The descriptive terminology of coccoliths evolved on an ad hoc basis until the 1950s. Then the development of electron microscopy stimulated a major revision and introduction of new terms, in a co-operative effort (Braarud et al. 1955a, 1955b; Halldal and Markali 1955, Hay et al. 1966). This concentrated on standardisation of names for the distinctive types of coccoliths found on coccospheres, e.g. placolith, caneolith. Subsequent work on diverse fossil coccoliths lead to a different approach concentrating on element-level structure. The appropriate terminology was synthesised during a Round Table Session at the Rome 1970 Plankton Conference (Farinacci 1971).
There had been intensive research on coccoliths since 1970 and so the existing guides had become increasingly obsolescent. In response to this a terminology workshop was held during the International Nannoplankton Association (INA) conference in Prague 1991. Following this a working group was set up and a two day workshop was held in London in 1992. Various publications have resulted from these discussions. Young (1992a), discusses new recommendations on controversial topics. Burnett and Bown (1992) provide a checklist for systematic descriptions. van Niel (1994) reviews in depth the descriptive terminology of nannoconids. Jordan et al. (1995) provide a glossary for living Haptophyta, including cytological terms and an overview of taxonomic concepts. The present paper represents the main proceedings of the working group and is a synthesis of the descriptive terminology applied to coccoliths and other nannoliths based on its discussions.
In addition to the workshop discussions this paper is based on a wide range of published sources including: Braarud et al. (1955a, 1955b), Halldal and Markali (1955), Farinacci et al. (1971), Black (1972), Hay (1977), Okada and McIntyre (1977), Romein (1979), Theodoridis (1984), Aubry (1984 et seq., 1989), Perch-Nielsen (1985a, 1985b), Bown (1987), van Heck and Prins (1987), Varol (1989, 1992), Young (1989), Young and Bown (1991), Kleijne (1991, 1992, 1993), Young and Westbroek (1991), van Niel (1992), Heimdal (1993), Winter and Siesser (1994). General works consulted include Brown (1954), Gower (1954), Fowler (1965), and Stearn (1983).


The main text is organised into thematic categories covering different aspects of coccolith morphology. This is followed by a section on special terms needed for particular taxonomic groups. The paper is confined to the calcareous structures and does not consider organic components, terminology for these is reviewed in Jordan et al. (1995). Synonyms which we have not included in the main text are discussed in an appendix.
The terms recommended are underlined and given short explanations - the primary purpose of these is to explain the use of the term to coccolith workers, not to give a rigorous dictionary definition, still less an encyclopaedic explanation. The figures are meant to clarify the logic, but for various reasons not all terms are illustrated. For many terms genera or species that show the feature particularly well are cited; good sources for illustrations of these taxa are Perch-Nielsen (1985a, 1985b) and Winter and Siesser (1994).
For terms which have been specially invented for coccoliths (e.g. placolith) the original author is given in curly brackets {}, this information is mostly from Hay et al. (1966).


The general objective of the work is to summarise existing terminology rather than to create a new system. Nonetheless in order to enhance precision it has been necessary in several cases to select between synonyms, or to assess the utility of obscure terms and, in a few cases, to coin new terms. The following principles have been used as guides.
Need. The purpose of specialist terminology is to make life easier for the reader, not for the author. The convenience of any terminological innovation should be weighed against the danger of producing unintelligible jargon.
Priority. Accepted usage must be respected. First usage / original definition is particularly important, but not necessarily binding.
Etymology. Words should not be given meanings that conflict with their etymology.
Ambiguity. Common words should not be given meanings that conflict with their normal meaning, or with their general scientific meaning, or that are more restrictive than a non-expert might reasonably anticipate (e.g. use of bar for structures with a particular optical orientation).
Obscurity. Obscure technical terms that are hard to remember and the meaning of which it is virtually impossible to guess (e.g. areolith), should be avoided, unless they are liable to be used so often that they will become part of routine vocabulary (e.g. placolith).
Synonyms and homonyms. As far as possible, only one term should be used for any given concept (poetic variation is not recommended). Equally, any given term should only have one meaning in a given context.
Where we have selected from possible alternatives the alternative is discussed in the appendix with a reference to it in the text - e.g. 'alternative spelling nanoplankton, see appendix'.

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