Myroconger pietschi, Espíndola & Caires & Tighe & De Pinna & De Melo, 2021

Espíndola, Vinicius C., Caires, Rodrigo A., Tighe, Kenneth A., De Pinna, Mario C. C. & De Melo, Marcelo R. S., 2021, A new species of the rare genus Myroconger Günther, 1870 (Anguilliformes Myrocongridae) from Brazilian waters, tropical western Atlantic, Zootaxa 4965 (3), pp. 529-540 : 531-538

Myroconger pietschi sp. nov.

( Figures 1–5 , Table 1)

LSIDurn:lsid:zoobank.org:pub: 86118D7F-7CFD-4FC2-B915-6FDAA6259BD1

Myroconger sp. ‒ Paiva et al. 2011.

Holotype: MZUSP 125266 (Ex CIDRO 81 ), 431.0 mm TL, Brazil, Ceará State, Aracati Bank , 3°28’38” S, 37°20’48” W, 253 m depth, 10 January 2001, Program REVIZEE, col. B/Pq ‘Professor Martins Filho’.

Diagnosis. Myroconger pietschi can be diagnosed by having 190 total anal-fin rays (vs. 195 in M. compressus , 229 in M. gracilis , 206–213 in M. nigrodentatus , 239 in M. prolixus , and 163 in M. seychellensis ) and a short pectoral fin (16.6 % HL vs. 18.4–30.9% HL in M. compressus , 20.1 % HL in M. gracilis , 22.1–24.6 % HL in M. nigrodentatus , 17.8 % in M. prolixus , and 18.7 % HL in M. seychellensis ). It can be further distinguished from its congeners by 291 total dorsal-fin rays (vs. 349 in M. gracilis , 298–313 in M. nigrodentatus , 398 in M. prolixus , 300 in M. seychellensis ); and 125 total vertebrae (vs. 139 in M. gracilis , 130 in M. seychellensis , and 147 in M. prolixus ). It possesses a single row of teeth arranged along the ethmovomerine tooth patch (vs. two irregular rows on the anterior portion and reduced to one in M. compressus , three rows on the anterior portion reduced to one in M. gracilis , and three rows on the anterior portion and contracted to two in M. seychellensis ). It further differs from M. gracilis and M. prolixus in having five lateral-line pores (vs. seven and 11, respectively), and from M. nigrodentatus by the ethmovomerine tooth patch extending to nearly half-length of upper jaw (vs. ethmovomerine tooth patch extending to posterior portion of maxilla in all other species), preanal vertebrae 48 (vs. 43), preoperculomandibular pores six (vs. five). Myroconger pietschi further differs from M. nigrodentatus and M. compressus in having 24 teeth on the lower pharyngeal (vs. 37 and 60, respectively), and 27 upper pharyngeals (vs. 33 and 60 or more, respectively), and 10 branchiostegal rays (vs. 13 and 11, respectively).

Description. Morphometric and meristic data are in Table 1. Body anguilliform, not remarkably compressed anteriorly, tapering along caudal region. Entire body and head scaleless. Greatest body depth at anterior fourth of TL. Pectoral fin short, round, lateral on body, inserted slightly posterior to gill opening. Dorsal-fin origin anterior to vertical through gill slit; anal-fin origin immediately posterior to anus. Dorsal-fin rays longer than anal-fin rays. Dorsal and anal fins well developed, confluent with caudal fin.

Head posterior limit almost indistinguishable from trunk, snout triangular in lateral view, dorsal portion of cranium with mild dorsal depression. Mouth terminal, gape of mouth extending well posterior to eye. Lower jaw projecting anterior to upper jaw. Upper and lower jaw lacking labial folds.

Anterior nostril tubular, at tip of snout and directed anterodorsally. Posterior nostril dorsal on snout, at vertical through dorsal margin of eye, with short dermal flap, closer to eye than to anterior nostril. Eye oval, anteroventrally elongated, positioned at middle of upper jaw. Gill opening lateral on body, oblique, with dorsal margin anterior to ventral margin; dorsal margin at level of dorsal most pectoral-fin ray.

Maxillary teeth conical, with smooth margins, arranged in three rows anteriorly and two rows posteriorly; teeth decreasing in size from anterior to posterior; medial teeth about twice size of lateral teeth, lateral row with 48 teeth, medial row with 31 or 33 teeth. Ethmovomerine teeth conical, with smooth margins, anteriorly arranged in subcircular patch, extending in single row to level of posterior third of upper jaw ( Fig. 2 , 3B ). Dentary teeth conical, with smooth margins, arranged in three rows anteriorly and two rows posteriorly; teeth decreasing in size from anterior to posterior; medial teeth about twice as large as lateral ones; teeth in internal row 29; teeth in lateral row 33 ( Fig. 2 , 3C ). Upper pharyngeal tooth plate rhomboid, restricted to upper pharyngeals 3 and 4, with 24 teeth; lower pharyngeal tooth plate antero-ventrally elongated, restricted to lower pharyngeal, with 27 teeth ( Fig. 4 ).

Infraorbital pores four; first and second pores located between verticals through anterior and posterior nostrils, third infraorbital pore at vertical through anterior margin of eye; fourth infraorbital pore at vertical through middle of eye. Preoperculomandibular pores six, all in lower jaw, extending from tip of chin to immediately anterior to rictus; first and second pores anterior to vertical through anterior nostril, third pore at vertical through first infraorbital pore, fourth pore at vertical through second infraorbital pore, fifth pore at vertical through anterior margin of eye; sixth pore slightly posterior to posterior margin of eye. Supratemporal pores absent. Supraorbital pores two or three; first pore anteroventral to anterior nostril; second pore anterodorsal to anterior nostril, third pore present only on left side, posterodorsal to anterior nostril. Lateral line short, last pore well behind the pectoral fin, with five pores.

Color in alcohol. General ground color of body and head orange. Ventral surface of head light yellow on lower jaw and ventral part of cheek. Body whitish on belly and ventral third of caudal portion of body. Single broad dichromatic stripe, pale yellow on dorsal and ventral margins, brown in center; extending medially on flank from posteriormost lateral-line pore to posterior third of body. Pectoral fin mostly orange, lighter on distal third. Anterior half of dorsal fin orange, posterior half yellowish. Anterior third of anal fin whitish; posterior two-thirds yellow. Color of live specimen not available.

Remarks. The only known specimen has some damage caused by collection. The head is slightly mashed, and there is a strong compression of the body slightly posterior to the pectoral fin.

Distribution. Myroconger pietschi is known only from its type locality on the Aracati Bank, Northern Brazilian Ridge, tropical western South Atlantic, Ceará State, Brazil ( Fig. 5 ).

Etymology. The species name honors Theodore Wells Pietsch III, in recognition of his outstanding contributions to the knowledge of deep-sea fishes.

Figures

FIGURE 1. Myroconger pietschi sp. nov., holotype, MZUSP 125266, 431.0 mm TL, Brazil, Ceará, Aracati Bank, 03°28’38” S, 37°20’48” W, 253 m depth.

FIGURE 2. Schematic of dentition in Myroconger pietschi sp. nov., holotype, MZUSP 125266, 431.0 mm TL; in (A) upper jaw and (B) lower jaw.

FIGURE 3. 3D reconstruction of the CT Scanned head bones of Myroconger pietschi n. sp., holotype, MZUSP 125266, 431.0 mm TL, with the dentigerous bones highlighted in differential colors: in (A), skull and upper jaw in lateral view; in (B), skull and upper jaw in ventral view; and in (C), lower jaw in dorsal view. Abbreviations: AAR, angulo-articulo-retroarticular; BS, basisphenoid; CMO, coronomeckelian ossification; DE, dentary; EP, epiotic; ETV, ethmovomer; EXO, exoccipital; BO, basioccipital; FR, frontal; MX, maxilla; PA, parietal; PRO, prootic; PS, parasphenoid; PTO, pterotic; PTS, pterosphenoid; RA, retroarticular; SO, supraoccipital; SPH, sphenotic. Scales bars equal 10 mm.

FIGURE 4. 3D reconstruction of the CT-scanned hyoid arch and branchial arches of Myroconger pietschi n. sp., holotype, MZUSP 125266, 431.0 mm TL – only bones illustrated, cartilaginous structures not recovered; (A), left and middle elements in lateral view; (B), arches in dorsal view, except upper elements of right branchial arch flipped to allow ventral view (indicated by dashed line) and right hyoid arch removed; and (C), upper pharyngeals and lower pharyngeals in anterior view. Abbreviations of the hyoid arch: BH, basihyal; HH, hypohyal; UH, urophyal; ACH, anterior ceratohyal; PCH, posterior ceratohyal; BR, branchiostegal rays.Abbreviations of the branchial arches: HB, hyobranchial; CB, ceratobranchial; EB, epibranchial; PB, pharyngobarnchial; UP, Upper pharyngobranchial; LP; lower pharyngobranchial. Scale bars equal 10 mm.

FIGURE 5. Known distribution of the species of Myroconger, with a detailed map of the northern portion of Northeastern Brazil indicating the seamounts and the type of Myroconger pietschi sp. nov. on the Aracati Bank. Symbols: star represents M. pietschi; circles, M. compressus; diamonds, M. nigrodentatus; triangles, M. prolixus; squares, M. gracilis; and pentagons, M. seychellensis.