Animal mesoderm forms by enterocoelic pouching, through invagination of the endoderm. The main deuterostome phyla are the Echinodermata and the Chordata. Echinoderms are exclusively marine and include starfish, sea urchins, and sea cucumbers. The chordates are dominated by the vertebrates (animals with backbones), which consist of fishes, amphibians, reptiles, birds, and mammals. The deuterostomes also include the Hemichordata (acorn worms). The Ecdysozoa are protostomes, named after their shared trait of ecdysis, growth by moulting. They include the largest animal phylum, the Arthropoda, which contains insects, spiders, crabs, and their kin. All of these have a body divided into repeating segments, typically
Spiny orb-weaver the smaller male lacks the spiny projections and instead has four to five stubby dark projections. Orb-weavers' bites are generally harmless to humans. , the World Spider Catalog accepted the following species: Spiny orb-weaver Spiny orb-weavers is a common name for Gasteracantha, a genus of spiders. They are also commonly called spiny-backed orb-weavers, due to the prominent spines on their abdomen (compare genus "Isoxya"). These spiders can reach sizes of up to in diameter (measured from spike to spike). Although their abdomen is shaped like a crab shell with spikes, it is not to be confused with a crab spider.