Tag Archives: phylogeny

The first molluscs probably arose during Precambrian times because fossils attributed to Mollusca have been found in geological strata as old as the early Cambrian period. On the basis of such shared features as spiral cleavage, mesoderm from the 4d blastomere, and trochophore larva, many zoologists argue that Mollusca are …

Sponges originated before the Cambrian period. Two groups of calcareous spongelike organisms occupied early Paleozoic reefs. The Devonian period saw rapid development of many glass sponges. Phylogenetic studies 2 using sequence data from large subunit rRNA, small subunit rRNA, and protein kinase C, indicate that sponges with calcareous spicules in …