The ultrastructure and life cycle of the coastal coccolithophoridOchrosphaera neapolitana(Prymnesiophyceae)

Abstract

Unialgal cultures of the widespread tremalith-bearing coccolithophorid Ochrosphaera neapolitana Schussnig were investigated using light and electron microscopy. O. neapolitana exhibits a heteromorphic life cycle identical to that described for the closely related tremalith-bearing genus Hymenomonas, involving an alternation between (diploid) coccolith-bearing cells and a (haploid) non-calcifying phase, characterised by the production of layers of mucilage. Differing scale ornamentation between the two phases together with chromosome counts confirms the diplo-haplontic nature of this cycle. The coccolith-bearing phase may be non-motile or possess flagella. The coccoliths of all strains studied exhibit the typical tremalith structure, but variation in size and shape is observed (vari-monomorphism). Unusual among coccolithophorids, the coccosphere of this species is not continually renewed, and progressive extracellular calcification of the coccoliths is observed in old cultures that may result in the formation of a calcareous 'pseudocyst'. At the ultrastructural level, the flagellar apparatus is of the Pleurochrysis type, consisting of two flagellar basal bodies linked by proximal, intermediary and distal bands, a vestigial haptonema consisting of five microtubules, and four asymmetrically arranged microtubular roots. Two roots are compound, each possessing a secondary crystalline microtubular component, and two are simple. The peripheral endoplasmic reticulum plays a role in coccolithogenesis, which occurs in the proximity of the plasma membrane. The taxonomy of the genus Ochrosphaera is discussed and suppression of the two other species in the genus, O. verrucosa Schussnig and O. rovignensis Schussnig, is suggested.

Eukaryotic Life Inhabits Rhodolith-forming Coralline Algae (Hapalidiales, Rhodophyta), Remarkable Marine Benthic Microhabitats

“…It is interesting to note that Ochrosphaera is a member of the Coccolithales, an order of haptophytes characterized by elaborate calcium carbonate scales, called coccoliths in the free-living taxa. Perhaps the production of coccoliths in certain taxa is only temporary44.…”

Coccolithogenesis In Scyphosphaera apsteinii (Prymnesiophyceae)

“…b). The fibrillar material (also termed columnar material; Rowson and Leadbeater , Fresnel and Probert , Probert et al. ) was a notable feature in S. apsteinii and formed a thick layer of filaments with an average length of 114 nm (SD ± 39, n = 21) and a densely stained spherical head (Fig.…”

Dynamics of formation and secretion of heterococcoliths byCoccolithus pelagicusssp.braarudii

“…In these species coccolith mineralization may occur simultaneously in more than one compartment (van der Wal et al, 1983b) and maturation occurs in Golgi-derived vesicles that move distally towards the plasma membrane and are not associated with the nucleus. In the case of O. neapolitana however, a small tubular structure appears to be associated with the coccolith vesicle and peripheral endoplasmic reticulum during coccolith calcification (Fresnel & Probert, 2005). In a morphological examination of U. sibogae, a placolith forming species closely related to C. pelagicus, a reticular body was not defined, although tubules associated with the endoplasmic reticulum system were noted as extending to and connecting with the coccolith vesicle and distally located Golgi body complex (Inouye & Pienaar, 1984).…”

“…Bundles of microtubules, resembling those commonly associated with flagellar roots of motile coccolithophores (Manton & Peterfi, 1969;Gayal & Fresnel, 1983;Inouye & Pienaar, 1988;Green & Hori, 1994;Fresnel & Probert, 2005), were observed in several ultrathin sections of the non-motile heterococcolith-bearing C. pelagicus (Figs 7, 8). The microtubular bundles were located in the gap between the two chloroplasts, extending some distance into the interior of the cell.…”

“…However the precise ontology of the coccolith vesicle in E. huxleyi remains uncertain. Many coccolithophores do not exhibit a reticular body associated with calcification, for example the cricolith forming Pleurochrysis carterae Braarud & Fagerland (Pienaar, 1969;Outka & Williams, 1971) and the tremalith-forming Ochrosphaera neapolitana Schussnig (Fresnel & Probert, 2005). In these species coccolith mineralization may occur simultaneously in more than one compartment (van der Wal et al, 1983b) and maturation occurs in Golgi-derived vesicles that move distally towards the plasma membrane and are not associated with the nucleus.…”