If you've eaten Dungeness Crab (Cancer magister), or have encountered adult crabs, but haven't yet seen one in the larval stage before, this is what a Dungeness Crab looks like when it's swimming around in the ocean before it undergoes metamorphosis and becomes a juvenile crab that lives on the bottom:
This is a Dungeness Crab megalopa. It's quite large for a larval crab. In the photo above, the length from the eyes to the base of the prominent rear spine is about 8-10 mm. At this stage it still has a long, narrow abdomen. In the photo above, the abdomen is tucked up underneath the body. But when the crab is swimming, it's extended out behind the crab (see below).
And here's a nice close-up:
The megalopa is the final larval stage. When the megalopa molts, it goes through an amazing transformation (like emerging from a magician's hat!) and becomes a juvenile crab:
The carapace (back) of this juvenile was only ~1 cm across. It has a long way to go before becoming legal size. In this area, a legal size Dungeness Crab is 5.75 inches (14.6 cm) carapace width. It will take a crab approximately 3.5-4 years to reach that size.
The basic reproductive cycle for Dungeness Crabs looks something like this:
- females with eggs from November-February
- eggs start hatching in December, peak in March
- larvae spend 3-5 months in the plankton passing through several stages (1 protozoea, 5 zoeal, 1 megalopa)
- metamorphosis to juvenile benthic crabs during April-June
- approximately 1.5 years (11 molts) to sexual maturity (carapace width 10 cm or 4 inches)