Odontesthes crossognathos, Wingert & Ferrer & Neves & Baumgartner & Malabarba, 2022

Wingert, Juliana M., Ferrer, Juliano, Neves, Mayara P., Baumgartner, Dirceu & Malabarba, Luiz R., 2022, A New Species of Silverside of the Genus Odontesthes (Atheriniformes: Atherinopsidae) with Hypertrophic Lips from a High-Altitude Basin in Southern Brazil, Ichthyology & Herpetology 110 (4), pp. 680-689 : 682-686

Odontesthes crossognathos , new species urn:lsid:zoobank.org:act:8DAF49EB-AB63-4217-A884-ABB05C3815AD

Figures 1–3 , Table 2

Odontesthes sp. — Delariva et al., 2019: pg. 8 (check list from Pelotas River); pg. 10, fig. 5N (photograph in lateral view); pg. 11 (comparison with congeners from Uruguay River basin).

Paratypes.— UFRGS 28745 , 1, 103.2 mm SL, collected with the holotype, tissue code in the UFRGS collection: TEC 9265B; GenBank accession number for COI: OL629034; LIRP 6101 , 2 , 221.9 – 275.7 mm SL, das Contas River , municipality of São José dos Ausentes, Rio Grande do Sul State, Brazil, 28834 0 36 00 S, 49843 0 20 00 W, A. Ribeiro, 11 February 2008 ; GIG 2312, 4, 133.1– 162.1 mm SL, UFRGS 28830 , 4 (1 CS) 134.6– 159.3 mm SL, Pelotas River , municipality of São Joaquim, Santa Catarina State, Brazil, 28828 0 46.0 00 S, 50802 0 36.4 00 W, Instituto Neotropical de Pesquisas Ambientais ( INEO), 12 August 2013 .

Diagnosis.— Odontesthes crossognathos is distinguished from all congeners by the autapomorphic presence of hypertrophied lips supported by numerous dermal papillae embedded in the upper and lower lips. These papillae are visible as thin filaments inside lips of cleared and stained specimens ( Fig. 2 ), and are visible externally when scraping the epidermis of the lips in specimens preserved in formalin or alcohol. Odontesthes crossognathos is further distinguished from congeners, except for O. humensis , by the upper jaw distinctly longer than the lower jaw with a subterminal mouth ( Fig. 3 ; vs. upper and lower jaws of same length or upper jaw slightly longer than lower jaw). Odontesthes crossognathos is distinguished from O. humensis by the first dorsal-fin origin positioned at the vertical line of anus or slightly posterior (vs. first dorsal-fin origin anterior to anus), smaller distance between the pectoral-fin insertion in dorsal view (43.9–51.9 vs. 53.3–64.4 of HL), endopterygoid teeth present (vs. absent), opercle with ventral border straight ( Fig. 4 ; vs. ventral border convex), cleithrum with dorsomedial wing exceeding in length the suture between scapula and coracoid ( Fig. 5 ; vs. dorsomedial wing not surpassing the suture between scapula and coracoid), pelvic girdle with dorsolateral process wide and forming an angle of nearly 90 degrees with dorsal plate ( Fig. 6 ; vs. dorsolateral process narrow and forming an angle larger than 90 degrees with dorsal plate), and pelvic girdle with the median process wide and directed anterolaterally ( Fig. 6 ; vs. median process narrow and directed anteriorly).

Description.— Morphometric data of 12 specimens in Table 2. Body elongate and slender. Dorsal body profile slightly convex from snout tip to origin of second dorsal fin; straight and slightly ascending along second dorsal fin to end of caudal peduncle. Ventral body profile slightly convex from tip of snout to origin of anal fin; straight and ascending along anal fin to end of caudal peduncle. Caudal peduncle longer than deep.

Head relatively long; dorsal profile markedly convex in snout and straight posteriorly, ventral profile straight with small concavity below lower jaw. Snout relatively long, rounded in dorsal view. Eye lateral, rounded and large. Mouth protractile, sub-terminal, with upper jaw distinctly longer than lower jaw. When closed, positioned at horizontal line through near ventral margin of eye. Upper and lower lips hypertrophied (see Lip histology section below).

Pectoral fin trapezoidal with i þ 12–14 (i þ 13) rays; unbranched and 1 st to 4 th branched rays longer with tips not reaching pelvic-fin origin. Pelvic fin triangular with i þ 5 (i þ 5); unbranched ray shorter and branched rays of same length, not reaching anal-fin origin. Pelvic-fin insertion close to each other with interpelvic membrane uniting them at base or half-length of rays. First dorsal fin smaller than second one, triangular with iv–vi rays (holotype with first dorsal fin damaged). First dorsal-fin origin at vertical line through anus or slightly posterior and anterior to anal-fin origin. Second dorsal fin triangular with distal margin concave and ii þ 8–9 (ii þ 8) rays. Second dorsal-fin origin approximately at vertical line through half-length of anal-fin base. Anal fin elongate with distal margin usually concave, ii þ 14–18 (ii þ 15) rays. Anal-fin origin approximately at vertical line through half-length of first dorsal fin. Caudal fin forked with slightly rounded lobe tips and scales at least up to half-length; principal caudal-fin rays i þ 15 þ i (i þ 15 þ i).

Scales large and cycloid with posterior margin smooth; striae forming complete circles. Scales of lateral line series over lateral stripe 50–57 (52). Pored lateral-line scales before the first dorsal fin 21–27 (23). Rows of scales between origin of first dorsal fin and origin of anal fin 10–11 (11). Rows of scales between origin of second dorsal fin and posterior insertion of anal fin 9–10 (10). Dorsal scales between posterior insertion of first dorsal fin and origin of second dorsal fin 6–8 (8). Longitudinal scale rows above left and right lateral stripes 11 (11). Predorsal scales 24–30 (26). Rows of longitudinal scales in the opercle 7–8 (8). Rows of longitudinal scales below eye 2 (2). Rows of longitudinal scales around caudal peduncle 18–20 (20).

Vertebrae 49; precaudal vertebrae 24, caudal vertebrae 25. Gill rakers 5–7 (5) on upper and 19–22 (21) on lower branches of first gill arch. Endopterygoid teeth present. Opercle with ventral border straight ( Fig. 4 ). Cleithrum with dorsomedial wing exceeding in length suture between scapula and coracoid ( Fig. 5 ). Pelvic girdle with dorsolateral process wide and forming angle of nearly 90 degrees with dorsal plate; median process wide and directed anterolaterally ( Fig. 6 ).

Color in alcohol.— Lateral surface of body dark yellow with wide dark brown stripe extending from pectoral-fin origin to caudal-fin base, slightly wider below dorsal fins. Specimens fixed directly in alcohol remain with lateral stripe silvery (UFRGS 27180 and UFRGS 28745). Lateral portion of body above lateral band weakly pigmented with black chromatophores on borders of scales. Dorsal surface of body dark yellow with black chromatophores; strongly concentrated on borders of scales in predorsal region. Ventral surface of body yellow. Dorsal surface of head strongly pigmented with black chromatophores, forming conspicuous blotches around eye and nostril, over dark yellow background. Lateral and ventral surfaces of head mostly dark yellow, weakly pigmented with black chromatophores in opercle, tip of snout, upper and lower lips. Pectoral, pelvic, first dorsal, and anal fins light yellow. Second dorsal fin light yellow, weakly pigmented with black chromatophores distally. Caudal fin light yellow with distal border strongly pigmented with black chromatophores.

Color in life.— Lateral surface of body light gray dorsally and bright white ventrally with wide bright silvery stripe delimited dorsally by thin black line extending from pectoral-fin origin to caudal-fin base ( Fig. 1 ). Lateral portion of body above silvery stripe with black chromatophores on border of scales. Dorsal surface of body light gray with black chromatophores, strongly concentrated on border of scales. Dorsal surface of head strongly pigmented with black chromatophores. Ventral surface of head bright white. Eye with white iris and black pupil.

Lip histology.— The lips of Odontesthes crossognathos are covered with numerous short filaments in specimens that have suffered abrasion of the lip epidermis during collection or that have been dehydrated after preservation. These filaments are not observable externally in living specimens, but they are visible as thin unpigmented filaments inside epidermal lip tissue in cleared and stained specimens ( Fig. 2 ). Histological examination shows these filamentous structures are dermal papillae constituted of loose connective tissue, originating from dermis and projected through epidermal layers of pavement cells and reaching stratified squamous epithelial tissue ( Fig. 7 ).

Sexual dimorphism.— No sexual dimorphism was observed in the specimens examined.

Distribution and habitat.— Odontesthes crossognathos is endemic to the Pelotas River basin ( Fig. 8 ). The Pelotas River, on the border of Rio Grande do Sul and Santa Catarina States, forms the Uruguay River after joining with the Canoas River. All records of Odontesthes crossognathos are from the Pelotas River or its tributaries near their mouths in altitudes varying from 750 to 1,000 m. In this area, rivers and streams drain through high slopes having translucent and cold waters with rock bottoms. According to surveys carried out in the region over one year, the species inhabits rapids and backwaters in tributaries and rapids and pools in the main channel of the Pelotas River ( Delariva et al., 2019). Stomachs of examined specimens contained ephemeropteran and trichopteran larvae.

Etymology.— From the Greek krossos (¼ fringes) and gnathos (¼ jaw) in reference to the fringed lips due to the presence of the dermal papillae. A noun in apposition.

Conservation assessment.— Odontesthes crossognathos has an extent of occurrence (EOO) less than 500 km 2, being known only for the main channel of the Pelotas River and some tributaries. The UHE Barra Grande, placed downstream of the distribution area of Odontesthes crossognathos , is the only hydroelectric power plant installed in the Pelotas River. However, the geomorphology of the Pelotas River basin makes it a target of incentive programs to install small hydroelectric plants ( Delariva et al., 2019), which can negatively affect the area of distribution, quality of habitat and the movement of the species. Considering that Odontesthes crossognathos apparently is not facing these immediate impacts of dams or any other, we suggest categorizing it as being of Least Concern (LC) according to IUCN categories and criteria (IUCN Standards and Petitions Committee, 2019).

Molecular analysis.— An alignment of 795 base pairs (bp) was obtained from COI sequences from 39 specimens with 473 positions conserved, 22 variable, and 15 parsimony informative. Genetic distances are presented in Table 3. Intraspecific genetic distance of Odontesthes crossognathos was 0.00%, and the interspecific genetic distance from its congeners varied between 1.18% (from O. ledae ) to 1.89% (from O. yucuman ). The network analysis resulted in 17 haplotypes with one hypothetical inferred ( Fig. 9 ). Haplotype diversity ¼ 0.91. Odontesthes crossognathos , O. humensis , and O. yucuman present one, two, and three single haplotypes, respectively, whereas the remaining species share one ( O. argentinensis and O. bonariensis ), two ( O. bicudo , O. ledae , and O. perugiae ), four ( Odontesthes sp. A ., O. piquava ), or five ( O. mirinensis ) haplotypes. The phylogenetic relationships of Odontesthes based on neighbor-joining analysis and the maximum likelihood tree obtained with RAxML recovered O. crossognathos as sister to O. humensis (Supplemental Figures A, B; see Data Accessibility).

Figures

FIG. 1. Odontesthes crossognathos, in lateral view. (A) Holotype, UFRGS 27180, 183.7 mm SL, Invernadinha Stream, tributary to the Pelotas River in the locality of Luisinho, upper Uruguay River basin, municipality of São Joaquim, Santa Catarina State, Brazil; (B) paratype, UFRGS 28745, 103.2 mm SL, collected with the holotype.

FIG. 2. Snout of Odontesthes crossognathos, in lateral view, anterior to left, paratype, UFRGS 28830, CS, 134.6 mm SL. Arrows indicate the dermal papillae. Scale bar ¼ 2 mm.

FIG. 3. Head of Odontesthes crossognathos, in lateral view. (A) Holotype, UFRGS 27180, 183.7 mm SL; (B) paratype, UFRGS 28745, 103.2 mm SL. Arrow indicates the dermal papillae.

FIG. 4. Opercle in dorsal view. (A) Odontesthes crossognathos, left side, anterior to left, paratype, UFRGS 28830, 134.6 mm SL; (B) Odontesthes humensis, left side, anterior to left, UFRGS 4130, 134 mm SL. Arrows indicate the ventral border. Scale bar ¼ 2 mm.

FIG. 5. Pectoral girdle in dorsal view. (Left) Odontesthes humensis, left side, anterior to left, UFRGS 22497, 130.3 mm SL; (Right) Odontesthes crossognathos, right side, anterior to left, paratype, UFRGS 28830, 134.6 mm SL. Arrows indicate the dorsomedial wing surpassing the suture between scapula (S) and coracoid (C). Scale bar ¼ 2 mm.

FIG. 6. Pelvic girdle in dorsal view. (Left) Odontesthes humensis, right side, anterior to left, UFRGS 22497, 130.3 mm SL; (Right) Odontesthes crossognathos, left side, anterior to left, paratype, UFRGS 28830, 134.6 mm SL. Black arrows indicate the angle of dorsolateral process (dp) with dorsal plate (dpl). Gray arrows indicate the shape and direction of the median process (mp). Scale bar ¼ 2 mm.

FIG. 7. Histological section of the lip of Odontesthes crossognathos showing dermal papillae (black arrows) as fingerlike projections from dermis constituted by loose connective tissue (lct), and projected through epidermal layers of pavement cells and reaching stratified squamous epithelial tissue (sste). EP ¼ epidermis; DE ¼ dermis; (*) ¼ technique artifact. Scale bar ¼ 200 lm.

FIG. 8. Distribution of Odontesthes crossognathos in the Pelotas River basin, Upper Uruguay River drainage, Rio Grande do Sul and Santa Catarina states, south Brazil. Star represents the type locality.

FIG. 9. Haplotype network illustrating the genetic connectivity of COI haplotypes of Odontesthes crossognathos and congeners. Each circle represents a unique haplotype with circle sizes being proportional to their frequencies. Each color represents a different species of Odontesthes. Crossed markers in the branches that connect the haplotypes represent the number of mutations.