Sometimes, the Pearl IS the Oyster

Yesterday, while visiting the fish store to pick up another porcelain crab, I noticed a strangely-shaped frag of zoanthids in the “cheapie” section of the store.

I noticed because zoas rarely grow in geometrically-regular colonies, and even when they do the colony “edges” are uneven, with independent polyps sticking away from the cluster at varying intervals. The colony I noticed was circular (almost ovoid), with sharply defined rounded edges.

Upon closer examination, it also had an open mouth along the edge.

What I’d found was a rare example of inter-species cooperation: a live oyster overgrown with at least two different zoanthid species. (Even now, as I write this, I’m not sure whether it’s two or three).

Oysters rarely survive in private aquariums, mostly because they require special, microscopic foods and because many popular “pet” species prey on molluscs. My reef, however, offers a “safe zone” for sensitive species. I’ve got several other thriving (and growing) bivalves, so I brought the zoa-covered oyster home.

After a 45 minute acclimatization drip, I moved the mollusc into the tank, placing it high on the reef in a spot where the current would flow toward the creature’s mouth. Then I left it and hoped for the best.

Within 30 minutes, the zoanthids decided they liked the location and opened (they won’t if they sense their positioning isn’t ideal–and it’s not always easy to tell what a species wants in a home). 15 minutes later, the oyster was open too. You can’t tell from the photos, because unfortunately the best orientation for Mr. Oyster required me to tilt him away from the front of the tank where I can’t see or photograph his mantle extension. So you’ll have to take my word for it that (s)he’s happy.

To the untrained eye, the oyster looks like a cluster of zoas growing over a rock. But look closely and you’ll see the edge of the oyster’s shell. Ironically, not one of the zoas is actually “on” the rocky plug. They’re all on the oyster.

In addition to the oyster, I brought home another porcelain crab–a peaceful, filter-feeding species that does well in soft-coral reefs. I’d seen the crab in the shop last week and asked them to hold it for me through the weekend. The manager and the owner were out, but one of the sales associates told me he’d make sure they kept the crab.

Today, I went into the shop and told the manager, Joe, that I’d come to retrieve my crab.

“Your crab?” he asked.

For a moment, I thought it was gone.

His eyes lit up with recognition. “Oh, HOLD CRAB!”

We went to the back of the store, where someone had written “HOLD CRAB” in grease pencil on the tank. No name, no date, no details, just “HOLD CRAB.” I’m in there often enough that, apparently, the salesman thought no name or details were necessary. (“Invertebrates on hold belong to Susan…”)

We had a good laugh, and the crab acquired a name. I’m calling him Hold. Hold Crab.

Did you spot the oyster hiding behind the zoanthids and the crab on the lower left in the midst of the blue-green palythoas?