Xestoleberis amazonica, Luz, Nathália Carvalho Da & Coimbra, João Carlos, 2015

Luz, Nathália Carvalho Da & Coimbra, João Carlos, 2015, The genus Xestoleberis (Ostracoda: Xestoleberididae) in the Northern, Northeastern and Eastern regions of the Brazilian continental shelf, Zootaxa 3974 (2), pp. 177-195 : 187-189

Xestoleberis amazonica sp. nov.

Fig. 4 :1–14

1999 Xestoleberis sp. 2 Coimbra et al., tab. 1.

Type series. Holotype: MP-O-1938, adult female, RV length 0.48 mm, height 0.32 mm. Paratypes: three adult males (MP-O-1939–MP-O-1941) and two adult females (MP-O-1942 and MP-O-1943).

Type locality. GEOMAR/Leg III—Sample 210 (04°35.5’N / 50°21’W); depth: 104 m; sediment: sand and bioclasts.

Etymology. With reference to the restricted distribution of the species to the Amazon region.

Material. 50 adults and 40 juveniles.

Dimensions. See table 3.

Diagnosis. A medium-sized Xestoleberis species. Carapace almost drop-shaped in lateral view with sinuous ventral margin. LV overlapping RV, except along ventral margin. Surface smooth with sieve-type, lip-type and simple-type normal pore canals. Xestoleberis -spot small, outlined and subdivided. Hinge antimerodont with median element crenulate and short. Adductor muscle scars a row of four sub-elliptical scars and a frontal Vshaped scar.

Description. A medium-sized and thick-shelled species of Xestoleberis . Somewhat drop-shaped in lateral view. In dorsal view ovate. Ventral surface flattened. LV overlapping RV, except along ventral margin. Maximum length in the top third of the height. Maximum height medianly. Maximum width just posterior of mid-length. Anterior margin obliquely rounded, protruding and angled ventrally. Posterior margin similar in both valves but slightly more rounded in LV. Dorsal margin arched. Ventral margin slightly convex anteriorly. Surface typically smooth, with three types of normal pore canals (sensu Sato & Kamiya 2007): sieve-type, lip-type and simple-type. Eye-spot inconspicuous. Xestoleberis -spot small, outlined and divided into two parts. Line of concrescence and inner lamella separated anterior and posteriorly, forming a relatively large vestibulum at the anterior end. Selvage peripheral in anterior margin and sub-peripheral in posterior margin. Marginal pore canals simple, straight and short. Hinge antimerodont, with well-developed teeth in posterior and anterior elements. Both terminal teeth in RV.

Median element crenulate and short. Adductor muscle scars a row of four sub-elliptical scars, the ventral-median more elongate. Frontal muscle scar V-shaped. Sexual dimorphism present: female conspicuously larger than male and more rounded in RV. In dorsal view male less tumid at the posterior end.

Remarks. Xestoleberis amazonica sp. nov. was already recorded by Coimbra et al. (1999) in open nomenclature. It has a similar shape to X. rigusa Müller 1908 , described from Antarctica. However, X. rigusa is larger and more inflated in dorsal view than X. amazonica sp. nov. Both species also differ from each other in the pattern of the Xestoleberis -spot, which is small and divided into two parts in the species herein described.

Occurrence and distribution. Xestoleberis amazonica sp. nov. occurs along the Northern region of the Brazilian continental shelf ( Fig. 2 ; Tab. 1) in a depth range of 30 to 240 m. It is restricted to the area between Orange Cape and the Parnaiba Delta.

Figures

FIGURE 2. Distribution of Xestoleberis species in Brazilian continental shelf. The hatched area corresponds to the Transitional Zone of Coimbra et al. (1995). Each dot represents one sample.

FIGURE 4. Xestoleberis amazonica sp. nov. 1. Female, RV (MP-O- 1938, holotype). 2. Female, LV (MP-O- 1942). 3. Female, dorsal view (MP-O- 1943). 4. Male, RV (MP-O- 1939). 5. Male, LV (MP-O- 1939). 6. Male, dorsal view (MP-O- 1940). 7. Hinge (MP-O- 1942). 8. Central muscle scars, LV (MP-O- 1942), not to scale. 9. Male, ventral view (MP-O- 1940). 10. Sieve-type normal pore canal (MP-O- 1941). 11. Lip-type normal pore canal (MP-O- 1941). 12. Simple-type normal pore canal (MP-O- 1941). 13. Xestoleberis - spot (MP-O- 1942). 14. Schematic drawing of some LV internal features.