Patagolycus melastomus, Matallanas, Jesús & Corbella, Cecília, 2012

Matallanas, Jesús & Corbella, Cecília, 2012, Redescription of Iluocoetes Jenyns, 1842; proposal of a new genus, Argentinolycus, for Iluocoetes elongatus (Smitt, 1898), and description of Patagolycus melastomus gen. et sp. nov. (Teleostei, Zoarcidae), Zootaxa 3296, pp. 1-18 : 8-15

publication ID	https://doi.org/ 10.5281/zenodo.280870
DOI	https://doi.org/10.5281/zenodo.6179158
persistent identifier	https://treatment.plazi.org/id/03DF87D6-8D1E-D64F-FF48-E2C1FD90FE60
treatment provided by	Plazi
scientific name	Patagolycus melastomus
status	sp. nov.

Treatment

Patagolycus melastomus View in CoL sp. nov.

( Figs. 3−10 View FIGURE 3 A View FIGURE 4 View FIGURE 5 View FIGURE 6 View FIGURE 7 View FIGURE 8 View FIGURE 9 View FIGURE 10 ; Tables 1, 2 & 4)

Diagnosis. As for the genus.

Description. Body robust, short, ovoid in cross section. Tail laterally compressed especially posteriorly. Head robust, not depressed, as wide as high in both males and females; snout gently sloping. Mouth inferior; lips without lateral lobes. Snout blunt, upper jaw slightly protruding, end of maxilla extending to posterior part of pupil in both males and females. Eyes slightly ellipsoid entering dorsal profile of head. Nasal tube pigmented at base, not reaching upper lip when depressed forward. Gill slit well developed, extending ventrally to below ventral edge of pectoral-fin base, but above pelvic fin insertion. Opercular lobe short, triangular ( Fig. 3a View FIGURE 3 A & b View FIGURE 3 B ).

Cephalic lateralis pore system with small pores. Nasal pores 3, one located anteromesial to nasal tube, two other posterodorsal to the nasal tube and the posterior one very small. Postorbital pores 1 and 4 present in all. Suborbital pores 6+1, in a reversed L-shaped pattern. Preoperculomandibular pores 8 ( Fig. 3b View FIGURE 3 A View FIGURE 3 B ). Interorbital pore absent. Supratemporal commissure and occipital pores absent. Lateral line mediolateral, extending from postorbital pore 4 to near tail tip.

Pectoral-fin origin at body midline; pectoral-fin base extending ventrally to abdomen; posterior margin of pectoral-fin ovoid; middle rays longest; 6−8 ventralmost rays thickened and exerted at tips ( Fig. 3b View FIGURE 3 A View FIGURE 3 B ). Flesh and skin firm; skin covering vertical fins. Scales relatively large, circular, non-overlapping, covering entire body, proximal two thirds of pectoral-fin base and axil, abdomen, tail, nape, posterior part of the interorbital space, cheeks, opercle, and vertical fins to nearly it margin. Two juvenile, BMNH 1936.8.26.984−987:(984.2), 107 mm TL and BMNH 1936.8.26.984−987: (984.3), 103 mm TL, also have extensive squamation, including nape and upper part of opercle. The 94 mm TL specimen, BMNH 1936.8.26.984−987:(984.4), has scales throughout its body, but a scaleless head.

Neurocranium well ossified, narrowed ( Fig. 4 View FIGURE 4 a & b). Frontal and parasphenoid well separated by pterosphenoid ( Fig. 4 View FIGURE 4 a); sphenotic broadly articulating with parietal ( Fig. 4 View FIGURE 4 b). Ascending rami of parasphenoid wing reaching mid-height of the trigeminofacialis foramen. Parasphenoid and prootic juncture, as well as prootic and pterotic juncture strongly interdigitating. Intercalar large, posteriorly set. Frontal ramus long, convex, with an anterior foramen in the interorbital space; frontal corner squared. Anterior portion of frontals fused with no trace of a suture, posterior portion showing a superficial suture; posterolateral edge of the frontals retreat. Supraoccipital wide, with a well developed median crest posteriorly; supraoccipital excluded from exoccipital by epioccipital; no supratemporal commissure across parietals. Ethmoid cartilage protruding well into orbital fenestra, with an anterior foramen.

Teeth in jaws, vomer and palate conical. Upper jaw with 2−3 (in males), to 3−4 (in females) rows near symphysis merging into single posterior row; first premaxillary tooth is canine-like in adult males. Lower jaw with 3−4 (in males), to 4−5 (in females) irregular rows in the anterior part and single row in the posterior part; teeth of outermost rows larger than the inner rows ones. In the middle of the lower jaw, a tooth is distinctly enlarged in males ( Fig. 5 View FIGURE 5 ). A patch of 4−7 vomerine teeth. Palatine teeth in a single row of 3−7 teeth. Lower jaw with reduced submental cartilaginous crests, not fused anteriorly ( Fig. 5 View FIGURE 5 ). Oral valve nearly reaching anterior edge of vomer and well separated from the palate laterally. Pyloric caeca two small nubs. Gill rakers 2−3+11−13=13−15, stout and scalloped ( Fig. 6 View FIGURE 6 ); in specimens preserved for a long periode of time, the indentations are likely to get damaged. Pseudobranch filaments 6−7, elongate.

Palatopterygoid series well developed ( Fig. 7 View FIGURE 7 ), with mesopterygoid overlapping more than half dorsal surface of quadrate and ectopterygoid overlapping half anterior surface of quadrate. Metapterygoid large. Posterior ramus of hyomandibula elongate. Hyoid bar with ceratohyal −epihyal joint with bone interdigitating dorsally ( Fig. 8 View FIGURE 8 ). Five branchiostegal rays: first, slender, attached on medial side of ceratohyal; remainder four thickened, 2 articulating on outer side of ceratohyal and 2 on outer side of epihyal.

Pectoral girdle ( Fig. 9 View FIGURE 9 ) with a strong posttemporal bearing a well-developed ventral ramus. Supracleithrum with a posteriorly-directed prong. Scapular foramen enclosed by bone; prominent postero-dorsal scapular strut. Coracoid with a well-developed posterior strut and a foramen. Radials (=actinosts) 4, the uppermost smaller. Four foramina in the cartilaginous basal plate: one between each two radials, and another between radial 1 and scapula. Postcleithrum present. Pelvic-fin rays joined, ensheathed by the dermis.

Vertebrae asymmetrical, 20–21+65–72=86–93. Last precaudal vertebra associated with dorsal-fin rays 18–20. Dorsal-fin origin associated with vertebra 4 with no free pterygiophores. Dorsal-fin rays 83–89. Anal-fin rays 67– 73. Terminal dorsal-fin ray associated with second preural vertebra. Terminal anal-fin ray associated with second preural vertebra. One epural. Caudal-fin rays 9−11, with 1−2 epural, four upper hypural and four or five lower hypural rays.

Fresh colouration. Medium to dark brown ground colour with 4–5 wide and darker vertical cross-bars from dorsal profile to well below body mid-line. Numerous circular and subcircular white spots on head, body, tail and pectoral fins; suborbital area without spots. Dorsal-fin with some slightly elongated white blotches. Edge of vertical fins black; anal-fin edge white in the male holotype. Edge of pectoral fins, ventral part of head, opercular edge, ventral fins and abdomen, white or dull white. A darker band across the snout between the anterior edge of the eye and the nasal tube ( Figs. 3a View FIGURE 3 A & b View FIGURE 3 B ). Lips pale; orobranchial cavity and peritoneum black. Coloration in preserved juvenile specimens of Patagolycus melastomus . Dorsolateral part of body mid-brown with dull white rounded spots; ventrolateral part lighter; dorsolateral part of head uniform mid-brown except a darker band on snout between the anterior edge of the eye and the nasal tube; ventrolateral part light. Edge of dorsal fin with 3−4 darker spots on its anterior half.

Counts and proportions. Table 1.

Reproduction. Despite the reduced sample used, head length, head width, snout length as well as dorsal-fin height, are proportionally higher in the male holotype (the larger specimen) than in both male and females paratypes indicating both sexual dimorphism and ontogenic change (Table 1). In the single ovary of three female paratypes two distinct clutches of oocytes can be distinguished: a large clutch of oocytes with a diameter between 1.33− 1.42 mm, and another with a diameter of about 0.72 mm. The single ovary of Patagolycus melastomus sp. nov. belong to the cystovarian type, the most common type in Teleosts, according to the classification of Hoar (1969). Ovaries in the female specimens of the new species are unripe, they are in a maturing stage, with oocytes visible to the naked eye. It is known that, in general, mature zoarcid eggs are large, about 4−9 mm in diameter ( Anderson, 1984) and those of the Patagonian species confirm this rule: Gosztonyi (1977) reports 5.0− 5.5 mm in diameter for Argentinolycus elongatus (as Iluocoetes elongatus ), 7.5−8.4 mm for Austrolycus laticinctus , 5.0 mm for Dadyanos insignis and 4.5 mm for Phucocoetes latitans ; Matallanas et al. (1990) described a demersal egg cluster of Austrolycus depressiceps , obtained in the Beagle Channel, formed by 465 spherical eggs with 9.2−9.8 mm in diameter, the largest reported size for zoarcids.

Distribution. Southwest Atlantic Ocean between 45º28’− 51º27’S and 60º21’ − 68º50’W, at depths of 164− 489 m.

Etymology. The specific name, melastomus , from the Greek melas (black, dark) and stoma (mouth), for the colour of its orobranchial cavity.