Lecture 10 Superfamilies: Orbitodacea, Spirillinacea, Duostominacea and Robertinacea

Superfamily Orbitodacea The orbitoids are a Late Cretaceous to Miocene group of "larger foraminifera" which originated in tropical Americas. Their tests are radial hyaline and perforate, with a discoidal mode of growth, the chambers being arranged in annular cycles rather than plane spirals. A median (equatorial) layer of chambers is differentiated from the lateral chambers, seen most clearly in axial thin sections (Discocyclina).

Superfamily Spirillinacea The wall consists of a single crystal of calcite. They are small benthic forms often found adhering to algae and other hard substrates. Spirillina has a long, planispiral second chamber and terminal aperture. Patellina has a trochospiral to biserial test in which the chambers are subdivided by a scroll-like median septum and numerous transverse septulae.

Spirillina Patellina

Superfamily Duostominacea The Duostominacea are an extinct group that may be intermediate in development between certain Endothracea and most Rotaliina. This is suggested by the wall structure which consists of both optically radial and microgranular calcite. In Duostomina (M. Triassic) the low trochospiral test has a basal aperture divided into two by a flap.

Duostomina

Superfamily Robertinacea The Robertinacea have optically radial bilamellar walls composed of aragonite instead of calcite, although this may revert to the latter mineral with time in the fossil state. The aperture is typically a basal slit extending up the face of the last chamber. In Robertina the test is high trochospiral, each elongate chamber subdivided by transverse partitions. Ceratobulimina (Upper Cretaceous) has a moderately low trochospiral test whilst that of Hoeglundina (M. Jurassic-Recent) is provided with a keel and peripheral slits marking the primary and relict (supplementary) apertures.

Robertina Ceratobulimina Hoeglundina