Shedd Aquarium

Longspine Urchin Scientific Name: Diadema setosum

The longspine urchin is as dangerous as it looks. The little round pin cushion-like body is guarded by over foot long sharp spines. Equipped with tiny barbs on the ends, the spines get stuck under the skin of any brave predators willing to take their chance at an attack. Once poked by a longspine urchin spine, it can only be surgically removed.

Region: Philippines

Appearance
Resembling a black pin cushion covered in thin, needle-sharp spines, this sea urchin has a relatively small body in comparison to them. The longspine urchin gets its name from these spines that can be over one foot long. The urchin also has shorter spines that hide within the taller ones. Its spines are hollow and very delicate, making it easy for any creature that bumps into them to find one lodged under their skin. Tiny hooks on the end ensure the spines remained lodged under the skin. A wound can be extremely painful and result in hours of swelling and itching. Between all the spines are tiny, pincer-like organs called pedecellarae, used for cleaning and additional defense.

The longspine urchin’s body tissue is protected by a round endoskeleton or outside skeleton called a test. About 3.5 inches (9 cm) in diameter, the test is made of skeleton-like plates that are fused together. The test is made up of 10 main sections of which five are scattered with tiny holes through which tube feet extend. Scattered over the surface of the test are microscopic, button-like dimples called sphaeridia, which are thought to help the creature balance.

Habitat
The longspine urchin lives in colonies in shallow coastal seagrass beds and coral reefs. During the day, these urchins hide in reef holes and crevices. At night they emerge to hunt for the algae that has grown that day.

Range
Longspine urchins live in the warm parts of the Pacific Ocean, Indian Ocean and Red Sea.

Diet
At night, longspine urchins feed on algae, tiny animals, waste material and rotten matter, helping keep reefs from being overgrown with algae that can smother the corals.

Sea urchins eat using five sharp wedges that come together like a beak and that are moved by muscles. This whole muscle and beak structure is called Aristotle’s lantern. Aristotle’s lantern is one of the most complex feeding structures of any animal in the world. This beak-like device allows the urchin to scrape algae off the hard reef coral and rocks. Even as the sharp wedges wear down from harsh use, they continue growing. The urchin can pull or push Aristotle’s lantern into and out of its body.

Reproduction
Longspine urchins reproduce by spawning or releasing eggs and sperm into the ocean at the same time. Females can produce millions of eggs each time they spawn. Since the egg and sperm are broadcasted into the sea, fertilization or the joining of egg and sperm to form a tiny urchin, is most likely to occur if a large number of sea urchins have gathered in the same area and spawn at the same time.

Urchins go through five growth stages before coming to be the star-shaped animals with which we are familiar. During the first month, the urchin freely floats around looking like a tiny jelly bean. It can barely be seen by the eye and feeds on tiny plants and animals floating in the ocean. The baby urchin then metamorphoses or changes shape starting to develop into a miniature adult. For the next six months, this juvenile slowly grows, finds a hidden home under reef rock and rubble, and begins feeding on algae. After they get big enough, these urchins emerge and begin to travel the reef in search food. After two years the urchin stops growing and is developed enough to reproduce.

>A species or group of organisms that is in danger of extinction or disappearing from the face of the earth in the near future if its situation is not improved.

A species that can be found throughout its natural range but is declining in number and may become endangered in the absence of special protection efforts.

A species that is not declining in number but is of special concern because it is sensitive to pressure by particular human activities or natural events.

A species that is not declining in number and is not sensitive to pressures by human activities or natural events.

Threats and Management
Large amounts of longspine urchins can over run a reef. Trying to eat algae, these urchins can scrape away at the reef and actually destroy it. Too many of these urchins can also eat all the algae on the reef, leaving none for other algae eaters like butterflyfish. The starving butterflyfish will die off, causing the animals that eat the butterflyfish to die off also. An overabundance of the urchins can cause a complete imbalance in the entire reef ecosystem. Urchin populations will explode if the animals that eat them, like triggerfish or parrotfish, are overfished or taken off the reef in large numbers. Without their predators, sea urchin populations will just keep growing.

Did You Know?
The long spines of the longspine urchin point toward anything that approaches it. These animals don’t have eyes, but they can detect changes in light.

Small fish and shrimp find a safe place to live within the sharp spines of the longspine urchin. Even bravest predator wouldn’t dare try to pick them out.

Urchins have a unique means of moving. They use an internal plumbing system called the water vascular system. It’s a system of water canals that run throughout the body. Water is sucked into the sea star through the madreporite or a small hole on the aboral surface or top of the animal. The ends of the canals can be found on the animal’s surface as tube feet. The tube feet move when there is a change in the water pressure within the canals. The tube feet of the urchin are used for movement, capturing food and breathing.

These creatures also use their spines to move. Small depressions in the test also allow for the spines to rotate freely in almost any direction. The test is covered with layers of skin and muscle that control the movement of the spines. Like oars on a boat, the urchin moves its spines back and forth to cruise the reef.

Some triggerfish, butterflyfish, parrotfish, surgeonfish and pufferfish will try to eat urchins. These fish struggle to flip over the urchin, trying to get at a soft spot, either the mouth or the anus. It can be very difficult to get a meal out of an urchin due to the dangerously long spines.

The Greek meaning of urchin is hedgehog.

References
Web Sites:
NOTE: The following Web sites are not maintained by the John G. Shedd Aquarium and will open in a new browser window.

Research by Ramkhamhaeng University, Thailand:
http://www.thaicoralreefs.com/bioerosion_bali.htm

Print Publications:
Allen, G. R. 1997. Tropical Marine Life. North Claredon, Vermont: Periplus Editions Ltd. 64p. ISBN# 962-593-157-0.

Colin, P. L. & Arneson, C. 1995. Tropical Pacific Invertebrates. Beverly Hills, California: Coral Reef Press. 296p. ISBN# 0-9645625-0-2.

Coleman, N. 1999. Dangerous Sea Creatures Aquatic Survival Guide. Australia: Neville Coleman’s Underwater Geographic Pty Ltd. 95p. ISBN# 0-947325-24-7.

Coulombe, D. A. 1984. The Seaside Naturalist. A Guide to Study at the Seashore. New York, New York: Prentice Hall Press. 246p. ISBN# 0-13-79710.

Hoover, J. P. 1998. Hawai’i’s Sea Creatures. A Guide to Hawa’i’s Marine Invertebrates. Honolulu, Hawaii: Mutual Publishing. 366p. ISBN# 1-56647-220-2.

Pechenik, J. A. 1985. Biology of the Invertebrates. Dubuque, Iowa: Wm. C. Brown Publishers. 567p. ISBN# 0-697-14203-5.

Perrine, D. 1997. Mysteries of the Sea. Lincolnwood, Illinois: Publications International, Ltd. 312p. ISBN# 0-7853-2430-5.

Vocabulary Words

Aboral surface – The topside of the body.

Broadcast – A method of reproduction in which hundreds and even thousands of eggs and sperm are released into the water where they are intended to unite.

Endoskeleton – A skeleton located outside of the body.

Extinction – An organism that has not been present on the face of the earth for over 50 years.

Fertilization – The uniting of egg and sperm to form a new individual.

Juvenile – A young version of an adult.

Madreporite – A small hole on the aboral surface that draws water into the water vascular system.

Metamorphosis – A change in the body form of an animal when changing from egg to adult.

Organism – A living thing.

Overfishing – The excessive fishing or catching of aquatic (ocean or freshwater) animals to the point that the amount of animals being caught is greater than the amount of animals born. When more animals are caught than are being born, the aquatic environment is left depleted of the targeted animals.

Pedecellarae – Small, pincer-like organs used for cleaning and defense.

Seagrass bed – A coastal ecosystem mainly inhabited by marine plants like seagrass as well as some fish, urchins, sea stars and corals.

Species – A group of organisms capable of breeding and producing fertile offspring; organisms that share the same gene pool.

Sphaeridia – Microscopic, button-like dimples that are scattered over the surface of the urchin’s test. They help in balance.

Test – Fused skeleton-like plates that enclose an urchin’s body.

Tube feet – Clear fleshy extensions of the water vascular system that have a sucker at the end.

Water Vascular System – An internal plumbing system of connected water canals that run throughout the body. The ends of the canals can be found on the animal’s surface as tube feet. This system makes moving, eating and breathing possible.