A minute spine.

(I,II) Fig. 90 A very small spine. The difference between spine and spinule is an arbitrary one. Like spines, spinules are also found on setae and on resting spores. In a few cases, such as C. rigidus and C. diadema, spinules may be scattered on the surface of some vegetative valves; they are usually at the limit of light microscope resolution.

minute spine, often broadened at base.

A small sharp projection.