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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Thecadinium

Thecadinium Kofoid & Skogsberg (ref. ID; 7726)

Order Peridiniales (ref. ID; 7726)
  1. Thecadinium kofoidii (Herdman) Schiller (ref. ID; 7726)
    Syn; Amphidinium kofoidi var. petasatum Herdman, 1922 (p.26, fig.3) (ref. ID; 7726); Amphidinium sulcatum Herdman, 1921 (p.61, fig.C1-C2) (ref. ID; 7726); Phalocroma kofoidi Herdman, 1923 (p.60) (ref. ID; 7726); Phalocroma kofoidi Lebour, 1925 (p.77, pl.11, fig.1) (ref. ID; 7726); Thecadinium kofoidi Dragesco, 1965 (p.103, fig.13) (ref. ID; 7726); Thecadinium petasatum Dodge, 1982 (p.57, fig.5A-C) (ref. ID; 7726)
  2. Thecadinium kofoidii Larsen, 1984 (ref. ID; 7726)
  3. Thecadinium neo-petasatum Saunders & Dodge, 1984 (ref. ID; 7726 original paper)

Thecadinium kofoidii (Herdman) Schiller (ref. ID; 7726)

Synonym

Amphidinium kofoidi var. petasatum Herdman, 1922 (p.26, fig.3) (ref. ID; 7726); Amphidinium sulcatum Herdman, 1921 (p.61, fig C1-C2) (ref. ID; 7726); Phalocroma kofoidi Herdman, 1923 (p.60) (ref. ID; 7726); Phalocroma kofoidi Lebour, 1925 (p.77, pl.11, fig.1) (ref. ID; 7726); Thecadinium kofoidi Dragesco, 1965 (p.103, fig.13) (ref. ID; 7726); Thecadinium petasatum Dodge, 1982 (p.57, fig.5A-C) (ref. ID; 7726)

Descriptions

The cell is strongly bilaterally flattened and has a very reduced epitheca. The overall shape is chordate as shown in Figs.3 and 12a but in dorsal or ventral view the cell is oval. The epitheca is strongly ridged and it is difficult to determine the individual plates. However, there appears to be a ring of 4 precingulars, 3 apical plates, a large pore plate containing a hook-shaped pore and a small intercalary plate. The girdle, which is horizontal, consists of 5 plates. Most of the hypotheca is covered by two large smooth plates (1''' and 3''') in which there are scattered pores. These are separated by the sulcus and two rectangular plates (2''' and 1''') which are perforated by numerous pores and are strongly areolate. The sulcus partly cuts into plate 3''' at the point where there is a large flagellar pore from which both flagella are thought to arise (Dragesco 1965). We have not been able to determine the number of sulcal plates but Sp, ss and sd are fairly distinct. The cell contains a number of yellowish chloroplasts which radiate from a central pyrenoid. The nucleus is usually situated in the lower part of the cell. Plate formula: Po, 3', la, 4'', 5c, ?s, 3''', 1''''. Size: length, 23-33 um; width, 6-11 um. (ref. ID; 7726)

Notes

This organism was first reported by Herdman (1921; fig.1a) who thought that it was Amphidinium sulcatum but the next year she carried out further studies of the beach dinoflagellates at Port Erin and decided that it was a yellow-coloured form of her new species A. kofoidi and she named it var. petasatum (Herdman 1922) (Fig.1b). It would appear that she then had some communication with Lebour who was at that time writing her book on dinoflagellates (Lebour 1925) and as a result the next year its name was changed to Phalacroma kofoidi (Herdman 1922). Lebour (1925), without indicating the source illustrated this species with an accurate picture of the chloroplasts and nucleus (Fig.1d). Kofoid and Skogsberg (1928) when creating their new genus Thecadinium, clearly based it on Herdman's 1922 description of this species but they, like some subsequent authors, thought that the specific epithet should be petasatum. A more recent description of this organism was given by Dragesco (Fig.1f) again clearly showing the present of chloroplasts. The first person to give this species it correct name, T. kofoidii, was Schiller (1933) and although he omitted to note that it was a "comb. nov." his intention was quite clear and he should be credited as the authority. Probably he thought that he was only correcting an error on the part of Kofoid & Skogsberg. Unfortunately, Larsen (1984) has recently reused this combination T. kofoidii (Herdman) comb. nov. but we feel that he has mistaken the organism which we describe as Sabulodinium undulatum for Herdmans's Phalocroma kofoidii. (ref. ID; 7726)

Thecadinium neo-petasatum Saunders & Dodge, 1984 (ref. ID; 7726 original paper)

Diagnosis

Cellula a latere compressa habens parvam epithecam tholiformem; hypotheca rotunda et cordata. Bracteae thecales leves, cum formula: Po, 3', 1a, 5'', ?c, ?s, 3''', 1''''. (ref. ID; 7726)

Descriptions

This species is rather similar in shape to T. kofoidii but it is slightly larger and more rounded. The thecal plates are all smooth and porate. The epitheca is domed and clearly consists of two parts as the first apical and the apical pore plates are set at a lower level than the remainder. The apical pore is horse-shoe shaped, enclosing two flattened projections, and is surrounded by a ring of 7 or 8 circular pores. There are three apical plates, one small intercalary, and five precingulars. No details have been obtained of the girdle and sulcus. The hypotheca consists of two main plates and two smaller ones. Plate formula: Po, 3', la, 5'' ?c, ?s, 3''', 1''''. Size: length, 34 um; width 14 um. (ref. ID; 7726)

Notes

This organism does not appear to have been described before but it clearly is a member of the genus Thecadinium. (ref. ID; 7726)

Examined materials

It was found in sand at Holy Island, Northumberland, In May. (ref. ID; 7726)