Largest sea urchin
- Who
- Giant red sea urchin, Mesocentrotus franciscanus
- What
- 18 centimetre(s)
- Where
- Not Applicable
- When
- N/A
The world's largest species of sea urchin is the giant red sea urchin (Mesocentrotus [=Strongylocentrotus] franciscanus). Native to shallow waters in the north-east Pacific Ocean from Alaska in the USA, along western Canada and southwards to Mexico's Baja California, it has an outer skeleton (test) diameter that can exceed 18 cm (7 in), and a maximum spine length of 8 cm (3.1 in).
Small, juvenile specimens with a diameter less than 5 cm (2 in) often hide underneath the adults.
In Alaska, reproduction occurs between March and September, and each female sea urchin can release as many as 2 million eggs into the sea, where they are then fertilized by sperm released by males. Each fertilized egg gives rise to a basic larval form known as a morula, which subsequently transforms into a characteristic eight-limbed larva called the echinopluteus. This in turn transforms into the juvenile sea urchin, which ultimately metamorphoses into the adult, complete with spines, tube feet and the full sea urchin complement of internal organs.
The giant red sea urchin is also among the longest-lived animals reaching ages of 100 and above.
At the other end of the spectrum, the world’s smallest species of sea urchin is Echinocyamus scaber, which is native to the waters off