The Hotel Wana, a bed-of-nails guesthouse

 

May 16, 2021

The first time I saw the sharp-spined sea urchins the Hawaiians named wana, I thought they were plants, like some kind of underwater cactuses. But when I learned that wana (pronounced vah-nah) are animals that walk around on suction cup tube feet, eating anything they come across with a mouth called Aristotle’s lantern, well, my love affair with the creatures began.

And it goes on. Even after decades of snorkeling and diving among wana, I still find these odd animals fascinating, including several I noticed last week.

Not everyone is fond of long-spined sea urchins, because connecting with their needle-sharp spines is painful. Wana punctures on Craig’s foot were he first marine injuries I saw in Hawaii after he fell off his board windsurfing in shallow water. But if you don’t step on, or touch, a wana, a close look is well worth the time.

Hawaii hosts several species of sharp-spine sea urchins that we Hawaii residents call wana, all bearing barbed spines that the animals wave toward you if you get too close. Sea urchins, however, cannot release, or shoot, their spines, which are attached to the skeleton by skin and muscles.

The most common wana we see snorkeling and in shallow water is called the banded urchin (Echinothrix calamaris), its long spines ranging from black-and-white, to gray, to all black. In young banded urchins, the shorter, slimmer inner spines are green or gold.

The mouth that Aristotle called a lantern is a 5-part set of teeth and jaws located on the underside of the sea urchin. On the top side of all wana is the animal’s anus enclosed by a balloon-like structure with a center opening that ejects wastes away from the creature’s body.

We see this spotted balloon only in young wana, however, because a parasitic crab (Echinoecus pentagonus) gets inside nearly all individuals’ anal sacs, and eats them away. The female crab spends it life just inside the urchin’s rectum eating its white fecal pellets. The smaller males live outside among the spines. Once the anal sac is gone, sharp-eyed snorkelers and divers can sometimes spot the female crab.

Other marine animals seek the protection wana spines can offer, making the sea urchin a living fortress for shrimp and small fish.

Triggerfish are among the few predators of long-spined sea urchins, but the urchin needs to be out in the open for the fish to be able to turn it over, and eat from the bottom. Because the nocturnal long-spined sea urchins rest during the day in nooks and crannies, they’re often hard to for us humans to observe, and for triggerfish to bowl over.

While snorkeling recently, I saw a flash of purple on a wana spine and was able to get a picture of a white-stripe urchin shrimp (Stegopontonia commensalis), below, hanging on in strong current.

Since wana are nighttime feeders that tuck into reef cracks during the day, it’s hard to see who’s all sharing their lairs. As is often the case, my camera saw better than my eyes, and rewarded me during the download.

You can see why I usually stop near wana to see who has checked into the Bed of Nails Hotel. And even if I can’t see the guests, I always get a wave as I pass by.