Planodinium

Planodinium Saunders & Dodge, 1984 (ref. ID; 7726 original paper)

[ref. ID; 7726]
Diagnosis; Cellula thoracata, a latere compressa, parvam habens epithecam et hypothecam rotundam quadrangulatamque, quae duas magnas bracteas in latere praebet et tres alias in margine. (ref. ID; 7726)
Description; Cell armoured, laterally compressed: epitheca very short reduced to about one tenth of body length; girdle almost horizontal; hypotheca mainly covered with two large lateral plates which are more or less rectangular in shape. Chloroplasts absent but rounded pigmented body may be present. Found in damp sand. (ref. ID; 7726)
Etymology; The name is derived from L. planus, flat. (ref. ID; 7726)
Type species; Planodinium striatum (ref. ID; 7726)

Planodinium striatum Saunders & Dodge, 1984 (ref. ID; 7726 original paper)
Syn; Thecadinium petasatum Baillie, 1971 (p.63, fig.7) (ref. ID; 7726)

Planodinium striatum Saunders & Dodge, 1984 (ref. ID; 7726 original paper)

Synonym

Thecadinium petasatum Baillie, 1971 (p.63, fig.7) (ref. ID; 7726)

Diagnosis

Naturae habnes propria sui generis: cuius bracteae hypothecales maiores iuga in longitudinem creba ferunt sparsasque pororum turmas. Absunt chloroplasti, sed praeest corpus quoddam globosum et pigmentatum prope cellulae centrum. Bracteae thecales cum formula: 3', 7'', 6c, s, 3''', 1''''. (ref. ID; 7726)

Descriptions

Cell covered with fairly thick thecal plates, those of the epitheca having pores, ridges, and small pimples, those of the hypotheca having mainly longitudinal ridges with scattered pores surrounded by a ring of smaller pore. Towards the antapex the ridges form a reticulate pattern. The epithecal is very small and slightly domed. It is penetrated by a narrow projection of the sulcus but has no obvious apical pore. There are seven precingular plates of various shapes and three plates which are here designated as apicals. The girdle is slightly offset and consists of six plates. The epitheca is connected to the sulcus by an unusual rhomboidal plate which has no clear homology in other dinoflagellates. It is here called the sulcal-transition plate (st). The lower part of the sulcus consists of a large concave oval (sp) plate which is smooth and has a peripheral ring of pores. The single curved flagellar pore is situated at the junction of girdle and sulcus. Two large +/- rectangular plates dominate the hypotheca but in addition there is a long narrow 3''' plate and a small rectangular antipical (1'''') plate. By light microscopy it can be seen that the ovoid nucleus lies in the lower part of the hypocone and there is a rounded pigmented body, yellow or blackish in colour, situated near the centre of the cell. It is possible that this may represent an endosymbiont. A few refractile granules are also present but the cell is essentially colourless and there are no choloroplasts. Plate formula: 3', 7'', 6c, s, 3''', 1''''. Size: length 27-30 um, width 10-11 um. (ref. ID; 7726)

Notes

This organism, which we have as yet only found in damp sand at Millport, Isle of Cumbrae and Holy Island, Northumberland, is almost certainly that found by Baillie (1971) in British Columbia and incorrectly identified as Thecadinium petasatum (= out T. kofoidii). Apart from the general shape of the cell, Baillie noted the hypothecal plate patterning and the central pigmented body, both features not seen in other flattened dinoflagellates which we have examined. There are some similarities between this organism and Balech's (1956) Roscoffia capitata which to the best of our knowledge has never been examined by any other worker. Balech noted a reticulate patterning of the epitheca which connected with the right sulcal plate as described for P. striatum. However, he also reported a lare apical pore, three girdle plates, five postcingular plates and a large flagellar pore touching the antapical plate, all features which distinguish it from P. striatum. Further study by SEM is needed before we can be sure of any relationship between these two organisms which are quite clearly distinct species. (ref. ID; 7726)