"Living sands are major primary producers and sinks of nutrients and carbonate in oligotrophic seas. Although all living sands contain one of a wide diversity of algal types, the diatom-bearing larger foraminifera are a unique form of the symbiotic phenomenon. So far, 19 different, and taxonomically widely separated, diatom species have been isolated from hosts, although usually only one species of diatom has been observed at a time in a single host. The diatoms which form endosymbioses are extremely rare in the habitat where the forams are found. Foraminifera eat mainly diatoms. Although symbionts are passed from generation to generation by asexual reproduction, the flagellated gametes released into the water column are too small to contain symbionts. The chain is broken unless the zygotes or young agamonts find new symbionts. How do they recognize them? Nothing is known about initial interactions. Some species in the same genus serve as food while other species become endosymbionts. Western blotting will be used to screen cross-reactive surface antigens and to affinity purify antibodies to specific antigens by eluting bound antibodies of interest. Later dot blot immunoassays will be used. After absorption of the antisera, blocking experiments will be performed. Fine structural studies will aid understanding the process. Human activities in most of their range (e.g. Persian Gulf) threaten their habitats and survival. We know little about their resistance or what their loss will mean to the global C02 balance.