TERMINOLOGY

Main text - terms applicable to any coccoliths


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1. GENERAL TERMS
2 COCCOSPHERE RELATED TERMS 3 TERMS FOR ENTIRE COCCOLITHS 4 ULTRASTRUCTURE RELATED TERMS 5 TERMS FOR DESCRIBING COCCOLITH RIMS 6 CENTRAL-AREA STRUCTURES 7 CRYSTALLOGRAPHY 8 INTRA-SPECIFIC VARIATION 9. NANNOLITH SHAPES

1. GENERAL TERMS

Nannoplankton plankton 2-63 m in diameter. (Alternative spelling nanoplankton, see appendix). Informal grouping including coccolithophores, Thoracosphaera, chrysophytes, etc., but excluding the bacterial picoplankton. {Lohmann 1909}
Calcareous nannoplankton nannoplankton with calcareous tests.{?Stradner 1961}
Nannofossil fossil <63 m in diameter, excluding fragments and juveniles of larger fossils.
Calcareous nannofossil nannofossil formed of calcium carbonate.
Coccolithophore noun, calcareous nannoplankton belonging to the division Haptophyta {Lohmann 1902}
Coccolithophorid adjective, e.g. Coccolithophorid algae.
Coccosphere test of coccolithophore (not necessarily spherical). An extracellular cover made up of numerous coccoliths. {Wallich 1860}
Coccolith calcareous structure formed by coccolithophore. {Huxley 1868}
Haptophyte unicellular alga belonging to the division Haptophyta, includes all coccolithophores, and also related non-calcifying forms, e.g. Prymnesium, Phaeocystis, Pavlova, Chrysochromulina (Alternative term Prymnesiophyte, see appendix).
Nannolith calcareous nannofossil lacking the typical features of calcareous dinophytes, heterococcoliths or holococcoliths and so of uncertain affinity, see also Young (1992a), Young et al. (1994, 1999). The division between coccoliths and nannoliths varies between authors and is liable to revision as new data becomes available. N.B. This rather restricted definition of the term has little etymological justification, but has been widely used, e.g. Perch-Nielsen (1985a, 1985b), Bown (1987), Aubry (1989). (The terms heliolith and ortholith provide an alternative basis for sub-dividing the calcareous nannofossils, see appendix). {?Perch-Nielsen 1985a}
Heterococcolith coccolith formed of crystal-units of variable shape and size. Crystal units typically arranged in cycles with radial symmetry. {Braarud et al. 1955a, 1955b}
Heterococcolithophore cell bearing coccosphere of heterococcoliths.
Holococcolith coccolith formed of numerous minute (<0.1 m) crystallites all of similar shape and size (N.B. Many of the terms below are not applicable to holococcoliths, and there is a separate section for specific holococcolith terms). {Braarud et al. 1955a, 1955b}
Holococcolithophore cell bearing coccosphere of holococcoliths.
Combination coccosphere coccosphere with both hetero- and holococcoliths. N.B. These are thought to represent a transitional state between heterococcolithophorid and holococcolithophorid phases of the life cycle. (The alternative term combination cell is less precise so is not now recommended). {Thomsen et al. 1991, Cros et al. 2000}
Xenosphere anomalous coccosphere containing coccoliths normally regarded as forming on quite discrete species (e.g. Emiliania huxleyi and Gephyrocapsa oceanica; Winter et al. 1979). N.B. These are very probably artefacts, the term is suggested specifically to suggest the abnormal nature of these structures. See also Young & Geisen (2002). {Young et al. 1997, from Greek xenos, stranger}

2 COCCOSPHERE RELATED TERMS

2.1 Descriptive Terms

(largely based on Okada and McIntyre 1977)
Monomorphic all coccoliths of similar type (e.g. Coccolithus).
Dimorphic coccoliths of two discrete types (e.g. Scyphosphaera).
Polymorphic coccoliths of more than two discrete types (e.g. Syracosphaera pulchra).
Varimorphic coccosphere with coccoliths whose size and/or morphology varies according to position on the coccosphere (e.g. Helicosphaera). {Young et al. 1997}
Dithecate with two discrete layers of coccoliths of different types (e.g. Syracosphaera pulchra).
Endotheca inner layer of coccoliths of dithecate coccosphere.
Exotheca outer layer of coccoliths of dithecate coccosphere.
Monothecate with a single layer of coccoliths (e.g. Scyphosphaera).
Multilayered with two or more layers of coccoliths but no differentiation into endo- and exotheca (e.g. Emiliania, Florisphaera, Coccolithus pelagicus phase hyalinus).
Shape coccospheres are three-dimensional so their shape should be described using appropriate terms for solid objects. Useful terms include: cylindrical, ellipsoidal, fusiform (elongate with tapering ends), obpyriform (inverse pear-shaped), ovoid (egg-shaped, i.e. one end broader than the other), spherical. See also Heimdal (1993), Jordan et al. (1995).

2.2 Orientation

(Fig. 1)
Apical pole end of coccosphere with flagellar opening.
Antapical pole opposite end of coccosphere.
Antapical coccoliths (abb. AAC)
coccoliths occurring at antapical pole.
Body coccoliths (abb. BC)
coccoliths other than polar coccoliths and exothecal coccoliths.
Circum-flagellar coccoliths / apical coccoliths (abb. CFC)
coccoliths occurring around flagellar opening. (Alternative term stomatal coccoliths, see appendix).
Exothecal coccoliths (abb. XC)
coccoliths of the exotheca
Flagellar opening opening in coccosphere through which the flagella and haptonema pass.
Polar coccoliths coccoliths occurring at poles of coccospheres. {Kamptner 1937}

2.3 Coccolith arrangement

(Fig. 1)
Overlapping adjacent coccoliths overlap.
Non-overlapping adjacent coccoliths arranged with edges directly butting rather than overlapping.
Interlocking adjacent coccoliths interlock.
Non-interlocking adjacent coccoliths do not interlock.
N.B. Interlock and overlap are separate phenomena, and can occur in any combination (see Fig. 1).

2.4 Informal taxon-based terms

As with coccoliths (see below), various terms have been coined to refer to coccospheres of particular taxonomic groups. These do not need any special definition, beyond noting the taxonomic groups included. E.g.; Braarudosphere Braarudosphaeraceae, Helicosphere Helicosphaeraceae.

3 TERMS FOR ENTIRE COCCOLITHS

3.1 Orientation

(Fig. 2)
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.

3.2 Parts

(Fig. 2) 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.

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.
Planolith rim not elevated (e.g. Rhabdosphaera, Discoaster). {Young 1992a, from Latin planus flat}
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). {Lohmann 1902}

3.4 Outline - coccolith shape in plan view

(Fig. 3)
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).

3.5 Coccolith size

(Fig. 2) 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 m), Very small, 1-3 m; Small 3-5 m; Medium 5-8 m; Large 8-12 m; Very large >12 m.

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 the appendix, for related terms).

4 ULTRASTRUCTURE RELATED TERMS

4.1 Types of ultrastructural component

(Fig. 4, largely based on Young and Bown, 1991).
Element Apparently discrete component of a coccolith. This is an observational term, several elements may unite to form a crystal-unit.
Crystal unit A group of elements from different cycles in crystallographic continuity. These are the fundamental components of coccoliths and their identification is a key objective of ultrastructural research.
Segment one symmetrically repeated part of the coccolith, including elements from each cycle, consisting of one or more crystal-units.
Lamina platy sub-structure within a crystal-unit (e.g. Braarudosphaera).
Contact-surface plane of contact between two elements. (alternative term attachment surface, see appendix).
Suture trace of contact-surface on surface of coccolith.
Cycle ring of elements or crystal-units.
Tier one of a set of vertically superposed cycles (e.g. Arkhangelskiella, Lapideacassis).

4.2 Element shapes

(Fig. 4, N.B. a,b,c three orthogonal axes, with any orientation)
Block nearly equidimensional element (a≈b≈c).
Tile broad and thin element (a≈b>c) N.B. Plate has been used in this sense but we prefer to use it for larger structures, not for single elements).
Lath elongate and wide element(a>b>c).
Rod elongate and narrow element (a>b≈c)
Wedge tapering nearly equidimensional element.
Petal/petaloid element tapering broad and thin element.
Ray tapering elongate and wide element.
Spine tapering elongate and narrow element.
Granule small and irregular or variable-shaped element (e.g. blanket elements of Helicosphaera, spine-forming elements of Cretarhabdus). N.B. Crystallite has been used in this sense but we prefer to only use it for holococcolith elements.

4.3 Element modifications

(Fig. 4)
Curvature curving of elements. Laevogyre - elements curve to the left when traced radially outward. Dextrogyre - elements curve to the right when traced radially outward. Straight - elements not curved.
Node block-shaped projection from element.
Keel lath-shaped projection from element.
Ridge rod-shaped projection running along element.
Tooth rod or wedge-shaped projection from element.
Kink angular bend in element.
Offset displacement of an element from radial growth due to a double kink.

4.4 Special structures

Scissor-structure crystal-unit structure formed of two elements growing at only slightly different angles, and forming a two-layered shield (e.g. Coccolithus upper and lower proximal shield elements, Fig. 6) or tube (e.g. Toweius inner and outer tube elements, Fig. 6). {Young 1992b}
Cross-over zone belt around which two cycles of crystal-units cross (this usually corresponds to the proto-coccolith ring, e.g. Coccolithus, Fig. 6). {Young 1992b}

4.5 Openings

(Fig. 4)
Canal narrow elongate opening within a coccolith or nannolith (Fig.s. 10, 14).
Cavity broad opening within a coccolith or nannolith (Fig.s. 10, 14).
Common opening opening formed by several individuals; i.e. the space within a coccosphere or group of associated nannoliths.
Depression pit on the surface of a coccolith or nannolith.
Hole opening running through one element (e.g. Pemma basquensis). {Farinacci et al. 1971}
Opening general term for any space not filled by elements.
Perforation small opening between two or more elements. {Farinacci et al. 1971}
Slit elongate perforation (e.g. Emiliania).

5 TERMS FOR DESCRIBING COCCOLITH RIMS

5.1 Parts of rims

(Fig. 5) Each of these parts may be formed of a single cycle of elements, part of a cycle or several cycles.
Shield broad (sub-)horizontal structure (placoliths).
Tube (sub-vertical structure between two shields (placoliths).
Wall (sub-)vertical structure not associated with shields (muroliths).
Flange (sub-)horizontal protrusion from rim.
Collar (sub-)vertical protrusion from rim (may occur on proximal or distal surface).
Crown discontinuous/beaded collar.

5.2 Directions on the rim

(Fig. 5, largely based on Black 1972)
Radial direction in the surface of the baseplate perpendicular to its margin: Inward-outward - toward-away from centre.
Tangential direction in the surface of the baseplate parallel to its margin: Clockwise/dextral/right, anticlockwise/sinistral/left senses of direction as seen in distal view. We recommend: use of clockwise/anticlockwise as the clearest of these terms for general purposes. Use of dextral/sinistral when it is wished to particularly emphasise that this is the orientation as seen in distal view.
Vertical direction perpendicular to the baseplate: Up/down distal-proximal directions.
Flare and taper divergence of orientation from horizontal/vertical in the radial direction. Flare surfaces diverge upward, producing obconical/funnel-shaped bodies. Taper surfaces converge upward, producing conical bodies.

5.3 Element arrangement as seen in side view

(Fig. 5)
Imbrication/inclination divergence from horizontal in the tangential direction. Imbrication is applicable to a cycle of elements, inclination to individual elements.
Clockwise/anticlockwise
imbrication
offset of upper part of element from lower.
Imbrication angle angle of contact-surface from the horizontal. High-angle - sub-vertical contact-surfaces. Low-angle - sub-horizontal contact-surfaces.
Zeugoid rim rim with high-angle imbrication, and without distinct shields. (Alternative terms loxolith rim, zygodiscid rim, see appendix).

5.4 Element arrangement as seen in plan view

(Fig. 5)
Obliquity horizontal divergence from radial direction. (Alternative term precession, see appendix).
Dextral/sinistral obliquity deflection from radial of outer part of element relative to inner part, as seen in distal view. Note that elements will show opposite apparent senses of obliquity in distal and proximal view. This can be described as follows: a dextrally oblique cycle displays clockwise obliquity in distal view but anti-clockwise obliquity in proximal view.
Butting elements with simple (sub-)radial sutures.
Interlocking elements with complex sutures.
Overlapping elements with low angle oblique sutures (N.B. This pattern has occasionally been described as imbrication, but we prefer to use imbrication for description of vertical structures).

5.5 Identification of elements

(Fig. 6) For description and discussion, the various elements/cycles of elements need to be identified. This is best done by reference to the location of the elements using the set of orientation and structure terms given above. Examples are given in Figure 8. Element shape is not recommended as an alternative since it is easily altered - by diagenesis, intra-specific variation and evolution.

6 CENTRAL-AREA STRUCTURES

6.1 Structural types

(Fig. 7)
Conjunct formed from crystal-units of the rim structure. E.g. Gephyrocapsa (bridge and grill), Helicosphaera sellii (bar), Kamptnerius (plate), Watznaueria biporta (bar). (Alternative term optically continuous structure, see appendix). {Young 1992a}
Disjunct formed from crystal-units discrete from the rim structure. E.g. Arkhangelskiella (plate), Coccolithus pelagicus (bar), Helicosphaera seminulum (bar), Watznaueria britannica (bar). (Alternative term optically discontinuous structure, see appendix). {Young 1992a}

6.2 Orientation in profile

(Fig. 7)
Basal occurring on the proximal surface.
Elevated occurring above the proximal surface.
Vaulted cone-shaped, rising from the rim toward the centre.
Longitudinal parallel with long axis of (elliptical) coccolith.
Planar flat, not vaulted.

6.3 Orientation in plan view

(Fig. 7)
Transverse parallel with short axis of (elliptical) coccolith.
Diagonal inclined relative to axes. Angle should be measured from transverse direction (but some authors use opposite convention, i.e. measure angle from longitudinal direction):
Low angle near to transverse direction;
High angle near to longitudinal direction.
Dextral/sinistral inclined to the right/left of the long-axis as seen in distal view. N.B. As with element obliquity the terms dextral/sinistral are preferred for describing orientations which appear different in proximal and distal view.
Relative width width of central-area relative to rim width:
Wide central-area width >2x rim width;
Normal central-area width 1-2x rim width;
Narrow central-area width <1x rim width.

6.4 Structures spanning central-area

(Fig. 7)
Arm part of crossbar, bridge or cross running from centre of coccolith to edge of central-area. (alternative terms limb, spoke, see appendix).
Bar any elongate central-area structure. N.B. This is a general term. When it is useful to be more specific terms such as longitudinal bar, cross-bar, and arm can be used. (Alternative term jugum, see appendix).
Blanket covering of small elements on distal side of central-area (e.g. Helicosphaera, Coccolithus).
Bridge elevated bar spanning the central-area (e.g. Gephyrocapsa).
Cross-bar bar spanning the central-area.
Cross pair of cross-bars meeting in centre.
Axial cross (abb. +), cross-bars longitudinal and transverse.
Diagonal cross (abb. X) cross-bars diagonal - may be symmetrical or asymmetrical relative to the axes.
Offset cross cross with an offset between the arms of one, or both, of the crossbars (e.g. Chiasmolithus).
Foot broadening of bar as it meets the rim (e.g. Cruciplacolithus tenuis).
Lateral bar bar running from rim to a cross bar (e.g. Retecapsa).

6.5 Structures closing central-area

(Fig. 7)
Central opening opening at centre of coccolith, may be spanned by bars or other central-area structures, but not by a continuous structure such as a grill or plate.
Closed central-area central-area without a central opening.
Grill system of bars closing central-area (e.g. Emiliania).
Net mesh-like structure closing central-area (e.g. Reticulofenestra, Cribrosphaerella). (Alternative term cribrate central-area, see appendix).
Open central-area central-area without any structures.
Plate continuous or nearly continuous structure closing central-area.
Perforated plate plate with perforations (e.g. Arkhangelskiella).

6.6 Processes

(Fig. 7)
Calyx flaring structure at tip of process (e.g. Podorhabdus, Papposphaera).
Boss low process, height similar to or less than width (alternative term knob, see appendix).
Process general term for any structure rising from the central-area.
Protrusion broad low process, with height similar to width, and width near that of entire central-area. Types:
Conical cone-shaped protrusion (e.g. Acanthoica);
Sacculiform sac-like protrusion with more or less rounded upper part (e.g. Algirosphaera). (N.B. labiatiform has been used for the elongate double-lipped sacculiform protrusions, see appendix).
Spine elongated process, height greater than width. (Alternative term column, see appendix). Types:
Styliform {Halldal and Markali 1955} - spine tapers toward the distal end;
Claviform {Halldal and Markali 1955} - spine has blunt end, without calyx. (N.B. helatoform has been used for nail-shaped processes, see appendix);
Calicate spine is surmountd by a calyx.
Salpingiform {Braarud et al. 1955a, 1955b} - spine (or protrusion) trumpet-shaped (e.g. Discosphaera).
Stem part of process below calyx.
Cavity wide opening within process (e.g. Podorhabdus grassei, Algirosphaera robusta).
Canal narrow opening running along length of process.
Proximal pore opening of canal, on proximal side of central-area.

7 CRYSTALLOGRAPHY

7. 1 Crystallographic orientation

(Fig. 8) Calcite c-axis orientation can be, summarised with the following terms. Based on Young and Bown (1991), Young et al. (1992). N.B. Actual orientations depart significantly (up to 30) from true vertical and radial.
V-unit crystal-unit with sub-vertical orientation of c-axis. {Young and Bown 1991}
R-unit crystal-unit with sub-radial orientation of c-axis, relative to its point of origin (nucleation) on the proto-coccolith ring. {Young and Bown 1991}
T-unit crystal-unit with sub-tangential orientation of c-axis (e.g. Braarudosphaeraceae, Polycyclolithaceae). {Young et al. 1997}
Compound formed of several crystal-units. E.g. Micula, Discoaster.
Pseudo-monocrystalline formed of several crystal-units with parallel c-axes, but non-parallel a-axes. E.g. Discoaster. These behave optically as single crystals, but will not fuse into a single crystal during overgrowth.
Monocrystalline formed of a single crystal-unit, and so all elements have identical crystallographic orientation of c- and a-axes and overgrow as one unit, e.g. apical spine of Sphenolithus heteromorphosus, entire nannoliths of Florisphaera, Marthasterites, Minylitha, Ceratolithus.

7.2 Graphical conventions for indicating crystallographic orientation

(Fig. 8)
Symbols A single symbol per element can indicate c-axis direction, see Fig.ure 8.
Shading To directly illustrate observations made with a gypsum plate hatching can be used - vertical and horizontal for parts in extinction (purple). Diagonal for birefringent parts (blue and yellow). The direction of diagonal hatching should of course be based on the c-axis orientation and since the gypsum plate orientation varies between microscopes the relationship between observed colour (blue, yellow) and c-axis direction has to be determined for each microscope.
Unit type shading For illustrating structure it is convenient to apply the same shading to all the elements of one crystal-unit cycle in all views of the nannolith. For this the following scheme is recommended: V-units stippled; R-units blank; T-units dashes.

7.3 Light microscopy based terms

(Fig. 8)
Birefringent/non-birefringent appearing bright/dark between cross-polars. N.B. A coccolith or part of a coccolith can only appear non-birefringent in one orientation (when the c-axis is vertical), so these terms should not be used without explicit description of specimen orientation; e.g. "discoasters are non-birefringent in plan view".
Extinction-figure appearance of a specimen in cross-polarized light, particularly pattern of isogyres.
Isogyre dark line in cross-polarized light caused by elements in extinction.
North/South, East/West orientations relative to the microscope body.

8 INTRA-SPECIFIC VARIATION

8.1 Primary coccolith variation

(Fig. 9) 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), 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.
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 requires preservation grades E1, X or O1.

9. NANNOLITH SHAPES

Nannoliths display a wide range of shapes, including the following types which all occur independently in more than one group. These shape terms are independent of structure, e.g. tetraradiate nannoliths may be formed of one, four or many crystal units.
Dibrachiate consisting of two sub-parallel arms joined at one end. Includes horseshoe, arrow-head, and arcuate shapes (e.g. Ceratolithus, Amaurolithus, Ceratolithina, Ceratolithoides - except C. verbeekii).
Compact more or less equidimensional nannoliths. Includes conical (e.g. Sphenolithus), obconical (i.e. inverted cone-shaped, e.g. Conusphaera), cylindrical (e.g. Fasciculithus) and cubic (e.g. Micula) shapes.
Rod-shaped elongate, and apparently without a basal disc. Includes bladed (e.g. Lithraphidites quadratus, Triquetrorhabdulus carinatus) and (sub-)cylindrical (e.g. Microrhabdulus) shapes.
Radiate with radial symmetry. N.B. the number of crystal-units may be larger or smaller than the number of rays.
Triradiate threefold radial symmetry (e.g. Marthasterites, Trochasterites).
Tetraradiate fourfold radial symmetry (e.g. Micula, Quadrum, Nannotetrina).
Pentaradiate fivefold radial symmetry (e.g. Goniolithus, Braarudosphaera).
Multiradiate more than fivefold radial symmetry (e.g. many Discoaster spp.).
Central body core part of radiate nannolith where elements are in contact.
Free rays parts of radiate nannolith extending beyond central body.
Short free rays length of free rays is less than radius of central body, resulting in a rosette-shaped outline.
Long free rays length of free rays is greater than radius of central body, resulting in a star-shaped outline.
Convex outline without free rays (e.g. Braarudosphaera). Including e.g. triangular, square, and pentagonal shapes.
Stellate with free rays (e.g. Micrantholithus, Discoaster). Including rosette and star-shaped.

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