SYNOPSIS. Tracer technic has proved to be an excellent tool in the study of predator‐prey relationships among the foraminifera. More than fifty axenic species of protists including diatoms, dinoflagellates, chlorophytes, chrysophytes, cyanophytes, bacteria and yeasts were tested as potential food for Allogromia sp (NF), A. laticollaris, Am. monia beccarii, Quinqueloculina spp, Rosalina floridana, Anomalina sp, Elphidium sp, Spiroloculina hyalina, Globigerina bulloides, and Globorotalia truncatulinoides. Although many types of potential food are present in the environment, foraminifera select only certain organisms. The yeasts, cyanophytes, dinoflagellates, chrysophytes and most bacteria tested were not eaten. Selected species of diatoms, chlorophytes and bacteria were eaten in large quantity. Three additional factors affect feeding: the “age” of the food organism, the “age” of the foraminifer or its position in the life cycle, and the concentration of the food. Feeding by foraminifera on most food is erratic below a concentration of 103 organisms and is approximately directly proportional to concentration within a range of 103‐106 organisms per 10 ml experimental tube. A natural bloom of Protelphidium tisburyensis was analyzed. A high concentration of 6 species of diatoms characterized the community. A “bloom”‐feeder hypothesis for foraminiferal nutrition is presented.
SYNOPSIS. A polymorphic allogromiid (our strain NF) was isolated in monoxenic culture but attempts at its axenic culture failed. Growth of monoxenic cultures was stimulated by various metals and vitamins. The morphology and life cycle of this allogromiid with a prominent collar have been studied in detail. It varied in form from ovoid to elongate bioral “Shepheardella‐like” forms and to irregular polyoral organisms. The organisms ranged in length from 56–385 μ (118 μ± 50.54) and in width from 35–385 μ (99 μ± 39.34). The number of nuclei per organism averaged 8.9 ± 6.3 (range 1–40). Reproduction of “Shepheardella‐like” forms was by binary fission. Three types of budding have been observed and, rarely, schizogony. No evidence for sexual reproduction has thus far been seen.
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