On 8 January 2012, I photographed this beautiful sponge cluster in the low intertidal zone. It's a calcareous sponge called Leucilla nuttingi. Each "vase" is about 1-2 cm tall. When reviewing the photos, I was surprised to spot an animal emerging from between the sponges -- can you find the green isopod?
Here's another photo when the green isopod emerged into the open.
To my surprise, I then noticed some interesting objects at the openings of the sponges -- some pink and white, some red, some brown and white. I think all of them might be isopods living in the sponges!
Here's a photo showing an isopod looking out from a sponge opening (on the left, look for its eyes and antennae) and the tail end of another isopod (on the right).
And here's one more showing the tail end of an isopod (at the top left) and I think perhaps another head (on the right).
Fish, shrimp, and other organisms are known to live inside some sponges, but I don't know if anything is known about the relationship between Leucilla and these tiny isopods!
ADDENDUM (16 January 2012)
We took a few pictures of these intriguing isopods under the microscope: