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
Cairo spiny mouse Red List of Threatened Species, lists it as being of "Least Concern". A recent study, still under peer review at the time of writing, indicates that this species could become a candidate animal model for the human menstrual cycle. It exhibits a 9-day cycle, and is the first rodent found to have such a cycle. Gene sequencing is currently underway to investigate this, and other unique physiological traits displayed by this species. Cairo spiny mouse The Cairo spiny mouse ("Acomys cahirinus"), also known as the common spiny mouse, Egyptian spiny mouse, or Arabian spiny mouse, is a nocturnal species of