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
Venom Other insects, such as true bugs and many ants, also produce venom. At least one ant species ("Polyrhachis dives") has been shown to use venom topically for the sterilisation of pathogens. There are venomous invertebrates in several phyla, including jellyfish such as the dangerous box jellyfish and sea anemones among the Cnidaria, sea urchins among the Echinodermata, and cone snails and cephalopods including octopuses among the Molluscs. Venom is found in some 200 cartilaginous fishes, including stingrays, sharks, and chimaeras; the catfishes (about 1000 venomous species); and 11 clades of spiny-rayed fishes (Acanthomorpha), containing the scorpionfishes (over 300 species), stonefishes