Mercedesia multistellata, Thomsen & Østergaard, 2015

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 multistellata sp. nov. ( Figs 9, 10, 14, 15)

Diagnosis: Cell elongate (c. 4 × 5 µm) with two flagella (12.5/9.5 µm) and a shorter haptonema (ca. 7 µm) ( Fig. 10). Nannoliths are monomorphic three-pointed stars ( Figs 9, 14, 15), with arms slightly bent in proximal direction. The individual arms gradually taper towards the tip. The mean value ‘tip-to-tip’ distance is 0.46 µm.

Holotype: Figs 9, 10, 14, 15 (same cell) from the Kane Basin, NW Greenland ( NOW st. #B7 at 79°00.096 N / 73°19.964 W) occurring in a sample from 40 meters depth and processed on 12 May 1998.

Etymology: from ‘multi’ (L) meaning many and ‘stella’ (L) meaning star.

Numerical details of M. multistellata have been accounted for in Table 2. The tip-to-tip distance between neighbouring arms is 0.46 µm (mean value) which is basically identical to the edge length in M. aspiphora coccoliths from the same geographical area ( Table 1).

The star-shaped nannoliths somewhat resemble the central three-armed rib-pattern on the nannoliths of M. aspiphora but without the membranous material between the arms of the ribs. However, we don’t think that M. multistellata nannoliths represent an extreme variation of the M. aspiphora morphological theme, because of the robust appearance of the stars in M. multistellata and the absence of intermediate forms in our material.

In nannoliths resting on all three arms these appear to be equally long ( Figs 9, 14, 15). A tilted position of nannoliths often causes these to display two complete arms and a ‘short’ arm ( Figs 9, 15 arrows), with the short arm appearing much darker in the micrograph as a microscopy artefact. Organic under layer scales have not been observed and there is no indication of life cycles involving M. multistellata .

The nature of the small spherical structures that appear among the nannoliths ( Figs 9, 10) is unknown to us.

Mercedesia multistellata was found in three different samples from NW Greenland (NOW) and has also been observed in a single sample from NE Greenland (NEW) (Gammelgaard, personal communication). A cluster of nannoliths reminiscent of M. multistellata have been observed by Østergaard (unpublished results) from tropical waters (Phuket, Thailand).