''Raphidiophrys contractilis'' is a species of freshwater

centrohelid The centrohelids or centroheliozoa are a large group of heliozoan protists. They include both mobile and sessile forms, found in freshwater and marine environments, especially at some depth. Characteristics Individuals are unicellular and spher ...

Discovery

This species was first isolated from a brackish pond in Shukkeien Garden, Naka-ku, Hiroshima City,

Japan Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...

Description

''Raphidiophrys contractilis'' is a spherical organism measuring between 7 and 19 μm in diameter and has several

axopodia A pseudopod or pseudopodium (: pseudopods or pseudopodia) is a temporary arm-like projection of a eukaryotic cell membrane that is emerged in the direction of movement. Filled with cytoplasm, pseudopodia primarily consist of actin filaments and ...

measuring between 60 and 110 μm. The axopodia are sustained by a set of

microtubule Microtubules are polymers of tubulin that form part of the cytoskeleton and provide structure and shape to eukaryotic cells. Microtubules can be as long as 50 micrometres, as wide as 23 to 27 nanometer, nm and have an inner diameter bet ...

s arranged in a complex of hexagons and triangles. The cell body is coated by a thin layer of small scales composed of

silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , commonly found in nature as quartz. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and abundant f ...

. These scales are oblong, with curved edges and with the surface always facing the cell body.

Feeding behavior

''Raphidiophrys contractilis'' preys on other protists, such as flagellates and ciliates, and captures them with its axopodia. The axopodia contain many organelles called kinetocysts, which are released on the prey's surface and probably have a paralyzing effect. After the prey is attached to the axopodium, the axopodium contracts rapidly, at a velocity of about 1 mm/s, this being the reason for the species being named ''Raphidiophrys contractilis''. Although ''R. contractilis'' is not a colonial species, several individuals can cooperate in the capture of larger prey. In this case, the individuals gather around the prey and fuse into a larger structure with partially joined cytoplasms and build a common food vacuole to ingest and digest the prey organism.

References

External links

Friday Fellow: Contractile Gentle-Scaled Centrohelid
at Earthling Nature. Haptista {{Hacrobia-stub