Heptapterus mandimbusu, Aguilera & Benitez & Terán & Alonso & Mirande, 2017

Aguilera, Gastón, Benitez, Mauricio, Terán, Guillermo Enrique, Alonso, Felipe & Mirande, Juan Marcos, 2017, A new species of Heptapterus Bleeker 1858 (Siluriformes, Heptapteridae) from the Uruguay River Basin in Misiones, Northeastern Argentina, Zootaxa 4299 (4), pp. 572-580 : 573-579

Heptapterus mandimbusu , sp. n.

Fig. 1 , Table 1

Holotype. CI-FML 7238, 134.2 mm SL, Argentina, Misiones, Uruguay River basin, Melo stream, 27°25'2.67"S, 54°42'7.93"W, November 13, 2016. G. Aguilera, J. M. Mirande, G. Terán, M. Benitez, D. Baldo, J. M. Ferro and F. Alonso.

Paratypes. All material collected with Holotype. CI-FML 7239, 6 ex. (2 ex. C&S), 54.6 – 175.6 mm SL; LGEP 529, 1 ex., 107.4 mm SL ; LGEP 530, 5 ex., 58.3–113.4 mm SL; LGEP 538, 1 ex. C&S, 70.5 mm SL; IBIGEO-I 446, 3 ex., 65.1–89.7 mm SL.

Diagnosis. Heptapterus mandimbusu is distinguished by its unique coloration pattern, with aggregated melanophores scattered on dorsal and lateral surfaces of body, forming conspicuous blotches of variable size ( Fig. 1 and 2 ) vs. absence of this pattern in the remaining species of the genus. Heptapterus bleekeri , H. fissipinnis , H. multiradiatus , H. mustelinus , H. qenqo , H. stewarti , H. sympterigium and H. tapanahoniensis present a rather uniform earth-brown coloration pattern (with some irregular markings on head and sometimes indistinct on back in H. bleekeri ); while H. mbya and H. ornaticeps have a uniform coloration pattern (greyish and blackish respectively).

There are three species of Heptapterus inhabiting Argentinean basins, the type species of the genus Heptapterus mustelinus , and the recently described, H. qenqo and H. mbya . Heptapterus mandimbusu n. sp., has a longer interdorsal distance (13.8–18.9 % SL), which distinguishes it from H. mustelinus (3.1–5.0 % SL), H. qenqo (9.5–13.2 % SL), and H. mbya (5.8–8.3 % SL). Heptapterus mandimbusu can be further distinguished from H. mustelinus by a shorter distance between the anal-fin origin and hypural plate (32.9–39.1 % SL vs. 39.6–45.7 % SL), a longer distance between the origins of pelvic and pectoral fins (24.5–28.1 % SL vs. 20.4–24.2 % SL), a shorter adipose-fin base (33.8–41.5 % SL vs. 51.5–59.6 % SL), a shorter anal-fin base (15.7–20.9 % SL vs. 20.9– 28.0 % SL), a smaller orbital diameter (10.3–14.1 % HL vs. 15.0–19.9 % HL), and a lower number of anal-fin rays (14–18 vs 18–22). The number of free vertebrae in Heptapterus mandimbusu (47) is lower than in H. qenqo (51– 52) and H. mbya (51–53), the caudal peduncle depth is shallowest than in H. qenqo (13.8–19.3 % SL vs. 19.8–25.4 % SL), and the adipose-fin base is shorter than in H. mbya (33.8–41.5 % SL vs. 47.4–58.55 % SL). From the remaining species of the genus, Heptapterus mandimbusu can be distinguished from H. stewarti Haseman and H.

sympterygium Buckup by the dorsal fin never reaching the adipose fin; from H. bleekeri Boeseman , H. fissipinnis Miranda Ribeiro , H. multiradiatus Ihering , H. ornaticeps Ahl , H. stewarti and H. sympterygium by the lower number of anal-fin rays (14–18 vs. 20–22; 23; 38–46; 19; 30 and 22–29 respectively); from H. bleekeri , H. fissipinnis , H. multiradiatus , H. stewarti , H. sympterigium , and H. ornaticeps by the shorter maxillary barbel length that never reaches the pectoral fin, even in small juveniles; and from H. tapanahoniensis Mees by the higher number of vertebrae (47 vs. 43) and branchiostegal rays (8–9 vs. 7) and the adipose fin confluent with the caudal fin (vs. separated). The monospecific genera Acentronichthys Eigenmann & Eigenmann , probably allied to Heptapterus due to the share of an elongated body and the adipose fin confluent to caudal fin, can be distinguished from Heptapterus mandimbusu by the caudal fin deeply forked (vs. distal profile of caudal fin slanted).

Description. Morphometric data of holotype and 16 paratypes presented in Table 1. Body and fins covered by small sharp papillae, more evident on dorsum. Papillae on first rays of dorsal, pectoral, and pelvic fins and upper caudal-fin lobe prolonged into small filament that can carry inside minute dark-brown soft structures, very thin and spiniform (see Figure 3 in Azpelicueta et al. 2011).

Dorsal profile of body slightly convex, from snout tip to dorsal-fin origin, almost straight through dorsal-fin base, concave along dorsal profile of peduncle. Ventral profile slanting ventrally from snout tip to vertical through middle opercle, slightly concave or straight to pelvic-fin origin, almost straight to anal-fin origin, and concave or almost straight to caudal fin. Maximum body depth at dorsal-fin origin. Maximum body width at level of pectoral fins, where body has circular section; posterior half of body increasingly laterally compressed to caudal peduncle.

Head depressed and broad, covered by thick skin. Anterior nostrils with tubular rim, located closer to snout tip than to eye. Posterior nostrils surrounded by a membrane, largest on anterior margin, and closer to eye than to snout tip. Snout rounded in dorsal view, moderated in size (2.4 to 2.9 times in HL). Small eyes (7.7 to 9.7 times in HL) covered by skin. Interorbital width containing 1.3 to 2.0 times orbital diameter. Mouth subterminal, wide and opening anteriorly. Premaxilla without backward projections, anterior margin convex and posterior one slightly slanted, with a single broad band carrying the teeth. Premaxillary teeth conical and fine placed in 8–10 irregular rows. One tooth band on each dentary; bands anteriorly broad and slender posteriorly; distal end of band following curvature of inner wall of dentary. Dentary teeth conical, placed in 6–8 irregular rows. Cranial fontanel long and slender, with its anterior margin at line through half length of lateral ethmoid and reaching posteriorly end of supraoccipital. Anterior fontanel slightly wider than posterior fontanel. Epiphyseal bar situated at line through posterior eye margin. Maxillary barbel base at same level that anterior nostril, with its basal third resting in deep sulcus. Maxillary barbel short (1.3 to 1.9 times in HL) not reaching pectoral-fin origin, even in small juveniles. Outer mental barbel base at vertical through posterior nostril, its tip reaching near vertical through tip of maxillary barbel. Inner mental barbel base at same level than outer mental barbel, its tip slightly surpassing vertical through posterior orbital margin.

Dorsal-fin origin a little anterior to vertical line trough pelvic-fin insertion, with one short unbranched ray (1.1–1.5 times in first branched dorsal-fin ray) and six branched rays. Dorsal fin not reaching adipose fin, separated from it by distance 1.1–1.8 of HL. Adipose-fin origin slightly anterior to vertical through anal-fin origin. Adiposefin base length short (2.4 to 3.0 times in SL) and confluent with caudal fin. Caudal-fin distal profile slanted, with i,6 + 6–7,i rays. Upper caudal-fin lobe longer and broader than lower lobe. Dorsal procurrent caudal-fin rays 9(3), ventral procurrent caudal-fin rays 12(1), 15(1), or 16(1). Anal-fin origin located on posterior half of body, with 14(1) 15(5), 16(6), 17(4*), or 18(1) rays. Anal-fin rays in two C&S specimens vi,10–11 (total anal-fin rays 16 and 17 respectively). Pectoral fin with i,7–8 (one specimen with 7 and 16* with 8). Tip of pectoral fin reaching halflength or less between pectoral- and pelvic-fin origins. Pelvic fin with i,5 rays. Pelvic, pectoral, anal, and dorsal fins with their distal margins rounded.

Cephalic sensory canal bearing five pores on supraorbital canal, five pores on infraorbital canal, and 11 on preoperculomandibular canal. Lateral line almost straight, complete, and uninterrupted, reaching compound caudal complex. Pores on anterior portion of lateral line well developed and almost inconspicuous on posterior portion.

Counts on C&S material: vertebrae 47(3), precaudal vertebrae 11(2)–12(1), caudal vertebrae 35(1)–36(2). Twelve to fourteen gill rakers of first gill arch (10–12 on ceratobranchial; one on cartilage between ceratobranchial and epibranchial, and one on epibranchial). Branchiostegal rays 8(2) to 9(1). First dorsal-fin pterygiophore between neural spine of sixth and seventh vertebrae (3), first anal-fin pterygiophore between hemal spine of vertebrae 22– 23(1), 23–24(1) or 24–25(1). Pleural ribs 8(2)–9(1).

Color in alcohol. Coloration pattern represented by aggregated melanophores scattered on dorsal and lateral surfaces of body, forming conspicuous size-variable blotches. Body background pale yellow, dorsum dark-brown with melanophores densely aggregated, especially over head, loosely aggregated on lateral surface of body, and ventral surface almost without melanophores, especially on prepelvic area. Five darker transverse bands, first one over supraoccipital region, second one at level of pectoral fins, third one just anterior to dorsal-fin origin and separated from fourth band by lighter area occupying dorsal-fin origin. Fourth dark band at insertion of third or fourth dorsal-fin rays and fifth band at interdorsal area. Second band is prolonged on lateral surface of body to pectoral-fin base. A very slender stripe from that band to end of caudal peduncle. Base of dorsal and anal fins with a dark band, not evident in all specimens, occupying one third of fin length. Caudal-fin base with dark band on distal margin of skin covering caudal-fin rays, more evident in small specimens. Pectoral and pelvic-fin base darker than distal end. Adipose fin with chromatophores scattered over entire fin and aggregated forming a diffuse dark band on distal margin of fin. All fins with minute chromatophores following each ray.

Distribution. Currently known only from its type locality at Melo stream ( Fig. 3 ), Uruguay River basin, Northeastern Argentina.

Habitat and ecological notes. At type locality, the stream is characterized by clear water and low current velocity. The structure of the stream presents sequences of pools of 1 to 1.5 meters and shallow riffles, surrounded by native vegetation ( Fig. 4).

Etymology. The specific name “ mandimbusu ” is the combination of two words from the Guaraní language, mandí=catfish and mbusu=eel, in allusion to its body form and the vernacular name used in Argentina to refer to Heptapterus (bagre anguila). The specific name is the apposition of two nouns.

Figures

FIGURE 1. Heptapterus mandimbusu sp. n., holotype CI-FML 7238, 134.2 mm SL, from Melo Stream, Nov 13, 2016.

FIGURE 2. Coloration pattern from two paratypes A. CI-FML 7239. 105. 2 mm SL. B: LGEP 529. 107.4 mm SL.

FIGURE 3. Map showing the collecting site on the Melo stream, indicated by a red dot, Uruguay river basin, Misiones province, Argentina.