Palaeozoic calcispheres are of uncertain affinity and are not discussed here. Most Mesozoic and Cenozoic calcispheres are now believed to be dinoflagellate cysts. Keupp (1991) gives an English-language synthesis of this group, Janofske and Keupp (1992) give a brief overview, these workers regard wall structures as the primary basis for classification. Williams et al. (1978), Sergeant (1982) and Evitt (1985) summarise the terminology for describing organic-walled cysts, much of which can be directly applied to calcispheres. Only the most important, relevant terms are included here.

1. Orientation

Dinoflagellates have clearly differentiated ends, shown by shape, flagellar disposition, behaviour, etc. Swimming direction is conventionally used to determine front and rear.
Apex/anterior end front of dinoflagellate when swimming, usually pointed. Almost always contains the archaeopyle.
Antapex/posterior end rear of dinoflagellate when swimming, usually flaring.
Ventral side side of dinoflagellate with longitudinal flagellum and sulcus.
Dorsal side side opposite longitudinal flagellum and sulcus.
general terms

2. General terms

Calcisphere hollow, typically spherical, calcareous nannofossil. Whereas coccospheres are composite structures formed of numerous coccoliths calcispheres possess a continuous wall.
Cyst wall formed around dinoflagellate during non-motile, non-vegetative, stage. These often show paratabulation but are continuous structures, except for the archaeopyle if present. Most calcispheres are thought to be cysts, however, the thoracosphere of Thoracosphaera heimii is formed during the vegetative stage and so is not a cyst.
Dinoflagellate informal taxon-based term for member of the phylum Dinophyta.
Theca non-resistant organic wall of motile vegetative stage of dinoflagellates, composite structures formed of plates.
Thoracosphere informal taxon-based term for calcisphere formed by Thoracosphaera. N.B. T. heimii has a wall structure of large elements (ca. 1 Ám) with their c-axes tangential to the wall, and randomly aligned.

3. Wall types

Oblique/Obliquipithonelloid formed of elements with their c-axes oblique to the wall and variably aligned relative to each other (e.g. Obliquipithonella multistrata).
Pithonelloid formed of elements with their c-axes oblique to the wall and sub-parallel to each other (e.g. Pithonella sphaerica, P.ovalis).
Radial/Orthopithonelloid formed of elements with their c-axes perpendicular to the wall (e.g. Calciodinellum, Rhabdothorax).
Tangential formed of elements with their c-axes tangential to the wall (e.g. Fuetterella conforma, Thoracosphaera heimii).

wall structures

4. Paratabulation features

Archaeopyle opening for excystment.
Operculum plate covering the archaeopyle.
Paratabulation structures on the cyst of a dinoflagellate reflecting the tabulation of the theca. Paratabulation may be developed on the inner or the outer surface of calcispheres.
Cingulum sub-equatorial channel occupied by the transverse flagellum.
Sulcus furrow occupied by longitudinal flagellum.
Horn protrusion from either end of dinoflagellate.

paratabulation types

5. Paratabulation types

Holotabulate paratabulation of ridges or edges on the cyst corresponding to plate boundaries on the theca.
Intratabulate paratabulation of processes on the cyst corresponding to plates on the theca.
Cingulotabulate paratabulation confined to cingulum and archaeopyle.
Cryptotabulate paratabulation confined to archaeopyle.

Return to terminology index