Pseudowigwamma Thomsen, 2013

Thomsen, Helge A. & Østergaard and Mikal Heldal, Jette B., 2013, Coccolithophorids in Polar Waters: Wigwamma spp. Revisited, Acta Protozoologica 52, pp. 237-256 : 252-253

Pseudowigwamma Thomsen gen. nov.

Diagnosis: Small coccolithophorids with two equal flagella and a short haptonema. Calcification, when present, limited to the rims of otherwise uncalcified plates. Rim crystallites rectangular, straight sided and joined end to end to form a single ring. A single enlarged, almost quadratic crystallite is found in most coccoliths. The unmineralized plate centres display a combination of radial threads and concentric fibrils.

Type species: Pseudowigwamma scenozonion ( Thomsen 1980c) Thomsen comb. nov.

Ethymology: The genus name Pseudowigwamma meaning ‘resembling Wigwamma ’ is chosen to emphasize a likely relationship with Wigwamma . Pseudowigwamma scenozonion represents – in comparison with Wigwamma – a simplistic approach with regard to coccolith morphology (only one ring of crystallites along the scale periphery and no superstructures).

P. scenozonion ( Thomsen 1980c) Thomsen comb. nov.

Syn. Wigwamma scenozonion Thomsen 1980c

This enigmatic former Wigwamma species is monomorphic ( Figs 45–47 ) and characterized by coccoliths with a much reduced base plate calcification compared to species of Wigwamma . The scale rim calcification here consists of a single ring of rod shaped crystallites as opposed to two rings in species of Wigwamma . A single enlarged crystallite reminiscent of those that support coccolith superstructures in species of Wigwamma is seen in most coccoliths ( Figs 46, 47 ).

The deviant base plate calcification of P. scenozonion and the complete lack of a coccolith superstructure was originally ( Thomsen 1980c) interpreted as reductional charateristics of this taxon. However, it was also anticipated ( Thomsen 1980c) that in the future it might prove relevant to establish a new genus to accommodate this taxon.

Arctic material from NEW yielded a combination cell ( Figs 48–49 ) that encompasses a lightly calcified coccolithophorid species with a rim calcification strongly reminiscent of P. scenozonion and an unknown counterpart (also found as a complete cell, see Figs 50– 52 ) with unmineralized scales furnished with a lateral protuberance. Unfortunately none of the calcified coccoliths shown in Fig. 48 display the enlarged crystallite singlet that is a key feature of P. scenozonion ( Fig. 46 ). This leaves an element of uncertainty with regard to the final identification of the calcified component of the combination coccosphere. However, it seemed to be a general feature of P. scenozonion from the NEW material that enlarged crystallite singlets were sparse if not absent in some complete specimens analyzed (e.g. Fig. 45 ). The scaly periplast of the life history counterpart of P. scenozonion cfr. comprises apparently unmineralized and weakly rimmed scales furnished with a peripheral protuberance that appear to be aligned along the longitudinal axis of the scale ( Figs 50, 52 ). This type of scale is unknown to us, although vaguely reminiscent of Ericiolus spp. ( Thomsen et al. 1995).

Pseudowigwamma scenozonion was considered enigmatic right from its original description ( Thomsen 1980c) due to major differences in calcification. The finding of P. scenozonion cfr. combination cells which demonstrates that these are not confirming to the ‘typical’ Wigwamma - Calciarcus scenario calls for a formal separation at the generic level between W. scenozonium and the remaining five Wigwamma species.

Figures

Figs 45–47. Pseudowigwamma scenozonion TEM whole mounts. 45 – complete cell (Arctic / NEW); 46 – detail showing base plate calcification (single layer) and the odd enlarged rim crystallite; Notice also the radial patterning of the organic base plate surface (Arctic Station); 47 – complete cell (Arctic Station).

Figs 48–52. Combination cells involving Pseudowigwamma scenozonion cfr. and an unidentified taxon. TEM whole mounts (Arctic / NEW). 48–49 – combination coccosphere; details of the scale types involved are shown in Fig. 49; 50–52 – partly complete cell (one flagellum missing) of the umineralized counterpart; details of the scales are shown in Fig. 50 (reversed printing) and Fig. 52.