5 Jul 2016

Green Sea Urchin - Interesting Facts

Green Sea Urchin

Strongylocentrotus droebachiensis Facts

Green sea urchin or Strongylocentrotus droebachiensis is named so because of its greenish color. It is an inhabitant of cold oceans- in the Northern part of the Atlantic and Pacific. It is mainly an algae and seaweed eater that can also eat other types of food. The green color made it look like a marine cactus!


The average size of a grown up green sea urchin is 4.5 cm to 5.3 cm (1.8 to 2 in). The biggest one ever recorded has a diameter of 8.7 cm or 3.4 in.  That diameter is measured without calculating the length of the spines. The size is depended on the availability of food and density of predators.

Habitat and Distribution

Green Sea Urchin Facts

Green sea urchins used to live in cold waters of the sub Polar Regions. They live in Northern cooler part of the Pacific and Atlantic Ocean. Some also live in the Arctic too.

The sea animal can be found in rocky sea beds. They often live in the low depth tidal zones. But some can inhabit sea beds below 1200 m of water.


Green Sea Urchin is a green food eater. They mainly feed on various types of sea weeds. But do not think that they are herbivorous creatures. They will gladly feast on other small sea invertebrates like mussels, barnacles, sand dollars, sponges etc.


Strongylocentrotus droebachiensis

The green sea urchin is globular in shape.  The two ends of the globe are slightly flattened. The animal lives face down. The face is on the bottom side and the anus is on the top.

The spine of a Strongylocentrotus droebachiensis has no venom. But its hard and pointed edge can still hurt or severally wound a small fish. These spines are used like spears by the urchin. These are also used for locomotion, too.

Tube Feet

The creature has special organs called tube feet. Tube feet have two parts - ampulla and podia. There are muscles to control the organ in the ampulla. It is the base of the organ. Podia are extended from the ampulla. Tube feet help to grab food to its mouth and for small movements.


Another curious organ is pedicellaria. These are small pincher shaped movable jaws on the test of the urchin. These organs can pinch or bite anyone or anything that passes the wall of the spines to the body of the urchin. These can be poisonous too. These help to make its defense system stronger. Curious thing about a pedicellaria is that is not connected with the main nervous system of the sea urchin, these organs are independent.

Aristotle's Lantern

S. droebachiensis has a special jaw or tongue like organ named Aristotle's Lantern. The lantern has several teeth and a hard body made of calcium. It is used to cut and grind food into small bits to digest. The urchin goes on top of its food and then uses the organ to scrap morsels of it into its mouth.


Green sea urchins under the ocean

S. droebachiensis has five gonads for reproduction purposes. These are protected by genital plates. The creature releases sperm and egg in the water. The fertilization takes place in the water outside the body. The best season of reproduction is early spring.

The larva is called an echinoplutes. It is a simple free swimming organization. It grows into many complex stages to become a stationary sea urchin. The process takes several months.

Some More Fun Facts About Green Sea Urchins

  • Green sea urchins are edible and so being eaten by native people of the colder regions and Japan. There is a growing Green sea urchin catching industry in USA. It is now termed as the "green rush".
  • These urchins cannot withstand high salinity. So, they flourish in low salinity areas.
  • They create their own caves or holes by drilling rocks using the Aristotle’s lantern. They come out of the hole in search of food and then return back into it.
  • They have no blood in their body. Sea water is used to do all the job of blood in their body.
  • Strongylocentrotus droebachiensis has no brain. A circuit of nerve rings operates the creature.
  • It can detect touch, smell, chemicals and light though they have no ears, tongue or eyes.
  • Green sea urchins have many predators. Some sea stars, crabs, many types of fishes etc feast on them.
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