Themesohyl, formerly known asmesenchyme or asmesoglea, is the gelatinous matrix within asponge. It fills the space between the externalpinacoderm and the internalchoanoderm. The mesohyl resembles a type ofconnective tissue and contains severalamoeboid cells such asamebocytes, as well asfibrils andskeletal elements. For a long time, it has been largely accepted that sponges lack truetissue, but it is currently debated as to whether mesohyl andpinacoderm layers are tissues.
The mesohyl is composed of the following main elements:collagen, fibronectin-like molecules,galectin, and a minor component,dermatopontin. Thesepolypeptides form theextracellular matrix which provides the platform for specificcell adhesion as well as forsignaltransduction andcellular growth.
The mesohyl includes a noncellular colloidalmesoglea with embedded collagen fibers, spicules and various cells, being as such a type ofmesenchyme.[1]
