Diagnosis.  Groshenyia  with  very  low  trochospiral  coil  and  petaloid  to,  more  rarely clavate last-formed chambers.

Description.  Test  is  very  low  trochospiral  with  the  distinct  tendency  to  become planispiral in the adult stage, unequally biumbilicate, and consisting of 7-8 chambers arranged in 1.5-2 whorls; there are 4-4.5 (commonly 4.5) chambers in the final whorl. Earlier chambers are globular, with low chamber size increase; chambers of the last whorl are tangentially elongate, petaloid, more rarely clavate, often backward oriented, and with higher size increase rate. Sutures are distinct, depressed and radial on both sides of the test; sutures between the chambers of the last whorl are deeply incised, resulting in a strongly lobate outline. Test is slightly asymmetrical in edge view due to the very low trochospire and the tendency to develop planispirally coiled tests. Aperture is a low arch, extraumbilical-peripheral in position and  bordered  by  an  imperforate  lip;  relict  periapertural  structures  can  be  occasionally observed in the umbilical region. Umbilici are shallow and wide, with a diameter of circa one half of the maximum test diameter. Chamber surface is smooth. Test wall is calcitic, hyaline, simple and perforate; pores are simple, circular or subcircular, and with a diameter of 0.9-1.3µm.

Remarks. Groshenyia groshenyae differs from all the species of the genus Leupoldina mainly by lacking last-formed chamber distal bulbous projections. It differs from Clavihedbergella subcretacea (Tappan, 1943) by having petaloid to, more rarely clavate rather than subcylindrical last formed chambers, lower trochospire resulting in an unequally biumbilicate test, simple periphery rather than with a peripheral band of low pore density and smaller pore size and (iv) smaller pores with a diameter of 0.9-1.3 µm rather than 1.5-3.2 µm. It differs from Pseudoclavihedbergella simplicissima (Magné and Sigal in Cheylan et al., 1954) mainly by having very low trochospire resulting in an unequally biumbilicate test rather than being mono-umbilicate, main aperture shifted more towards the periphery, smooth chamber surface rather than ornamented with dome-like pustules and smaller pores (0.9-1.3 µm rather than 0.9-2.2 µm in diameter). It differs from P. amabilis (Loeblich and Tappan, 1961) mainly by having simple test wall rather than incipiently reticulate and smaller pores, with a diameter of 0.9-1.3 µm rather than 1.8-5.0 µm. The gross test architecture of G. groshenyae resembles that of the Aptian “Globigerinelloides” sigali Longoria, 1974, but the porosity is different, with larger pores in the former; apparently the two species evolved iteratively, and there is a gap comprising the late Aptian-early late Albian time interval between the LO of “G.” sigali and FO of G. groshenyae.

References: