Sometimes really big tides bring in unexpected treasures. Last week’s full moon left all kinds of trees floating in the water, big tangles of seaweed and the odd single old boot. But it was the low tide that presented the unlikely find on a rare, glassy calm late afternoon. With barely enough water to cover its spiny skin and enough silt floating above it to just about hide it from the undiscerning eye, a rare sea star lay on the soft bottom just a few feet from shore. Some careful maneuvering with a paddle lifted the sea star up into the light where we could see its slightly ruddy coloring and bright orange spot on its back marking its madreporite — the hole where it pumps water in and out of its body to control its movement.

Starfish in the Tidal Touch Tank at the Children’s Museum and Theatre of Maine in Portland. Shawn Patrick Ouellette / Portland Press Herald file photo

This particular sea star, Asterias vulgaris, is also called a common sea star — because it is the most common one we find in Maine. This is one of five species native to Maine. The others include the northern sea star, the blood-red blood star, the relatively small horse star, the spiny sea star, and the purple sunstar, which is distinguished from the others by its many arms. The others tend to have five arms, although one of the phenomenal things about sea stars is their ability to regrow arms. So, if a predator happens to snip one off, it can regrow it. Sometimes you’ll find one with a runty looking little arm that is in the process of growing enough to catch back up to the others.

The common sea star is usually not very bright in coloring — orangish brown most typically but sometimes a bit purple and always with a pale underside. They aren’t particularly large — often the size of an average adult hand. They live all throughout the northeastern Atlantic Ocean, including Maine, and, although the most common of the Maine species, it still isn’t all that common to come across one. That made this find a bright spot on a gray, calm afternoon.

When we brought it out of the water to look at it up close, we could feel the sea star’s rough skin, a reminder that sea stars belong to a family of similarly spiny-skinned creatures known as echinoderms. These also include the more obviously spiny sea urchins as well as less obvious ones like sand dollars and those strange slug-like creatures, sea cucumbers. Their spines are mostly inside, although their skin can be somewhat warty like a bumpy cucumber. The spines of the common sea star are in rows along the arms and aren’t super sharp but rather give the skin a rough texture. You can imagine that eating a bunch of those spines wouldn’t be very appealing — the major reason that they have them.

One other amazing characteristic shared by echinoderms is their multitudinous feet. These aren’t just any feet; these feet are equipped with tiny suction cups that help them both to stick to things and also to move around. They use an impressive system of hydraulics to get them to move: sucking water in through their madreporite — the aforementioned sieve plate on the top of their bodies — and then pumping that water out to their feet and arms. When holding one in my hand, I could see these hydraulics in action, the arms slinking to one side and curling around my palm, looking for a more familiar surface to attach to or perhaps something to eat. When trying to dislodge the star from my hand, I was reminded of the tenacity and strength of their tubed feet — something they employ when achieving the remarkable feat of prying open a tightly shut mussel shell, one of its favorite items of prey.

The rare ability of a sea star to pry open a mussel is only matched by the oddity of its eating habits. Although it is able to get the two sides of the shell to separate, it doesn’t need to get them very far apart because a sea star is able to make its stomach come out of its body and push its way inside the two shells of the mussel, doing its digesting right there before pulling it back inside its body. It’s highly unlikely to witness this or to otherwise see a sea star’s stomach, as it is usually tucked back in through its mouth, which is found on the underside of the animal in the center of its arms.

I’ll take our low-tide discovery any day for the chance to look up close at an animal so different from us that lives so close and demonstrates abilities to survive that stymy and impress the careful observer.

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