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
Bacterial phyla Despite these lineages not being officially recognised (due to the ever-increasing number of sequences belonging to undescribed phyla) the ARB-Silva database lists 67 phyla, including 37 candidate phyla (Acetothermia, Aerophobetes, Aminicenantes, aquifer1, aquifer2, Atribacteria, Calescamantes, CKC4, Cloacimonetes, GAL08, GOUTA4, Gracilibacteria, Fermentibacteria (Hyd24-12), Hydrogenedentes, JL-ETNP-Z39, Kazan-3B-09, Latescibacteria, LCP-89, LD1-PA38, Marinimicrobia, Microgenomates, OC31, Omnitrophica, Parcubacteria, PAUC34f, RsaHF231, S2R-29, Saccharibacteria, SBYG-2791, SHA-109, SM2F11, SR1, TA06, TM6, WCHB1-60, WD272, and WS6), the Ribosomal Database Project 10, lists 49 phyla, including 20 candidate phyla (Acetothermia, Aminicenantes, Atribacteria, BRC1, Calescamantes, Cloacimonetes, Hydrogenedentes, Ignavibacteriae, Latescibacteria, Marinimicrobia, Microgenomates, Nitrospinae, Omnitrophica, Parcubacteria, Poribacteria, SR1, Saccharibacteria, WPS-1, WPS-2, and ZB3),