microtubules arranged in a double spiral pattern characteristic of the order. Due to their long, parallel construction these microtubules demonstrate strong birefringence. These axopodia are used for prey capture, in movement, cell fusion and perhaps division. They are stiff but may flex especially near their tips, and are highly dynamic, undergoing frequent construction and destruction. When used to collect prey items, two methods of capture have been noted, termed axopodial flow and rapid axopodial contraction. Axopodial flow involves the slow movement of a prey item along the surface of the axopod as the ectoplasm itself moves, while rapid axopodial contraction involves the collapse of the axoneme's microtubule structure. This behavior has been documented in many species, including Actinosphaerium nucleofilum, Actinophrys sol, and Raphidiophrys contractilis. The rapid axopodial contraction occurs at high speed, often in excess of 5mm/s or tens of body lengths per second. The axopodial contractions have been shown to be highly sensitive to environmental factors such as temperature and pressure as well as chemical signals like Ca2+ and colchicine. Reproduction Reproduction in actinophryids generally takes place via fission, where one parent cell divides into two or more daughter cells. For multinucleate heliozoa, this process is plasmotomic as the nuclei are not duplicated prior to division. It has been observed that reproduction appears to be a response to food scarcity, with an increased number of divisions following the removal of food and larger organisms during times of food excess. Actinophryids also undergo autogamy during times of food scarcity. This is better described as genetic reorganization than reproduction, as the number of individuals produced is the same as the initial number. Nonetheless, it serves as a way to increase genetic diversity within an individual which may improve the likelihood of expressing favorable genetic traits. Plastogamy has also been extensively documented in actinophryids, especially in multinucleate ones. Actinosphaerium were observed to combine freely without the combination of nuclei, and this process sometimes resulted in more or less individuals than originally combined. This process is not caused merely by contact between two individuals but can be caused by damage to the cell body. Cyst function and formation Under unfavourable conditions, some species will form a cyst. This is often the product of autogamy, in which case the cysts produced are zygotes. Cells undergoing this process withdraw their axopodia, adhere to the substrate, and take on an opaque and grayish appearance. This cyst