Octactis
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| Octactis | |
|---|---|
 | |
| Illustration of Octactis speculum silica skeletons by Stöhr (1880)[1] | |
Scientific classification  | |
| Domain: | Eukaryota |
| Clade: | Sar |
| Clade: | Stramenopiles |
| Division: | Ochrophyta |
| Class: | Dictyochophyceae |
| Order: | Dictyochales |
| Family: | Dictyochaceae |
| Genus: | Octactis Schiller, 1925[2] emend. F.H.Chang, J.M.Grieve & J.E.Sutherland, 2017[3] |
| Species[3] | |
Octactis is a genus of silicoflagellates,[3] marine photosynthetic unicellular protists that take the form of either flagellates or axopodial amoebae.[4] Described by Josef Schiller in 1925, Octactis contains various species of marine phytoplankton, some of them responsible for algal blooms that are toxic to fish.[5]
Octactis species are unicellular protists that appear as several different multinucleate forms (i.e. with multiple nuclei). The most prevalent form is as amoebae surrounded by an external, basket-like siliceous skeleton, consisting of two conspicuous rings: a smaller apical ring supported by short struts that are attached to a larger basal ring. The skeleton pikes sometimes occur on the surface of the basal ring. The large window that the apical ring encloses is undivided. Other forms also present are naked amoebae and sometimes mucocyst-bearing amoebae. Both skeleton-bearing and naked cells present a long flagellum. The mucocysts appear on the periphery of skeleton-bearing cells, absent in the naked cells.[3]
Within each Octactis cell there is a pyrenoid embedded within a chloroplast. The chloroplast has a short thylakoid intrusion. The skeleton-bearing cells contain between 6 and 8 Golgi bodies. The chloroplasts contain all three accessory chlorophylls, c1, c2 and c3, as well as fucoxanthin as the main carotenoid, with diadinoxanthin and one or two oxyfucoxanthin derivatives. They lack lutein.[3]