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A sea urchin is a ball-shaped echinoderm with long, pointy, and moveable spines all over its body. Sea urchins usually live on ocean seabeds and warm waters. They are also known as sea hedgehogs. Not all species of sea urchins are poisonous, but those that are can be deadly.
See the fact file below for more information on the Sea Urchin or alternatively, you can download our 28-page Sea Urchin worksheet pack to utilise within the classroom or home environment.
Key Facts & Information
Etymology and Location
- The term urchin is derived from “herichun” in Old French and “ericius” in Latin which means hedgehog.
- It resembles a hedgehog so it was named as such.
- There are more than 200 known species of sea urchins.
- They inhabit warm ocean waters and are usually found near coral reefs or kelp beds on the rocky ocean floor.
- Sea urchins vary in shape, size, and color.
- The average sea urchin is 3 to 10 centimeters in diameter.
- The biggest known sea urchin species is 36 centimeters in diameter.
- Sea urchins do not have a recognizable face, but they have an identifiable mouth and anus.
- They exhibit radial symmetry: they have five sections in equal size.
- Sea urchins can be many colors, including black, brown, right pink, dark purple, green, and sand colored.
- A sea urchin’s shell is called a test or a shell.
- Their shells are made of rigid, bony plates.
- Their shells serve as protection for their soft inner body parts.
- They have long and pointy spines all over their body.
- Some species have spines that are soft and poisonous.
- Their spines are typically 1 to 2 mm thick and 1 to 3 cm long.
- Scattered on their spines are claw-like structures called pedicellaria (plural: pedicellariae).
- Pedicellariae have three uses: gathering food, defending themselves against predators, and keeping their body clean.
- They have five rows of paired tube feet that act as legs to push themselves across the ocean floor and also as suction to attach themselves to rocks or similar surfaces.
- A sea urchin’s mouth is dubbed “Aristotle’s Lantern” and is located at their underside.
- In a sea urchin’s mouth, there are five rigid teeth made of calcium carbonate and another structure acting as a tongue.
- A sea urchin does not have a brain.
- They have a water-vascular system that acts as their circulatory system by running water through their body.
Diet and Predators
- Sea urchins are omnivores, meaning they eat both plants and meat of animals.
- Their diet mainly consists of algae, seaweed, and plankton from nearby underwater rocks and corals.
- They also feed on decomposing matter from fish at times.
- Their common predators are those that can claw through a sea urchin’s protective spines, such as sea otters, fish like triggerfish and wolf eels, sea birds, crabs, lobsters, sunflower stars, and humans.
Mating and Reproduction
- Sea urchins mate in the spring.
- Sea urchins practice external reproduction.
- Females release eggs and males release sperm cells in the water.
- Females release 1000 eggs at a time and only a small percentage of those are fertilized.
- Within 12 hours, the fertilized egg becomes an embryo.
- Fertilized eggs undergo the larval stage for several months before maturing into adults.
- Larva sea urchins swim with other small sea creatures. Together they form a zooplankton.
- The lifespan of most sea urchin species can reach up to 30 years.
- The red sea urchin can live up to 200 years in the wild which is the longest life span among earthly creatures.
The Flower Urchin
- The Flower Urchin is the most dangerous urchin because of its venomous spines.
- The Flower Urchin inhabits the Indo-West Pacific region.
- It has a symbiotic relationship with the clownfish.
- The poison of the Flower Urchin contains Contractin A and Peditoxin.
- Contractin A causes red blood cells to clump and body spasms.
- Peditoxin can cause convulsions, anaphylactic shock, and death.
- Species belonging to the Diadematidae and Echinothuriidae families are also venomous.
- A puncture wound from a poisonous sea urchin looks swollen and red and must be treated immediately before it causes infection.
- Multiple puncture wounds may cause muscle paralysis, respiratory failure, and even death.
- The recommended treatment for a sea urchin puncture is to submerge the affected body part in hot water for an hour to break down the venom and relieve the pain.
- If there are spines stuck in the wound, they must be carefully removed.
- If it’s close to nerves or blood vessels, it might be too dangerous to remove it with tweezers, so it’s best to have a doctor remove it surgically.
Captivity and Uses
- Some species are listed as endangered.
- Major threats to sea urchins are ocean pollution and overfishing.
- Sea urchins are not able to reproduce very well in captivity because there must be certain conditions (such as ocean currents) present for breeding to take place.
- Sea urchin roe (or eggs) are served as “uni” in Japan and can be eaten as raw sashimi or in sushi.
- One way to help protect the sea urchin population is to keep oceans clean.
Sea Urchin Worksheets
This is a fantastic bundle which includes everything you need to know about Sea Urchin across 28 in-depth pages. These are ready-to-use Sea Urchin worksheets that are perfect for teaching students about a sea urchin which is a ball-shaped echinoderm with long, pointy, and moveable spines all over its body. Sea urchins usually live on ocean seabeds and warm waters. They are also known as sea hedgehogs. Not all species of sea urchins are poisonous, but those that are can be deadly.
Complete List Of Included Worksheets
- Sea Urchin Facts
- It’s A Sea Urchin!
- Body Terms
- Figure It Out
- Choosing One
- 4 Pics, 1 Sea Creature
- Zooplankton Hunt
- Ouch! Help!
- Serving Urchins
- A Sea Story
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Link will appear as Sea Urchin Facts & Worksheets: https://kidskonnect.com - KidsKonnect, November 22, 2018
Use With Any Curriculum
These worksheets have been specifically designed for use with any international curriculum. You can use these worksheets as-is, or edit them using Google Slides to make them more specific to your own student ability levels and curriculum standards.