Fire Urchin growth? ?

[Gone Tidepoolin]

I have had a fire urchin for 8 months, it started out yellow, then turned beautiful red.
I guessed it was part of its growth cycle.
The question: How does it get a larger body/shell?
Do they molt?

[ncaldwell]

That's a good question. I couldn't find anything in the subject but now I need to know how it grows too

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[Ron Reefman]

The internal skeleton of a sea urchin, or test, is made up of many hexagonally shaped calcareous plates known as ossicles. Each ossicle is a single crystal of calcium carbonate in a form known as calcite. The ossicles are fenestrated (have holes) which, remarkably, increases their relative strength. The adjoining plates or ossicles in a sea-urchin test are not fused; rather, they are separated by tissue sutures within which crystalline calcium carbonate is secreted for growth. A newly metamorphosed sea urchin Strongylocentrotus purpuratus has 10 interambulacral plates (5 in each column). The number of interambulacral plates increases wtih age/size from 10 to over 40 in 70-80mm diameter individuals.

[Gone Tidepoolin]

So if I understand correctly, the plate separate as it grows?
They don't molt a section off (like a crab or shrimp)

[Ron Reefman]

So if I understand correctly, the plate separate as it grows?
They don't molt a section off (like a crab or shrimp)

Exactly, no molt. :thumbsup: They are not crabs or shrimp.

[Bongo Shrimp]

You might find this link helpful. It's where Ron Reefman quoted all of his information from:

http://www.asnailsodyssey.com/LEARNABOUT/URCHIN/urchTest.php

[Ron Reefman]

Yup, and I should have included the link, my bad. It's what happens when you are in a hurry!

[dendrite]

Think of it like the suture lines in a baby's skull