Radiocyathus, Okulich, 1937

Wrona, Ryszard, 2004, Cambrian microfossils from glacial erratics of King George Island, Antarctica, Acta Palaeontologica Polonica 49 (1), pp. 13-56 : 24

Radiocyathus ? sp. cf. R. minor Bedford and Bedford, 1934

Fig. 5L.

“ Lenastella ”; Wrona 1989: 541, pl. 8: 6.

Material.—Two sclerites from erratic boulder Me66. Figured specimen, ZPAL V. VI /40S9.

Description.—Simple sclerite consisting of a rounded plate and a six−ribbed stellate rosette. The rays are slightly inclined toward the central perpendicular ray, which is shortened to a central knob (Fig. 5L 1). Distally tapering stellate rays are usually broken and hollow. The rounded star−shaped plate, formed by radial rays and numerous small projections in between, has on its external surface a characteristic, radially arranged, granular, starlike sculpture (Fig. 5L 2, L 3).

Remarks.—The described sclerites represent phosphatic overgrowth (sheaths) of originally calcareous nesasters. This sclerite was described and figured earlier as “ Lenastella ”− type rosettelike spicules ( Wrona 1989: 541, pl. 8: 6), and their heteractinid provenance was also considered ( Wrona and Zhuravlev 1996: 16). The rosette−like sclerites very much resemble radiocyathan nesasters, and are superficially somewhat similar also to the South Australian? Heteractinid calcareous spicules ( Bengtson et al. 1990: fig. 14F–H). The starlike sculpture on the external plate of Antarctic specimens is very similar to the external sculpture of Radiocyathus minor nesasters figured by Debrenne et al. (1970: pl. 6: 1). Moreover, the latter species was also recorded in thin sections of Early Cambrian glacial erratics from King George Island, Antarctica ( Wrona and Zhuravlev 1996). R. minor was originally described from the Ajax Limestone, Flinders Ranges , South Australia ( Bedford and Bedford 1934) and Todd River Dolomite (Amadeus Basin), central Australia ( Kruse and West 1980). The figured specimen (Fig. 5L) is probably a partial nesaster, because, unlike sclerites, nesasters were interlocked to form a continuous mineralised skeleton. The discussed homology between radiocyathid nesasters and receptaculitid meroms, and the close relationship between both these groups ( Nitecki and Debrenne 1979) was finally rejected by Nitecki (1986) as highly speculative.

Occurrence.—Allochthonous Early Cambrian (Botomian) boulders (Me66), King George Island, Antarctica.