Nannotax3 - ntax_main - Syracosphaerales

Citation: Syracosphaerales Hay, 1977 emend. Young et al., 2003

Taxonomic discussion: Taxa included: Families Syracosphaeraceae, Rhabdosphaeraceae and Calciosoleniaceae. The families are united here on the basis of V/R/T coccolith structure. The order is also characterised by polymorphism, sine formstion, motility of the heterococcolith phase and holococcolith formation in the alternate phase, although none of these are unique to the group or universal within it.

Distinguishing features:
Parent taxon (ntax_main):
This taxon: 2N: Coccoliths with radial lath cycle of T-units, and disjunct, often complex, axial structure, coccospheres often polymorphic, usually motile
N: Form holococcoliths, highly variable

Coccolith structure: Coccoliths are unusually complex consisting typically of three components
1. A rim showing normal V/R structure, but with the proto-coccolith ring embedded within the rim;
2. A radial lath cycle with openings between the laths, outer ends interdigitate with rim elements. In some species the laths are composite, formed of two or more elements;
3. An axial structure in the centre of the coccolith. This may be a low mound, flat plaque, elevated ridge or spine and may be formed from the radial lath elements and/or from additional, disjunct, elements.
The radial lath cycle is especially distinctive, these elements interdigitate with the rim elements, in the case of S. pulchra the laths have tangential c-axis orientations (Young et al. 2004) and we hypothesise that this is a general pattern. Hence, it appears likely that the proto-coccolith ring consists of three repeating nuclei types (V/R/T), rather than the usual V/R alternation. This distinctive structure makes it likely that this grouping is monophyletic in origin. The lath cycle is absent in some Rhabdosphaeraceae, probably as a result of secondary loss.
LM appearance: Isolated body coccoliths typically show a narrow rim with high birefringence and strongly curved isogyres. The central area is weakly birefringent and shows tangential orientation (so blue and yellow sectors show the opposite to normal disposition) and two central elements.

The only species which have been cultured from this very diverse order are Syracosphaera pulchra (Inouye & Pienaar 1998; Geisen et al. 2002), Algirosphaera robusta (Probert et al. 2007) and Coronosphaera mediterranea (Geisen et al. 2002). Of these, single strains of C. mediterranea and S. pulchra have undergone phase changes, producing holococcoliths of respectively Zygosphaera hellenica and Calyptrosphaera pirus (Geisen et al. 2002, Houdan et al. 2004). Numerous other species of the Syracosphaeraceae and two species of Rhabdosphaeraceae (Acanthoica quattrospina, Algirosphaera robusta) have been observed to form combination coccospheres with holococcoliths (Cros et al. 2000, and refs. therein, Cros & Fortuño 2002, Triantaphyllou & Dimiza 2003). This suggests that heteromorphic life-cycles are a common feature of the order.

Of the taxa included in the order the Calciosoleniaceae originate in the Mesozoic and so may be ancestral to the other Cenozoic taxa. NB Mesozoic workers have tended to include the Mesozoic Calciosolenicaeae in the Stephanolithales, this is obviously anomalous and should be reationalised - but for now we have followed taxonomic convention.

Geological Range:
Notes: Whist this order is highly diverse in the modern nannoflora it is poorly represented in the fossil record, especially in the Neogene. This is probably because the coccoliths produced by it are mostly small and delicate, so they have low preservation potential and when they are preserved they are difficult to observe or identify especially in the light microscope. In addition many species are very rare. This is discussed further in Young et al. (2005).
Last occurrence (top): Extant. Data source: Total of ranges of the species in this database
First occurrence (base): within Early Hauterivian Substage (130.60-132.60Ma, base in Hauterivian stage). Data source: Total of ranges of species in this database

References:

Cros, L. & Fortuño, J. -M. (2002). Atlas of northwestern Mediterranean coccolithophores. Scientia Marina. 66: 1-186. gs

Cros, L., Kleijne, A., Zeltner, A., Billard, C. & Young, J. R. (2000b). New examples of holococcolith-heterococcolith combination coccospheres and their implications for coccolithophorid biology. In, Young, J. R., Thierstein, H. R. & Winter, A. (eds) Nannoplankton ecology and palaeocology, Proceedings of the INA7 conference, Puerto Rico, February 1998. Marine Micropaleontology . 39(1-4): 1-34. gs

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

Hay, W. W. (1977). Calcareous nannofossils. In, Ramsay, A. T. S. (ed.) Oceanic Micropalaentology. Academic Press, London (2): 1055-1200. gs

Houdan, A., et al. (2004a). Flow cytometric analysis of relative ploidy levels in holococcolithophore-heterococcolithophore (Haptophyta) life cycles. Systematics and Biodiversity. 1(4): 453-465. gs

Inouye, I. & Pienaar, R. N. (1988). Light and electron microscope observations of the type species of Syracosphaera, S. pulchra (Prymnesiophyceae). British Phycological Journal. 23: 205-217. gs

Probert, I., Fresnel, J., Billard, C., Geisen, M. & Young, J. R. (2007). Light and electron microscope observations of Algirosphaera robusta (Pymnesiophyceae). Journal of Phycology. 43: 319-332. gs

Triantaphyllou, M. & Dimiza, M. D. (2003). Verification of the Algirosphaera robusta - Sphaerocalyptra quadridentata (coccolithophores) life-cycle association. Journal of Micropalaeontology. 22(1): 107-111. gs

Young, J. R., Geisen, M., Cros, L., Kleijne, A., Probert, I. & Ostergaard, J. B. (2003). A guide to extant coccolithophore taxonomy. Journal of Nannoplankton Research. S1: 1-132. gs

Young, J. R., Henriksen, K. & Probert, I. (2004b). Structure and morphogenesis of the coccoliths of the CODENET species. In, Thierstein, H. R. & Young, J. R. (eds) Coccolithophores - From molecular processes to global impact. Springer, Berlin 191-216. gs O

Young, J. R., Geisen, M. & Probert, I. (2005). A review of selected aspects of coccolithophore biology with implications for palaeobiodiversity estimation. Micropaleontology. 51(4): 267-288. gs

Daughter taxa (time control age-window is: 0-800Ma)		Granddaughter taxa
	Calciosoleniaceae Narrow-rimmed muroliths with central-lath structures but no axial structure. Often strongly varimorphic	Calciosolenia
	Rhabdosphaeraceae BCs planoliths with radial lath cycle and highly-variable axial structures. Often polymorphic and/or varimorphic	Acanthoica Algirosphaera Blackites Cyrtosphaera Discosphaera Palusphaera Rhabdosphaera Solisphaera
	Syracosphaeraceae BCs muroliths or placoliths with radial laths and axial structure, ofen with higlhy modified exothecal coccoliths	Syracosphaera Calciopappus Michaelsarsia Ophiaster

Syracosphaerales

References:

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