Cloudina, Germs, 1972

Zhuravlev, Andrey Yu., Liñán, Eladio, Vintaned, José Antonio Gámez, Debrenne, Françoise & Fedorov, Aleksandr B., 2012, New finds of skeletal fossils in the terminal Neoproterozoic of the Siberian Platform and Spain, Acta Palaeontologica Polonica 57 (1), pp. 205-224 : 218

Cloudina ex gr. C. hartmanae Germs, 1972

Figs. 3B, F–H , 4A, B .

1989 “microorganismos tubulares”; Palacios Medrano 1989: pl. 16.

1990 Cloudina sp. ; Grant 1990: fig. 7C, D.

1994 Cloudina hartmannae [sic] Germs, 1972; Vidal et al. 1994: fig. 12A, B.

1994 Cloudina sp. ; Vidal et al. 1994: fig. 12C.

Material.—Two thin sections with six fossils and five etched fragmentary steinkerns from the Tirteafuera River locality, Abenójar Anticline, East Lusitanian–Alcudian Zone, central Spain; lower La Grajera−Cañuelo unit, Ibor Group, upper Ediacaran. As well, the same species is present in Ibor Group outcrops of the Navalpino Anticline, East Lusitanian–Alcudian Zone and in the Río Huso Group of the Río Huso section, northern flank of the Valdelacasa Anticline, Galician–Castilian Zone; central Spain ( Grant 1990; Vidal et al. 1994).

Description.—Tubicolous calcareous microfossils consisting of apically slightly flaring funnel−like segments (up to 2.8 mm in diameter) eccentrically placed within each other and imparting an irregular polygonal shape to the cross−section. The tube length is over 4.2 mm. The wall thickness is ca. 0.08 mm. The wall is replaced by fine transparent sparry calcite mosaic whereas the tube cavity is sealed by coarse transparent sparry calcite beneath a possible tabula and by sediment above the tabula. Beneath the tabula, within sparry calcite mosaic, some rodlike, slightly curved transparent structures are preserved which can be either broken wall fragments (the thickness is the same) or bacterial borings ( Fig. 4A ).

Remarks.—Etched fossils from Spain were studied as goldcoated samples under scanning electronic microscope ( SEM) Jeol JSM 6400 at the Servicio de Microscopía Electrónica, Universidad de Zaragoza in both secondary electron emission and backscattering regimes.

By its morphology and size range, this fossil is close to Cloudina hartmanae Germs, 1972 from the Nama Group of Namibia.

Hua et al. (2005b) discounted a presence of any tabula (“transverse cross wall”) within Cloudina tubes. At the same time they demonstrated a “hemispherical basal end” ( Hua et al. 2005b: fig. 1A, B, F; also see Chen and Sun 2001: pl. 1: 6–13, pl. 2: 4–6). Also, a longitudinal section of a Cloudina ex gr. C. hartmanae tube in our material shows that lower funnel−like tube segments are occupied by sparry calcite while the uppermost ones contain sediment only ( Fig. 4A ). Thus, the character of sediment and marine cement infilling indicates that some continuous transverse structures are present in tubes of this species at least. In any case, these are not tabulae typical of tubicolous polychaetes. The latter secrete tabulae, possibly in response to damage of the posterior end of the tube, but such tabulae bear an apparent perforation to accommodate tufts of chaetae on the worm’s posterior abdominal segment ( Hedley 1958). The presence of both “hemispherical basal end” and tabulae favours a microconchid lophophorate affiliation for this fossil. However, microconchids possess much more elaborated microstructure and perforated shells ( Taylor and Vinn 2006).

Figures

Fig. 3. SEM images of late Ediacaran Cloudina. A, C–E. Cloudina ex gr. C. riemkeae Germs, 1972; Kyyry−Ytyga (1.6 km downstream from Ulakhan−Ytyga Creek mouth), Yudoma River, right bank, Siberian Platform, Russia, Ust’−Yudoma Formation. A. SNIIGGiMS 1630/1, tube fragment with abraded shell wall. C. SNIIGGiMS 1630/2, fragment of tube with holes formed after microdolomite crystal dissolution. D. SNIIGGiMS 1630/3, detail of tube fragment with holes formed after microdolomite crystal dissolution. E. SNIIGGiMS 1630/4, tube nested funnels. B, F–H. Cloudina ex gr. C. hartmanae Germs, 1972; Tirteafuera River, Abenójar Anticline, East Lusitanian–Alcudian Zone, central Spain, lower La Grajera−Cañuelo unit, Ibor Group. B. MPZ 2007/3918, abraded tube fragment with imprints of mica crystals of the matrix. F. MPZ 2007/3919; F1, tube fragment with wall preserved; F2, detail of F1; F3, detail of F1, wall microstructure. G. MPZ 2007/3920, abraded tube fragment. H. MPZ 2007/3921; H1, tube fragment with wall preserved; H2, detail of H1 showing wall microstructure. Scale bars A, D, E, H1 100 µm; B, C, F2 300 µm; F1, G 1 mm; F3 50 µm; H2 30 µm.

Fig. 4. Late Ediacaran calcareous fabrics from Ibor Group, Abenójar Anticline, East Lusitanian–Alcudian Zone, central Spain. A, B. Cloudina ex gr. C. hartmanae Germs, 1972, lower La Grajera−Cañuelo unit, Tirteafuera River. A. MPZ 2007/3923, longitudinal section showing wall fragments or bacterial microburrowing within skeleton ̕arrow). B. MPZ 2007/1465, oblique longitudinal section. C. MPZ 2009/496, longitudinal section of corolla−bearing “Cloudina” carinata Cortijo, Martí Mus, Jensen, and Palacios, 2010, lower La Grajera−Cañuelo unit, Tirteafuera River. D. MPZ 2007/3925, thrombolite structure, breccia unit “calizas de Abenójar”, Abenójar. Scale bars 250 µm.