Zygodiscales


Ancestry: Coccolithophores -> Zygodiscales
Sister taxa: Isochrysidales, Coccolithales, Zygodiscales, Syracosphaerales, Coccolith families inc sed, Mesozoic Survivors, Holococcoliths, Braarudosphaerales, Discoasterales, Nannolith families inc sed, hidden,

Short diagnosis: Heterococcoliths with V-units forming upper/outer cycle of imbricated elements and R-units forming basal plate and central mass of irregular elements


Daughter taxa (blue => in age window 0-300Ma) Granddaughter taxa
Varimorphic; liths placolith-like but with helical shield structure; arranged in spiral on coccosphere

Monomorphic or dimorphic; liths muroliths with perforate central area

Muroliths with rim formed from well-developed V- and variably developed R-units, with opposite imbrication directions, and central area structures that include disjunct transverse bars and diagonal crosses. R-units vestigial or not observed in several genera (Chiphragmalithus, Isthmolithus, Neococcolithes).

Taxonomy:

Citation: Zygodiscales Young & Bown, 1997
Rank: Order
Notes & discussion: Taxa included: The extant families Helicosphaeraceae and Pontosphaeraceae and extinct Family Zygodiscaceae. These show highly variable shape, but similar structure, and there is strong palaeontological evidence for their evolutionary connections (Romein 1979; Aubry 1989).

Farinacci & Howe catalog pages:

Short diagnosis: Heterococcoliths with V-units forming upper/outer cycle of imbricated elements and R-units forming basal plate and central mass of irregular elements


Morphology remarks: Coccolith structure: V-units form outer rim; in Pontosphaeraceae and Zygodiscaceae, this is a narrow cycle of anticlockwise-imbricating elements, in the Helicosphaeraceae, a helical flange. The R-units form a proximal plate of rather regular, inward-growing elements and a distal blanket, which typically appears as a mass of minute, tangentially-elongated crystallites. Growth does not occur downwards from the proto-coccolith ring and so the alternating belt of V-R nuclei remains clearly visible on the proximal surface.

Biology & life-cycles: Helicosphaera carteri has been cultured repeatedly (Inouye pers. comm., Probert unpubl. data) and Scyphosphaera apsteinii once (Probert unpubl. data). Life-cycle transitions have been observed in Helicosphaera cultures, and combination coccospheres have been observed for Helicosphaera (Cros et al. 2000, Geisen et al. 2002), Pontosphaera and Scyphosphaera (Frada et al. 2009). These indicate that the haploid phase forms holococcoliths with distinctive rhomboid-array ultrastructure - these were previously placed in the genus Syracolithus.

Geological Range:
Last occurrence (top): Extant Data source: Total of range of species in this database
First occurrence (base): within Danian Stage (61.61-66.04Ma, base in Danian stage). Data source: Total of range of species in this database

Plot of occurrence data:

References:

Aubry, M.-P., (1989). Handbook of Cenozoic calcareous nannoplankton. Book 3: Ortholithae (Pentaliths, and others), Heliotithae (Fasciculiths, Sphenoliths and others). Micropaleontology Press, American Museum of Natural History, New York, 279 pp.

Cros, L.; Kleijne, A.; Zeltner, A.; Billard, C. & Young, J.R., (2000). New examples of holococcolith-heterococcolith combination coccospheres and their implications for coccolithophorid biology. Marine Micropaleontology, 39(1-4): 1-34.

Frada, M.; Percopo, I.; Young, J.R.; Zingone, A.; de Vargas, C. & Probert, I., (2009). First observations of heterococcolithophore-holococcolithophore life cycle combinations in the family Pontosphaeraceae (Calcihaptophycideae, Haptophyta). Marine Micropaleontology, 71(1): 20-27.

Geisen, M.; Billard, C.; Broerse, A.T.C.; Cros, L.; Probert, I. & Young, J.R., (2002). Life-cycle associations involving pairs of holococcolithophorid species: intraspecific variation or cryptic speciation? European Journal of Phycology, 37: 531-550.

Perch-Nielsen, K., (1985). Cenozoic calcareous nannofossils. In: Bolli, H.M., Saunders, J.B. and Perch-Nielsen, K. (Editors), Plankton Stratigraphy. Cambridge University Press, Cambridge, pp. 427-555.

Romein, A.J.T., (1979). Lineages in Early Paleogene calcareous nannoplankton. Utrecht Micropaleontological Bulletins, 22: 231.

Young, J.R. & Bown, P.R., (1997). Cenozoic calcareous nannoplankton classification. Journal of Nannoplankton Research, 19(1): 36-47.


Nannotax3 - Coccolithophores - Zygodiscales by: Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 25-6-2017

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AphiaID: 236094 Nomenclatural data on WoRMS

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