Spicules are tiny needle-like elements of silica forming the sponge skeleton.
Body spicules are termed megascleres (M) or microscleres (m), depending on their size. Spicules in the outer coat of the gemmule are called gemmoscleres (g or g1, g2 if differing).
- Shaped like an axle with a disk at each end
- Shaped like a dumbbell with hooks at the tips
- Of 2 kinds, both the axle-with-disks kind and the hooked kind
- Lacking structures at the tips