Radiolarians have many needle-like pseudopodia supported by bundles of microtubules, which aid in the radiolarian's buoyancy. The cell nucleus and most other organelles are in the endoplasm, while the ectoplasm is filled with frothy vacuoles and lipid droplets, keeping them buoyant. The radiolarian can often contain symbiotic algae, especially zooxanthellae, which provide most of the cell's energy.
Ernst Haeckel was fairly famous in the 1800s, known as a “biologist, naturalist, philosopher, physician, professor, marine biologist, and artist who discovered, described and named thousands of new species, mapped a genealogical tree relating all life forms, and coined many terms in biology, including anthropogeny, ecology, phylum, phylogeny, stem cell, and Protista.” (source)
Nowadays Haeckel is known mostly as the source of the quote, “Ontogeny recapitulates phylogeny,” which summarizes his Recapitulation Theory. Basically, he suggests that the stages in the development of an embryo (ontogeny) resemble the stages in the evolution of the animal's ancestors (phylogeny).