While working at Midway, Craig and I made a new friend and invited him to stay with us for a couple of days before he went home to Canada. Because Luke loves snorkeling, and so does Craig’s mother, Claire, visiting from Seattle, we went to my favorite North Shore beach and plunged in.

I know the area well and guided our guests to a turtle spa, where we watched damselfish nibble algae off the turtles’ shells and pluck parasites from their skin. In addition to the usual reef fish, we found a scorpionfish, some marbled shrimp and a yellow-margin moray eel hiding under a rock.

It was a great day, we all agreed, and headed for the beach. But Luke wasn’t done. Calling my name, he motioned for me to come look.

I arrived to find a gray, nearly 3-foot-long trumpetfish standing on its head. The sight is always marvelous, but was even more so because I know that fish. The big predator hangs out near the turtle cleaning station pretending to be a stick. When a gullible fish swims close, the trumpetfish inhales it.

You would think the fish in that area might figure out that that’s no stick in the water, but no. The trumpetfish is huge, healthy and nearly always there.

Cornetfish, close cousins of the trumpetfish, also hang out on that reef. (It has a strong horn section.) Both species have long narrow bodies, but with a notable difference.

From above looking down, and also head-on, trumpetfish look so slim, you can totally miss seeing the fish. But view the same fish from the side and it’s several inches tall, the body broad and beefy.

Cornetfish bodies are the reverse: Their backs are wide enough to be obvious from above, but from the side the fish is flat as a plate and nearly invisible. To further fool their prey, both types can change colors and patterns to blend in with their backgrounds.

Trumpetfish grow about 30 inches long and are like sticks in that they can’t bend their bodies. But cornetfish can. They spring-load their 63-inch-long (maximum length) bodies in an S shape and lunge for their prey.

Trumpetfish and cornetfish are easy to tell apart by their tails. The trumpetfish’s tail is a stubby stalk ending in a fan. The cornetfish’s tail looks like a whip. Both species use the vacuum cleaner method of capture: The fish suck prey into their expandable mouths.

By swimming often in the same place, I recognize some of the undersea locals and consider them friends. As I do 33-year-old Luke and 92-year-old Claire. Snorkeling is a communal ocean sport where neither age nor species matters. What does matter is where you do it.

Reach Susan Scott at susanscott.net.