Hyolithellus micans ( Billings, 1871 )

Wrona, Ryszard, 2004, Cambrian microfossils from glacial erratics of King George Island, Antarctica, Acta Palaeontologica Polonica 49 (1), pp. 13-56 : 46-48

Hyolithellus micans ( Billings, 1871)

Fig. 25E.

Hyolithellus cf. micans (Billings) Morphotype C ; Brasier 1984: 236, fig. 1v–x.

Hyolithellus micans (Billings) ; Demidenko in Gravestock et al. 2001: 94, pl. 9: 10 [full synonymy].

Material.—Six well preserved tube fragments from erratic boulders Me32, 33, 66. Figured specimen, ZPAL V. VI /32S4.

Description.—Slightly tapering tubes, with low angle of divergence, up to about 5° (usually less), straight or gently curved and circular in cross−section. Tubes are broken at both ends,in fragments up to 40 µm wide and up to 3 mm long. The wall is phosphatic and up to 30 µm thick. The outer surface is covered with variably spaced (in range 20–80 µm), weakly ex−

Fig. 23. Mongolitubulus squamifer Missarzhevsky. A. Oblique lateral view, showing almost complete tapering at the top end and damage at the base; ZPAL Ą V. VI /28S28, erratic Me66. B. Lateral view showing scale ornamentation arranged clearly in spiral rows, ZPAL V. VI /28S27, erratic Me66. C. Spine with corroded surface, ZPAL V. VI /106S11, erratic Me66; C 1, lateral view; C 2, detail of surface sculpture. D. Middle part of broken spine ZPAL V. VI /29S16, erratic Me66; D 1, lateral view showing scale pattern and wall structure at the broken ends; D 2, broken end showing layered wall structure and fibrous inner layer; D 3, apical oblique view showing imbrication of the scales; D 4, detail showing surface sculpture. D 5, detail of imbricated scale ornamentation in apical view. E. Middle part of broken spine showing scale pattern, ZPAL V. VI /106S21, erratic Me66. F. Middle part of the spine ZPAL V. VI /106S22, erratic Me66; F 1, lateral view, showing scale pattern; F 2, adapical end of the spine, in oblique lateral view, showing broken section of the wall; F 3, detail of the same section, showing outer and inner layer; F 4, detail showing surface sculpture. G. Polished and etched cross−section through the wall, parallel to the spine axis, showing fibrous structure of the inner layer (at right), ZPAL V. VI /22U2, erratic Me66. H. Etched inner surface of the internal (pulp) cavity of the spine, ZPAL V. VI /22U1, erratic Me66; H 1, basal oblique view, showing fibrous inner layer (centre); H 1, detail of the same.

pressed transverse ribs (annulae), probably representing growth lines. No opercula closing the aperture and any structure for attachment to the substrate have been observed.

Remarks.—The Antarctic specimens demonstrate distinctive characters clearly similar to Australian specimens of H. cf. micans ( Bengtson et al. 1990) and H. micans (Gravestock et al. 2001) , and match well H. micans in the broad interpretation of many authors (see synonymy in Bengtson et al. 1990). The new Antarctic collection reinforces Bengtson’s (in Bengtson et al. 1990) concept of hyolithelmiths as animals with tubes lacking a mineralized operculum.

Occurrence.—Cosmopolitan in the Early Cambrian: (Atdabanian/Botomian) Kulpara Formation and Parara Limestone, Horse Gully, Yorke Peninsula, Stansbury Basin, South Australia; Northwest Territories, Canada; Massachusetts and New York, USA; Scania and Bornholm, Sweden; Salaany Gol and Khairkhan Formations, Zavkhan, Salaany Gol, Mongolia; allochthonous Early Cambrian (Botomian) boulders (Me32, 33, 66), King George Island, Antarctica.