Buccinosphaera invaginata Haeckel 1887, p.99, pl.5, fig.11; Nigrini, 1971, p.445, pl.34.1, fig.2 (with synonymy)
Similar to Collosphaera tuberosa, but with short (8-16 µm), inwardly directed spines projecting from the larger pores found where the shell indents. Pores generally smaller and shell with a thinner wall than C. tuberosa (Nigrini, 1971).
Based on 20 specimens. Maximum shell diameter 88-119 µm (Nigrini, 1971).
This species is distinguished by having inwardly directed spines in the depressions of the shell wall.
This species is superficially similar to a Miocene species, Collosphaera brattstroemi Bjørklund and Goll, 1979, p. 1315, pl.3, figs.10-26, pl.4, figs.13-16. However, the Miocene form is much larger (diameter = 112-192 µm), has pores that tend to be more polyconal in shape and has closed latticed invaginations rather than open apertures.
This is a relatively rare and delicate species found in latitudes lower than 30°. Its morphotypic first appearance marks the base of the youngest Quaternary zone (Buccinosphaera invaginata Zone) and the event is probably synchronous. It is extant.
B. invaginata arose from Collosphaera orthoconus (Haeckel) (= Collosphaera sp. A in Knoll and Johnson, 1975) by the development of wall invaginations.
For further taxonomic discussion, see Collosphaera invaginata in Bjørklund and Goll, 1979.
Additional illustrations can be found in Knoll and Johnson, 1975, pl.1, figs.3-7.
Recognition of this species requires a well-preserved assemblage and reliable core-top recovery; drilled cores may not be adequate.