And it was covered, both sides, edge to edge, with an encrusting bryozoan.
I put it in the aquarium while I was busy with other things, and the hermits picked at it, emptying out the bryozoan cases. The next day, I collected it, and examined it with a microscope. All that was left were the white walls of each animal.
|All lined up in alternating rows, like a brick wall.|
The individual cases are not quite rectangular; they're often more the shape of a first birthday candle, with the fat base and the overhang at the top. (On the candle; I don't know which end is the lophophore or mouth end of the bryozoans.)
Compare them to the kelp bryozoans we usually find.
|Kelp bryozoan colony, 2009. They form circles on the kelp, radiating out from a central point.|
|Zooming in. The cases are less regular, slightly rounded. The walls are thinner.|
I looked at hundreds of photos of encrusting bryozoans. Some of the Membranipora membranacea, the kelp-encrusting bryozoans, stretch out on giant kelp, not limited to the narrower blade of bull kelp. The outer edges of these colonies become more rectangular and orderly, much more similar to the "birthday candle bryozoan" (my name).
In the Wikipedia article on M. membranacea, I found this:
Zooids within a colony can communicate via pores in their interconnecting walls, through which coelomic fluid can be exchanged.It may be that the discontinuities in the walls are the pores. Hard to tell. I really wish I had examined them before the hermits finished them off. I just might have found some still alive.
|Living encrusting bryozoans. Feeding zooids in their individual boxes. Image from U of Washington.|
Basic description of bryozoan anatomy and "weird stuff".