Heterostegina cubana Cizancourt, 1947

Torres-Silva, Ana. I., Eder, Wolfgang, Hohenegger, Johann & Briguglio, Antonino, 2018, Morphometric analysis of Eocene nummulitids in western and central Cuba: taxonomy, biostratigraphy and evolutionary trends, Journal of Systematic Palaeontology 17 (7), pp. 557-595 : 585-586

Heterostegina cubana Cizancourt, 1947

( Fig. 18C )

1947 Heterostegina cubana de Cizancourt : 518, pl. 25, figs 4, 5.

2017 Heterostegina cubana de Cizancourt ; Torres-Silva, Hohenegger, Cori ́́c, Briguglio, & Eder: 57, fig. 10E.

Material. Ten megalospheric specimens in equatorial section and numerous random thin sections from Loma Candelaria section (98LC-1).

Description.

External features. Test involute, flattened, biconvex, with diameter of the megalospheric forms ranging from 4.1 to 5.9 mm. The piles appear more pronounced near the central portion of the test. No trace of septal sutures and secondary chamberlets is visible due to bad preservation of the individuals at the Loma Candelaria locality. Cizancourt’s (1947) original description is based on specimens with a granulate surface and primary and secondary septa forming the typical reticulate network in Heterostegina , and with septal sutures slightly curved towards the periphery.

Internal features. Megalospheric generation characterized by large mean proloculus diameter value (0.25 mm) followed by a second reniform chamber and by a rapidly increasing, loosely coiled spiral. Primary septa with stronger backwards bend angle form elongated chambers, which increase in height during ontogeny. After the second chamber, one to five operculinid chambers (undivided chambers) are followed by chambers subdivided into chamberlets by very incompletely developed secondary septa or septula. The first chamberlet closest to the marginal spiral is extremely elongated compared to peripheral chamberlets. Chambers subdivided by complete septula form rectangular chamberlets.

Occurrences. Late middle Eocene to late Eocene, NP 16/ 17, Loma Candela Formation.

Remarks. Heterostegina cubana was first described from the late Eocene of western Cuba by Cizancourt (1947) and was almost unrecorded until Cole (1957) considered it a synonym of Heterostegina ocalana . This species is distinguished by its characteristic incomplete septula and larger proloculus. Caudri (1996) reported Heterostegina indicata with very incompletely developed or absent septa in the basal late Eocene of Trinidad. As suggested by Caudri (1996) for Trinitarian species, H. cubana could also be a transitional form between operculinid and heterosteginid morphologies. Note, however, that H. indicata has a complete evolute enrolment similar to Planostegina and Planoperculina , whereas H. cubana shows a distinct thickening of the central test.

Stratigraphical and geographical distribution. Late middle Eocene to late Eocene (Bartonian to early Priabonian); Cuba.

Figures

Figure 18. A, B, D–H, Heterostegina ocalana Cushman; A, Loma Viǵıa, CA-216-D1a; B, Norona, NOR-UN 15/14; D, Loma Viǵıa, CA-216-79; E, F, Loma Jabaco; E, LM-52-756; F, LM-52-752; G, H, Norona, NOR-UN 24. C, Heterostegina cubana Cizancourt, Loma candelaria, 98LC-1H-809. I, Heterostegina sp. indet., Loma Candelaria, 98LC-1H-808. A, B, A forms in axial section; C–G, I, A forms in equatorial section; H, external view.