At first glance, a tunicate salp looks like a jellyfish that forgot its tentacles. It’s tubular, transparent, and drifts through the water like a loose piece of glass. But the resemblance is misleading. Salps aren’t jellyfish at all. They’re sea squirts, and evolutionarily they sit far closer to humans than to anything in the jellyfish family.
The giveaway is anatomical. Salps are chordates. At one stage of life they develop a notochord, a simple spinal structure that muscles attach to. It’s a small detail, but it puts them on the same deep evolutionary track as vertebrates, humans included.
They come in wildly different sizes. Some are barely visible to the naked eye. Others grow longer than a forearm. While diving off the coast of Indonesia, underwater photographer Massimo Giorgetta encountered a relatively small one, about two inches long, drifting through the water column after feeding. The resulting photograph recently won a bronze award in the Nature/Underwater category of the Tokyo Foto Awards.
The image is initially confusing. Because the salp’s body is almost perfectly transparent, it’s hard to tell where the animal ends and its meal begins. Everything appears layered together. Look longer and shapes start to resolve. A yellowish mass resembles a juvenile boxfish. Tiny crabs and shrimp larvae seem to be suspended inside, caught mid-journey.
Salps normally feed on phytoplankton, pumping seawater through a fine mesh of mucus that traps food particles. The process isn’t selective. Anything small enough gets swept in. As Giorgetta explains, “Inside the tunicate salp is a boxfish in juvenile form, some very small flatworms in juvenile form, then some larval Squilla mantis, some heteropods, and several animals that I cannot determine.”
What makes the photograph compelling isn’t just the rarity of the moment, but its clarity. The salp becomes a kind of living cross-section, revealing how much life drifts unnoticed through open water—and how easily it can end up inside something that looks, at first, like nothing at all.
h/t thisiscolossal