Home, home on the seaweed

  

Recently Eric noticed these small crustaceans clustered on a seaweed washed up on the beach.

Here's what it looked like when first discovered:

 

 

This is the seaweed Sea Sacs (Halosaccion glandiforme), which consists of water-filled sacs (with a small volume of gas) normally attached to intertidal rocks.  When they're pulled off the rocks by waves, they'll float at the surface of the ocean.  If you look closely in the photo above, you can see the small clusters of crustaceans.  Under the microscope, more details are visible:

 

 

 

 

These are barnacle cyprids, the final swimming stage, of Pelagic Gooseneck Barnacles (Lepas sp.).  These cyprids will attach to floating structures like driftwood or a feather or this seaweed and then undergo metamorphosis into juvenile barnacles.  The appendages they use for swimming in the cyprid stage will morph into feeding appendages (called cirri) in the juvenile/adult barnacle.  Here's a diagram with arrows pointing to the appendages as they change during metamorphosis from their function in swimming to feeding:

 

 

 

What's cool is that the cyprids are partially transparent, so you can see those dark, feathery appendages in the close-up photos:

 

 

 

Fun!