3. Terms for entire coccoliths


This page gves descriptive terms for coccolith size and shape, indepependant of structure. They are primarily applicable to heterococcoliths. Holococcolths and nannoliths have different shapes and terms for them are given elsewhere.

3.1 Orientation

Proximal directed toward centre of coccosphere/cell. On nannofossils this is usually assumed to be the concave side, but cannot always be determined.
Distal directed toward outer surface of coccosphere/cell.
Horizontal perpendicular to proximo-distal direction.
Vertical proximo-distal direction.
Internal/inner/inward toward centre of coccolith.
External/outer/outward away from centre of coccolith.
Longitudinal direction parallel to long axis of an elliptical / elongated coccolith.
Transverse direction parallel to short axis of an elliptical / elongated coccolith.
End edge of coccolith parallel to short axis.
Side edge of coccolith parallel to long axis.
Length/width/height maximum dimensions of coccoliths in the longitudinal, transverse and vertical directions respectively.

lith orientation

3.2 Parts

In the vast majority of heterococcoliths there is an outer part which is somewhat higher than the inner part of the coccolith. This provides a convenient basis for starting any description of the shape and structure of coccoliths. It also is in large part a reflection of the coccolithogenesis process; growth outward and upward from the proto-coccolith ring forms the rim whilst growth inward forms the central-area .
Central-area Inner part of coccolith, enclosed by the rim. Usually characterised by less regularly cyclical elements than the rim and by inward element growth. May be entirely closed, or include a central opening. N.B. We recommend hyphenating central-area since it has a special meaning.
Rim Outer part of coccolith, usually characterised by regular cycles, some vertically directed structures and outward element growth (alternative term marginal area, see appendix). N.B. Use of this term was agreed after considerable discussion at the workshops.

lith profiles

3.3 Profile - coccolith shape in vertical cross-section

(Fig. 2) Although there is a very wide range of coccolith shapes the three types listed below recur frequently in disparate groups, see also Young (1992a). They are probably homoeomorphic adaptations for organising coccoliths on the cell. Intermediates between the types occur and any of them can occur with or without processes. These terms have no taxonomic implications.
Murolith rim elevated but without well developed shields (e.g. Zeugrhabdotus, Pontosphaera). (Discolith has been used in this sense, see appendix). {Young 1992a, from Latin murus wall}
Placolith rim has two, or more, well developed shields (e.g. Coccolithus, Emiliania, Watznaueria). {Lohmann 1902}
Planolith rim not significatly elevated (e.g. Rhabdosphaera, Discoaster). {Young 1992a, from Latin planus flat}

3.4 Outline - coccolith shape in plan view

Axial Ratio (abb. AR) ratio of length to width. Suggested descriptive terms, for elliptical coccoliths, are: Circular ; Sub-circular; Broadly elliptical; Normally elliptical; Strongly elliptical..
Asymmetrical without bilateral symmetry, due to a wing or similar structure.
Elliptical continuously curved with two axes of symmetry. Close to, but not necessarily an exact, mathematical ellipse (alternative terms oval, ovoid, see appendix).
Irregularly elliptical with an approximately elliptical shape but departing noticeably from regular form.
Lenticular symmetrical form intermediate between a rhombus and ellipse, i.e. with pointed ends (e.g. Syracosphaera prolongata, Stradnerlithus).
Oblong symmetrical form intermediate between a rectangle and ellipse, i.e. with curved ends but sub-parallel sides (e.g. Calciopappus caudatus, Ellipsolithus macellus). N.B. This is recommended botanical use (Stearn 1983).
Polygonal with straight sides (triangular, pentagonal etc., e.g. scapholiths, Corollithion). (alternative term geometric, see appendix).
Reniform concavo-convex, kidney-shaped (e.g. Nephrolithus).
Ring-shaped circular or elliptical with narrow rim and open central-area (e.g. Cricosphaera, Manivitella).
Wing local extension of rim (e.g. Helicosphaera, Kamptnerius).

coccolith shape

3.5 Coccolith size

Coccolith size is normally given as maximum dimension in plan view, i.e. length. The following sequence of terms are suggestions, based primarily on appearance in the light microscope. Minuscule (<1 Ám), Very small, 1-3 Ám; Small 3-5 Ám; Medium 5-8 Ám; Large 8-12 Ám; Very large >12 Ám.
cocolith size

3.6 Informal taxon-based terms for entire coccoliths

Many terms, originally defined as descriptive morphological terms, have become, restricted taxonomically. For instance most authors would agree that the term helicolith should be restricted to coccoliths of the Helicosphaeraceae, and not to any unrelated homoeomorphs. These terms are useful in many contexts, for example where it is important to distinguish between the organism and the coccolith/nannolith, or for describing polymorphic coccospheres. In general these terms are more widely used by workers on living coccolithophores than by palaeontologists. Comprehensive reviews are given by Tappan (1980), Chretiennot-Dinet (1990), Heimdal (1993), Siesser and Winter (1994), Jordan et al.(1995).
We do not give detailed definitions here, since essentially they are defined by the characteristic morphology of the taxa on which they are based. New terms of this sort can be formed by adding to an appropriate generic root either (1) the suffix -lith (e.g. sphenolith) or (2) the suffix -id + coccolith, murolith, planolith, or placolith (e.g. reticulofenestrid coccoliths).
Only modern usage is given here and many terms have undergone a complex evolution of meaning so that literature usage needs to be interpreted with caution - this applies particularly to the terms cricolith, cyrtolith, discolith, rhabdolith, and tremalith.
Caneolith* Syracosphaeraceae, endothecal coccolith. (N.B. The terms complete/incomplete caneoliths have been used, see appendix). {Braarud et al. 1955a, 1955b}
Cricolith* Pleurochrysidaceae, placolith with narrow rim and open central-area . {Braarud et al. 1955a, 1955b}
Cyrtolith* Syracosphaeraceae, exothecal coccolith. {Braarud et al. 1955a, 1955b}
Discolith* Pontosphaeraceae, murolith without flanges. {Huxley 1868}
Helicolith Helicosphaeraceae, coccoliths with helical flange.
Lopadolith high rimmed equatorial murolith of Scyphosphaera. {Lohmann 1902}
Osteolith whorl coccoliths of Ophiaster. {Halldal and Markali 1955}
Pappolith* Papposphaeraceae.
Podorhabdid coccolith Podorhabdaceae.
Protolith Stephanolithaceae, Parhabdolithaceae (cf. Bown 1987).
Rhabdolith Rhabdosphaeraceae, planoliths +/- spines. {Schmidt 1870}
Scapholith Calciosolenia, Anoplosolenia. (Alternative term rhombolith). {Deflandre and Fert 1954}
Tremalith* Hymenomonadaceae, vase-shaped murolith. {Lohmann 1913}
Reticulofenestrid coccolith Reticulofenestra and descendants. {Young 1989}
Coccolithid placolith Coccolithaceae. {Jordan et al. 1995}
(N.B. See also the sections on nannoliths and holococcoliths, and appendix 2, for related terms).
* These terms are now (2017) almost never used in modern literature and can be considered obsolete. [JR Young, 2017]
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