Endoskeleton three phyla and one subclass of animals, endoskeletons of various complexity are found: Chordata, Echinodermata, Porifera, and Coleoidea. An endoskeleton may function purely for support (as in the case of sponges), but often serves as an attachment site for muscle and a mechanism for transmitting muscular forces. A true endoskeleton is derived from mesodermal tissue. Such a skeleton is present in echinoderms and chordates. The poriferan 'skeleton' consists of microscopic calcareous or siliceous spicules or a spongin network. The Coleoidae do not have a true endoskeleton in the evolutionary sense; there, a mollusk exoskeleton evolved into several sorts of internal
Bacterial phyla CPR3, Kazan, Perigrinibacteria, SM2F11, WS6, and WWE3 were more recently proposed to belong to the larger CPR Group. To complicate matters, it has been suggested that several of these phyla are themselves actually superphyla (see the section on cryptic superphyla below). The proposed superphylum, Terrabacteria, includes Actinobacteria, Cyanobacteria, Deinococcus–Thermus, Chloroflexi, Firmicutes, and candidate phylum OP10. It has been proposed that several of the classes of the phylum Proteobacteria are phyla in their own right, which would make Proteobacteria a superphylum. It was recently proposed that the class Epsilonproteobacteria be combined with the order Desulfurellales to create the new phylum Epsilonbacteraeota.