Armoured marine planktonic dinoflagellate. Generally, it is a cold-water coastal species found in low numbers mainly along the West coast of Europe. Cells are large and nearly spherical. Cells are single, but are often found in two-celled colonies. Epitheca and hypotheca equal in height. This species has thin thecal plates and a characteristic large ventral pore on the first apical plate (1'). Faint surface pores are numerous and unevently distributed. Cells range in size between 40-56 µm in length and 40-50 µm in transdiameter width. The plate formula: Po, 4', 6'', 6c, 10s, 5''', 2''''. The apical pore complex (APC) is triangular or rectangular in shape. the apical pore plate (Po) is relatively large with a large comma-shaped foramen. It can be iether in direct contact with the first apical plate (1') or indirectly connected via a thin suture (thread_like process). The most distinctive plate of this species is the 1' ventral pore : it bears a large characteristic ventral pore, and a 90 degree angle is ofrmed at the point where the ventral pore and the 4' plate come in contact. The distinctive sixth precingular plate (6'') is wider than high. The borad epitheca is convex-conical, while the hypotheca is hemispherical with an obliquely flattened antapex. The slightly excavated cingulum is equatorial and displaced in a descending fashion less than one time its width; it has narrow lists. The sulcus is slightly depressed and inconspicuous. The nucleus is U-shaped and equatorial. Producing paralytic shellfish poisoning (PSP) toxins.