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The genus Amphidinium (am-fee-din-ee-um) testudo is a commonly encountered and speciose member of the dinoflagellates. There is a circumferential groove on the cell surface that runs around the anterior half of the cell, and a second one running along the length of the body. There is a flagellum in each groove. The asymmetrical location of the horizontal groove gives this genus its name (cf. Gymnodinium). This is an atypical member of the genus, encountered adhering tightly to the substrate. The recurrent flagellum usually located under the cell. There is a second image of this cell showing the recurrent flagellum. The anterior flagellum is located around the very reduced epicone, or anterior part of the body. Differential interference contrast.
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Amphidinium (am-fee-din-ee-um) testudo is a commonly encountered and speciose member of the dinoflagellates. There is a circumferential groove on the cell surface that runs around the anterior half of the cell, and a second one running along the length of the body. There is a flagellum in each groove. This photograph is of the ventral side and shows the recurrent flagellum. Differential interference contrast.
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Amphidinium (am-fee-din-ee-um) testudo Herdman 1924. The image shows a cell in ventral view. The epicone is small, and does not protrude above the hypocone. The plastids are yellow-brown. This is a non-motile stage.
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Amphidinium (am-fee-din-ee-um) testudo Herdman 1924. The image shows a cell in ventral view. The epicone is small, and does not protrude above the hypocone. The plastids are yellow-brown. The round pyrenoid is visible in the centre of the cell.
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Amphidinium (am-fee-din-ee-um) testudo Herdman 1924. The image shows a cell in ventral view. The epicone is small, and does not protrude above the hypocone. The plastids are yellow-brown. This is a non-motile stage.
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Cells rounded-oblong to pear shaped, dorso-ventrally flattened. Length 24 - 36 microns, width 19 - 26 microns, breadth (lateral) approximately 12 microns, length to width ratio 1.1 - 1.7. Epicone 2 - 4 microns wide, club-shaped, with two lobes, often slightly deflected to the left. Cingulum beginning 0.1 - 0.3 of the cell length from the apex, relatively wide (1 - 3 microns), incompletely encircling the epicone, distal end approximately 2 - 3 microns higher than proximal. Longitudinal groove (0.5 - 2 microns wide) present on the dorsal side, beginning at the apex and descending through the middle of the cell to 0.6 - 0.9 of the cell length from the apex. Hypocone forms a 'collar' around the epicone in dorsal view, this has a division in the middle due to the dorsal longitudinal groove. Sulcus indistinct. Longitudinal flagellum originating 2 - 3 microns below the proximal end of the cingulum. Nucleus in the posterior part of the hypocone, rounded to crescent shaped, may be to the left of the cell, 9 - 11 x 5 - 10 microns. Chloroplasts yellow-brown, 1 - 2 x 1 - 4 microns, often more concentrated in the centre of the cell. A central, pyrenoid-like structure sometimes observed. Indented around the inside of the periphery of the ventral side, 1 - 2 microns from the cell rim. Non-motile cells more circular, with the hypocone encircling the epicone, surrounded by a hyaline layer. Non-motile cells more commonly observed than motile cells.
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Amphidinium testudo Herdman 1924. Just dividing cell.
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Amphidinium testudo Herdman 1924.
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Amphidinium testudo Herdman 1924.
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Amphidinium testudo Herdman 1924.
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Dorsal view of this sand-dwelling dinoflagellate from Sippiwisset Marsh, Massachusetts, USA. Photo by Shauna Murray and Bob Moore.
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Ventral view of this sand-dwelling unarmoured dinoflagellate. From Sippiwissett Marsh, Massachusetts USA. Image by Shauna Murray and Bob Moore.
