The Helicosphaeraceae constitute an important family of heterococcoliths ranging from the Early Eocene to the present day (extant species H. carteri, H. pavimentum). There is only one genus but numerous fossil species, many of which are of biostratigraphic value, though mainly as secondary markers (see also Neogene range chart). The morphology is unusually complex so some special terminology is needed.

Informal taxon-based term: Helicolith - nannolith formed by the Helicosphaeraceae.
Orientation: The asymmetry of helicoliths allows more-precise description of orientation than for most other coccoliths.

Anterior end with origin of flange and usually with broader flange on distal side often with distinct wing or spur. (Alternative term pterygal, see appendix).
Posterior opposite end to anterior. (Alternative term antipterygal, see appendix).
Dextral/sinistral right/left sides of helicolith as seen in distal view with anterior end upwards. As with other uses the terms dextral/sinistral are recommended in place of left/right for terms referring to one particular orientation. The wing, when present is on the sinistral side.

Bar structure crossing central opening. Types;
Conjunct bar developed from rim elements (e.g. H. carteri). (Alternative terms optically continuous bar, bar, bridge, see appendix).
Disjunct bar formed from elements discrete from the rim (e.g. H. intermedia). (Alternative terms optically discontinuous bar, bridge, bar, see appendix).
Normally oriented bar diagonal bar with dextral orientation; i.e. rotated to the right of the long axis in distal view/ anterior end on opposite side to the wing.
Inversely oriented bar diagonal bar with sinistral orientation; i.e. rotated to the left of the long axis in distal view/ anterior end on same side as wing.
N.B. Use of the terms normal/inverse is a ubiquitously adopted convention based on their relative abundances.
Blanket mass of elements forming distal cover. {Theodoridis 1984}
Flange rim structure of helicolith (shield is also used by some workers).
Origin location of first/shortest elements of flange on the proximal side.
Proximal plate inward radiate elements on proximal side of central-area.
Spur spike-like expansion of flange near its termination (e.g. H. recta).
Termination location of last elements of flange on the distal side.
Wing broad expansion of flange near its termination (e.g. H. carteri).

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