Lyonsiella cf. Ƒagilis Allen & Turner, 1974, 1879

Pacheco, Leonel I., Teso, Valeria & Pastorino, Guido, 2024, Use of traditional tools and micro-computed tomography for the taxonomy of carnivorous bivalves from the deep waters of Southwestern Atlantic, Zoological Journal of the Linnean Society 202, pp. 1-23 : 16

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. Ŋe 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 laưer has more radial lines, an anterior projection widely rounded instead of acute, and a more vertically inclined anterodorsal margin.

Figures

Figure 10. Lyonsiella spp. A, original illustration of Lyonsiella fragilis from Allen and Turner (1974). B, C, Lyonsiella cf.fragilis MCZ 353551: lateral view of both specimens. Scale bars: 5 mm in A; 1 mm in B, C.