Answer: radiolarians

AnswerCrossword Clue
radiolariansRADIOLARIAN, any member of an order of marine Protozoa, or unicellular animals, with fine radial tentacles for feeding and movement
radiolariansA single-celled aquatic animal that has a spherical, amebalike body with a spiny skeleton of silica. Their skeletons can accumulate as a slimy deposit on the seabed