Marine life individuals per square meter and accounting for about 80% of all individual animals on earth, their diversity of life cycles, and their presence at various trophic levels point at an important role in many ecosystems. Echinoderms (Greek for "spiny skin") is a phylum which contains only marine invertebrates. The adults are recognizable by their radial symmetry (usually five-point) and include starfish, sea urchins, sand dollars, and sea cucumbers, as well as the sea lilies. Echinoderms are found at every ocean depth, from the intertidal zone to the abyssal zone. The phylum contains about 7000 living species, making it the second-largest
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