The wall of the tubes is thick (100 Mm). In some areas the tubes are hispid.

Cells with yellow granules are present in the mesohyl, as are embryos (138/75 Mm), which are always found near choanocytes. The cells with yellow granules are distributed homogeneously throughout the mesohyl.

The skeleton comprises equiangular and equiradiate triactines (Fig. 18A). Tetractines are also present, but they are rare (Fig. 18A). Actines are conical or cylindrical, but they always have sharp tips. Sometimes, they are slightly undulated. Diactines are abundant on the external tubes (Fig. 18B); they are curved or straight, vary in size and have sharp tips, one of which is club-shaped (Fig. 18C). The largest diactines are curved at the tip. They project through the surface in some parts of the cormus only, and the club-shaped portion of the spicule lies inside the tube.

Remarks: We did not find oscula in the lectotype, although Dendy (1891) described ‘very small, round apertures, situated on the apices of small papillae formed by the anastomosis of several Ascon-tubes’, which we understand to be water-collecting tubes.

Dendy drew attention to the similarity between C. dubia and C. cavata Carter, 1886, in relation to the presence of ‘great numbers of ‘yellow granules’ embedded in the mesoderm’. He even supposed that C. dubia could be a young form of C. cavata. We do not agree, since C. cavata is not even a Clathrina, but an Ascaltis. The curious point about this subject is that Wörheide & Hooper (1999) described some cells for C. adusta (another Australian species) that we consider very similar to those found in C. dubia and Ascaltis cavata.