Food uptake and fine structure of Cryothecomonas longipes sp nov., a marine nanoflagellate incertae sedis feeding phagotrophically on large diatoms

Cryothecomonas longpipes Schnepf and Kuhn sp. nov. is a colourless biflagel late organism, 9-14 mu m long and 7-9 mu m wide when not filled with food v acuoles. It was detected in the North Sea, feeding with pseudopodia on diat oms. It penetrates the host shell, while the main body of the flagellate re mains outside the frustule. Cells are covered with a multilayered theca. Th e pseudopndium protrudes through a preformed slit in the theca. Each flagel lum also emerges through a pit in which the theca forms a funnel of complex structure that girdles each flagellum. The anterior flagellum is 9-15 mu m long and oriented forward; the ventral flagellum, posteri orly directed, i s 20-24 mu m long and bears fine hairs. The flagellar roots consist of micr otubules that emerge at satellites around the basal bodies and run along th e flagellar pits. In addition, the ventral flagellum is accompanied by a ba nd of six microtubules. It is proximally attached to a small fibrillar band , which interconnects the basal bodies. Cryothecomonas longpipes has two or three types of extrusomes which pierce the theca when discharged. Their mo de of discharge is discussed. Microbody-like vesicles containing small tubu les are closely associated with older digestion vacuoles. Cryothecomonas lo ngpipes is compared with other species of the genus and a diagnosis is give n.