoral fin and first third of adpressed pelvic fin. Inner mental barbel, when parallel to main body axis, reaching between pectoral-fin origin and second third of adpressed pectoral-fin. Supraoccipital process subrectangular to triangular, wide. Dorsal lamina of Weberian complex vertebrae moderately deep, usually reaching the ventral margin of the supraoccipital process along its first third ( Fig. 2A ). Branchiostegal 6(17).

Dorsal fin triangular, distal margin convex, moderate in length (second branched dorsal-fin ray almost 4.5 to 6.0 times in SL), depressed tip reaching between vertical line through half and terminus of adpressed pelvic fin. Dorsal fin with II,6(24), being the anteriormost the spinelet. Distance between terminus of dorsal-fin base and adipose-fin origin at least a third shorter than dorsal-fin base. Anteriormost dorsal-fin pterygiophore posterior to neural spine of vertebra 4(17); posteriormost dorsal-fin pterygiophore anterior to neural (or pseudoneural) spine of vertebra 10*(7)–12(2). Second unbranched dorsal-fin ray mostly ossified as a spine, long (spine three-fourths of first dorsal-fin ray total length). Dorsal-fin spine robust, bearing small, straight spinules along distal three-fourths of its posterior margin. Second unbranched dorsal-fin ray may present a nonspinuous filamentous portion (see Discussion).

Pectoral-fin rays I,7(4)–I,9(5) (holotype I,8), pectoral-fin triangular with convex or slightly straight distal margin. First pectoral-fin ray curved, with proximal part rigid, forming a spine, and short distal tip, flexible and distinctly segmented. Pectoral-fin spine long, 5.5 to 6.5 times in SL. Anterior margin of pectoral-fin spine with small, straight spinules along its basal two-thirds and flat spinules along its distal third ( Fig. 3A ). Posterior margin of pectoral-fin spine bearing 13–23 (holotype 17) retrorse blades along basal two-thirds ( Fig. 3A ). Blades larger and more inclined, hook-like, near distal tip, meanwhile smaller, less inclined, near pectoral-fin base.

Pelvic-fin rays i,5(23), pelvic fin triangular with convex distal margin when expanded. Pelvic-fin origin at vertical through penultimate branched dorsal-fin ray. Tip of adpressed pelvic fin between verticals through second eighth and second fifth of adipose fin. First unbranched ray distinctly shorter than subequal branched second and third rays; remaining rays progressively shorter.

Anal-fin rays iv,7(6); v,7*(4); iv,8(3); or v,8(2); distal border of expanded anal fin convex. One or two anteriormost anal-fin rays vestigial, unsegmented, embedded in thick skin fold. Anal-fin origin between verticals through second third and half adipose-fin base; adpressed anal-fin terminus between verticals through last eighth and terminus of adipose fin. Anteriormost anal-fin pterygiophore posterior to hemal spine of vertebrae 20(1), 21*(5), 22(7) or 23(4); posteriormost anal-fin pterygiophore anterior to hemal spine of vertebrae 27(2), 28*(9), 29(5) or 30(1).

Adipose fin 2.5 to 3.0 times in SL, forming ascending elevated curve in lateral profile, with deepest point approximately midlength. Adipose fin emerging gradually, its posterior limit as a rounded, free lobe. Adipose-fin origin usually at vertical through vertebral centra 16*(6)–18(4), rarely 15(1) or 19(1); adipose-fin terminus usually at vertical through vertebral centra 35(2)–37(7) (holotype 36), rarely 34(1) or 38(1).

Caudal fin deeply forked, lobes subequal, or ventral lobe slightly longer than dorsal. Caudal peduncle length posterior to adipose fin roughly equal to or slightly larger than its depth. Dorsal lobe with 7(18) branched, 1(18) unbranched principal, and 13(2)– 23(1) (holotype 17) procurrent fin-rays. Ventral lobe with 7(2)–8*(14) branched, 1(18) unbranched principal, and 14(2)–22(1) (16*) procurrent fin-rays. Hypural 5 completely free, not fused to hypural 3+4. Median caudal-fin rays not articulated directly to caudal plate. Seven* (13) or 8(3) rays articulated to dorsal caudal-fin plate (5 or 6 on hypurals 3+4, and 2 on hypural 5) and 7*(14) or 8(2) rays articulated to ventral caudal-fin plate (5 or 6 on hypurals 1+2, and 2 on parahypural). Total vertebrae usually 41(7)–42*(7), rarely 43(2) or 44(2). Ribs 7*(6)–9(1).

Epiphyseal branch of supraorbital canal on the head (S6) with contralateral canals connecting at midline, proceeding posteriorly as a single canal and opening in a single pore (diaulic S6+S6 pore).

Coloration in alcohol. Background body coloration pale yellow, dorsal and lateral regions of body with sparsely distributed dark brown chromatophores, more concentrated dorsal to midlateral stripe. Ventral region of body and head lacking pigmentation. Brown midlateral stripe wide, faint, not well-delimited, extending from snout to eye and posterior to eye onto the caudal-fin origin. Dorsal region of body with slightly more concentrated brown chromatophores from dorsal-fin origin to half adipose-fin base, fading posteriorly. Pseudotympanum area darker than surrounding areas. Dorsal region of head with scattered dark brown chromatophores. Cephalic brown pigment at posterior fontanel region. Paired dorsal dark-brown stripes, weakly delimited, extending along supraoccipital process. Maxillary barbel dorsal surface brown; mental barbels weakly pigmented along their dorsal surfaces. Dorsal fin with scattered brown chromatophores, more heavily pigmented at the dorsal-fin spine. Dorsal fin with light brown stripe near its base, followed by a hyaline stripe, and distal half darkened. Pectoral-fin spine and branched rays with scattered chromatophores along their extension. Pelvic, anal and caudal fins almost hyaline, with sparse brown chromatophores along rays. Adipose fin hyaline.

Geographical distribution. Pimelodella guato is known from the rio Paraguai basin, which includes all rivers where the new species was sampled, i.e. the rio Miranda, rio Coxim, rio Taquari, and rio Paraguai itself ( Fig. 4 ). The rio Miranda drains from Mato Grosso do Sul State, ultimately joining the rio Paraguai on its left bank within the municipality of Corumbá. Moreover, the rio Miranda basin interconnects with the northwest region of the rio Taquari basin (Mendes et al., 2004). The rio Taquari originates in the highlands of Mato Grosso State and courses into Mato Grosso do Sul, in Brazil (Galdino et al., 2003). In the latter State, the rio Taquari flows east-towest, with the rio Coxim serving as its primary tributary before its confluence with rio Paraguai on its left bank (Galdino et al., 2003).

Ecological notes. Within the rio Taquari, Pimelodella guato was sampled at the Palmeiras waterfall, in an area characterized by shallow waters, moderate water flow, and a sandy substrate (Slobodian et al., 2022). This species exhibits abundance during the rainy season and is notably easy to capture, particularly during the nighttime (Slobodian et al., 2022).

Etymology. The species name guato is in honor of the indigenous Guató people, who are affectionately known as “people of the Pantanal waters” due to their primary mode of transportation, canoes. Historically, the Guató people inhabited an extensive area along the rio Paraguai (Schmidt, 1942). However, in the 1940s, they began to lose their territory due to cattle ranching, and many relocated to cities such as Cáceres and Corumbá. This dispersal led to a reduction in the Guató population, and since then, they have been fighting for recognition of their ethnicity and the demarcation of their lands (Costa, 2015). The choice of guato is a homage to the resilience and cultural significance of these people who inhabit the same region where the new species is found. It also recognizes the ongoing struggles with land delimitation that indigenous communities continue to face, particularly in Brazil. A noun in apposition.

Conservation status. Pimelodella guato has predominantly been documented within the rio Miranda in the rio Paraguai basin. Despite several anthropic activities in this region, such as ecotourism and land use, which adversely affect water quality, comprehensive conservation plans and projects are notably lacking (Boin et al., 2019; Leite et al., 2022). Moreover, both the rio Taquari and rio Coxim confront significant challenges related to erosion and river siltation (Galdino et al., 2003, 2006; Rabelo, Souza, 2021), also correlated to road paving in the Coxim municipality region (H. Gimênes-Júnior, 2023, pers. comm.). While geological factors in the region render it more susceptible to these issues, deforestation and livestock activities exacerbate erosion and siltation to alarming levels (Galdino et al., 2003, 2006; Rabelo, Souza, 2021). Biological and ecological information on P. guato remains unavailable, posing a challenge to accurately categorizing its conservation status. Nevertheless, despite the restrictive known distribution of the species, we suggest that P. guato be classified as Least Concern (LC), according to the International Union for Conservation of Nature (IUCN) categories and criteria (IUCN Standards and Petitions Subcommittee, 2022).

Figures

FIGURE 1 | Pimelodella guato, holotype, ZUFMS-PIS 8515, 78.5 mm SL, Brazil, Mato Grosso do Sul, Corumbá municipality, rio Paraguai basin, rio Miranda, sandy beaches at Passo do Lontra region, 19°34’37”S 57°00’42”W. A. Dorsal; B. Left lateral; and C. Ventral views. Scale bar = 1 cm.

FIGURE 2 | Left lateral view of radiographs of Pimelodella species, illustrating the dorsal lamina of Weberian complex vertebrae of A. Pimelodella guato, paratype, ZUFMS-PIS 647, 90.1 mm SL; B. P. taeniophora, ZUFMS-PIS 6320, 68.9 mm SL; C. P. mucosa, holotype, CAS 63720, 97.4 mm SL; and D. P. serrata, LIRP 10022, 83.6 mm SL.

FIGURE 3 | Pectoral-fin spine of A. Pimelodella guato, paratype, CIUnB 1772, 91.2 mm SL, length of spine 16.7 mm; B. P. taeniophora, ZUFMS-PIS 6320, 68.9 mm SL, length of spine 11.4 mm; C. P. mucosa, holotype, CAS 63720, 97.4 mm SL, length of spine 22.8 mm; D. P. serrata, holotype, FMNH 57979, 55.7 mm SL, length of spine 18.3 mm; and E. P. howesi, holotype, ANSP 69036, 79.3 mm SL, length of spine 17.8 mm.

FIGURE 4 | Geographic distribution of Pimelodella guato in the rio Paraguai basin (red star, type-locality; red dots, paratype localities). The symbols might represent more than one voucher specimen each.