Paragenidens grandoculis (Steindachner 1877) Marceniuk & Ingenito & Lima & Gasparini & Oliveira, 2019

Marceniuk, Alexandre Pires, Ingenito, Leonardo Ferreira Da Silva, Lima, Flávio César Thadeo, Gasparini, João Luiz Rosetti & Oliveira, Claudio, 2019, Systematics, biogeography and conservation of Paragenidens grandoculis n. gen. and n. comb. (Siluriformes; Ariidae), a critically endangered species from southeastern Brazil, Zootaxa 4586 (3), pp. 425-444 : 430-434

publication ID	https://doi.org/ 10.11646/zootaxa.4586.3.2
publication LSID	lsid:zoobank.org:pub:DAFD77FB-77E6-4C1C-BCB0-09B4420977ED
DOI	https://doi.org/10.5281/zenodo.3510438
persistent identifier	https://treatment.plazi.org/id/03D0CE16-C02A-034D-988D-FC57BD9CFAAA
treatment provided by	Plazi
scientific name	Paragenidens grandoculis (Steindachner 1877)
status	comb. nov.

Treatment

Paragenidens grandoculis (Steindachner 1877) , new combination

( Figures 2 View FIGURE 2 , 3 View FIGURE 3 and Table 1 View TABLE 1 )

Arius grandoculis Steindachner 1877: 644 View in CoL –646, pl. 11 (type-locality: "Rio Doce" southeastern Brazil).

Potamarius grandoculis View in CoL .-Marceniuk & Ferraris 2003:452 (only name).—Marceniuk & Menezes 2003:43 (only name).— Marceniuk 2005:98 (identification key).- Marceniuk & Menezes 2007:98 View Cited Treatment (taxonomy), Vieira & Gasparini 2007: 90 (conservation).-Ferraris 2007:53 (only name).— Marceniuk et al. 2012:668 (phylogenetic relationships).

Diagnosis. Paragenidens grandoculis is distinguished from other Neotropical ariids by having vestigial accessory tooth plates [vs. very conspicuous accessory tooth plates in all other ariid representatives including Potamarius ussumacintae and excluding Chinchaysuyoa labiata , C. ortegai and mouth-brooders males of Genidens genidens , or absent in P. izabalensis and P. nelsoni , Figure 3 View FIGURE 3 (a), (b)]. Paragenidens grandoculis differs from Potamarius izabalensis and P. nelsoni from Central America, and the sympatric Genidens genidens , by having snout length 1.0–1.5 times in cephalic shield width at frontal area [vs. 1.6–1.7 times in G. genidens and 0.5–0.8 times in P. izabalensis and P. nelsoni , Figure 4 View FIGURE 4 (b)], and snout length 2.2–2.7 times in body width [vs. 2.9–4.3 times in G. genidens , 1.6–1.8 times in P. izabalensis and P. nelsoni , Figure 4 View FIGURE 4 (c)] and from Chinchaysuyoa labiata and C. ortegai from Ecuador and Peru, in the eastern Pacific, by longer head (27.0–29.4% SL vs. 17.9–19.7% SL in C. labiata and 19.9–21.7% SL in C. ortegai ) and narrow cephalic shield at lateral ethmoid area (9.7–11.5% SL vs. 11.7–12.0% SL in C. labiata and 12.4–13.3 in C. ortegai ).

Description. Morphometrics data summarized in Table 1 View TABLE 1 . Head long, very narrow and depressed at lateral ethmoid and frontal area, with profile elevated posteriorly, straight from mesethmoid to parieto-supraoccipital process. Snout long and narrow. Anterior nostril round, with fleshy edge, posterior nostril covered by flap of skin; nostrils quite close to one another and distant to orbit, not connected by fleshy furrow. Eye lateral and very large; relatively close to each other. Three pairs of long teretiform barbels; maxillary barbel surpassing base of pectoralfin spine, lateral mental barbel surpassing margin of gill membrane, and mesial mental barbel not reaching margin of gill membrane. Mouth subterminal to terminal, relatively small and lower jaw arched. Lips thin, lower lip thinner than upper lip. Vomerian tooth plates absent. Accessory tooth plates vestigial. Premaxilla relatively long and narrow, with sharp teeth. Dentary separated at midline, with sharp teeth. Gill membranes fused, attached to isthmus. Fifteen to 17 acicular gill rakers on first arch, 16–18 spike-shaped gill rakers on second arch. Mesial surfaces of first and second gill arches with or without developed gill rakers, lateral and mesial surfaces of first and second gill arches lacking fleshy papillae intercalated with gill rakers.

Bony bridge formed by lateral ethmoid and frontal relatively long and slender, readily discernible under skin. Cephalic shield exposed, moderately rough and granulated, long and relatively straight on lateral ethmoid, frontal, and supra cleithrum areas. Anterior portion of dorsomedial groove of neurocranium fleshy, inconspicuous to level of posterior nares; posterior portion of dorsomedial groove of neurocranium osseous, deep and conspicuous, with straight margins tapering posteriorly. Parieto-supraoccipital process slightly tapered antero-posteriorly, long and narrow on posterior portion, with profile straight. Nuchal plate crescent-shaped, moderately short and wide.

Body width slightly greater than body depth at pectoral-girdle area, progressively compressed from pectoral fin to caudal peduncle. Lateral line sloping ventrally on anterior one-third, extending posteriorly to caudal peduncle, bending abruptly onto dorsal lobe of caudal fin. Dorsal-fin spine long and thick; anterior margin with granules on basal two-thirds, distal one-third with short serrations; posterior margin with serrations along almost its entire length. Seven dorsal-fin soft rays. Pectoral-fin spine long, as long as dorsal-fin spine; anterior margin with granules on basal two-thirds and distal one-third with short serrations; posterior margin straight on basal onefourth, distal three-fourths with conspicuous serrations. Nine to 10 pectoral-fin soft rays. Posterior cleithral process exposed, smooth and triangular shaped, long and pointed posteriorly. Pelvic fin deep and short at base, with six rays. Adipose-fin base short, less than one-half the length of anal-fin base, anterior origin at level of anterior half of anal fin. Anal fin very deep and relatively short at base, with 15-17 rays and ventral profile markedly concave. Caudal peduncle low. Caudal fin forked, dorsal and ventral lobes relatively long, posteriorly pointed; dorsal lobe longer than ventral lobe.

Morphological variation. The well-developed gill rakers on mesial surfaces of first and second gill arches, present in the specimens from Espírito Santo [ Figure 3 View FIGURE 3 (c)], were not observed in the single specimen from Rio de Janeiro [ Figure 3 View FIGURE 3 (d)].

Distribution and habitat. Paragenidens grandoculis is known from lagoa Juparanã [MZUSP 79459 and MZUSP 10104–10114, Figures 2 View FIGURE 2 (d), (e)] and lagoa Nova [LBP 24068, Figure 2 View FIGURE 2 (f)], municipality of Linhares, Espírito Santo state, both natural lakes that connect with lower river Doce basin only in floods periods, and from lagoa Feia [MZUSP 2295, Figure 2 View FIGURE 2 (c)] at Campos dos Goytacazes municipality, Rio de Janeiro state, southeastern Brazil ( Figure 5 View FIGURE 5 ). Recent collect efforts at the lower rio Doce at the municipality of Linhares (including the district of Regência) have shown that the species is not present in the main channel of rio Doce, where only specimens of Genidens genidens were collected (CZNC 2467; specimens not deposited). Based on the know distribution of the species, supported by museum specimens, we infer that the distribution of Paragenidens grandoculis is restrict to freshwater coastal lakes from southeastern Brazil.

Remarks. Arius grandoculis was described by Steindachner (1877) based on specimens deposited at Naturhistorisches Museum, Wien [holotype, NMW 48272, Figure 2 View FIGURE 2 (a)] and two other specimens from the Museum of Comparative Zoology [MCZ 7680–81, Figure 2 View FIGURE 2 (b)], all collected by Charles F. Hartt and Edward Copeland during their travel as members of the Thayer Expedition across the lower rio Doce, between Aimorés (Minas Gerais State) and Linhares (Espírito Santo State). Additional specimens were collected by Ernst Garbe (naturalist traveler from the Museu Paulista, currently MZUSP) probably in 1906, in rio Doce at Linhares, Espírito Santo State (MZUSP 2294) and at lagoa Feia at Campos dos Goytacazes, Rio de Janeiro State [MZUSP 2295, Figure 2 View FIGURE 2 (c)]. Garbe’s specimen from rio Doce was not found in the MZUSP collection and is possibly lost, while the specimen from lagoa Feia was examined here.

During the 1960’s decade three other putative records of Paragenidens grandoculis were reported. In 1965, Heraldo A. Britski and Izaurio A. Dias collected 20 specimens of P. grandoculis at lagoa Juparanã (Linhares), which is the largest and most complete record of the species in scientific collections [MZUSP 10104–10114, Figure 2 View FIGURE 2 (e)]. Most of the specimens from that expedition were examined here and had their identity confirmed, but some of them (MZUSP 22995) were not found at the museum collection and are possibly lost. Another lot, possibly collected with the specimens from lagoa Juparanã, was discovered at MZUSP and identified as P. grandoculis [MZUSP 79459, Figure 2 View FIGURE 2 (d)].

Attempts of finding Paragenidens grandoculis in nature may have been hindered by the difficulties inherent in the recognition of the members of the family Ariidae ( Marceniuk 2005) and, particularly, the lack of information about the species itself. Additionally, the historic low number of records of P. grandoculis may also be a consequence of the poor knowledge of the fish fauna of the areas where the species occurs ( Vieira 2010; Sarmento- Soares et al. 2012, 2013, 2014). The external morphological resemblance between P. grandoculis and G. genidens certainly contributed to the mistaken identifications detected with the museum specimens ( Figure 6 View FIGURE 6 ; e.g. MNRJ 3581, MNRJ 9732, NPM 318). Nevertheless, local artisanal fishermen recognize both species as rabo seco (dry tail), but distinguish them as two different varieties, one from the main channel of the river [ G. genidens , Figure 6 View FIGURE 6 (d)] and the other from the lakes [ P. grandoculis , Figure 2 View FIGURE 2 (f)].

Material examined. Type-specimens: MCZ 7680 View Materials (1, 196 mm SL), Minas Gerais e Espirito Santo, rio Doce , between Linhares and Aimorés ; MCZ 7681 View Materials (1, 193 mm SL), Minas Gerais e Espirito Santo, rio Doce , between Linhares and Aimorés. Non type-specimens: MZUSP 10104–10114 View Materials (9, 156– 204 mm SL), Espírito Santo, lagoa Juparanã at Linhares ; MZUSP 79459 View Materials (1, 247 mm SL), Espírito Santo, lagoa Juparanã at Linhares ; LBP 24068 (1, 240 mm SL), Espírito Santo, lagoa Nova at Linhares ; MZUSP 2295 View Materials (1, 251 mm SL), Rio de Janeiro, lagoa Feia at Campos dos Goytacazes .