Sea urchins are tiny water creatures found in oceans in different parts of the world. They belong to the phylum echinodermata which makes them closely related to sea stars, crinoids and other members of the phylum. Belonging to the sub-phylum echinozoa, sea urchins are further divided into several sub-classes. Furthermore, over seven hundred species of the animal are found.

Physical Appearance of Sea Urchins

Sea urchins are referred to as hedgehogs of the sea owing to the presence of spines which cover their entire body. They are small creatures with a spherical body which varies from 3 to 10 centimeters in diameter. They may be black, brown, red, pink or purple in color. The distinguishing physical traits of sea urchins are discussed below.

Test

The skeleton of a sea urchin is referred to as its test. It is composed of plates of calcium carbonate fused together to impart hardness to the skeleton. The test is covered by a thin layer of epidermis.

Shell

The shell of a sea urchin is found within the rigid test. The shells are also composed of plates fitted together tightly in order to provide protection to the organism from physical damage. Spines outline the shells and help the animal camouflage or fight predators. Each spine ranges from 1 to 3 centimeters in length with a width of 1 to 2 millimeters on average.

Teeth

The tiny organism also possesses a set of five teeth which are found at the bottom of the body. As in the case of all other organisms, sea urchins use their teeth to ingest and breakdown food material. Interestingly, the teeth keep on growing throughout the lifespan of the animal. The arrangement of the teeth is in a circular form which is referred to as Aristotle’s lantern.

Tube Feet

Hundreds of transparent tubes emerge from ambulacral grooves found on the sea urchin’s test. The length of these tubes is much longer than the animal’s spines and they serve various purposes. Since they help the organism move, they are referred to as “tube feet”. They serve the following several purposes.

  • Sea urchins move with the help of their tube feet. The movement of the feet is carried out by water vascular system which makes use of hydraulic pressure for the purpose of pumping water in and out of the tubes. This enables the tube feet to bring about movement.
  • The organism sticks to the ocean bottom with the help of its tube feet. This provides protection against being washed away by waves and currents.
  • Tube feet help in trapping food particles.
  • The tubes also help in the process of respiration.

Facts about Sea Urchin Habitat

Sea urchins possess a strong ability to adapt to different conditions. Due to this reason, they are found in oceans all over the world regardless of the type of environment and temperature of water. They are found on coral reefs, in rock pools, on rocks exposed by waves and in muddy areas. In addition, they are present in different depths of oceans.

Following facts reveal more information about the habitat of sea urchins.

  • Mostly, the animal thrives in areas where abundant food sources are found.
  • More commonly, large populations of sea urchins are found on coral reefs in Hawaii, Australia and the Caribbean.
  • The species Cidarisabyssicola can be found at the depth of thousands of meters in oceans.
  • Pourtalesiidae is a unique sea urchin family with its home at the deepest areas of the sea. In the Java Trench, this family was found flourishing at a depth of 6,850 meters.
  • Sterechi nusneumayeri or polar sea urchin can survive in the freezing temperatures of the polar seas.
  • Shingle urchin is one of the rare varieties of the animal which can survive for many hours outside the water. It possesses special resistance to waves.
  • Although different varieties of sea urchin can survive in various types of marine ecosystems, a large number of populations are found on the coastlines of the temperate as well as tropical regions. In addition, despite their ability to survive in deep waters, sea urchins mostly reside near the surface owing to the presence of photosynthetic sources of food.

Facts about Sea Urchin Diet

Being omnivores, sea urchins feed on tiny plants and animals found in the sea. Mostly, their diet comprises of algae and sea weed which is found at the surface of oceans. During the unavailability of their favorite food, several species of sea urchins turn to new food varieties which may include remains of dead animals, sponges, mussels, sea cucumbers and other tiny ocean creatures.

Fact about Sea Urchin Reproduction

The mode of reproduction for sea urchins is sexual and two different genders exist. The animal attains sexual maturity between the ages of two to five years. The females release their jelly-coated eggs in the water while the males release their sperms. Upon their successful union, the eggs are fertilized. A fertilized egg develops into a larva which is also referred to as pluteus. At the larval stage, individuals cannot be distinguished as males or females until they attain sexual maturity and release eggs or sperms.

Facts about Sea Urchin Adaptation & Safety Measures:

Their ability to adapt gives sea urchins survival during unfavorable conditions, such as shortage of food. Moreover, the animals also possesses features which help them protect themselves against their predators. These features are discussed below.

  • Sea urchins react instantly when a foreign body comes in contact with their shell. Their response involves all the spines being pointed in the direction of the region receiving the sensation of touch.
  • They possess strong sensitivity to light. Sea urchins adjust the direction of their spines in response to shadows in order to be prepared to fight against predators.
  • Their tube feet help them stick to the bottom of the ocean which helps them stay at one point instead of being washed away with the sea waves.
  • Sea urchins can regenerate damaged or lost spines.

Interesting Trivia about Sea Urchins

The following random facts reveal some interesting information about sea urchins.

  • Depending upon the species, the body of the sea urchins varies in shape from spherical to bottle-shaped to irregular.
  • Sea urchins possess radial symmetry in their bodies. In other words, the body of the organism can be divided into two equal parts across various planes.
  • In the case of some sea urchin species, the spines are filled with poisonous venom. An example is the flower urchin.
  • The teeth of the animal can drill holes in rocks.
  • Among the animal’s predators are humans, fish, sea birds, otters, crabs and sunflower stars.
  • Sea urchins have a long life span which can extend to a period of up to thirty years.
  • The type of sea urchin with the longest life span is the red sea urchin. On average, it can live for two entire centuries.
  • The organism has made it to the list of threatened species. In near future, it is in danger of being extent.

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