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
Starfish site and Sheffield. The new "Special Fire" decoys were set up to simulate the bomb drops of German pathfinder squadrons. By 23 January 1941 the programme had been increased to 43 sites protecting 13 town and cities and by March operational sites numbered over 100. By the end of the war there were 237 Starfish sites protecting 81 locations. One of the first decoy sites was constructed on Black Down on the Mendip Hills; it was code-named "Starfish", derived from Turner's original SF code, and built to protect the nearby city of Bristol. The Starfish name was eventually adopted to describe