Eigenmannia correntes, Campos-Da-Paz, Ricardo & Queiroz, Igor Raposo, 2017

Campos-Da-Paz, Ricardo & Queiroz, Igor Raposo, 2017, A new species of Eigenmannia Jordan and Evermann (Gymnotiformes: Sternopygidae) from the upper rio Paraguai basin, Zootaxa 4216 (1), pp. 73-84 : 76-82

Eigenmannia correntes , new species

Figures 1–2

Holotype. MNRJ 47046 , 113.0 mm LEA, Brazil, Mato Grosso do Sul, Sonora, córrego de Baixo, left margin tributary of rio Correntes , at road MS-213, 17o42’46”S 54o21’25”W, R. Campos-da-Paz, 4 Oct 2003.

Paratypes. All collected along with holotype. MNRJ 46334, 29, +2 c&s, 14.0–118.0 mm LEA.

Non-type material. All from Brazil. MNRJ 46335, 21 , 61.0–83.0 mm LEA, Mato Grosso do Sul, Sonora, córrego de Cima, left margin tributary of rio Correntes , at road MS-213, 17o39’52”S 54o14’48”W, R. Campos-da- Paz, 4 Oct 2003 ; MNRJ 46336, 10 , 44.0–69.0 mm LEA, Mato Grosso, Itiquira, stream at right margin of rio Correntes , near highway BR-163, 17o28’36”S 54o43’23”W, R. Campos-da-Paz, 5 Oct 2003 .

Diagnosis. Distinguished from all congeners, except those species included in the Eigenmannia trilineata species-group, by the presence of a conspicuous superior midlateral stripe ( Fig. 1 ; vs. absence). Eigenmannia correntes can be differentiated from all members of the Eigenmannia trilineata species-group, except E. vicentespelaea , E. waiwai and E. besouro , by the mouth subterminal ( Fig. 2 ; vs. terminal in remaining species of the E. trilineata species-group). It differs from E. vicentespelaea by: 1) lower number of premaxillary teeth (17–20, in three irregular rows vs. 25–26, in four rows); 2) lower number of dentary teeth (16–18, in two irregular rows vs. 38–45, in three or four rows); 3) higher number of longitudinal series of scales above lateral line (11–12 vs. 7–8); 4) lower number of pectoral-fin rays (ii,12–13 vs. ii,15–17); 5) lower total number of anal-fin rays (143–164 vs. 169– 191); 6) larger body width (6.4–8.1% of LEA vs. 3.5–5.8%); and 7) larger oral width (23.5–26.0% of HL vs. 9.5– 17.2%). It differs from E. waiwai by: 1) larger oral width (23.5–26.0% of HL vs. 9.5–14.6%); 2) longer snout (32.2–35.2% of HL vs. 23.8–31.5%); 3) smaller eye (orbital diameter 10.6–13.3% of HL vs. 22.6–28.8%);) greater postorbital distance (56.8–62.1% of HL vs. 43.9–55.4%); 5) smaller head depth at supraoccipital (63.7–70.0% of HL vs. 73.6–86.2%); 6) longer mouth (19.9–24.6% of HL vs. 12.1–17.7%); 7) lower number of premaxillary teeth (17–20, in three irregular rows vs. 35–40, in five rows); 8) lower number of dentary teeth (16–18, in two irregular rows vs. 37–38, in four rows); 9) higher number of longitudinal series of scales above lateral line (11–12 vs. 9–10); and 10) lower total number of anal-fin rays (143–164 vs. 167–195). Finally, it is distinguished from E. besouro by: 1) larger oral width (23.5–26.0% of HL vs. 9.5–19.1%); 2) longer snout (32.2–35.2% of HL vs. 23.7–31.9%); 3) larger eye (orbital diameter 10.6–13.3% of HL vs. 16.9–25.1%); 4) shorter postorbital length (56.8–62.1% of HL vs. 46.9–55.9%); 5) greater suborbital depth (25.2–32.3% of HL vs. 18.3–24.8%); and 6) higher number of longitudinal series of scales above lateral line (11–12 vs.7–10).

Description. Morphometric and meristic data of holotype and paratypes summarized in Table 1 . Body compressed, more markedly posterior to abdominal cavity and to posterior half of TL. Greatest body depth at abdominal region, near vertical through tip of pectoral fin. Dorsal profile of body nearly straight to gently convex anteriorly; ventral profile slightly convex.

Head compressed, widest at opercular region and deepest at occiput. Dorsal profile of head convex from tip of snout to vertical through opercular opening; ventral profile of head slightly concave from tip of mandible to opercular opening. Snout elongate, subconical; eyes of moderate size, circular, covered with thin skin, laterally oriented on anterior third of head length. Mouth of moderate size and subterminal, upper jaw projected, mandible included, rictus near a vertical through posterior naris; teeth present on both jaws, premaxillary and dentary teeth similar in size on each bone. Anterior nares small, tubular, on anterior half of mouth length and close to tip of snout; posterior nares not tubular, elliptical, near a vertical through rictus, about one eye diameter from anterior eye margin. Opercular (branchial) opening of moderate size, immediately anterior to pectoral fin origin, with membranous margin; branchial membranes joined to isthmus. Anus and well-developed urogenital papilla adjacent, ventral to opercular region, with no apparent significant shifting anteriorly with age. Pectoral fin elongate, ellipsoid, with ii,12(9) or ii,13(1) [ii,12] (total pectoral-fin rays, 14–15 [14]). Scales cycloid, present over body posterior from head, including postcranial portion of body and mid-dorsal region, maximum number of scales above lateral line at mid-body 11(4) or 12(6) [11]. Lateral line scales usually larger than those immediately dorsal and ventral to that series, 100–116 [100] to vertical to posterior end of anal fin. Anal-fin origin slightly posterior from vertical through pectoral-fin origin; anterior unbranched anal-fin rays 11–16 [11], less developed and smaller than posterior branched ones; total anal-fin rays 143–164 [143] rays. Tail cylindrical, elongate, tapering to pointed posterior end.

Relevant osteological features of Eigenmannia correntes as follows: vomer arrow-shaped anteriorly; lateral ethmoids and nasals present; antorbital and infraorbitals 1–4 enlarged, partial cylinders, with laminar bony arches, fifth and sixth infraorbitals slender and tubular; antorbital 25–30% of total length of infraorbital bones 1+2; infraorbital bones 1+2 with enlarged posterodorsal expansion (depth of posterodorsal expansion [DPE] 40% of length of infraorbital bones 1+2 [LIB]); infraorbitals 3 and 4 closely associated; premaxilla somewhat circular, with 17–20 pointed conical teeth of similar size in three irregular rows (N=2); maxilla edentulous, slender and gently curved posteriorly, with well-developed sickle-shaped anterodorsal process (about 20% of total length of maxilla, equal to width of posterior nostril); dentary triangular, with 16–18 pointed conical teeth of similar size, vertically directed in two irregular rows (N=2); small triangular coronomeckelian bone associated to posterodorsal margin of Meckel’s cartilage, about 20% of Meckel’s cartilage length; endopterygoid with well-developed dorsally directed process; small, pointed, conical teeth located ventrally sometimes in two irregular rows at anterior margin of endopterygoid, 4–5 (smaller, regenerated, c&s specimen) and 8–9 (larger c&s specimen, 112.0 mm LEA); five small elongate basibranchials, the two posterior ones unossified; five hypobranchials, the two posterior ones unossified; epibranchials 1–5 ossified; lower pharyngeal tooth plate with 7–12 conical teeth (N=2); infrapharyngobranchials 1–4 ossified; upper pharyngeal tooth plate with 7 conical teeth (N=2); urohyal broad, with irregular arrow-shaped head and well-developed posterior laminar portion, slightly larger than longest branchiostegal ray; five branchiostegal rays, three anterior ones filamentous, two posterior ones triangular, laminar distally. Scapular foramen present. Three independent pectoral proximal radials, proximal three and four coossified. Fourteen precaudal vertebrae, 10 anterior and 4 transitional vertebrae (N=2); 60 total vertebrae up to the end of anal fin (n=1). Anal pterygiophores slender and thin.

Coloration in alcohol. Background colour yellowish pale brown, darker dorsally, lighter ventrally below superior midlateral stripe. Dorsal region of head, opercle area and middorsum brown. Eyes dark. Four longitudinal dark stripes along body: lateral-line stripe, thin, extending from anteriormost perforated lateral-line scales to posterior region of caudal filament, darker and conspicuous posterior from abdominal region; superior midlateral stripe, thicker (2–3 scales deep anteriorly), dark and conspicuous, extending posteriorly from abdominal region;inferior midlateral stripe, thick, extending from postero-ventral region of abdominal region; anal-fin base stripe, moderately thick, extending along anal-fin base. Area between superior midlateral stripe and inferior midlateral stripe light. Pectoral and anal fins hyaline, with scattered chromatophores over rays, interradial membranes hyaline. Caudal filament uniform brown.

Geographic distribution. Eigenmannia correntes is currently known only from three streams, all tributaries of the rio Correntes , a major tributary of the rio Piquiri system, upper rio Paraguai basin: córrego de Baixo (typelocality; Fig. 3 ) and córrego de Cima (both left margin tributaries, municipality of Sonora, Mato Grosso do Sul state, Brazil); and another stream (not named, at the right margin of the rio Correntes , Itiquira, Mato Grosso, Brazil). To date, the only remaning valid species belonging to the Eigenmannia trilineata species-group recorded in the rio Paraguai basin is E. desantanai (see Peixoto et al., 2015; Fig. 4 ). Eigenmannia correntes is readily separated from E. desantanai , for instance, for its conspicuous subterminal mouth (vs. terminal in this latter species), premaxilla with 17–20 teeth in three irregular rows (vs. 24–25 teeth in four rows), endopterygoid with 4– 9 teeth in two irregular rows (vs. 14–15 teeth in two rows), anterior vertebrae 10 (vs. 9), transitional vertebrae 4 (vs. 2–3), precaudal vertebrae 14 (vs. 11–12), 143–164 anal-fin rays (vs. 170–198), and oral width 23.5–26.0% of HL (vs. 13.1–18.4%).

Specimens in museum and other institutional collections, usually referred to as E. virescens , are also frequently recorded from the rio Paraguai basin (e.g., Britski et al., 1999), but their actual taxonomic identity needs to be properly addressed.

Remarks. Eigenmannia is currently poorly defined within the Sternopygidae , and there is no objective evidence unequivocally demonstrating its monophyly (see “Introduction”, above). For this reason, E. correntes is herein referred to that genus on the basis of a combination of characters either plesiomorphic or of uncertain polarity (e.g., Tagliacollo et al., 2016): eyes covered by skin; scales present over entire postcranial portion of body; nasal capsule length equal to at least two diameters of the posterior nostril; teeth present posteriorly beyond the anterior portion of the dentary; teeth absent from oral valve; teeth present on endopterygoid; infraorbital bones 1+2 with enlarged posterodorsal expansion; 8) gill rakers short, unossified; and absence of any dark and clear alternating wide vertical bands on body.

Giora and Fialho (2009) studied the reproductive biology of, E. trilineata , from southern Brazil, and their results showed a high frequency of mature females from October to February, indicated that the first maturation size estimated for females was 80.5 mm TL, and that the species showed multiple spawining type. Some females of Eigenmannia correntes (individuals collected in October 2003 in the rio Correntes system,> ca. 80.0 mm TL), exhibited conspicuous distended bellies, with translucent/whitish (diameter <1.0 mm) as well as mature oocytes (diameter>1.0 mm, dark yellow/orange coloration), clearly visible inside their abdomen through transparency ( Fig. 5 ) what, as with E. trilineata , suggests a multiple spawning type. Kirschbaum (1979), for instance, also reported multiple spawning type regarding specimens identified by him as E. virescens .

Three specimens of Eigenmannia correntes (MNRJ 46335 [01, ca. 65.0 mm LEA, tail broken] and MNRJ 46336 [02, 40.0 mm and 63.0 mm LEA) had cysts containing parasites (probably metacercariae; M. M. Ishikawa and S. B. de Pádua, pers. comm.), apparently representing the first evidence of this kind of parasitism in the genus ( Fig. 6 ).

Etymology. The specific epithet correntes refers to the rio Correntes , the main river at the rio Piquiri system, upper rio Paraguai basin, from where all specimens used in the original description were collected. A noun in apposition.

Comparative material. Eigenmannia microstoma : ZMUC [“Jrn. 24”], 1, syntype, Brazil, Minas Gerais, Lagoa Santa ; MNRJ 24494, 3 , Brazil, Alagoas, Penedo ; MZUSP 22955, 2 , Brazil, Minas Gerais, Três Marias, rio São Francisco ; MZUSP 24643, 1 c&s, Brazil, Três Marias, Três Marias dam; Eigenmannia trilineata : MZUSP 22616.0, 1, Argentina, Buenos Aires, Rio de La Plata; Eigenmannia vicentespelaea : MZUSP 42605, 1 , holotype, Brazil, Goiás, São Domingos, Caverna (“ cave ”) São Vicente II, rio Tocantins basin ; MZUSP 47984, 1 paratype, collected along with holotype; Eigenmannia matintapereira : MZUSP 29973, 1 , paratype, Brazil, Amazonas, rio Arirará ; MZUSP 29974, 1 , paratype, Brazil, Amazonas, rio Marauiá, rio Negro basin ; MZUSP 29975, 3 , Brazil, Amazonas, rio Negro ; MZUSP 29981, 1 , Brazil, Amazonas, rio Negro .

Figures

FIGURE 1. Eigenmannia correntes, MNRJ 47046, holotype, 113.0 mm LEA, Brazil, Mato Grosso do Sul, Sonora, córrego de Baixo. Lateral view of body. Scale bar: 10 mm.

FIGURE 2. Eigenmannia correntes, MNRJ 47046, holotype, 113.0 mm LEA. Head and anteriormost portion of body. Scale bar: 10 mm. Arrow indicates anus position.

FIGURE 3. View of córrego de Baixo (downstream), left margin tributary of rio Correntes, at point where it crosses road MS- 213, Brazil, Mato Grosso do Sul, Sonora, 17 o 42 ’ 46 ” S, 54 o 21 ” 25 ” W. Type locality of Eigenmannia correntes.

FIGURE 4. Map of South America showing approximate type-localities of species belonging to the Eigenmannia trilineata species-group. Circle: Eigenmannia correntes; squares: 1 = E. antonioi; 2 = E. besouro; 3 = E. desantanai; 4 = E. guairaca; 5 = E. matintapereira; 6 = E. microstoma; 7 = E. muirapinima; 8 = E. pavulagem; 9 = E. trilineata; 10 = E. vicentespelae; 11 = E. waiwai.

FIGURE 5. Lateral view of dissected distended abdominal region of paratype of Eigenmannia correntes (MNRJ 46334, 76.0 mm LEA) showing translucent / whitish (diameter <1.0 mm) as well as mature oocytes (diameter> 1.0 mm, dark yellow / orange) inside abdomen. Head to right. Scale bar: 5 mm.

FIGURE 6. Lateral view of body of non-type specimen of Eigenmannia correntes (MNRJ 46336, 40.0 mm LEA) showing cysts (probably of metacercarie; specimen before it was dissected for removal of parasites). Scale bar: 5 mm.

Tables

TABLE 1. Morphometric and meristic data for Eigenmannia correntes, new species. See text for details. Legends: Min. = Minimum; Max. = Maximum; N = Number of specimens measured; SD = standard deviation.

Measurements	Holotype	Paratypes	Mean	SD	N
		Min.—Max.
Absolute values (mm)
Total length (TL)	160.0	104.0–145.0	-	-	10
Length to end of anal fin (LEA)	113.0	76.0–115.0	-	-	10
Head length (HL)	16.7	11.4–15.5	-	-	10
Percentage of LEA (%)
Head length	13.0	13.1–14.9	13.9	1.0	10
Snout-to-opercle length	12.8	11.2–14.3	13.0	0.9	10
Preanal distance	17.5	14.7–19.2	17.2	1.5	10
Prepectoral distance	15.1	12.9–15.8	14.5	0.8	10
Snout-to-anus length	7.7	7.0–8.2	7.5	0.4	10
Body depth at pectoral-fin tip	15.4	12.1–16.2	14.7	1.3	10
Body depth at anal-fin origin	14.0	11.0–15.1	13.2	1.1	10
Body width	7.51	6.4–8.1	7.1	0.7	10
Anus to anal-fin origin distance	10.7	7.0–11.6	9.7	1.4	10
Anal-fin length	82.3	75.4–84.3	80.9	2.8	10
Pectoral-fin length	8.8	7.5–8.8	8.4	0.4	10
Snout-to-occiput length	11.7	9.5–12.6	11.5	0.9	10
Caudal-filament length	41.5	22.8–38.9	32.3	5.6	10
Caudal filament width	0.7	0.6–0.7	0.7	0.1	10
Caudal filament depth	1.5	1.1–1.4	1.3	0.2	10
Percentage of HL (%)
Snout length	33.6	32.2–35.2	33.8	0.8	10
Internasal distance	10.8	9.3–11.9	10.3	0.7	10
Snout-to-posterior naris distance	23.6	21.5–25.9	23.2	1.3	10
Posterior naris-to-orbit distance	9.6	8.5–10.5	9.5	0.7	10
Internarial width	15.8	13.6–18.8	15.6	1.5	10
Head width at opercle	51.8	47.4–53.6	50.4	2.2	10
Head width at orbits	41.6	36.1–42.3	40.2	2.1	10
Orbital diameter	12.4	10.6–13.3	12.0	0.8	10
Postorbital distance	58.2	56.8–62.1	58.9	1.3	10
Eye-to-opercle length	47.6	44.5–48.4	46.4	1.2	10
Opercular opening	25.8	21.0–25.0	23.0	1.5	10
Suborbital depth	31.8	25.8–32.3	29.0	2.0	10
Interorbital distance	25.9	25.2–30.1	28.0	1.7	10
Head depth at supraoccipital	65.9	63.7–70.0	66.6	2.1	10
Head depth at orbits	46.1	46.6–51.4	47.8	1.5	10
Mouth length	24.6	19.9–23.8	21.9	1.5	10
Oral width	23.7	23.5–26.0	24.7	1.0	10