Grovesella Davydov and Arefifard, 2007

Davydov, Vladimir I., 2011, Taxonomy, nomenclature, and evolution of the early schubertellid fusulinids, Acta Palaeontologica Polonica 56 (1), pp. 181-194 : 186-188

Genus Grovesella Davydov and Arefifard, 2007

Fig. 2A–T.

2000 Levenella ? Ueno, 1991; Vachard et al. 2000: 794.

2007 Grovesella gen. nov.; Davydov and Arefifard 2007: 5–6 (pars).

Type species: Grovesella tabasensis Davydov and Arefifard, 2007 , Khan Formation , latest Sakmarian –early Artinskian , Madbeiki section, Kalmard area, East−Central Iran .

Description.—Test very small (0.09–0.2 mm in length and 0.2–0.3 mm in diameter), discoidal to barrel−shaped, with broadly rounded periphery and weakly to slightly umbilicate flanks. Proloculus is quite large. The proloculus/test ratio is 1:3 to 1:5, sometimes up to 1:7. Coiling planispiral or nearly planispiral with half or full first volution coiled at small angle in respect to following volutions. Length of the test is equal or significantly less than the width and consequently the means of form ratio is equal or less than one. Wall thin, its internal structure poorly visible. Wall probably two−layered with a darker thin tectum and slightly lighter structureless layer below the tectum. Chomata are not observed.

Remarks.— Grovesella is probably the ancestral taxon to all schubertellids. It closely resembles Schubertina in its small test size and relatively large proloculus, but differs from the latter in its barrel−shaped outline and planispiral or nearly planispiral coiling as opposed to the subglobose to ovoid outline and strongly skewed coiling in Schubertina . It also lacks chomata. Grovesella probably evolved from Semistaffella or Eostaffellina stocks as they all possess a similar barrel−shaped outline. Grovesella differs from Semistaffella in its much smaller size, two−layered wall as oppose to undifferentiated wall in Semistaffella , planispiral coiling and absence of chomata. Although Grovesella is similar to Eostaffellina in the outline, it differs from the latter in its loosely coiled volutions, larger proloculus and consequently a smaller proloculus/test ratio that is 1:3 to 1: 5 in Grovesella and 1:15 to 1: 30 in Eostaffellina and in the lack of chomata or pseudochomata that are always present in Eostaffellina .

Because Schubertina was unknown to the writer in 2007, several specimens belonging to Schubertina were included in the original description of Grovesella ( Davydov and Arefifard 2007: 5–6) , i.e., Schubertina mosquensis (Rauser−Chernousova in Rauser−Chernousova et al. 1951); Schubertina compressa (Rauser−Chernousova in Rauser−Chernousova et al. 1951); Schubertina miranda (Leontovich in Rauser−Chernousova et al. 1951); Schubertina globulosa (Safonova in Rauser−Chernousova et al. 1951); Schubertina borealis (Rauser−Chernousova in Rauser−Chernousova et al. 1951)— all from the Moscovian of Russian Platform and surrounding areas. Now that, the genus Grovesella is restricted to barrel−shaped forms with planispiral coiling the above mentioned species are considered to belong to Schubertina .

The presence of a barrel−shaped test with a large proloculus and planispiral coiling make Grovesella homeomorphic to Permian Levenella Ueno, 1991 and Zarodella Sosnina, 1981 . The latter genus has never been reported beyond the occurrence of the topotype in Far East Russia. Besides, it belongs to staffellids i.e., possesses specific wall structure with glassy luminotheca that is easily re−crystallized. Typical Grovesella sometimes identified as Levenella (for example Leven 1995: pl. 1: 3) as both genera possess similar morphology. The wall structure of these genera during ontogenesis, however, is quite different. It is structureless one−layered initially in Levenella ( Ueno 1991 b) , but two−layered in Grovesella . In the outer volutions the wall in Levenella becomes two layered with dark tectum and fine alveolar keriotheca, whereas it does not changed in Grovesella . Besides this, the test size of Levenella doi:10.4202/app.2010.0026

three times greater than those of Grovesella . It might be that Grovesella and Levenella are related each other and thus the Levenella , Pamirina , and Misellina are originating from Schubertellida.

Stratigraphic and geographic range.— Grovesella is poorly known. Because of its very small size (> 0.2 mm) it might be overlooked in Permian rocks where workers generally look for large fusulinids On the other hand, these forms are perhaps often considered as juvenile forms of Schubertella and therefore were ignored. Grovesella is distributed globally from Peri−Gondwana up to Panthalassa shelves and ranged from the middle Bashkirian up to Wordian.