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
Conserved signature indels subgroups within the phylum Thermotogae. Main-line CSIs are those in which a conserved insert or deletion is shared by several major phyla, but absent from other phyla. Figure 2 shows an example of 5aa CSI found in a conserved region that is commonly present in the species belonging to phyla X, Y and Z, but it is absent in other phyla (A, B and C). This signature indicates a specific relationship of taxa X, Y and Z and also A, B and C. Based upon the presence or absence of such an indel, in out-group species (viz. Archaea), it can