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
Rudolf Leuckart of Parasitology). Leuckart is credited with splitting George Cuvier's "Radiata" into two phyla: Coelenterata and Echinodermata. As a scientist, his provided excellent descriptions of morphologic details giving credence to the idea that zoological evolution can be learned through its anatomical changes. Between 1877 and 1892, he developed a series of zoological wall charts that have been used worldwide as teaching aids. In the field of entomology, he conducted investigations into the micropyle and fertilization of insect eggs, the reproduction and development involving members of Pupipara, parthenogenesis among insects, and studies on the anatomy and life history of the honeybee. A