Have you ever been walking at the seashore and come across an object that looks a little bit like a sand-choked alien organ or a small mammal that's been turned inside out? Maybe you bore this event with philosophy, thinking to yourself, What is the ocean but a vast container full to the brim with mysterious blobs? This could be a dolphin pancreas or a scrap of Jimmy Hoffa's brain or some extremely firm manatee vomit. What a world! Or maybe the encounter still haunts your dreams like the creepy doll you saw that one time at the Goodwill. Either way, it is possible that gelatinous scrap you found was some sea pork.
Sea pork is the common name for a tunicate, the ocean's most common — yet most unaccountably complicated — invertebrates. Around 3,000 species of tunicates exist today, whiling away the hours filtering small particles of food out of their surroundings by pumping water in and squirting it back out. For this reason, they're also commonly called sea squirts, which makes some sense. They're called sea pork because somebody with naming power once thought they resembled little slabs of pig fat — which they sometimes do, but not always.
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Tunicates come in a variety of shapes (barrels, bottles, balls), textures (from brains to pockmarked putty) and colors (lavender, deep red, beige, translucent blue), most of which could never be mistaken for a pork product. But in the case of most tunicates, the color you're seeing is actually a slimy outfit, or "tunic," worn by a colony of tiny creatures called zooids. Although some tunicates are solitary (not colonial) and others are pelagic (meaning they drift around out in open water), the majority of these organisms find strength in numbers, cemented to the sea floor — usually no deeper than 660 feet (200 meters) under the surface — in their protective bag. They just find each other as babies, huddle together and eat their lives away in their goopy little housing co-op. The ones you find on the beach were most likely ripped from their homes during a storm.
What tunicates lack in adventurous daily lives, they make up for in fascinating and unique life history. They are hermaphroditic, which isn't all that unusual, but they avoid self-fertilization through a variety of mechanisms, depending on species, including broadcasting sperm and egg cells at different times, and even formulating their gametes in such a way that they reject each other. But perhaps the weirdest thing about tunicates is that they're actually considered chordates, even though the adults don't have backbones.
Caught somewhere in the muddy middle area between vertebrates and invertebrates, sea pork larvae spend the first part of their lives looking a lot like tadpoles — they have a tail and a notochord. When they're ready, they swim down to the bottom of the ocean, find a nice colony to hang out with, or a pleasant patch of rock, and attach themselves with some glue-y glands at the front of their heads. At this point, most species lose the tail and notochord (all except one class of free-floating tunicate called the Larvacae, which retains its characteristics from the Chordata phylum), and sit around squirting water for the rest of their lives.
So, the next time you see a bit of sea pork on the beach, have a little respect — it's a chordate like you, after all!
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