Mercedesia pusilla Thomsen & Østergaard

Thomsen, Helge A. & Østergaard, Jette B., 2015, Coccolithophorids in Polar Waters: Quaternariella and Porsildia gen. nov. Mercedesia gen. nov., Ericiolus,, Acta Protozoologica 54 (3), pp. 155-169 : 159

Mercedesia pusilla Thomsen & Østergaard ( Figs 11–13)

Syn.: ‘Coccolithophorid sp. 1’ in Thomsen et al. 1988 (loc. cit. Fig. 46).

Diagnosis: Cell elongate (c. 2.5 × 4 µm) with two flagella (19.5/22 µm) and a shorter haptonema (ca. 13 µm). Nannoliths are monomorphic, shaped like three-pointed stars with arms slightly bent in proximal direction. The central part, the base of the arms is fairly broad. The nannolith centre is characterized by a central pore. The mean value ‘tip-to-tip’ distance is 0.28 µm.

Holotype: Figs 11, 13 (same cell) from the Weddell Sea , Antarctica ( EPOS st. #186 at 57°57 S / 49°00 W) occurring in a mixed sample from 10 and 20 meters depth and processed on 28 December 1998.

Etymology: ‘pusillus’ (L) meaning very small.

The Antarctic EPOS material comprised a few cells ( Figs 11–13) closely reminiscent of M. multistellata in many aspects except for the dimensions and the shape of the central part of the three-armed, star-shaped nannoliths ( Figs 12, 13). Numerical details have been accounted for in Table 2. It appears that M. pusilla is on the average half the size of M. multistellata when comparing dimensions of the individual nannolith. The central nannolith pore, which is very conspicuous in the material examined here ( Figs 12–13), was also evident in the AMERIEZ cell previously illustrated by Thomsen et al. (1988; loc. cit. Fig. 46). This structural element thus appears to constitute a fairly prominent diagnostic feature of this new taxon.