Pappomonas garrisonii Thomsen and Østergaard, 2014

Thomsen, Helge A. & Østergaard, Jette B., 2014, Coccolithophorids in Polar Waters: Pappomonas spp. Revisited, Acta Protozoologica 53 (3), pp. 235-256 : 245-247

Pappomonas garrisonii Thomsen and Østergaard sp. nov.

Diagnosis: Cell spherical, ca. 5 µm in diameter with two flagella and a somewhat shorter haptonema. Coccoliths of two types. Body coccoliths ( Fig. 39) are oval, 1.0 ± 0.095 × 0.65 ± 0.09 µm. The rim consists of large pentagonal elements (0.2–0.25 µm in height) forming a densely aggregated and upright ring. Adnate and rod-shaped elements occur interdispersed at the base of the pentagonal elements ( Fig. 58D ). The central area is supporting ca. 5 lines of rod-shaped elements arranged in parallel with the longitudinal axis of the coccolith and crossed in the middle by a single line of elements arranged along the shortest axis of the coccolith. Radial elements from the base plate scale upper surface ornamentation are visible in between elements. Other coccoliths carry central processes that are diagnostic for the species. These coccoliths are best developed at the flagellar pole but occur scattered all over the cell surface ( Fig. 41). The quasi-circular coccolith (diam. 0.7– 0.8 µm) has a rim that is basically similar to that of the body coccoliths, whereas the central area calcification is reduced to a cross-like structure where the arms coa- lesce at the centre to support the central shaft ( Figs 38, 42). The central shaft is up to 1.5 µm long and formed by densely aggregated elements ( Fig. 39). Two elongat- ed elements (1.2–1.3 µm in circumflagellar coccoliths and 0.8–0.9 µm in coccoliths at the posterior cell end) diverge from the tip of the central shaft. They are each furnished with two triangular and wing-like blades. The smaller blades from each pair are placed centrally. The cleft between these is terminated above the tip of the central shaft through the insertion of a rhomboid element ( Fig. 39). The width of the terminal structure varies from 1–2 µm. Small unmineralized under layer scales (ca. 0.35 × 0.5 µm) can be observed scattered among the coccoliths ( Figs 39, 40). These scales display radiating ridges and loose concentric fibrils.

Combination cells with Trigonaspis sp. have been observed ( Figs 43–45 ).

Type specimen: Fig. 41 (TEM micrograph 20454).

Type locality: Weddell Sea (7°19.3 W, 68°14 S), Antarctica; collected on 13 April 1992 at 10 m depth .

Etymology: The species is named in honour of Dr. David L. Garrison who has contributed significantly to our understanding of pelagic polar ecology and who was also instrumental in providing the possibility of participating in the ANT X/3 cruise.

Pappomonas garrisonii shares with other species of Pappomonas : 1) an armour of dimorphic coccoliths which with reference to patterns of calcification and elaboration of the central process on ‘flagellar pole’ coccoliths have diagnostic features in common, and 2) a life history that implements species from the holococcolithophorid genus Trigonaspis ( Thomsen 1980a) . However, P. garrisonii also deviates from the mainstream Pappomonas concept as defined by P. flabellifera , P. borealis and P. weddellensis , by having: 1) coccoliths with central processes evenly distributed over the entire cell surface (albeit with the largest ones encircling the flagellar pole), 2) a central process termination that is not a simple modification of the ‘triangle’ theme, 3) a rim calcification on body coccoliths which in size and overall morphology is much reminiscent of that observed in species of Papposphaera , e.g. P. sagittifera ( Fig. 58D, E ), and 4) a layer of organic under- layer scales.

Despite the fairly long list of features that distin- guishes P. garrisonii form the core species of Pappomonas we prefer for the time being to ascribe the new taxon to Pappomonas . The life history relationship with Trigonaspis sp. is a strong supporting argument behind this decision. Unpublished findings indicate that species which are at present allocated to Papposphaera , e.g. P. sagittifera Manton, Sutherland and McCully 1976a , are in fact often found with dimorphic coccoliths (Thomsen, Østergaard and Heldal, unpublished findings) thus in this aspect critically blurring the distinction between Pappomonas and Papposphaera . It can be anticipated that any strategy with regard to a possible redefinition of the genera Pappomonas and Papposphaera will need to be assisted by gene sequencing techniques and preferably also TEM thin sectioning.

The currently known biogeographical range of P. garrisonii is summarized in Table 2.

Figures

Fig. 58. Interpretation of rim calcification (body coccoliths) in spe- cies of Pappomonas and Papposphaera. A – Pappomonas flabellifera (NEW / micrograph 25036); B – Pappomonas borealis (NEW / micrograph 24879); C – Pappomonas weddellensis (ANT X/3 / mi- crograph 20549); D – Pappomonas garrisonii sp.nov. (ANT X/3 / micrograph 21149); E – Papposphaera sagittifera (NEW / micro- graph 24930); F–G – Balaniger virgulosa HET scale rim (F) and base plate calcification (G) (West Greenland / micrograph 10322).

Figs 43–45. Pappomonas garrisonii sp. nov. combination cells with Trigonaspis sp. TEM whole mounts from the Weddell Sea, Antarctica (ANT X/3). 43 – whole cell with Trigonaspis parts pointed out; 44 – a second combination cell with Trigonaspis parts pointed out; 45 – detail of the periplast from Fig. 44 showing the Trigonaspis tower-like coccoliths and their triangular substructure (arrow).