IN VITRO STUDIES ON THE EFFECTS OF CELL-FREE COELOMIC FLUID, CALCIUM, AND/OR MAGNESIUM ON CLUMPING OF COELOMOCYTES OF THE SEA STAR ASTERIAS FORBESI (ECHINODERMATA: ASTEROIDEA)

¹ Department of Biological and Environmental Sciences, Western Connecticut State University, Danbury, CT 06810

In asteroid echinoderms the loss of coelomic fluid due to injury is prevented by the clumping of coelomocytes at the site of the wound. Plasma (cell-free coelomic fluid = CF) coagulation has not yet been demonstrated in these animals. An in vitro system was used to quantify the effects of CF, Ca²⁺, and/or Mg²⁺ on coelomocyte clumping in the sea star Asterias forbesi.

The results show that the coelomocytes of A. forbesi require threshold levels of Ca²⁺ and/or Mg²⁺ for clumping in vitro, and these levels depend on whether the ions are used separately, in combination, or as components of CF. The findings also suggest that the in vitro coelomocyte clumping is mediated by a factor present in CF which requires Ca²⁺ and Mg²⁺ to be effective. A two-phase clumping, consisting of a fast phase followed by a slow phase, is also demonstrated.

The observed biphasic clumping is explained by the existence of two functional subpopulations among the coelomocytes which differ in their permeability characteristics and ability to establish surface adhesiveness for clumping. Morphological identities of these two subpopulations remain to be ascertained.