Barathronus linsi, Nielsen & Mincarone & Dario, 2015

Nielsen, Jørgen G., Mincarone, Michael M. & Dario, Fabio Di, 2015, A new deep-sea species of Barathronus Goode & Bean from Brazil, with notes on Barathronus bicolor Goode & Bean (Ophidiiformes: Aphyonidae), Neotropical Ichthyology (Neotrop. Ichthyol.) 13 (1), pp. 53-60 : 55-58

Barathronus linsi , new species

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Figs. 1-4

Holotype. MNRJ 41723, 101 mm SL, male with fully developed testes, Brazil, Potiguar basin, off Rio Grande do Norte, 04°25.83’S, 36°37.38’W - 04°25.87’S, 36°36.48’W, 1,964-2,045 m depth, RV Seward Johnson, sta. ArMT84 , bottom trawl, 5 June 2011.

Diagnosis. Barathronus linsi can be distinguished from all congeners by the following combination of characters: peritoneum transparent, deep-set eyes not visible, eight fangs on vomer, anal fin rays 69, predorsal length 42.0% SL, preanal length 49.5% SL, penis long, slender, and lacking a pair of lobes at its base, and the ventral flexure of anterior 2-3 vertebrae. Regarding the other Atlantic species of the genus, B. linsi differs from B. multidens by the presence of a ventral flexure of the anterior 2-3 vertebrae (vs. no flexure), eight fangs on vomer (vs. 11), penis in mature males long and slender (vs. short and thick), predorsal length 42.0% SL (vs. 46.5-51.0%), and preanal length 49.5% SL (vs. 55.0%). Barathronus linsi differs from B. bicolor by the number of fangs on vomer (8 vs. 1-5), the ventral flexure of the anterior vertebrae (vs. no flexure), a transparent (vs. bluish) peritoneum, eyes not visible (vs. eyes most often visible), and anal fin rays 69 (vs. 46-59). Barathronus linsi differs from B. unicolor by the number of fangs on vomer (8 vs. 4), predorsal length 42.0% SL (vs. 48.0-54.0% SL), preanal length 49.5% SL (vs. 54.0-59.0% SL), and by the long and slender penis without paired lobes at its base (vs. short and thick penis with lobes). Barathronus parfaiti is known only from a single, poorly preserved, juvenile specimen. However, B. linsi and B. parfaiti are clearly distinct by the number of precaudal (33 vs. 37) and total (78 vs. 84) vertebrae.

Barathronus linsi and the six Indo-Pacific congeners differ in a series of features, which are summarized in Table 2 . In addition, no species of Barathronus have so far been recorded in both the Atlantic and Indo-Pacific oceans. Among Indo-Pacific species, B. linsi is most similar to B. affinis (known from a single juvenile specimen) in meristic characters, by the presence of a ventral flexure of the anterior vertebrae, and the transparent peritoneum, but they differ by the number of fangs on vomer (8 vs. 2) and the number of long gill rakers (25 vs. 20).

Description. Meristic and morphometric data of holotype are presented in Tables 1 and 2 . Scales absent, skin loose, gelatinous and translucent, sensory pores highly indistinct. Head down-bent, slightly thicker than body. Dorsal, caudal and anal fins united. Dorsal-fin origin well anterior to vertical through midpoint of body, anal-fin origin at midpoint of body. Pelvic fins each with a single, slender ray; pelvic-fin base below hind part of operculum. Pectoral peduncle as broad as long. Eyes not visible. Mouth opening oblique. Nostrils with low rim. Opercular spine covered by skin. Musculi infracarinalis mediales yellowish white; ratio between length and height of “middle fields” ( Nielsen, 1969: 9) ca. 0.5. Anterior gill arch with 26 prolonged rakers (up to 2.2% SL): four on upper branch, one in the angle and 21 on lower branch. About 30 very small gill filaments (0.6% SL). Pseudobranchial filaments apparently absent. Testes large (22% SL), nearly filling abdominal cavity. Intromittent organ a 9-mm long slender penis, covered proximally by urogenital hood. Lobes at base of penis absent.

Otolith: Otolith 2.2 mm long, compact, with nearly flat inner face and strongly convex outer face. Outline round, with somewhat depressed predorsal rim. Otolith height 1.2 in length; otolith thickness 1.7 in height. Sulcus moderately large, positioned centrally on inner face and terminating at some distance from otolith rims. A single, undivided, small, narrow colliculum located in anterior part of sulcus. Small bulge on inner face in front of sulcus ( Fig. 2 ).

Dentition: Palatines edentate. Vomer with two small teeth located between eight distally placed fangs (three broken). Premaxilla with 1-2 rows of small teeth in its full length. Dentary with seven fangs on posterior half and small teeth on anterior half.

Axial skeleton: Precaudal vertebrae 33, all centrae short and high, anterior 2-3 vertebrae ventrally flexed. First vertebra with very short neural spine. Vertebrae 2-8 with long and slightly laterally compressed neural spines decreasing in length posteriorly. Short parapophyses developed on vertebrae 4-33. Pleural and epipleural ribs absent. Vertebral centrae hourglass-shaped ( Fig. 3 ).

Color. Recently collected specimen ( Fig. 1A ) overall yellowish to reddish white due mostly to the underlying, somewhat darker, muscle coloration and blood vessels (mostly skin capillaries). No black pigmentation observed either in skin or on peritoneum. Preserved specimen ( Fig. 1B ) yellowish white (no evidence of bleaching after two years of preservation).

Distribution. Known from the holotype, collected between 1,965 and 2,045 m depth in the Potiguar basin, of Rio Grande do Norte, northeastern Brazil ( Fig. 4 ).

Etymology. Named after Prof. Jorge Eduardo Lins de Oliveira (Universidade Federal do Rio Grande do Norte - UFRN), in recognition of his lifetime commitment to the understanding of marine biodiversity of northeastern Brazil. A noun in genitive case.

Notes on Barathronus bicolor in the western South Atlantic. A female specimen (73 mm SL) of B. bicolor , collected in 1987 at 610 m depth off Rio de Janeiro State, southeastern Brazil (Séret & Andreata, 1992), represented until recently the single record of this species in the western South Atlantic. Twenty years later, Franco et al. (2007) reported an additional specimen (98 mm SL, male) collected between 1,605 to 1,640 m off Rio de Janeiro State. Meristic and morphometric data of these two specimens and of one additional specimen reported herein (NPM 1243; Fig. 5 ) are compared to those from the currently known 51 specimens of B. bicolor collected in the western Central Atlantic ( Table 1 ). Morphological characters examined are highly congruent between the two clusters, even though the geographic distance between southeastern Brazil and the western Central Atlantic is more than 5,000 km. The only significant difference between examined characters occurs in the penis length, which measures about 4% SL in the only fully mature male collected off southeastern Brazil (NPM 1243), vs. 10-14% SL in specimens from the western Central Atlantic.

Figures

Fig. 1. Barathronus linsi, new species, holotype, MNRJ 41723, 101 mm SL: (A) recently collected; (B) after two years in preservative (horizontally inverted, right side depicted).

Fig. 2. Sagittal otolith of Barathronus linsi, holotype, MNRJ 41723: (A) median view; (B) ventral view.

Fig. 3. Radiograph of Barathronus linsi, holotype, MNRJ 41723, 101 mm SL.

Fig. 4. Records of Barathronus linsi, holotype (triangle) and Barathronus bicolor (squares) in the western South Atlantic. Selected Brazilian states: RN - Rio Grande do Norte, and RJ - Rio de Janeiro.

Fig. 5. Barathronus bicolor, NPM 1243, 117 mm SL, collected off Rio de Janeiro State, Brazil. Photo taken just after collection.