Lyonsiella Friele 1879

Lyonsiella cf. Ƒagilis Allen & Turner, 1974 (Fig. 10B, C) Distribution Literature records: Uruguayan Continental slope as Lyonsiella fragilis (Allen and Turner 1974, Allen 2008). Bathymetry: 497–1470 m. Material examined: 36°27 ʹ S, 53°31 ʹ W, 497–518 m (MCZ 353551) two individuals; 36°35 ʹ 35″S, 53°22 ʹ 59″W, 993–1011 m (MCZ 353553) one individual. Description Shell small (~ 1.5 mm L, 1.1 mm H), elongate. Surface covered by 9–10 radial lines clearly marked by coloration. Posterodorsal margin straight, followed by a truncated posterior margin. Anterodorsal margined inclined, followed by a prolonged and rounded anterior margin. Ventral margin widely rounded. Remarks Allen and Turner (1974) identified Lyonsiella specimens collected from the Uruguayan Continental slope as Lyonsiella fragilis during the Atlantis II expedition. Two lots, MCZ 353551 (station 236) and MCZ 353553 (station 237), are housed at the Museum of Comparative Zoology, but only the former had well-preserved individuals. The authors mentioned a record from station 239, but the lot was not found in this collection. The studied material exhibits a posterior margin truncated instead of rounded, as originally described for L. fragilis (Allen and Turner 1974). Consequently, the curvature between posterodorsal and posterior margin forms a right angle instead of an obtuse one. Additionally, the anterior margin is rounded instead of straight, and the scalloped edge was not observed in the studied specimens. Lastly, the largest specimen recorded by the authors is 8.9 mm long, whereas the Uruguayan specimens measure ~ 1.5 mm long. The holotype of L. fragilis is fragmented into several pieces, and the paratype consists of a microscope slide, making a direct comparison with these Uruguayan specimens challenging. Although these differences could be interpreted as ontogenetic, a conclusive identification will be possible when more specimens become available. Lyonsiella cf. fragilis, in addition to Lyonsiella abyssicola (GO Sars, 1872), has an elongated contour. However, the latter has more radial lines, an anterior projection widely rounded instead of acute, and a more vertically inclined anterodorsal margin.