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The mesohyl, formerly known as mesenchyme or as mesoglea, is the gelatinous matrix within a sponge. It fills the space between the external pinacoderm and the internal choanoderm . The mesohyl resembles a type of connective tissue and contains several amoeboid cells such as amebocytes , as well as fibrils and skeletal elements.
The mesohyl functions as an endoskeleton in most sponges, and is the only skeleton in soft sponges that encrust hard surfaces such as rocks. More commonly the mesohyl is stiffened by mineral spicules , by spongin fibers or both.
In order to differentiate the use of the word mesenchyme in vertebrate embryology (that is, undifferentiated tissue found in embryonic true [ento-]mesoderm from which are derived all connective tissues, blood vessels, blood cells, the lymphatic system, and the heart) and the use in invertebrate zoology (a more-or-less solid but loosely organized tissue consisting of a gel matrix [the mesoglea ...
The mesenchyme originates from the mesoderm. [6] From the mesoderm, the mesenchyme appears as an embryologically primitive "soup". This "soup" exists as a combination of the mesenchymal cells plus serous fluid plus the many different tissue proteins.
Repeated cleavage of the zygote egg takes place in the mesohyl and forms a parenchymella larva with a mass of larger internal cells surrounded by small, externally flagellated cells. The resulting swimming larva enters a canal of the central cavity and is expelled with the exhalant current.
Three grades of organization, asconoid, syconoid, and leuconoid, reflect the degree of elaboration of the choanoderm layer and mesohyl. In the asconoid plan the interior water space, or atrium, is large and unpartitioned. In the syconoid plan the periphery of the atrium is divided into numerous small flagellated chambers with increased surface ...
Pinacocytes are filled with mesohyl which is a gel like substance that helps maintain the shape and structure of the sponge. [3] Types. Basipinacocytes. These are the ...
In most cases, the first growth phase is intracellular; it starts in sclerocytes (amoeboid cells responsible for spicule formation) in mesohyl [74] [75] and is mediated by silicatein, a special enzyme that initiates formation of the axial filament (harboured by the axial canal) which provides the vertical axis of the spicule. [76]