Hadimopanella staurata, Wrona, 2004

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

Hadimopanella staurata sp. nov.

Figs. 18G–M, 19–22.

Holotype: Specimen shown in Fig. 20 ; ZPAL V. VI/24 S3, from erratic boulder Me66.

Type horizon: The inferred upper part of the Lower Cambrian.

Type locality: Erratic boulders of Antarctic origin. Me 33 in glacio−marine Cape Melville Formation (Lower Miocene), King George Island, South Shetland Islands, West Antarctica.

Derivation of name: From Greek stauratos, cross−shaped, referring to the cross pattern on the nodular upper face.

Material.— Several dozen isolated sclerites from erratic boulders Me33, 40, and 66. Figured specimens, ZPAL V. VI/24 S3, 18 , 24, 30, 32, 33, 34; 35S24; 103 S11, 15.

Diagnosis.— Hadimopanella species with sclerites having an upper nodular crown with a flat or shallowly concave crest parallel to the basal side and covered with wedge−shaped nodes or ridges arranged in the form of a Saint George cross. Description.—These small circular phosphatic sclerites (diameter 39–60 µm) consist of two layers (Fig. 18G–M). The lower layer forms an expanded base, with smooth and flat or slightly convex lower surface ( Fig. 22 ). The upper layer forms the crown (diameter about 21–36 µm), bearing three to five wedge−shaped nodes or ridges arranged in the form of a Saint George cross (Figs. 18H, I, 19, 20) or clover−leaf pattern ( Fig. 19 ). Some sclerites with a fractured external layer show the arrangement of phosphate crystallites constituting this hyaline layer ( Figs. 20C , 21C, D ). The nodes are triangular, usually 10 µm wide and 15 µm high. Some specimens (Fig. 18K, L) have a fine corrugation on the node surfaces. The crown sometimes does not cover the base; in such cases the suture between the outer and inner layers is displayed, revealing a radially striated basal margin typical for Hadimopanella sclerite (Figs. 18M, 19) in a finer radiating pattern. The elevation of the upper surface ranges from about 20–25 µm.

Remarks.—The sclerites described here differ markedly in their morphology and size from any other known Hadimopanella species. They are slightly similar in size, as well as, in their shape and lower number of nodes (elongated as ridges), to some Australian single tubercles (plate sensu Conway Morris 1997) of Kaimenella dailyi Brock and Cooper found in fragments of palaeoscolecid cuticle from the Lower Cambrian (Toyonian) Wirrealpa, Aroona Creek and Ramsay Limestones of the Stansbury Basin (tuberculate unit sensu Brock and Cooper, 1993: fig. 8: 10–12and fig. 9: 2). The characteristic striated basal margin (Fig. 18G, K, L) with a finer radiating pattern may reflect radially arranged apatite crystallites, as in the external hyaline layer ( Figs. 20C , 21C, D ).

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

Figures

Fig. 20. Holotype of Hadimopanella staurata sp. nov., ZPAL V.VI/24S3, errratic boulder Me66. A. Oblique lateral view, stereo−pair. B. Upper view. C. Enlargement showing (in a hole) arrangement of phosphate crystallites in the external sclerite layer.

Fig.22. A. Diagrammatic cross section of the sclerite Hadimopanella staurata sp. nov. B. Energy dispersive spectrum (EDS) for the H. staurata sclerite.

Fig. 19. Representatives of Hadimopanella staurata sp. nov. sclerites showing variability in shape and ornamentation. A. ZPAL V.VI/24S24. B. ZPAL V.VI/24S26. C. ZPAL V.VI/24S33. D. ZPAL V.VI/19S9. E. ZPAL V.VI/24S33. F. ZPAL V.VI/24S30, in oblique lateral (F1) and upper (F2) views. G. ZPAL V.VI/24S3, holotype, in oblique lateral (G1) and upper (G2) views. H. ZPAL V.VI/35S24, in oblique lateral (H1) and upper (H2) views. I. ZPAL V.VI/14S9, in oblique lateral (I1) and upper (I2) views. J. ZPAL V.VI/17S8, in oblique lateral (J1) and upper (J2) views.

Fig. 21. Sclerite of Hadimopanella staurata sp. nov., ZPAL V.VI/24S24, errratic boulder Me40. A. Oblique lateral view. B. Upper view. C, D. Enlargements of B showing arrangement of phosphate crystallites in the external layer.