ALISPHAERACEAE

Archontikis, Odysseas A., Millán, Josué G., Winter, Amos & Young, Jeremy R., 2023, Taxonomic re-evaluation of Ericiolus and Mercedesia (Prymnesiophyceae) and description of three new species, Phycologia 62 (2), pp. 179-193 : 191

ALISPHAERACEAE – POLYCRATER PHASE

The Alisphaeraceae are a group of heterococcoliths, which, in their alternate life cycle phase, produce aragonitic nannoliths that were formerly placed in the genus Polycrater Manton & Oates ( Cros et al. 2000; Cros & Fortuño 2002; Šupraha et al. 2018). Well-developed nannoliths of the ‘ Polycrater ’ phase are monomorphic and form monothecate coccospheres but, unlike Ericiolus , they are typically asymmetrical and four-sided, i.e. they are seen as quadrate in plan view and with an hour-glass shape in side view. The nannolith long axes are directed equatorially, and the nannoliths are seen to embrace the cell in regular meridian rows. The size of the nannoliths (c. 0.4–1.0 μ m) is similar to that observed in Ericiolus . A range of different analogues (e.g. forms with holes, tubercles, ladle-like or petal-like forms) to the ray structures of Ericiolus have previously been documented ( Cros & Fortuño 2002; Young et al. 2003), and these also partially resemble the more skeletal Polycrater - type species; however, the basic four-fold symmetry seems to be a significant difference between these and the Ericiolus forms. In addition, it is still unclear whether Ericiolus nannoliths are calcitic or aragonitic, although the presence of calcium in the periplast has been confirmed ( Thomsen et al. 1988). Therefore, it would be useful to determine if Ericiolus nannoliths were formed of aragonite or calcite and, if aragonitic, then affinity with Polycrater nannoliths would be indicated.