FIG. 29 in A revision of the supraspecific classification of the subclass Calcaronea (Porifera, class Calcarea)

FIG. 29. — Diagram of one parasagittal (p) and two sagittal (s) spicules in Heteropiidae. The arrow indicates the unpaired angle, and u indicates the unpaired actine. The double line represents the cortex (cx). Note that the two paired actines of the parasagittal spicules are of quite different sizes, and they are always in a subcortical position with the longer paired actine directed inwards.