Also known as serpent stars, or ophiuroids
Although ophiuroids resemble starfish, they are quite different from them.
First, they move with their flexible arms, whereas starfish use tube feet attached to their rigid and practically immobile arms.
Also, starfish have separate digestive and excretory systems, while brittle stars use a single opening for consumption and excretion because their digestive systems are not fully developed.
1.Brittle stars appeared on Earth in the early Ordovician era about 500 million years ago.
The oldest known representative of the group is Pradesura jacobi, which lived between 478,6 to 644 million years ago. Unfortunately, there are not many brittle star fossils as dead animals were quickly consumed by their living counterparts.
2.They are widespread over the globe.
They can be found in cold, polar waters as well as in warm tropical environments.
3.There are over 2000 discovered species distributed around the world.
Scientists estimate that there might be over 3000 species in total.
4.Serpent stars have very different body colors.
There are individuals black, white, brown, blue, red with dotted and striped patterns.
5.Despite they resemble starfish, they are different organisms.
Their body is symmetrical, divided into five segments. The Center of an ophiuroid most often resembles a disk and is the thickest part of its body. Here are located most crucial organs of an animal - and that is what differs brittle stars from the starfish.
6.The disk can be round or pentagonal.
Depending on the species, its size may range from 3 mm to 15 cm in diameter.
7.The mouth is located on the underside of a disc.
They are equipped with five toothed jaws and are used for both food intake and excretion. Each jaw is made of skeletal plates and one of them hosts the madreporite.
8.The madreporite is a sieve plate with numerous holes that are a part of the skeleton of most echinoderms.
In most present-day species it is located at the apex of the upper side of the body, only in brittle stars, it is located beneath the body.
9.Brittle star stomach is divided into ten pouches where food is digested.
The stomach makes up most of the ophiuroid disc.
10.They live on many depths, can be even found 6 kilometers underwater.
Most of them live in shelf waters (over 1300 species), bathyal zone (over 1200 species). In the abyssal waters (below 4000 m) so far 100 species have been found.