The tail has haemal arches, a feature lost in all other modern turtles.
The water vascular system, haemal system and perihaemal system form the tubular coelomic system.
Haemal and perihaemal systems are derived from the coelom and form an open and reduced circulatory system.
It consists of five tail vertebrae, a sacral vertebra, a left humerus, haemal arches and rib fragments.
Crinoids also possess a separate "'haemal system "', consisting of fluid-filled sinuses within the connective tissue.
It includes a partial anterior cervical vertebra, multiple caudal vertebrae and five haemal arches, a nearly complete pelvis, and the left femur.
Many mammals have tiny spleen-like structures known as haemal nodes throughout the body that are presumed to have the same function as the spleen.
In the caudal region, elongate transverse processes take the place of ribs, and the haemapophyses are paired, one on each side of the haemal canal.
A central haemal ring surrounds the pharynx next to the ring canal of the water vascular system, and sends off additional vessels along the radial canals beneath the ambulacral areas.
Phagocytic coelomocytes, somewhat similar in function to the white blood cells of vertebrates, are formed within the haemal vessels, and travel throughout the body cavity as well as both circulatory systems.