~ 19 Invertebrates The invertebrates were assayed because of their potentiality as food for humans and for animals that might serve as food. The giant clam, longusta or spiny lobster, and coconut crab undoubtedly are eaten by the natives. Corals and sea cucumbers are considered chiefly because of their abundance and role in the ecology of the atolls. Radioactivity in Rongelap invertebrates declined from about 102 - 104 uc/kg on March 26, 1954 to approximately 107! - 10! yc/kg on October 2122, 1955, as shown in Tables 5 and 6 and Figures 5 - 10. Levels of radio- activity in October 1955 at Kabelle, Labaredj, and Rongelap Islands and at Enibuk Island (Ailinginae Atoll) were, respectively, 3+, 6+, 2, and 1 ywc/kg of wet tissue. Individual values for the October 1955 collections appear in Appendix C. Liver of the spider snail (Fig. 8) averaged highest in radioactivity throughout the 1. 6-year period of study, being most closely approached early by the hermit crab liver, which declined rapidly (Fig. 6) and at the end of the period, by the slowly-declining coconut crab carapace (Fig. 5). The low level of activity of the basic coral organisms (Fig. 10) is of special interest. Of the tissues analyzed muscle had least activity, that of the giant clam in October 1955 being less than 0.1 wcvkg (Fig. 7). | The low level of activity in the giant clams, Tridacna and Hippopus, presumably results from feeding upon plankton, which is also low. In contrast, the spider snail, Pterocera, with activity about 10 times that of the plankton-