The last thing I expected when I jumped into the water off Kailua-Kona last week was to be surrounded by dozens of fellow writers.

OK, these creatures can’t really write, but they’re equipped with writing devices as quaint as quill pens. To my surprise, I had found myself snorkeling in an expanse of bright red pencil urchins, a burst of primary color in a sea of pastels.

Pencil urchins are relatives of the long-spined urchins that we in Hawaii call wana (pronounced vah-na), but belong to a different family distinguished by solid, as opposed to needlelike, spines. The striking red pencil urchins win the beauty prize in this family, each having bright red clubs extending from a domelike skeleton.

Tiny tiles, either white, red or a mixture of both, cover the calcium carbonate skeleton.

Although this species is found throughout the warm waters of the world, they are sparse in other areas and mostly yellow or brown. The red ones in Hawaii are abundant, at least off the Kona coast, where the 8- to 12-inch-wide (spines included) urchins are a common sight.

One longtime resident told me that in the past, people visiting Waikiki and other Oahu beaches took the lovely red urchins from the water and left them on the beach, where they died.

At night, I’ve read, the bright red “pencils” turn a pale pink. I haven’t seen this because I don’t snorkel at night. I like sunshine on my reef.

We snorkelers and divers sometimes see red pencil relatives with similar clubby spines that are covered with algae and other marine growth. That doesn’t happen to red pencil urchins because a thin layer of tissue grows on each blade, preventing marine organisms from attaching.

Years ago, when blackboards were made of slate and some children did their lessons on their own small slates, teachers sometimes used the pencil urchin’s spines as chalk, hence the animal’s other name, slate pencil urchin.

Some artists carve images or designs into the animals’ flat spines or make jewelry of them. I have a handful of maroon pencil spines that I found on a beach in the Tuamotus. Given the remoteness, I presumed the animal died of natural causes. Triggerfish and other predators eat sea urchins.

Like all sea urchins, red pencil urchins have a mouth equipped with tiny jaws and teeth on their center underside. The Greek philosopher Aristotle compared the urchins’ mouth parts to the lanterns of the day. To this day the eating apparatus of all sea urchins is called Aristotle’s lantern.

Red pencil and other urchins graze on algae, moving about the reef on suction cup tube feet that can withdraw into the skeleton when disturbed.

One red pencil urchin is always a bright sight to behold when snorkeling, but the dozens that decorated Kailua-Kona’s rocky reef last week made my day. It was the best writers conference I’ve ever attended.