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
Libbie Hyman masterly integration of information." Declining health did not allow her to finish the entire subject. In it she developed her scientific theory that the Phylum Chordata, including all vertebrates, was evolutionarily related to the apparently very different and very much more primitive Echinodermata, such as starfish. This group is now known as the deuterostomes. Her theory was based upon the morphological data of classical embryology, and has since been confirmed by molecular sequence analysis. In addition to her major project, Hyman extensively revised "A Laboratory Manual for Comparative Vertebrate Anatomy" in 1942 into a textbook as well as laboratory manual;