I wrote recently about how to get into beachcombing, and I’m excited to inform you that you have some neat new critters to look for! Sadly, they’ve usually perished by the time they wash up, but you can still get a good look at living beings that you normally would never know are out there under the waves.

Sea cherub, or sea angel, is the common name for the Gymnosomata, a group of marine mollusks without shells in the order Pteropoda (shelled Pteropods, or sea butterflies, are formally classified as Thecosomata.) All of which means sea cherubs are little sea slugs. Unlike their terrestrial relatives, they can swim freely through the water, using winglike structures called parapodia.

Despite their innocent-sounding name, sea cherubs are quite insatiable predators. Their wings propel them forward in pursuit of nearby sea butterflies, and when they catch their target, they grasp the hapless creature with tentacles around their mouth and drag it to the radula, a rasping tongue-like structure that functions similarly to teeth. The sea butterfly’s protective shell will only hold up to this assault for so long, and then the hungry cherub devours what’s inside.

Sea butterflies, for their part, far outnumber sea cherubs, with the group making up over 90% of all Pteropods. They also drift freely through the water, though these tiny herbivorous snails largely float upside-down at the mercy of currents in search of phytoplankton.

To ensnare their prey for an easy feast, they exude nets of mucus. Their calcium shells, meanwhile, offer protection against predators like sea cherubs. Both, however, are prey for larger predators, including filter-feeders like gray whales.

Sea butterflies and cherubs prefer shallow water and are not found in the deeper, darker layers of the ocean. However, nutrients that drift up along continental shelves create excellent feeding grounds, so they often congregate there. It’s not uncommon for both types of Pteropod washed up on the beach together, and in recent weeks, they’ve been quite common.

Keep in mind that these are rather tiny things, with the largest sea cherubs being under 2 inches long, and sea butterflies a fifth of that size.

It will be easiest to notice the predatory slugs as semi-transparent, elongated blobs that quickly disintegrate in the sun, but sharp eyes will catch the tinier snails, too.

They quickly expire out of water, and often, the waves washing over them will push them further onto the sand. The boundary between sea and land is a dangerous place when you’re so small.

But it’s not just the ocean’s power threatening the Pteropods.

Ocean acidification causes calcium to dissolve, which means sea butterflies’ shells are growing weaker, often to the point where they can’t survive. Fewer sea butterflies means less food for the sea cherubs, so they’re at risk, too. And climate change is driving an increase in carbon dioxide levels that causes water to become more acidic.

Not all the marine life washing up is so difficult to observe. Pyrosomes are large groups of animals called tunicates, which bridge the gap between invertebrates and vertebrates.

While they have no skeleton and spend most of their lives anchored to a substrate, during their free-swimming larval stage, they have a notochord and dorsal nerve cord like all vertebrates, making them one of the very few invertebrate chordates.

An individual is perhaps 1/3 inch long, about the size of a sea butterfly. But instead of facing the harsh ocean alone, they instead become zooids — a name for the members of a much larger colony, the pyrosome.

Pyrosomes are much more common in tropical waters, but ocean currents may carry them as far north as Alaska. Despite its name, Pyrosoma atlanticum is not limited to the Atlantic but lives in all the oceans of the world and is the species most common here.

Its colonies may reach 2 feet in length and can be bioluminescent, glowing a brilliant blue-green. This light is part of how zooids communicate, since they do not share a nervous system but are simply individuals stuck together.

Pyrosomes can float with the currents or use the zooids’ cilia to move in a particular direction. They float toward the surface of the water in the evening and return to deeper locations for the day. A large colony may migrate 2,500 feet in each direction.

Occasionally, they end up tossed onto shore, which is where most people get to encounter them — and now you know what you’ve found when you stumble across one of these odd, gelatinous masses.