Allonnia Doré and Reid, 1965

Wrona, Ryszard, 2004, Cambrian microfossils from glacial erratics of King George Island, Antarctica, Acta Palaeontologica Polonica 49 (1), pp. 13-56 : 26

Genus Allonnia Doré and Reid, 1965

Type species: Allonnia tripodophora Doré and Reid, 1965 .

Remarks.—Originally this genus was introduced for chancelloriid sclerites having three rays (formula: 3+0), but Qian and Bengtson (1989) also included in this genus sclerites with four (formula: 4+0) and two (formula: 2+0) rays; for synonymy and detailed discussion see Qian and Bengtson (1989) and Bengtson et al. 1990.

Allonnia ex gr. A. tripodophora Doré and Reid, 1965 Figs. 5J, 6D, F.

Material.—A dozen isolated marginal rays from erratic boulders Me32, 33, and 66. Figured specimens, ZPAL V. VI / 385S19; 103S11 and 15.

Description.—Small sclerites with 3 equally long, slender tapering lateral rays (formula: 3+0), which strongly diverge from the basal plane. Basal ends of rays have lateral faces diverging at 60° from each other. This reflects the arrangement of articulated marginal rays diverging at 120° from each other. Basal end of rays are somewhat flattened, forming large basal areas without distinct sutures. Basal foramina are small, circular and situated at top of basal end. This morphology indicates absence of a central ray. Distal ends of lateral rays may be recurved (Fig. 5J). Outer surface of rays and basal facet is partly covered with mineral grains.

Remarks.—All specimens are phosphatic internal moulds of isolated slender, recurved rays, with characteristic circular, basal openings and sagittal shape of the ray basal parts, may also represent elements of A. ex. gr. tripodophora .

Occurrence.—Allochthonous Early Cambrian (Botomian) boulder (Me32, 33 and 66), King George Island, Antarctica.

Allonnia cf. tetrathallis (Jiang, 1982in Luo et al. 1982) Fig. 5K.

Material.—Four internal moulds of sclerites, often with broken−off distal ends from erratic boulders Me33 and 66. Figured specimen, ZPAL V. VI /365S7.

Description.—Bilaterally symmetric sclerites with long slen− der rays (formula: 4+0), which slightly diverge from the basal plane. Outer surface of the ray is provided with weak longitudinal striae, which may reflect originally aragonitic fibres composing the sclerite wall. Basal facet is relatively large with a distinct suture. Basal foramina well developed, but partly covered with mineral grains.

Remarks.—Similar chancelloriid sclerites with formula 4+0 were first assigned to the genus Onychia by Jiang (in Luo et al. 1982) and included by Qian and Bengtson (1989: see detailed discussion) as a junior homonym in a broadened concept of the genus Allonnia . A number of small and slender internal moulds, which have characteristic one large facet and sagittal shape of the base of each ray, may also represent the species A. cf. tetrathallis .

Occurrence.—Allochthonous Early Cambrian (Botomian) boulders (Me33 and 66), King George Island, Antarctica.