Palusphaera bownii Archontikis & Jer.R. Young, 2021

Archontikis, Odysseas A. & Young, Jeremy R., 2021, A reappraisal of the taxonomy and biodiversity of the extant coccolithophore genus Palusphaera (Rhabdosphaeraceae, Prymnesiophyceae), Phycologia 60 (6), pp. 589-602 : 597-598

Palusphaera bownii Archontikis & Jer.R. Young sp. nov.

Figs 22–24

DESCRIPTION: Coccosphere, monomorphic of subspherical to spherical shape, usually found collapsed, with c. 80–120 BCs. BCs broadly elliptical to circular in outline with slightly convex planolith bases. Rim shows the typical Rhabdosphaeraceae rim structure. Central area, filled by lamellar cycle, with overlapping tabular elements showing clockwise curvature in distal view. The radial cycle is absent. Central process is a trumpetshaped spine without a collar, formed of vertically elongate elements arranged in spiralling series; the distal end is formed of blockier elements, but these appear to have developed from the spiral elements of the spine. Trumpet aperture wider than the basal spine width. On the proximal side of the coccolith there is a central pore surrounded by two to three nodes.

DIMENSIONS: Coccosphere diameter c. 10–15 μm. BCs 1.0–1.5 μm long and wide; rim c. 0.2 μm in width. Spine c. 1.5 μm long and trumpet aperture c. 0.5 μm wide, although few spines tend to bear slightly closer apertures at their outermost part.

HOLOTYPE: 302-04 (specimen illustrated in Fig. 22 ), stub no. 756/1, deposited at the collections of the Natural History Museum, London under the designation PM NF 4930 302-04.

PARATYPE: 308-031 (stub no. 768/0, designation PM NF 4932 308-031), 308-032 (stub no. 768/0, designation PM NF 4932 308-032) . One specimen of this stub is illustrated by Figs 23, 24 .

TYPE LOCALITY: Subtropical waters of the South Atlantic Ocean (8° 49.52' S, 24°59.72'W, depth 0 m, 28 October 2008, AMT18 Expedition, Station CTD063) .

NUMBER OF SPECIMENS STUDIED: Two.

ETYMOLOGY: After Professor Paul R. Bown (University College London),

in recognition of his many contributions to Jurassic, Cretaceous and Paleogene coccolithophore taxonomy.

REMARKS: We have only found two coccospheres of this species and to our knowledge no other specimens have been published. Nonetheless, this is a distinctive form and clearly separate from any other coccolithophore, so we are confident it is a discrete species. The species shows possible affinities to several genera. The trumpet-like spines resemble those of Discosphaera , but the base lacks a radial cycle, and the spine shows a structure that is not seen in Discosphaera . The spine structure is closer to that of Rhabdosphaera , but in Rhabdosphaera coccospheres are dimorphic with both spine-bearing and non-spine-bearing BCs. Finally, the species resembles Palusphaera in being monomorphic and lacking a radial cycle. In addition, the rows of the laminar cycle elements show the same curvature (clockwise in distal view) as that of Palusphaera coccoliths and the opposite of that shown by Rhabdosphaera coccoliths. Therefore, we place the species in Palusphaera .

Figures

Figs 22–24. SEM micrographs of Palusphaera bownii sp. nov. Scale bar = 2 μm. Fig. 22. Holotype. Collapsed coccosphere bearing nearly circular planolith bases with outer rim cycles that are broader on the distal side (arrow a) than on the proximal side (arrow b); the central process displays a short trumpet-shaped process (arrow c). Fig. 23. Collapsed specimen bearing trumpet-shaped spines with spirally arranged crystal segments (see arrow) extending outwards forming distinct apertures. Fig. 24. Detailed view of Fig. 23 showing the ultrastructure of the spine aperture (arrows) and the dextrogyral curvature of lamellar elements in distal view.