Pileolosphaera

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

PILEOLOSPHAERA

The extant nannolith-bearing species Pileolosphaera longistirpes K.J.S. Meier, Kinkel & Jer.R. Young , which is the type species of the genus Pileolosphaera , is composed of about six to eight circular shield-like nannoliths. The nannoliths are formed exclusively of V-units ( Meier et al. 2014) showing on the coccosphere, radially oriented calcite axes under light microscopy ( Meier et al. 2014). The nannoliths possess three radial segments with a central triradiate process. Light microscopy observations indicate that all three elements are formed of crystal units with their c-axes vertical relative to the nannolith, and therefore, radial relative to the coccosphere ( Meier et al. 2014). Pileolosphaera shares with Ericiolus the key features of triradiate symmetry and radial growth of the elements from the centre, rather than around a rim. There are, however, notable differences between the two taxa: 1) Pileolosphaera coccospheres have far fewer nannoliths than those of Ericiolus (6–8 vs 30–70); and 2) the Pileolosphaera nannoliths are considerably larger than those of Ericiolus (3.0–4.0 μ m vs 0.2–1.3 μ m). Despite these quantitative differences, Pileolosphaera nannoliths are structurally the closest extant forms to Ericiolus , and affinity between the two genera remains likely.