Hypopygus varii, Campos-Da-Paz, 2018

Campos-Da-Paz, Ricardo, 2018, A new species of Hypopygus Hoedeman (Gymnotiformes: Rhamphichthyidae) from the rio Trombetas system, Amazon basin, Brazil, Zootaxa 4410 (1), pp. 190-200 : 192-198

Hypopygus varii , new species

( Figures 1–2 , Table 1)

Stegostenopos sp. n. — Lin et al., 2003 [habitat and biological notes; indication of Stegostenopos Triques as possible junior synonym of Hypopygus Hoedeman ].

Holotype. MNRJ 46752 , 89.0 mm LEA, Brazil, Pará, Oriximiná, Amazonas basin, rio Trombetas system, igarapé Saracá , 1o31’22”S 56o19’52”W, D. S. Lin, A. M. Castro, Roníkon & M. C. Santos, 15 Mar 2001 .

Paratypes. Brazil, all collected along with holotype: MNRJ 46753, 7, + 1 c&s, 60.0–85.0 mm LEA.

Diagnosis. Hypopygus varii differs from all congeners, except H. hoedemani , by a larger interocular width (35.0–37.3% HL vs. 15.0–34.5% HL in all congeners but H. hoedemani ; 29.6–63.3% HL in H. hoedemani ). It also differs from congeners by the terminal mouth (except H. hoedemani and H. isbruckeri ; vs. mouth subterminal in remaining species) and by a higher total number of pectoral-fin rays (13 vs. 9–12; except H. benoneae , H. cryptogenes , H. hoedemani and H. isbruckeri ). Hypopygus varii can further be distinguished from all remaining Hypopygus species by the following unique combination of morphometric and meristic traits (either primitive or of uncertain polarity): 1) snout length (30.0–33.0% HL vs. 20.3–28.6% HL in H. benoneae , 21.9–29.8% HL in H. cryptogenes , 22.2–29.5% HL in H.isbruckeri , 18.3–28.0% HL in H. neblinae and 52.8–57.9% HL in H. ortegai ); 2) postorbital length (64.4–67.8% HL vs. 55.2–64.4% HL in H. hoedemani , 57.8–63.4% in H. isbruckeri , 56.4– 63.3% HL in H. minissimus , 60.0–63.7% HL in H. nijsseni and 60.6–63.3% HL in H. ortegai ); 3) pectoral-fin length (60.4–65.9% HL vs. 45.2–59.3% HL in H. benoneae , 41.5–52.9% HL in H. cryptogenes and 52.8–56.9% HL in H. minissimus ); 4) snout-to-occiput length (9.6–11.2% of LEA vs. 11.4–14.4% LEA in H. neblinae and 12.5–13.8% LEA in H. nijsseni ); 5) caudal-filament length (47.0–50.7% LEA vs. 21.2–37.7% LEA in H. minissimus and 59.5–72.9% LEA in H. cryptogenes ); 6) total number of anal-fin rays (148–157 vs. 115–134 in H. benoneae , 102–118 in H. hoedemani , 109–135 in H.lepturus , 102–113 in H. minissimus and 137–145 in H. neblinae ); 7) presence of fourth mandibular canal bone (vs. absence in H. benoneae , H. hoedemani , H. lepturus and H. minissimus ); 8) presence of fifth mandibular canal bone (vs. absence in H. benoneae , H. hoedemani , H. lepturus and H. minissimus ); 9) presence of medial ridge on the posterior portion of dorsal surface of basihyal (vs. absence in H. benoneae , H. hoedemani , H. lepturus and H. minissimus ); 10) unossified second basibranchial (vs. ossified in H. benoneae , H. hoedemani , H. lepturus and H. minissimus ); 11) ventral propercular sensory canal present (vs. absent in H. benoneae , H. hoedemani , H. lepturus and H. minissimus ); 12) infraorbital canal aperture present (vs. absent in H. benoneae , H. hoedemani and H. minissimus ); 13) extrascapular canal present (vs. absent or partially lost in H. benoneae , H. hoedemani and H. minissimus ); 14) number of total precaudal vertebrae (15 vs. 14 in H. cryptogenes and H. isbruckeri , and 16 in H. hoedemani ); 15) 2–3 transitional vertebrae (vs. 4 in H. nijsseni ); and 16) anal-fin chromatophores, when present, only covering rays (i.e., interradial membrane hyaline vs. scattered chromatophores on anal-fin rays and membrane in H. cryptogenes and H. neblinae ).

Description. Morphometric and meristic data of holotype and paratypes summarized in Table 1. Body compressed, more markedly so posterior to abdominal cavity and to posterior half of TL. Greatest body depth at abdominal region or slightly posterior to that area. Dorsal profile nearly straight to gently convex anteriorly; ventral profile slightly convex. Head somewhat compressed, widest at opercular region and deepest at occiput; snout rounded and blunt; eyes small, covered with thin skin, laterally oriented on anterior third of head length. Mouth small and terminal, upper jaw sometimes only slightly projected, rictus not surpassing a vertical through anterior half of snout length; teeth absent from both jaws. Anterior nares not tubular, inside upper lip, laterally located; posterior nares absent. Branchial opening reduced to a short slit immediately anterior to pectoral fin origin, with membranous margin; branchial membranes amply joined to isthmus. Postpectoral accessory electric organ present; two columns with around five to six electrocytes each, with well-developed associated dorsal and ventral grooves anteriorly directed; dorsal groove extending anteriorly to approximately one to two orbital diameters behind posterior border of eye. Anterior-most perforated lateral line scale at vertical through pectoral-fin origin. Lateral line discontinuous posterior from mid-body. Five (six) or six (three) [six] subepidermic irregular canals (“grooves”) associated to lateral line portion at posterior third of LEA. Anus and urogenital papilla adjacent, ventral to opercular region, with no noticeable anterior shifting with age. Pectoral fin small, rounded distally; pectoral-fin rays ii, 11 (2), iii, 10 (3) or iv, 9 (4) [iii,10] (total pectoral-fin rays 13 [13]) (N= 9). Anal-fin origin slightly posterior from vertical through pectoral-fin origin; anterior unbranched anal-fin rays ix (2), x (2) or xi (5) [ix], less developed and smaller than posterior branched ones (N=9); total anal-fin rays 148 (1), 152 (3), 153 (1), 155 (2) or 157 (1) [152] (N=8).

Scales small, cycloid, present over body posterior from head, including mid-dorsal region; region over anal-fin pterygiophores area partially scaled. Lateral line scales usually larger than those immediately dorsal and ventral to that series. Maximum number of scales above lateral line at mid-body 9 (5), 10 (3) or 11 (1) [10] (N=9); maximum number of scales below lateral line at mid-body 9 (4) or 10 (5) [10] (N=9). Tail elongate, compressed, with pointed posterior end.

Relevant osteological features of Hypopygus varii as follows. Oromandibular region: premaxilla laminar, edentulous; maxilla slender, edentulous, with narrow descending process; dentary bone edentulous, with straight posterodorsal margin; Meckel's cartilage well developed; coronomeckelian bone somewhat elongate, one-fourth of Meckel’s cartilage length; five tubular independently ossified mandibular canal bones. Supraorbital and infraorbital series: parietal branch of supraorbital canal over frontal bone absent; supraorbital canal independent from frontal bone; infraorbital series represented only by ossified canal-bearing portion of sixth infraorbital bone; infraorbital canal aperture presente. Supensorium: endopterygoid broad, edentulous, with tiny dorsally directed process; dorsal margin of metapterygoid straight, without any anterodorsally directed process. Intermuscular bones: post-Weberian dorsal myorhabdoi with branched structure. Neurocranium: vomer absent; ventral ethmoid absent; anterior dorsomedian fontanel wide, although narrower than the lateral portion of frontal bone; lateral lamella on frontal bone presente; nasal laterosensory canal present; first ossified postotic laterosensory canal bone present; extrascapular canal bones presente; Baudelot’s ligament ossified, wide. Opercular series: ventral and dorsal sensory canals of preopercle present; dorsal preopercular sensory canal present; last preopercular sensory canal fused to preopercle; dorsal profile of opercle nearly straight. Pectoral girdle: supracleithrum independent from post-temporal; mesocoracoid bridge absent; extension of posteroventral portion of coracoid present; four ossified independent proximal pectoral radials. Hyoid arch: anterior-most branchiostegal ray absent; second branchiostegal ray narrow, third to fifth broader and laminar. Gill arches: medial ridge on posterior portion of dorsal surface of basihyal present; all five basibranchial elements unossified; urohyal broad, with small head and well-developed posterior laminar portion, larger than longest branchiostegal; all hypobranchials unossified; all five epibranchials unossified, posterior process of the fifth epibranchial short; gill rakers present as tiny irregular rounded ossified elements; lower pharyngeal tooth plates with 8–9 teeth; upper pharyngeal tooth plates with 7 teeth; first and fourth infrapharyngobranchial unossified. Total precaudal vertebrae 15 [15] (N=9); 12 (5) or 13 (4) [13] anterior, plus 2 (4) or 3 (5) [2] transitional vertebrae) (N=9); 4 (9) [4] slender displaced-hemal spines (N=9); 57–60 [59] total vertebrae to posterior end of anal fin (N=8); anal pterygiophores slender and thin.

Coloration in alcohol. Head brown, darker at dorsal and opercular areas. Eyes dark. Membranous tissue around branchial opening hyaline. Accessory electric organ area, behind pectoral fin, depigmented. Pale yellow area around anus at ventral region of head. All specimens with oblique, irregular, alternate dark and light brown stripes running from dorsum to base of anal fin (darker stripes usually wider than lighter ones, sometimes broken into irregular dark blotches). Body somewhat darker dorsally, dorsum usually crossed by dark and lighter brown stripes, sometimes with irregular round dark brown spots. Tail uniform brown. Pectoral-fin rays and anal-fin rays covered with chromatophores proximally, interradial membranes hyaline.

Distribution. Hypopygus varii is currently known only from its type locality, the igarapé (“stream”) Saracá, a tributary at the right margin of the lower portion of the rio Trombetas ( Brazil, Pará State, Oriximiná municipality) ( Fig. 3 ).

Biological and ecological notes. Lin et al. (2003) presented a short communication on some biological features of Hypopygus varii (identified there tentatively as an undescribed species of Stegostenopos ), based on the type material described herein. Collections were originally made during the day, at marginal areas of the igarapé (stream) Saracá, with muddish bottom and dense vegetation on the permanently submerged margins. Additional gymnotiform species were collected along with types of Hypopygus varii , namely: Brachyhypopomus sp. ( Hypopomidae ); Hypopygus lepturus ; Gymnotus arapaima Albert & Crampton, 2001 (Gymnotidae) ; and Sternopygus cf. macrurus (Bloch & Schneider, 1801) ( Sternopygidae ). Stomach content of one specimen (not seen, and not included in the present study) revealed Ephemeroptera larvae and insects remains ( Lin et al., 2003).

Remarks. As mentioned above, types of Hypopygus varii were collected syntopically at the igarapé Saracá with specimens of H. lepturus . Nijssen & Isbrücker (1972) and de Santana & Crampton (2011) also mentioned museum lots of H. lepturus from the rio Trombetas system (those later authors included one lot from the “municipality of Oriximiná”, MZUSP 8211). Hypopygus varii can be readily separated from H. lepturus by the larger interocular width (35.0–37.3% HL vs. 18.7–24.4% HL); higher maximum number of scales above lateral line at midbody (9–11 vs. 4–5); higher pectoral-fin number (13 vs. 9–10); and higher total number of anal-fin rays (148–157 vs. 109–135).

Etymology. The specific epithet varii is a patronym in honour of Richard P. Vari (1949–2016), American ichthyologist, who greatly contributed to the knowledge of the Neotropical characiphysan fish fauna, and also produced a number of papers on gymnotiform taxonomy and systematics in recent years. For his work, enthusiasm and encouragement to many ichthyologists.

12345678901234567890123456789012345678901234567 Gymnorhamphichthys rondoni 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 100000000000000000110000 Rhamphichthys marmoratus 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 100000100000000000000000 Steatogenys duidae 0 0 0 0 0 0 0 0 0 11100000001000000100000000000010000000 Hypopygus benoneae 11???0011??? 111110 ??11??1???11?111???11?1020111 Hypopygus cryptogenes 11001000011111001011011100101101010000010020111 Hypopygus hoedemani 111110111111111112-11111111011101100011-1020111 Hypopygus isbruckeri 11000000011111001001011100101111000000010020111 Hypopygus lepturus 1100 ?0011111111010111111001011111000011-1020111 Hypopygus minissimus 111111111111111111-11111111011101100011-1121111 Hypopygus neblinae 11000000011111001001010100111101000000010020111 Hypopygus nijsseni 11000000011111001011011100101111000110010020111 Hypopygus ortegai 11000000011111001011011100101111001000010020111 Hypopygus varii 11000000011111001011011100101101010000010020111 Phylogenetic relationships. Four equally most parsimonious cladograms were obtained from the data matrix in Table 2 (length 55, CI = 0.89, RI = 0.92; strict consensus tree exhibited in Fig. 4 ). Hypopygus varii is included in Hypopygus on the basis of the following 12 synapomorphies (see de Santana & Crampton, 2011, for details): anterior nares located inside upper lip (character 1, state 1); posterior nares absent (chracter 2, state 1); loss of fourth infraorbital bone (character 13, state 1); loss of fifth infraorbital bone (character 14, state 1); loss of parietal branch of supraorbital canal (character 17, state 1); dermal vomer not ossified (character 22, state 1); supracleithrum independent from posttemporal (character 29, state 1); mesocoracoid bridge absent (character 30, state 1); loss of anterior-most branchiostegal ray (character 32, state 1); portion of anal-fin pterygiophores covered by scales (character 43, state 2); opaque tissue covering base of anal fin (character 45, state 1); lateral line intermittent (character 46, state 1); and presence of postpectoral accessory electric organ (with associated dorsal and ventral grooves anteriorly directed; character 47, state 1).

In Hypopygus varii , the ventral ethmoid is absent (character 23, state 1), a derived condition shared with all Hypopygus species, except H. neblinae (ventral ethmoid present and fused to parasphenoid in this latter species; uncertain in H. benoneae ). Two additional putative synapomorphies also appear in the different fundamental most parsimonious cladograms sometimes supporting that same clade (i.e., depending on their topology and optimization), namely: 1, supraorbital canal independent from the frontal bone (character 19, state 1; also in H. cryptogenes , H. lepturus , H. ortegai , H. nijsseni ; not applicable to H. hoedemani and H. minissimus , uncertain in H. benoneae ); 2, presence of an extension of the posteroventral portion of the coracoid (character 31, state 0; also in H. neblinae and H. cryptogenes ; absent in remaining species of the genus, uncertain in H. benoneae ). Within that clade above, however, relationships of Hypopygus varii are currently uncertain. Concerning the four most parsimonious fundamental cladograms obtained, the new species appears as the sister-group to H. cryptogenes in two, while in the other two it is alternatively depicted as the sister-group to a clade including ( H. cryptogenes ( H. lepturus ( H. benoneae ( H. minissimus , H. hoedemani )))). Also, Hypopygus varii is never placed as the sister-group to H. isbruckeri , H. nijsseni or H. ortegai in any of the four most parsimonious cladograms.

Lin et al. (2003), when briefly discussing the biology of Hypopygus varii (then tentatively identified as an undescribed species of Stegostenopos ), suggested that this later genus could be a possible junior synonym of Hypopygus , a position objectively held only recently by de Santana & Crampton (2011). For instance, Lin et al. (2003) questioned the indication of the “scattered chromatophores of the anal fin” as an autopomorphic feature of the nominal Stegostenopos , as originally suggested by Triques (1997: 33).

Notes about recent contributions on Hypopygus . Morphometrics presented in de Santana & Crampton (2011, tables 4 and 5), concerning all Hypopygus species, misrepresent values of anal-fin length. It seems that comparisons there were actually made with TL, instead of LEA. For instance, recent examination of paratypes of H. cryptogenes concerning that feature (MZUSP 47986; N=12) revealed values of 84.2–89.7% LEA in that species (48.3–52.0% LEA according to de Santana & Crampton, 2011, table 4) (vs. 83.3–87.1% LEA in Hypopygus varii ; N= 8). Objective information about anal-fin length was not given in the original description of H. cryptogenes (see Triques, 1997). Values of caudal-filament depth, regarding H. cryptogenes , also need attention in de Santana & Crampton’s paper, since those authors indicate 7.8–15.3% CFL concerning that species (2011: 1124, table 4); however, recent examination of paratypes of that species revealed values of 1.6–1.8% CFL (N=12) (vs. 3.0–3.6% CFL in Hypopygus varii ; N= 8).

A further correction should be made in a key to species of Hypopygus provided by Peixoto et al. (2013: 236– 237), where Hypopygus nijsseni appears as having “seven to eight scales above lateral line” and Hypopygus isbruckeri “five to six”. The actual ranges are, instead, “four to five” and “seven to eight”, respectively, according to de Santana & Crampton (2011; see original descriptions of those species).

Comparative material examined. Hypopygus cryptogenes : Brazil: MZUSP 47986, 12, paratypes of Stegostenopos cryptogenes , Amazonas State, rio Negro basin, rio Cuieiras, igarapé Sirinau. Hypopygus lepturus : Surinam: AMNH 54759, 1, Nickerie District, Corantijn river, Kapoeri Creek; AMNH 54781, 1, Nickerie district, Matabi creek; AMNH 54975, 2, Nickerie District, Corantjn river, unamed stream south of Tiger Falls; AMNH 54984, 1, Nickerie District, Corantijn river, small creek off Corantijn river; MZUSP 30172, 384, 2 c&s, Amazonas State, Tefé, rio Amazonas basin, rio Tefé, igarapé Jurupari; USNM 225648, 1, Nickerie District, Corantijn river, tributary to Sisa creek. Hypopygus neblinae : Venezuela: AMNH 58669 (apparently, part of original MBUCV- 14741), 5, paratypes, Estado Amazonas, Departamento Río Negro, Casiquiare Canal system, caño Manu; ANSP 162618, 4, Estado Amazonas, Río Pamoni system, outflow stream from series of morichals ca. 5.0 km from mouth of Rio Pamoni; ANSP 162656, 2, Estado Bolivar, Ciudad Bolivar, morichal Merecure, 35 km east of rio Caura, and 1.0 km north of Caicara.

Figures

FIGURE 1. Hypopygus varii, MNRJ 46752, holotype, 89.0 mm LEA, Brazil, Pará, Oriximiná, igarapé Saracá. (a) Left lateral view of body; (b)dorsal view of same specimen, head to left. Scale bar:10 mm.

FIGURE 2. Hypopygus varii, MNRJ 46752, holotype, 89.0 mm LEA. Head and anteriomost portion of body. Scale bar: 10 mm. Arrow indicates anus position.

FIGURE 3. Map of northern South America showing approximate type-localities of Hypopygus species. Square: Hypopygus varii; circles:1 = H. benoneae; 2 = H.cryptogenes; 3 = H.hoedemani; 4 = H.isbruckeri; 5 = H. lepturus; 6 = H.minissimus; 7 = H. neblinae; 8 = H.nijsseni; 9 = H. ortegai.

FIGURE4. Strict consensustree of four fundamental most parsimonious cladograms (length 55, CI = 0.89, RI =0.92) showing phylogenetic relationships between Hypopygus species.See text for details and discussion.