Nannotax

Description: Motile, coccospheres typically elaborate, often showing dithecatism (development of distinct inner and outer layers of coccoliths) and/or modified polar coccoliths. The endothecal (inner layer) coccoliths are normally relatively conservative in form, typically muroliths with a well-developed central-area lath-cycle and variable inner central-area (coccoliths with this structure have been termed caneoliths). Exothecal coccoliths are much more variable, including planolith, murolith and dome-shaped forms (the planoliths have been termed cyrtoliths).

Remarks: These coccoliths are typically delicate and only rarely preserved. The recent tendency, following Jordan & Young (1990), has been to include most species forms in the single genus Syracosphaera. The main exception is a set of genera with highly modified circum-flagellar and/or antapical coccoliths forming appendages, instead of exothecal coccoliths.

The fossil record of the family is poor but extends back into the Paleogene; fossil specimens are normally assigned to Syracosphaera.

Key references: Okada & McIntyre (1977) - many new spp.; Gaarder & Heimdal (1977) - detailed descriptions of several species; Inouye & Pienaar (1988) - detailed description of S. pulchra cytology and coccolith structure; Kleijne (1993) - illustration and notes on most spp. and many undescribed forms; Cros (2000) - analysis of exothecal coccoliths; Cros et al (2000) - holococcolith-heterococcolith combinations; Cros & Fortuño (2002) - detailed description of most species; Young et al. (2003), identification notes and illustration of most species; Young et al. (2004) description of coccolith structure.