Holoplicatella margarita, Clausen & Álvaro, 2006

Clausen, Sébastien & Álvaro, J. Javier, 2006, Skeletonized microfossils from the Lower-Middle Cambrian transition of the Cantabrian Mountains, northern Spain, Acta Palaeontologica Polonica 51 (2), pp. 223-238 : 232-233

Holoplicatella margarita gen. et sp. nov.

Fig. 5F, G.

Etymology: After “margarita ” (in Spanish, daisy), the broad aspect of the convex side of the sclerite.

Type locality: Eastern Esla nappe, in the vicinity of the locality of Crémenes, Cantabrian Mountains, Spain.

Type horizon: Up to 10 m above the base of the “Beleño” facies, upper member of the Láncara Formation.

Holotype: Sclerite DGO 21146 ( Fig. 5G).

Material.— Eight specimens from the “Beleño” facies, section Cr 4.

Diagnosis.—Bilaterally symmetrical, concavo−convex sclerites, oval to subtrapezoidal in outline, bearing one prominent notch and two subduded domes on concave side, two distinct pits and radially symmetric folds or invaginations on anterolateral margins.

Description.—Two faces, convex and concave, can be distinguished in these sclerites. One margin of the sclerite bears a prominent notch, and is here considered (by analogy with marginal notches of Wushichites ; Conway Morris et al. 1997) as the posterior margin. On the convex face, the opposite (anterior) margin bears two symmetrical (perpendicular) folds or invaginations, which form prominent sulci on margin, and attenuate toward the centre. The lateral margins connecting both folds and the posterior notch are slightly convex−concave in a rounded sinuous pattern that also attenuates toward the centre. The anterior margin of the concave face bears two symmetrical domes with rounded tops, which correspond to the prolongation of the above−described folds, connected by a faint depression, the whole framework elevated above the rest of the face; the centre of the concave face is depressed anteriorly and laterally bounded by an amphitheatre−like wall. The lateral (concave upward) view of the sclerite is subtriangular, increasing in thickness toward the anterior margin, and bears two lateral pits (60 µm in outer diameter) in the wall at both anterolateral sides.

Comparison.— Wushichites minutus and W. polyedrus were originally defined in Xinjiang ( China) by Qian and Xiao (1984) as cambroclaves of uncertain affinity. Although Bengtson et al. (1990: 103) reported both taxa as “doubtful species” likely referable to the genus Cambroclavus , their morphological characters are so striking that it seems reasonable to place them in a separate genus ( Conway Morris et al. 1997). These authors revised new material from the type area, and considered W. polyedrus to be a junior synonym of W. minutus . The presence of a prominent spine broadly transverse to the disc (Qian Yi 1989: 235) was the criterion for keeping Isoclavus and Wushichites separate ( Conway Morris et al. 1997: 180). Holoplicatella differs from Wushichites sensu Conway Morris et al. (1997) in the presence of folds and lateral pits, and the broadly inflated (and not flattened) character of the sclerites.

Triplicatella ( Bengtson et al. 1990; Skovsted 2003) is composed of bilaterally symmetric, concavoconvex sclerites, with strongly developed folds and invaginations concentrated at both margins of the axis of symmetry. In contrast, Holoplicatella has a prominent notch (as in Wushichites ) and two anterolateral pits.

Stratigraphic and geographic range.—Lowermost Middle Cambrian “Beleño” facies, upper member of the Láncara Formation, eastern Esla nappe, in the vicinity of the locality of Crémenes, Cantabrian Mountains, Spain.