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Diagnosis.– Sigalia with weak ornamentation and well-developed adult stage with multichamber growth.
Description.– Test with the early subtriangular stage consisting of 9-12 chambers alternately added with respect to the test growth axis resulting in a biserial arrangement; chambers of the early stage increase in size at a moderate rate. The adult flaring stage begins with the biaperturate progressive chamber, which is smaller or equal in size to the last chamber of the early biserial stage; chambers of the multichamber growth adult stage petaloid, with highly variable width/height ratio. Adult stage consists of four to nine sets of two to four chambers each; irregular chamber increase or reduction in number between successive sets, without a constant pattern throughout the adult stage (Pl.7, Figs. 2, 5, 8). Sutures between the earlier chambers indistinct due to the addition of successive layers of calcite during the ontogeny (Pl. 7, Figs. 2, 5, 8); those in the adult stage lined by curved phaneroridges, which are more prominent in the earlier portion of the test; central suture straight often covered with additional layers of calcite. Test compressed in edge view, with quasi-parallel sides and periphery with transverse keels; transverse keels result from the fusion of the phaneroridges from the opposite sides of the test across the periphery (Pl. 7, Figs. 1, 6, 9). Aperture simple in the earlier biserial stage, an arch at the base of the last formed chamber and multiple in the adult stage (Pl. 7, Figs. 1, 6, 9); chambers of the adult stage can be monoaperturate (relapsed) or biaperturate; apertures are bordered by metaflanges, which are rarely preserved. Chambers ornamented with leptocostae (2.1-6.0 µm), which are more prominent in the periphery, over the earlier chambers and in the phaneroridges; ornamentation is often absent on the lateral sides (Pl. 7, Figs. 2, 5, 8). Peri- apertural pustulose area well-developed. Test wall calcitic, hyaline and perforate (pore diameter 1.0-5.5 µm); pores simple, situated between the leptocostae in the earlier portion of the test or interrupting them in the adult stage.
Size: Dimensions of the holotype.– L = 0.442 mm; W = 0.445 mm; W/L = 1.007; T = 0.117 mm; T/L = 0.265; A = 86°.
Etymology: From the Latin verb proliferare (= to increase in number), with reference to the adult stage, which is characterized by an increase in chamber number.
Extra details from original publication
Remarks.– Sigalia proliferans differs from the earlier species of the directional lineage by the well-developed adult stage with multichamber growth, which consists of up to nine sets of chambers with irregular increase or reduction in number between the successive sets.
Sigalia proliferans compiled by the pforams@mikrotax project team viewed: 24-7-2021
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