Final answer:
Radiolarians are protists with silica skeletons and spines contributing to variable symmetry, and they are known for intricate designs and needle-like pseudopodia for feeding.
Step-by-step explanation:
The group of protists characterized by cytoplasm that surrounds an internal skeleton and typically features spines, which contribute to variability in symmetry, is the Radiolarians. These protists have intricate exteriors made of glassy silica with radial or bilateral symmetry, and their needle-like pseudopodia, supported by microtubules, radiate outward to catch food particles. The skeletons of deceased radiolarians sink to the ocean floor and can accumulate in significant depths, and their presence is also common in the fossil record.