Polyzygia beckmanni beckmanni Krömmelbein, 1954

Maillet, Sebastien, Milhau, Bruno, Vreulx, Michel & Posada, Luis-Carlos Sánchez De, 2016, Givetian ostracods of the Candás Formation (Asturias, North-western Spain): taxonomy, stratigraphy, palaeoecology, relationship to global events and palaeogeographical implications, Zootaxa 4068 (1), pp. 1-78 : 36-37

Polyzygia beckmanni beckmanni Krömmelbein, 1954

(Pl. II: Fig. 24)

1954a Polyzygia beckmanni nov. sp.; Krömmelbein: 253–255, pl. 2, figs. 7–9. 1964 Polyzygia beckmanni Krömmelbein ; Le Maître & Magne: 130.

1964 Polyzygia beckmanni Krömmelbein ; Magne: 136, pl. 23, figs. 137–141. 1968 Polyzygia beckmanni Krömmelbein ; Lecompte: 43, pl. 17.

1970 Polyzygia beckmanni Krömmelbein ; Lethiers: 71, pl. 6, fig. 5–6.

1971a Polyzygia beckmanni Krömmelbein; Becker: 44.

1972 Polyzygia beckmanni Krömmelbein ; Michel: 225–226, pl. 7, figs. 1–6, pl. 9, figs. 1–2.

1974 Polyzygia beckmanni beckmanni Krömmelbein ; Becker & Bless: pl. 8, fig. 4. 1974 Polyzygia beckmanni Krömmelbein ; Lethiers: 77, text-figs. 1–2.

1977 Polyzygia beckmanni beckmanni Krömmelbein; Casier: 8, 9.

1979 Polyzygia beckmanni beckmanni Krömmelbein; Casier: 5, 6.

1982 Polyzygia beckmanni Krömmelbein ; Milhau: 22, pl. 5, fig. 135.

1983a Polyzygia beckmanni Krömmelbein ; Milhau: 351, 353, pl. 1, fig. 1.

1985 Polyzygia beckmanni Krömmelbein ; Coen: pl. 6, fig. 2.

1985 Polyzygia beckmanni Krömmelbein ; Lethiers et al.: 76–77, pl. 13, figs. 8–9. 1997 Polyzygia beckmanni beckmanni Krömmelbein ; Casier et al.: 156–158, pl. 2, fig. 1. 2009 Polyzygia beckmanni beckmanni Krömmelbein ; Casier in Casier & Préat: pl. 5, fig. 7. 2010 Polyzygia beckmanni beckmanni Krömmelbein ; Maillet: 40, pl. 3, figs. 26–27. 2010a Polyzygia beckmanni beckmanni Krömmelbein ; Casier in Casier et al.: 41, pl. 3, fig. 9. 2013 Polyzygia beckmanni beckmanni Krömmelbein ; Maillet: 110, pl. XIV, figs. 16–20. 2013b Polyzygia beckmanni beckmanni Krömmelbein ; Maillet et al.: figs. 7U–V.

Material. 18 specimens (9 C, 6 V, 3 F).

Diagnosis. Krömmelbein (1954a, p. 253).

Description. Large and almost equivalve carapace, sub-oval in lateral view, sub-rectangular in dorsal view. Hmax slightly anterior; Lmax slightly ventral; Wmax at mid-length along the carina. Regularly convex dorsal and ventral margins. Dorsal and ventral margins converging both anteriorly and posteriorly. Highly arched anterior and posterior margins. Carapace is flattened along the anterior and posterior margins. Anterior part of the carapace slightly higher than the posterior one. Well developed “W”-shaped carina along free margins of the valves. Valves with three lobes connected at their bases near the centre of the valves, thus forming also a smaller “W”. Central bulbous lobe pointing towards anterior. Anterior and posterior lobes symmetrically sub-triangular and reticulated. Marked sulcus extending between the carina and these lobes.

Discussion. This species, exhibiting a characteristic morphology, marks the Givetian/Frasnian boundary ( Lethiers 1984). Some variations on the carapace were observed among our specimens, with a carina sometimes flatter and more extended, a carapace sometimes more elongated, a “W”-shaped sulcus with a medio-ventral base varying from a straight to a clearly curved line, and reticulated lobes with a connection more or less narrow.

Occurrences. Upper Givetian to Lower Frasnian (Fromelennes Fm, Fort Hulobiet Mb, Nismes and Presles Fms), Ardenne (Aisemont, Nismes, Sourd d’Ave, Barvaux, Flohimont and Aisne sections), Upper Givetian to Lower Frasnian (Candás Fm, mb D), Asturias (Peran-Perlora and Carranques sections); Lower Frasnian, Boulonnais, Eifel and Morocco.