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The echinoderms are deuterostomic animals with a nonspecific immune system similar to that of vertebrates. Among coelomocytes, phagocytic amoebocytes have a key role in the nonspecific immune response in sea urchin, being responsible for microorganisms elimination through phagocytosis and also for humoral secretions of a wide spectrum. Sub-populations of phagocytic amoebocytes (PA) have been previously described and two distinct sub populations in the oral (OR) and aboral (AB) regions of the perivisceral coelom of L.variegatus in the present study were found. In the OR there is a higher number of PA with higher phagocytic capacity after 30 minutes of incubation with yeast and higher percentage of intranuclear iron crystalloids. The germicide capacity under the fluorescence technique did not show any difference. SDS-PAGE analysis showed different protein patterns between coelomocytes of OR and AB. Gravitational force had no effect in PA distribution and no physical barrier was found in the perivisceral coelom. The other coelomocyte (vibratile cells, red spherulocytes and white spherulocytes) populations were not different in OR compared with AB in their distribution. Some aspects of the possible causes of the differences found for PA are discussed in the paper.

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