Axial canal

Definition

Most siliceous sponge spicules are formed around a proteinaceous axial filament that, after decay, leaves an axial canal a few micrometers in diameter. It can be observed in both extant and fossil sponge spicules. In D., the axial canal is triangular or hexagonal in cross section, whereas in H. it is square. In fossil spicules, the a. c. is bigger and its shape is typically less well defined due to diagenetic processes; see also axial filament.

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