Hadimopanella antarctica Wrona, 1987

Wrona, Ryszard, 2004, Cambrian microfossils from glacial erratics of King George Island, Antarctica, Acta Palaeontologica Polonica 49 (1), pp. 13-56 : 40-42

Hadimopanella antarctica Wrona, 1987

Figs. 17 , 18A–D.

Hadimopanella sp. ; Gaździcki and Wrona 1986: 611, fig. 7g.

Hadimopanella antarctica Wrona ; Wrona 1987: 42, pls. 5–8.

Hadimopanella antarctica Wrona ; Wrona 1989: 542, pl. 8: 7.

Holotype: Specimen ZPAL V. VI/28 S3, figured by Wrona (1987: pl.8: 2) . Topotype: Specimen figured (Fig. 18A); ZPAL V. VI/24 S9.

Material.— Over one hundred isolated sclerites from erratic boulders Me33, 40, and 66. Figured specimens, ZPAL V. VI/ 103 S11, 15 ; 24 S9, 27, 28, 31.

Description.—See Wrona 1987: 42.

Remarks.—Some unusual sclerites show small circular plate−like nodes in a marginal position (Fig. 18B). Such exceptionally preserved sclerites may document accretional mode of sclerite growth: from very small sclerites, having only a single apex, to much larger sclerite, having numerous apices arranged in a specific pattern (Fig. 18A 2, B 2, D 1). The nodes are equal in size, usually 10 µm in diameter and 15 µm high. They are generally oriented upwards ( Figs. 17 , 18A 1, A 3, D 2). Some specimens (Fig. 18D) have a fine corrugation on the node surfaces. The crown (cap) sometimes does not cover the base; in such cases the suture between the outer and inner layers is displayed, revealing a striated basal margin in a finer radiating pattern (Fig. 18C). The specimens are assigned to Hadimopanella Gedik, 1977 because of their similar morphology and number of nodes, although both characters are variable. The correlation between sclerite size and the number of nodes ( Bengtson 1977; Dzik 1986b) suggests that Milaculum − type sclerites may also have arisen from an increase in the number and accretion of sclerite nodes. Some sclerites of Hadimopanella from Antarctica have one node, as is common in H. apicata . These sclerites (with one node) are somewhat like rare forms of H. apicata Wrona, 1982 figured by Bendix−Almgreen and Peel (1988: fig. 5). These authors also noted an unusual sclerite of H. apicata from Greenland having fewer marginally distributed tubercles (probably about 5), being reminiscent of H. antarctica Wrona, 1987 . Their ornamentation can also be compared with much smaller platelets occurring in many articulated cuticles of several palaeoscolecid genera (see Müller and Hinz−Schallreuter 1993). H. antarctica , both in morphology and size, closely resembles elements

Fig. 18. A–D. Hadimopanella antarctica Wrona. A. Sclerite ZPAL V.VI /24S9, erratic Me66; A 1, oblique lateral view; A 2, upper view; A 3, detail of basal mar− Ą gin in oblique view, with nodes and suture. B. Sclerite ZPAL V. VI /24S28, erratic Me40; B 1, oblique upper view; B 2, detail of basal margin, showing marginal nodes (arrowed) fused. C. Sclerite ZPAL V. VI /24S27, erratic Me40; C 1, upper view; C 2, detail of wide basal margin showing suture and striae. D. Sclerite ZPAL V. VI /24S31, erratic Me66; D 1, upper view; D 2, detail of sclerite in oblique view, showing circular rim (arrowed) surrounding central apex.

E, F. Hadimopanella apicata Wrona. E. Slightly coated sclerite ZPAL V. VI /24S36, erratic Me66; E 1, oblique upper view; E 2, detail of basal margin showing striae. F. Sclerite, slightly coated with mineral grains, ZPAL V. VI /24S20, erratic Me66; F 1, oblique upper view; F 2, detail of basal margin and striae.

G–M. Hadimopanella staurata sp. nov. G. Sclerite in upper view, ZPAL V.VI/24S26, erratic Me40. H. Sclerite, slightly coated with mineral grains, in upper view, ZPAL V.VI/24S18, erratic Me66. I. Sclerite, coated with mineral grains, in upper view, ZPAL V.VI/24S30, erratic Me40. J. Sclerite in upper view, ZPAL V.VI/35S24, erratic Me66. K. Coated sclerite in oblique view, ZPAL V.VI/24S32, erratic Me33. L. Slightly coated sclerite in oblique lateral view, ZPAL V.VI/24S33, erratic Me40. M. Sclerite, coated with mineral grains, in upper view, ZPAL V.VI/24S34, erratic Me40.

of the tuberculate ornament on sclerites of Chalasiocranos exquisitum Brock and Cooper, 1993 from the Ramsay Limestone of Yorke Peninsula, South Australia ( Brock and Cooper 1993). The latter has nodes arranged in a ring around a central node and resembles also some specimens of Hdimopanella cassiniana ( Repetski, 1981) . It is possible that H. antarctica represents intermediate smaller sclerites of the same animal that bears C. exquisitum sclerites, similarly to the palaeoscolecid animals possessing sclerites of different kinds (see Kraft and Mergl 1989; Müller and Hinz−Schallreuter 1993).

Figures

Fig. 17. Diagrammatic reconstruction of the Hadimopanella antarctica Wrona sclerite in oblique lateral (A) and dorsal (B) views; see also Wrona (1987). C. Energy dispersive spectrum (EDS) for the H. antarctica sclerite.