Monaxon

The monaxons are all of large size, being at least twice as thick as the basal rays of the triradiate systems, and not less than 300 μ in length, allowing for those which are apparently not full-grown.

Source: wiktionary

In this sponge the ordinary monaxons vary greatly in size but agree in their characters, and form one class in which every gradation can be found between the two extremes of size. […] Again, his fig. 25, intended to represent a large monaxon with many cells on it, is not convincing to me, as it is not possible with the magnification given (300) to determine the relation of the cells to the spicule.

Source: wiktionary

A desma consists of an ordinary minute monaxon, triradiate or tetraxon spicule called crepis, on which layers of silica have been deposited irregularly.

Source: wiktionary