Microworld

world of amoeboid organisms

Menu

Left: ultra-structure of a kinetocyst of Raphidiophrys contractilis); right: two kinetocysts in an axopodium.

Kinetocysts In centrohelid heliozoa, extrusomes are called kinetocysts, and are present in close association with the plasma membrane of axopodia. A kinetocyst is an extrusive organelle that discharges its contents upon food capture. The posterior part of a discharged kinetocyst is always attached to the plasma membrane of the heliozoon, while the anterior end is directed towards the prey, often making close contact with a food organism. This association possibly provides a cell surface scaffold that aids in extension of pseudopodia during formation of the food cup. A kinetocyst is a globular organelle that measures about 0.4 µm in height and 0.3 µm in width, and is surrounded by a membrane. It contains a bipartite central element (core) enclosed by a jacket of less electron dense material with fine striations, most likely being composed of stacked disks. The central core and the jacket are covered with a mushroom-shaped cap structure that is associated with the surrounding membrane at its tapered edges. Filamentous antennae are located outside the plasma membrane with apparent structural connection to the central core. During prey capture, kinetocysts expel some material towards prey organisms. After discharge, the basal part of the kinetocyst keeps its association with the surrounding membrane, which, as a result of exocytosis of the kinetocyst, becomes incorporated into the plasma membrane. The jacket of discharged kinetocysts spread out and transform into a much less distinct structure, while the appearance of the central core remains unchanged. The distal end of the core is connected to or fused with the cell surface of the prey. Reference: Sakaguchi, M., Suzaki, T., Kamal Khan, S.M.M. and Hausmann, K. (2002). Food capture by kinetocysts in the heliozoon Raphidiophrys contractilis. Europ. J. Protistol. 37, 453–458.
Recent posts

Penardochlamys arcelloides

P. arcelloides – from Penard, 1904 Penardochlamys arcelloides  (Penard, 1904) Deflandre, 1953 Diagnosis: Colorless or very slightly yellowish envelope, bag or cauldron-shaped, very thin, chitinous,

Read More »

Reticulomyxa hannae

R. hannae, plasmodium – photomicrograph Steffen Clauss Reticulomyxa hannae Völcker and Clauß, 2020 Diagnosis: Trophozoites surrounded by a very thin mucous envelope, with slowly moving plasmodia, variable

Read More »

Velamentofex saxonensis

V. saxonensis, feeding (photomicrograph Steffen Clauss) Velamentofex saxonensis Völcker and Clauß, 2020 Diagnosis: Trophozoites ovoid, 30-95 μm, granuloreticulopodia up to 1000 μm long. with a hyaline, thin

Read More »

Velamentofex tyrolensis

V. tyrolensis (photomicrograph Steffen Clauss) Velamentofex tyrolensis Völcker and Clauß, 2020 Diagnosis: Trophozoites ovoid, 98-125 μm, with reticulopodia up to 300 μm long, with a hyaline,

Read More »

Velamentofex berolinensis

V. berolinensis Velamentofex berolinensis Völcker and Clauß, 2020 Diagnosis: Trophozoites ovoid, 50-300 µm, with a hyaline, extremely flexible, membranous test. Nuclei numerous, 11.6-16.2 µm in diameter,

Read More »

Lieberkuehniidae

 Lieberkuehniidae  Siemensma, Holzmann, Apothéloz-Perret-Gentil, Clauß, Voelcker, Bettighofer, Khanipour Roshan, Walden, Dumack and Pawlowski, 2020 Diagnosis: Multinucleate organic-walled monothalamous foraminifera. Test very flexible, elongated to broadly

Read More »