FIGURE 3. Many surface-dwelling Polycystina host symbiotic algal cells in their cytoplasm; both organisms, the host and the alga, benefit from this association. The micrograph of this surface-dwelling radiolarian from the Caribbean about 300 micrometers (approximately 1/8th of an inch) across shows its cytoplasmic pseudopodia (thin rays radiating from the specimen), and the symbiotic algae - tiny yellow-green spherules. Photo courtesy of Atsushi Matsuoka (from Matsuoka, A., 1993. Observations of living radiolarians from the surface water in the Caribbean Sea. News of Osaka Micropaleontologists, Special Volume 9, pp. 349-363).