Chancelloria sp. A

Wrona, Ryszard, 2004, Cambrian microfossils from glacial erratics of King George Island, Antarctica, Acta Palaeontologica Polonica 49 (1), pp. 13-56 : 25

Chancelloria sp. A

Fig. 6A, B, G–K, S.

Material.— A number of chancelloriid sclerites and their isolated marginal or central rays with broken distal ends from erratic boulders Me32, 33, and 66. Figured specimens, ZPAL V. VI/28 S24; 35S18; 103S5; 105 S3, 16 , 19; 108S12.

Description.—Radially symmetric chancelloriid sclerites, which vary in size and number of rays. They seem to be originally composed of 6–8 radial rays and one usually larger central ray (Fig. 6J) or rarely 4–6 radial rays without central element. Radial rays are 0.7–1.6 mm long, and expand slightly from the basal plane. The outer surface of the ray in some cases shows longitudinally oriented needle−like replicas of the originally aragonitic fibres, which composed the sclerite wall (Fig. 6J, S). This pattern corresponds to that observed by Kouchinsky (2000). The basal facet is flat, with radial rays straight, lying in the same plane, or slightly curved and divergent from the basal plane. These articulated sclerites and isolated rays obviously represent phosphatic moulds of their internal cavities.

Remarks.—A number of internal moulds of individual disarticulated sclerite rays correspond to the normal sclerite type of Chancelloria eros Walcott, 1920 in a broad sense (Bengtson in Bengtson et al. 1990; Mehl 1998). As the figured specimens are very variable in shape and ray composition, some of them may also represent the species Ch. ex gr. symmetrica Vasileva recovered from the Stansbury and Arrowie Basins, South Australia (Demidenko in Gravestock et al. 2001). Such specimens were also reported earlier from erratic blocks of Middle Cambrian limestone occurring in moraines of the Argentina Range in Antarctica ( Solovjev and Grikurov 1979; Popov and Solovjev 1981). The Antarctic articulated sclerites (Fig. 6J) also resemble closely the articulated specimens of Ch. lenaica Zhuravleva and Korde, 1955 from the Lower Cambrian of Comley, Shropshire, England ( Hinz 1987: pl. 2: 10, 11).

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