The tri- and quadriradiates of Leucosolenia complicata are described in four aspects: surface view, transverse view, side view, and planar view. The spicule form and size vary with the distance from the oscular edge in all four cases.
In planar view (when the eye is directed along the optic axis) the spicule rays usually appear straight and thus exhibit a tendency to grow in planes which intersect in a line having the direction of the optic axis. The angle between the oscular ray planes (the planar angle) is always greater than 120° and the spicules hence belong to the ‘secondary sagittal’ class of von Ebner. The planar angle is not closely correlated with the optic angle and varies from about 160° at the oscular edge to about 1400 at the base of the tube. This variation precludes the possibility that the angle is simply controlled by the crystallizing properties of calcite.
The curvature of the choanoderm is a factor controlling spicule form because the formative calcoblasts move in contact with this layer when secreting their respective rays.
Reasons are given for returning L. coriacea (Montagu) to a separate genus, Clathrina.