Sea urchins
Sea urchins are typically spiny, globular animals with a hard shell.
There are about 950 sea urchin species throughout the world. They
inhabit in all oceans, from intertidal zone to the depths of about
5000m. They are slow locomotors. They use tube feet and
sometimes their spines for locomotion.
Their taxonomic hierarchy is as follows;
Sea urchins belong to the same Echinodermata phylum as starfish, brittle star and sea cucumbers.
Normally grown sea urchin’s size is from 3cm-10cm, but largest species can reach up to 36cm. their globular body consists of five equal sized parts radiating out from their central axis. Their mouth is at the base of their body and the anus at the top. So, the lower surface is known as oral and the upper surface is known as aboral.
Sea urchins don’t have eyes or legs. But they can move freely and slowly on rough surfaces using their tube feet. Their internal organs are enclosed in a hard shell of CaCO3. This shell is covered by a thin epidermis and dermis. They produce CaCO3 of their shell by using aqueous CO2. They use Ni as the catalyst for this process. Most species have primary long spines and secondary short spines on the surface of the body. They have a water vascular system. Their movement basically related to their feeding.
They have a digestive system, respiratory system, blood circulatory system, nervous system and reproductive system.
Female sea urchins squeeze eggs to the water. But some species hold them among their spines. These eggs are fertilized with sperms released to the water by male animal and develop into a blastula embryo within 12 hours. Blastula transforms into a cone-shaped echinopluteus larva. This larva has 12 elongated arms. These arms are used to capture food particles and transport them to the mouth. In a few species, there is a nutrient yolk sac so they don’t need external feeding. Larvae need several months to complete their development. The developed larvae sink to the bottom of the ocean. It takes about two years for a larva to become an adult urchin.
Sea urchins normally feed on algae. But they can feed on sea cucumbers, polychaetes, sponges, mussels and brittle stars too. So, urchins belong to omnivores.
One disease in sea urchins is spotting disease. This disease can be divided into two forms as cool-water spring disease and hot-water summer disease. Another disease is bold sea urchin disease. This disease cause loss of their spines and skin lesions. This is believed to be a bacterial infection.
Well grown, sharp spines in adult sea urchins help them to protect from predators. Spines of some species can be venomous. Lobsters, crabs, sea otters and wolf eels feed on sea urchins. These animals have adapted to feed on sea urchins by escaping from their protective features.
Sea urchins have spread from the intertidal zone to the extreme
ranges of depths. Some species like Cidaris abyssicola can live at
depths of several thousand meters. But many species are only found
in abyssal zone. This species includes cidaroids, most of the genera in
echinothuriidae family and the cactus urchins (Dermechinus).
Pourtalesiidae family live in the deepest habitats. They are bottleshaped and live only in the hadal zone. When compared to brittle
stars, starfish and crinoids urchins can be seen mostly in shallow
areas.
Their population density varies by habitat. High population density can be seen in kelp forests. Even in the kelp forests more dense population can be seen in shallow water. If wave action is present population can be found in deep water too. Because of the storms in winter season population density decrease. That is because storms cause them to move to the cracks in the sea bottom for protection. Shingle urchin can survive without water few hours. Sea urchins can be found in all climates. They have spread from warm seas to polar oceans. But most species are found in tropical oceans close to photosynthetic food sources.
Sea urchin’s relation to humans.
Their taxonomic hierarchy is as follows;
- kingdom - Animalia
- Phylum - Echinodermata
- Subphylum - Echinozoa
- Class - Echinoidea
Sea urchins belong to the same Echinodermata phylum as starfish, brittle star and sea cucumbers.
Normally grown sea urchin’s size is from 3cm-10cm, but largest species can reach up to 36cm. their globular body consists of five equal sized parts radiating out from their central axis. Their mouth is at the base of their body and the anus at the top. So, the lower surface is known as oral and the upper surface is known as aboral.
Sea urchins don’t have eyes or legs. But they can move freely and slowly on rough surfaces using their tube feet. Their internal organs are enclosed in a hard shell of CaCO3. This shell is covered by a thin epidermis and dermis. They produce CaCO3 of their shell by using aqueous CO2. They use Ni as the catalyst for this process. Most species have primary long spines and secondary short spines on the surface of the body. They have a water vascular system. Their movement basically related to their feeding.
They have a digestive system, respiratory system, blood circulatory system, nervous system and reproductive system.
Female sea urchins squeeze eggs to the water. But some species hold them among their spines. These eggs are fertilized with sperms released to the water by male animal and develop into a blastula embryo within 12 hours. Blastula transforms into a cone-shaped echinopluteus larva. This larva has 12 elongated arms. These arms are used to capture food particles and transport them to the mouth. In a few species, there is a nutrient yolk sac so they don’t need external feeding. Larvae need several months to complete their development. The developed larvae sink to the bottom of the ocean. It takes about two years for a larva to become an adult urchin.
Sea urchins normally feed on algae. But they can feed on sea cucumbers, polychaetes, sponges, mussels and brittle stars too. So, urchins belong to omnivores.
One disease in sea urchins is spotting disease. This disease can be divided into two forms as cool-water spring disease and hot-water summer disease. Another disease is bold sea urchin disease. This disease cause loss of their spines and skin lesions. This is believed to be a bacterial infection.
Well grown, sharp spines in adult sea urchins help them to protect from predators. Spines of some species can be venomous. Lobsters, crabs, sea otters and wolf eels feed on sea urchins. These animals have adapted to feed on sea urchins by escaping from their protective features.
Their population density varies by habitat. High population density can be seen in kelp forests. Even in the kelp forests more dense population can be seen in shallow water. If wave action is present population can be found in deep water too. Because of the storms in winter season population density decrease. That is because storms cause them to move to the cracks in the sea bottom for protection. Shingle urchin can survive without water few hours. Sea urchins can be found in all climates. They have spread from warm seas to polar oceans. But most species are found in tropical oceans close to photosynthetic food sources.
Sea urchin’s relation to humans.
- As a food.
- For scientific purposes.
- For aquariums.
- Cause accidents and injuries.
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