"Isodictya Edwardii, Bowerbank.
Sponge. Sessile, parasitical, coating. Surface uneven, hispid. Oscula inconspicuous, simple, dispersed. Pores inconspicuous.. Dermal membrane pellucid, sparingly spiculous; tension spicula acuate, long, and slender; retentive spicula bidentate equi-anchorate, slender, minute, few in number. Skelton. Diffusive and irregular; primary lines multispiculous; secondary lines very irregular, occasionally bi or trispiculous; spicula acuate, rather long. Interstitial membranes. Tension spicula rather abundant, acuate, variable in size; retentive spicula same as those of the dermal membrane, very few in number. Germmules membranous, aspiculous.
Colour. – Dried, ochreous yellow.
Habitat. – Banff, Scotland, Mr. T. Edward.
Examined. – In the dried state.
This sponge coats the stems of Tubularia for the length of seven inches, at no part exceeding two lines in thickness. Its general aspect in the dried state is rough and irregular in consequence of the prominent hispidation of its surface, produced by the prolongation of the primary lines of the skeleton beyond the dermal membrane, frequently to the extent of the length of two or three times that of a spiculum. The oscula are not visible without the aid of a lens of an inch focus. The construction of the skeleton is very irregular and diffusive, and the secondary lines especially, and to such an extent as to frequently render it difficult to decide whether they are really secondary skeleton lines or dispersed skeleton spicula. The skeleton spicula are regularly acuate and rather slender. The retentive spicula are not visible in a fragment of the sponge immersed in water, and it is only when mounted in Canada balsam that they can be distinctly seen in situ in the dermal membrane, on which they are not equally dispersed, but occur in clusters at intervals. In the interstitial membranes they are very few in number, and rarely more than one occurs in the field at the same time.
There is a considerable degree of resemblance in the descriptions of I. Alderi and I. paupera to that of I. Edwardii, which may possibly lead to a doubt in the mind of the student as to which of the three the specimen he might have under examination belonged; but a comparison of the spicula alone of these three species readily distinguish each from the other. The length of the spicula of I. Edwardii as compared with those of both I. paupera and I. Alderi is as seven to five, and although thus much longer, the diameter is less than either of the spicula of the other two species, and the form is much more purely acuate.”
(Bowerbank, 1866)
