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.