DEFENSIVE-MECHANISMS OF HOLOTHUROIDS (ECHINODERMATA) - FORMATION, ROLE, AND FATE OF INTRACELOMIC BROWN BODIES IN THE SEA-CUCUMBER HOLOTHURIA-TUBULOSA

Brown bodies are pigmented aggregates of amoebocytes found in the coel omic cavities of most holothuroids (sea cucumbers). Brown body formati on was induced by injection of carmine particles into the perivisceral coelom of Holothuria tubulosa. Formation begins with release of a fib rillar material by the spherulocytes. This fibrillar material acts as an extracellular matrix upon which amoebocytes and carmine particles c ollect. Amoebocytes develop an extensive pseudopodial network and prog ressively condense into aggregates with varying degrees of compactness . While condensing, amoebocytes either phagocytose or encapsulate carm ine particles. A destructive process begins once particle aggregation is complete, resulting in numerous intracellular residual bodies and e xtracellular residual body-like structures, depending upon whether the carmine particles were phagocytosed or encapsulated. Induced bodies h ave the same ultrastructural features as naturally occurring ones. Bro wn bodies are progressively eliminated to the outside through coelo-re ctal canaliculi, and the body cavity is essentially cleared of all ind uced bodies within seven days following injection.