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

Abstract 

Cryothecomonas longipes Schnepf and Kühn sp. nov. is a colourless biflagellate organism, 9–14 µm long and 7–9 µm wide when not filled with food vacuoles. It was detected in the North Sea, feeding with pseudopodia on diatoms. It penetrates the host shell, while the main body of the flagellate remains outside the frustule. Cells are covered with a multilayered theca. The pseudopodium protrudes through a preformed slit in the theca. Each flagellum 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 µm long and oriented forward; the ventral flagellum, posteriorly directed, is 20–24 µm long and bears fine hairs. The flagellar roots consist of microtubules that emerge at satellites around the basal bodies and run along the flagellar pits. In addition, the ventral flagellum is accompanied by a band of six microtubules. It is proximally attached to a small fibrillar band, which interconnects the basal bodies. Cryothecomonas longipes has two or three types of extrusomes which pierce the theca when discharged. Their mode of discharge is discussed. Microbody-like vesicles containing small tubules are closely associated with older digestion vacuoles. Cryothecomonas longipes is compared with other species of the genus and a diagnosis is given.