Farinacci & Howe catalog - Zygrhablithales.pdf
Original descriptions of taxa - also emended descriptions for a few taxa. For coccolithophores, and many calcispheres, these are pages from the Farinacci & Howe Catalog of Calcareous Nannofossils. In other cases (e.g. non-calcifying haptophytes) the data is directly compiled on this site. The "Catalogue of Calcareous Nannofossils" was originally compiled by Prof A. Farinacci 1969-1989, since 2000 it has been updated and extended by Richard Howe - see The Farinacci and Howe Catalog - an Introduction.
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Farinacci & Howe catalog - Zygrhablithales.pdfCurrent identification/main database link: Holococcoliths of Young et al. 2003
Compiled data
Diagnosis: Holococcoliths constructed from rhombohedral crystals and hexagonal prisms, which lack confirmed associations with heterococcoliths or for which holococcolith formation holds taxonomic priority, are classified within a single order, Zygrabhlithales. Holococcoliths are produced externally in the haploid life-cycle phase. They are composed of minute calcite rhombohedral crystals or hexagonal prisms, each approximately 0.1 µm in size, arranged in continuous arrays. The holococcolith order Zygosphaerales Hay in Ramsay (1977) is now considered a junior synonym of Syracosphaerales. This reclassification is due to the type species Zygosphaera hellenica being identified as part of the life cycle of Syracosphaera mediterranea (Karatsolis et al., 2014; Triantaphyllou et al., 2016). The rhomboidal crystal or hexagonal prism structure of taxa can be identified directly through SEM and indirectly through LM based on their optical properties. Rhomboidal crystals display inclined (oblique) or symmetrical extinction lines, while hexagonal prisms exhibit parallel (straight) extinction lines. Holoccoliths are the distinctive product of haploid phase calcfication they occur in sevwral different orders and so making an order for them is contrary to fundamantal principles of biological taxonomy.
Original Description
Editors' Notes
Varol, O. (2025). A practical guide to optical studies of calcareous nannofossils. Grzybowski Foundation Special Publication. 29: 1-222. gsReferences:
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Zygrhablithales: Catalog entry compiled by Jeremy Young. Viewed: 10-10-2026
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