Name the Bug: Sticholonche zanclea

Sticholonche zanclea (photo from here).

Sticholonche zanclea is a very unusual marine protist. In the past, it has been classified among the heliozoans, a group of organisms united by their generally radial arrangement of long cytoplasmic extensions called axopodia. However, both molecular and ultrastructural studies have established that the 'heliozoans' are a polyphyletic assemblage of a number of unrelated groups that have converged on a similar morphology. 'Heliozoans', in general, are passive trappers of other micro-organisms and food particles by means of their axopodia; the helizoan morphology provides for significant area coverage without massively increasing the cell cytoplasm. Compare this to the 'radiosa' form adopted by amoebae that become detached from their substrate and which serves a similar purpose (though in that case the aim is increasing the chance of recontacting the substrate). In the case of Sticholonche, molecular analysis has placed it among the also-axopod-bearing radiolarians with which it shares the production of siliceous spicules. Sticholonche differs from other radiolarians in lacking a central capsule dividing the cell into internal and external sectors; however, said molecular analyses place it nested among rather than sister to radiolarians. Indeed, it may be the sister to the spumellarid family Litheliidae (Kunimoto et al., 2006).

Sticholonche differs from other 'heliozoans' in being flattened with the axopodia concentrated laterally. The axopodia are rigid, reinforced by a central core of microtubules, and anchored on small cup-shaped depressions on the nuclear envelope (Cachon et al., 1977). By flexing the nuclear envelope, Sticholonche can move by rowing itself with the axopodia. If your day has so far provided insufficient awesomeness, follow this link, scroll down the page a bit, and you will find a video of a Sticholonche doing just that.

REFERENCES

Cachon, J., M. Cachon, L. G. Tilney & M. S. Tilney. 1977. Movements generated by interactions between the dense material at the ends of microtubules and non-actin-containing microfilaments in Sticholonche zanclea. Journal of Cell Biology 72: 314-338.

Kunimoto, Y., I. Sarashina, M. Iijima, K. Endo & K. Sashida. 2006. Molecular phylogeny of acantharian and polycystine radiolarians based on ribosomal DNA sequences, and some comparisons with data from the fossil record. European Journal of Protistology 42 (2): 143-153.