Type B

This body is somewhat rounded leaf like structures with a leathery surface. The specimens show radial symmetry and a skeleton of spongin fibers. Spicules are absent (Fig. 3, Plate 1, Figs. 2, 5 and 7). The canal system may be of Leuconoid type.

The present specimens resemble with leaf sponge, Phylospongia of subclass Karatosa that are known as horny sponge. Spongin fibers are protein secretions of amoeboid cells, which form anatomizing network on the body wall. They are resistant to digenesis and decay and resemble hair and silk in chemical composition.

The Buxa dolomite is well exposed in Arunachal Pradesh as windows or linear belts from Kameng District in the west to Siang district in the east. Cherty bands, oolites, stromatolites and interaclasts characterize this dolomite. The stromatolites and microbiota are known from Kameng area and the Menga window in the Upper Subansiri District. Recently an assemblage of diversified organic-walled microfossils has been recovered in petrographic thin sections of lenses and bedded chert belonging to the Buxa Dolomite exposed near Igo Bridge, Daring - Basar road in West Siang District of Arunachal Pradesh. This assemblage which shows dominance of the spinated forms and coiled cyanobacterial remains viz. Obruchevella indicates Vendian age for these beds. The non-mineralized sponges are being reported for the first time from the same location. The assemblage of these fossil specimens represents three types of extinct sponge forms.

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