A species of Amphidinium bloomed in a mariculture sedimentation pond that was used to grow bivalves near the Gulf of Eilat, Israel. Its overall length averaged 13 μm, the hypocone was 11 μm, and its width was 8μm. It has a ventral ridge. The sulcus begins at the longitudinal flagellar pore and does not project forward in the apex toward the transverse flagellar pore and left margin of the cingulum. The sulcus is a very shallow groove that projects variably about a third of the body length toward the antapex. The cingulum is a deep groove as it circles the cell from the left ventral side to the dorsal side and then becomes very shallow on the right ventral side as it arches posterior toward the longitudinal flagellar pore. Using a modified method for studying dinoflagellate chromosomes in the SEM, we observed 31 chromosomes. The plastid is dorsal and peripheral with 6 ventrally projecting peripheral digital lobes that wrap around the sides of the ventral and posterior nucleus. Amphidinium eilatiensis n. sp. is morphologically closest to Amphidinium carterae and Amphidinium rhynchocephalum , but it does not have the obvious thecal plates or polygonal units described for the former species. Instead, it has a series of spicules, bumps, and ridges on its surface. It differs from A. rhynchocephalum by two morphological characters: surface morphology and gross plastid architecture.

The amplified fragments of the rDNA from A. eilatiensis n. sp. isolated from 2 separate sedimentation ponds in Eilat include the 3′‐end of the SSU rDNA (about 100 nt), the whole ITS region (ITS1 + 5. 8S + ITS2) and the 5′‐end of the LSU rDNA (about 900 nts). The total length of the sequences ranged from 1,460 nt. (A. eilatiensis isolate #1) to 1,461 nts. (A. eilatiensis isolate #2). The latter sequences are identical, the difference in length being due to three insertions. Amphidinium eilatiensis is genetically more closely related to A. carterae than to A. klebsii, with respectively 2. 36% and 6. 93% of sequence divergence.