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
Branching order of bacterial phyla (Woese, 1987) Branching order of bacterial phyla (Woese, 1987) There are several models of the Branching order of bacterial phyla, one of these was proposed in 1987 paper by Carl Woese. The branching order proposed by Carl Woese was based on molecular phylogeny, which was considered revolutionary as all preceding models were based on discussions of morphology. ("v." Monera). Several models have been proposed since and no consensus is reached at present as to the branching order of the major bacterial lineages. The gene used was the 16S ribosomal DNA. The names have been changed to reflect more current nomenclature used by