logo TERMINOLOGY

8. Intra-specific variation

8.1 Primary coccolith variation

As a general principle styles of variation should be described without reference to inferred causal factors - e.g. heavily calcified E. huxleyi is preferable to cold-water morphotype. Terms used here are largely based on Young and Westbroek (1991) and Young (1994).
Normally formed with typical form.
Abnormally formed departing from normal form in some way, includes all the categories below.

A. Degree of completion / ontogenetic variation variation in degree to which the coccolith has grown. (N.B. terms such as juvenile and mature are not recommended for use in this context).
Coccolithogenesis process of coccolith development and growth {Outka and Williams 1971}
Proto-coccolith ring earliest stage of coccolith growth, crystal-units simple without differentiation of elements. {Young 1989}
Incomplete coccolith elements differentiated but incompletely grown.
Complete coccolith all elements fully grown.

intra-specific variation
Drawings are of pairs of Emiliania huxleyi segments (redrawn from Young 1994)

B. Teratological Malformation abnormal form developed as result of irregular growth. N.B. The use of the term malformation to describe other types of variation (e.g. degree of calcification, or growth) is not recommended.

C. Degree of calcification primary variation in amount of biogenic calcite incorporated in a coccolith.
Under-calcified coccolith with elements markedly thinner than normal for the species.
Normally calcified coccolith with elements of normal thickness for the species.
Over-calcified coccolith with elements markedly thicker than normal for the species.

8.2 Secondary alteration of coccoliths - diagenetic and water-column effects

(Fig. 9)
Overgrowth secondary inorganic growth of calcite on elements.
Etching secondary inorganic dissolution of calcite from elements.

Descriptive scheme, {from Roth and Thierstein 1972, Roth 1983}.
X Excellent preservation coccoliths appear pristine.
E1 Slight etching serrate outlines, partial dissolution of delicate structures.
E2 Moderate etching irregular outlines, dissolution of most delicate structures and species.
E3 Strong etching much material fragmented, only resistant species left.
O1 Slight overgrowth overgrowth of shield and central-area elements noticeable but does not obscure details.
O2 Moderate overgrowth many elements with large overgrowths, many details obscured.
O3 Strong overgrowth only overgrown elements, identifications very limited.

N.B. Overgrowth and etching commonly both occur in the same sample, this can be shown by codes such as E1-O2. This scheme is primarily for light microscopy, successful electron microscopy typically requires preservation grades E1, X or O1.
Return to terminology index