The body wall of cnidarians consists of an outer layer or epidermis, an inner layer or gastrodermis, and a middle layer or mesoglea. Cnidarians lack organs and posses a primitive nervous system known as a neural net. Cnidarians exhibit two basic structural forms, a medusa and a polyp. The medusa form is a free-swimming structure which consists of an umbrella-shaped body (called a bell), a fringe of tentacles that hang from the edge of the bell, a mouth opening located on the underside of the bell, and a gastrovascular cavity.
Tropic of Capricorn, parallel of latitude at 23Â°30â south of the equator; it is the southern boundary of the tropics.This parallel marks the farthest point south at which the sun can be seen directly overhead at noon; south of the parallel the sun appears less than 90Â° from the northern horizon at any day of the year.ropic of Capricorn, parallel of latitude at 23Â°30â south of the equator; it is the southern boundary of the tropics.
The equator is the circle where the Sun is directly overhead at noon on the equinoxes. The Arctic and Antarctic Circles are located at Â±66.5 degrees latitude. Note that 66.5 + 23.5 equals 90 degrees. This means that on December 21, when the Sun is directly over the Tropic of Capricorn at noon, it will not be visible from the Arctic Circle. So above the Arctic Circle, there is a period during the winter when the sun remains below the horizon.