Long-spined sea urchin

The Long-spined sea urchin, also known as the black long-spined sea urchin, is a species of sea urchin in the taxonomic Class Echinoidea. They are often kept as pets, despite the fact they are covered with venomous spines. They are often referred to as the 'hedgehogs of the sea'. The long-spined sea urchins play a very important part in many coral reef's ecosystem, especially in Bermuda. They give shelter to many small fish and other ocean creatures and keep algae from suffocating the coral.

Anatomy
The long-spined sea urchin (Diadema antillarum) has a disc shaped body that is two inches in diameter. The body is covered in two to four inch spines that are covered in small barbs. These spines are fragile and easily break off but they are nevertheless venomous. The anus is surrounded by shiny, blue rings. They may look sessile at first glance but can actually move in two different ways, both by using their spines and by using their tube feet. The tube feet are very sensitive and thin. The feet covering the bottom half of the long-spined sea urchin are extremely adhesive and can extend out of the body for walking and grasping, while tube feet on the top of the body are less adhesive and used more for respiration. 

Reproduction
Long-spined sea urchins assemble into herds when it is time to mate. The males and females release their sperm and eggs into the water. For reproduction to occur the sperm and eggs must be released into the water at the same time. To make sure this happens, the male or females send chemicals into the water, which causes all male and females close enough to smell this chemical to release their sperm and eggs. They can mate at anytime of the year but seem to mate the most from February to May. After the egg is fertilized it becomes a blastula, which is free swimming. Next it develops into the echinopluteus stage where it has between 4 and 6 pairs of arms. in about a month it begins to sink and becomes a sea urchin. These sea urchins begin to grow very quickly a first, 5mm in the first month. Young long-spined sea urchins are shy and secretive, only coming out of crevices to feed. 

Ecology
These sea urchins live in the Indian and Pacific Ocean, from Asia to Australia, and also the coast of South America. Long-spined sea urchins were once extremely common off the coasts of Bermuda but after some pathogen, which is still a mystery to the science community, attacked theses creatures in 1983 their sightings have decreased a notable amount. The sea urchins began to cease eating and shed patches of skin. They live in shallow water, attached to rocks in coral reefs and beds of sea grass to hundreds of meters under the ocean. Dark colored urchins live on sand and lighter ones live in water or in cracks and crevices of rocks. Long-spined sea urchins graze on algae, scraping it off of hard surfaces. They avoid eating algae off of places that have been eaten from the night before. They and are nocturnal, coming out at night, for the most part but can eat at anytime of the day. The life expectancy is five years for these sea urchins. Their predators are uncommon because of their spines, but include gastropods, crabs, starfish, surgeonfish, porcupine fish, and wrasses. Small creatures, such as shrimps and small fish live between the spines of long-spined sea urchins to hide from predators. 

Relationship with Humans
Long-Spined Sea Urchin's spines are venomous and can cause infection when stepped on, as their very, very sharp spines can crumble after piercing into your skin, causing very severe pain, burning, throbbing, numbness, and in rare cases, paralysis. They do not intentionally try to harm humans unless they feel threatened. Although they can cause harm to humans they also benefit us, even if their affects are not direct. For example; when a large amounts of long-spined sea urchins are removed from a section of coral reef the algae will spread and overtake that part of coral reef, messing up and changing the food chain in that region. Sea Urchin's ovaries are eaten in many Asian countries as an expensive delicacy. It is usually eaten raw or with egg. The larvae if these urchins have been used for medicine in embryology and molecular biology research and also biomedical.