Spumellaria

Like other radiolarian groups, morphology has been key to classifying phylogeny, with skeleton symmetry being one of the most important factors for classification. Generally, Spumellaria feature a concentric structure with radial or spherical symmetry, much like other radiolarian orders. Beyond that, however, Spumellaria have high diversity in their shell morphology. They have been found to maintain the shape of their shells by controlling where silification happens on their skeletons. Some species, such as Haliommilla capillacea, have very fragile spherical shells, while other species, like Spongosphaera streptacantha, have very long spines. This diversity includes a variety of strategies for growing shells. There are multiple types of growth: external shell growth, where silica is being deposited on the outside, and the shell is actively getting bigger, and internal growth, where silica is being deposited on the inside and the shell does not outwardly appear to be growing. One species, Spongaster tetras tetras, was found to go through different patterns of silica gain based on life stage (divided into young, progressively growing, and full-grown). Spumellaria also feature a complex protoplasmic meshwork, which is a system of living protoplasm, like cytoplasm, around the skeleton. With this comes their pseudopodia, which are cytoplasmic prolongations that they use to stick prey. ==Families==