Sea urchins are small and spiny animals which are found in the Oceans of all over the world. Their shell is round and spiny which ranges to a size of (3 to 10) cm. Their shells are made up of packed and fitted plates and these plates protect these species from damage. The different color patterns can be found on their body such as brown, red, green, purple, olive and black. There are five teeth on the bottom side and these teeth help them to ingest algae and also to break down the food which they consume. These species have transparent tubes known as "tube feet", which helps them to stick to the ocean floor. These tubes help them to move slowly and work as their feet. Moreover, their tubes also help them to trap food as well as help them in respiration. They are also light sensitive which helps them to move in the shadow area.
Sea urchins are mostly known to feed on algae. These species are also known to feed on bits of small sea animals and plants. These species use their five teeth to break down their food and ingest it.
These species are in the Oceans of all over the world. They have been seen in both cold and warm water. Moreover, they can be found in variety of environments. The common places where they can be found easily are on wave-exposed rocks, on coral reefs in the kelp forests rock pools and mud, and in sea grass beds. They are also seen in mud, sand or holes. These species live there, so that they can remain protected from the sea waves and currents of water. These urchins live in these holes or crevices during the day and feed themselves mostly at nights. These urchins are common on the reefs of Hawaii, Australia and of the Caribbean.
The sea urchins are known to reproduce sexually. They have five gonads which secrete sperm or eggs. But, the fertilization is external. First, the males release their sperm and after that the females release million of jelly-coated eggs. The eggs and sperm meet and fertilize externally. After the fertilization occurs the larvae is formed, and this larvae is called as a pluteus. These species become mature to reproduce at the age of (2-5) years. The sex of these species is identified only when these species release eggs or sperm.
These species are currently not in the list of endangered species, but in the past, these species decreased tremendously in their numbers, due to increase in pollution level and hurricane. But, due to increase in the pollution level and global warming, these species may come in the endangered list in the near future.
The sea urchins play an important role in the ecosystem. These species have several predators and if urchins become distinct, then all their predators will also become extinct. Those predators are star fish, sea otters, etc. Thus in order to keep a healthy balance in the environment it is very necessary to keep the balance of their population.