Sea Urchin Facts: Amazing Spiny Creatures
Sea urchins are fascinating ocean animals found in every ocean. Despite their simple appearance, these spiny echinoderms have remarkable biology.
What Are Sea Urchins?
- Phylum: Echinodermata (related to starfish)
- Class: Echinoidea
- Species: Over 950 different species
- Size: 1-10 inches diameter (most 2-4 inches)
- Lifespan: 15-200 years (species dependent)
Anatomy
External Features
- Spines: For protection and movement
- Test: Hard shell underneath spines
- Tube feet: For movement and feeding
- Pedicellariae: Tiny pincer-like structures
Mouth Structure
- Located on bottom (oral surface)
- Called "Aristotle's lantern"
- Contains 5 hard teeth
- Can scrape algae off rocks
- Teeth continuously grow
Movement
Sea urchins move using:
- Tube feet: Hundreds of tiny hydraulic tubes
- Spines: Also help with locomotion
- Speed: Very slow (inches per hour)
- Direction: Can move any direction
Diet
What They Eat
- Primary food: Algae
- Also consume: Seaweed, kelp
- Scavengers: Dead animals, detritus
- Some species: Sponges, coral
Feeding Method
- Scrape surfaces with teeth
- Continuously graze
- Important for reef health (control algae)
Defense Mechanisms
| Defense | Purpose |
|---|---|
| Spines | Primary protection |
| Venom (some species) | Deter predators |
| Camouflage | Cover with debris |
| Nocturnal behavior | Avoid predators |
Reproduction
Spawning
- Release eggs and sperm into water
- External fertilization
- Millions of eggs per female
- Temperature triggers spawning
Life Cycle
- Fertilized egg
- Larval stage (planktonic)
- Settlement and metamorphosis
- Juvenile urchin
- Adult
Are Sea Urchins Dangerous?
Venomous Species
Some tropical species have venomous spines:
- Flower urchin (most venomous)
- Long-spined urchin
- Fire urchin
Stepping on Sea Urchins
- Painful puncture wounds
- Spines can break off in skin
- Some require medical attention
- Rarely life-threatening