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Facts About Sea Urchins

Sujata Iyer
A sea urchin is a gorgeous marine animal. To know some facts about it, read on here.
The very thought that comes to mind after hearing the words 'sea urchin', is a mythical sea creature, that surfaces maybe just once in a hundred years. A person not familiar would think it as a fierce and venomous creature, that attacks at the slighest or even without provocation.
Breeding in colonies, they fiercely protect their territory in the water by warding off any evil predators that may come wandering. Sounds fascinating, doesn't it?
As most childhood fantasies turn out, sea urchins turned out to be anything but mythical creatures! Quite the opposite, in fact. Sea urchins are considered a very integral part of marine biology, not to mention those gorgeous shells that we see adorning tables as embellishments.
There's a lot that we don't know about sea urchins, which can make them quite misunderstood. For instance, did you know that though considered extremely poisonous by many, it is only the Asteroidea, Echinoidea, and Holothuroidea classes that can cause some serious damage with the venom that they squirt?

Facts About Sea Urchins


  • A sea urchin is a marine animal which belongs to the Echinodermata phylum, Echinoidea class and order Echinoida.
  • Other family members include the sea cucumber, sea star and sand dollar.


  • They are found all over the world.
  • There are more than 200 varieties of sea urchins.
  • They live in the deep parts of the ocean but are also found in the shallow parts.
  • They prefer to live in coral reefs and areas that are more prone to tidal waves.

Physical Appearance

  • Their body structure is globular with long spikes protruding out of it. This structure is generally hard. The spikes protect them from predators.
  • The average size of a sea urchin is 4-5 inches.
  • They have 5 teeth and a flabby structure resembling a tongue at the oral opening which is taken to be a mouth.
  • According to Aristotle's description of the oral opening, it is termed as 'Aristotle's lantern'.


  • No locomotive organs like legs are seen on a sea urchin, but experts believe that it uses its spikes and small tube feet to move around easily in the water.
  • Even a slight movement near it will elicit a strong reaction from it. The spikes give an instant reaction and it moves away immediately.


  • Slate pencil urchin
  • Caribbean sea urchin
  • Sea potato
  • Purple sea urchin
  • Red sea urchin (longest living)


  • Sea urchins are omnivores, i.e., they eat plant and animal matter.
  • So, they are perfect scavengers and feed on whatever they find in the ocean.
  • The general diet of a sea urchin includes algae.
  • In fact, they are mainly responsible for the regulation of algae in the oceans.
  • Apart from algae, they also like to feed on seaweed, kelp, sand and mud.
  • They also eat dead fish or different types of sponges and mussels found in the ocean.


  • Though a sea urchin is a peace loving animal, it is in constant danger of being eaten by bigger fish in the sea.
  • Its main predators are sea otters, starfish, triggerfish, sea turtles, wolf eels and almost any other fish that is bigger than it.
  • But their biggest predators are humans. They are believed to be strong aphrodisiacs, and hence sea urchin farming is carried out extensively.
  • Japanese food, sometimes includes sea urchins as a refined delicacy.


  • Sea urchins have a unique way of reproduction. First, the males release their sperm into the water.
  • The females, then come and release their eggs in the vicinity of the sperm.
  • If the sperm and the eggs touch each other, then a baby urchin will be born.
  • They carry out reproduction in groups, so that the chance of the eggs and sperm uniting are increased.
The eggs and gonads (organ that produces gametes) are considered quite a delicacy in Japan. Apart from food, the shells that remain after the sea urchin dies are used as decorations. So, as you can see, there's a lot more to a this marine creature than its mere spiky appearance. Let's preserve them and do our bit in maintaining the balance of the ecosystem.