Clot Formation in the Sipunculid Worm Themiste petricola : A Haemostatic and Immune Cellular Response

Abstract EN

Clot formation in the sipunculid Themiste petricola, a coelomate nonsegmented marine worm without a circulatory system, is a cellular response that creates a haemostatic mass upon activation with sea water.

The mass with sealing properties is brought about by homotypic aggregation of granular leukocytes present in the coelomic fluid that undergo a rapid process of fusion and cell death forming a homogenous clot or mass.

The clot structure appears to be stabilized by abundant F-actin that creates a fibrous scaffold retaining cell-derived components.

Since preservation of fluid within the coelom is vital for the worm, clotting contributes to rapidly seal the body wall and entrap pathogens upon injury, creating a matrix where wound healing can take place in a second stage.

During formation of the clot, microbes or small particles are entrapped.

Phagocytosis of self and non-self particles shed from the clot occurs at the clot neighbourhood, demonstrating that clotting is the initial phase of a well-orchestrated dual haemostatic and immune cellular response.