Ceratolithales
The order Ceratolithales includes a diverse group of coccoliths with distinct morphologies and optical properties, falling into two primary families:
Family Ceratolithaceae Norris, 1965 includes horseshoe-shaped coccoliths that may be associated with simple ring-shaped coccoliths in one of their life cycles, while the family Triquetrorhabdulaceae Lipps, 1969 includes rod-shaped coccoliths.
The following diagnostic features help identify and classify various genera within the order Ceratolithales based on optical properties and their morphologies under XPL.
Amaurolithus (syn. Nicklithus) and Pennalithus have a vertical optic axis relative to the microscope stage.
Triquetrorhabdulus, Ceratolithus, Velonalithus, and Diplotsekouri have radial optic axes parallel to the microscope stage. Orthorhabdus has an inclined optic axis.
Ceratolithus, Orthorhabdus, and Velonalithus elongation characteristics are length-slow (+), while Triquetrorhabdulus and Diplotsekouri are length-fast (-).
Varol, O. 2025a. A practical guide to optical studies of calcareous nannofossils. Grzybowski Foundation Special Publication. 29: 1-222
