A clear barrel that pumps water through itself to swim and to feed at the same time.
A transparent barrel, open at both ends, with visible muscle bands running round it like the hoops of a keg and a small opaque gut mass at one end. Salps occur singly and in chains, and the chains — dozens of linked individuals in a line, a spiral or a wheel — are what most divers notice first. They are confused with doliolids, which are smaller and have complete muscle rings, and with comb jellies, which beat cilia rather than pumping.
A salp is a tunicate, which puts it closer to vertebrates than to any jellyfish. It swims by contracting the muscle bands and driving water through the body, and the same current is passed across an internal mucus net that strains out phytoplankton. Swimming and feeding are one action. Salps grow very fast when food is abundant and can bloom in enormous numbers, and their dense faecal pellets sink quickly, which makes them a significant route by which surface carbon reaches deep water.
The life cycle alternates. A solitary salp buds off a long chain of clones; the chain individuals are sexual, and each produces a single embryo that grows into a new solitary form. The two generations look different enough that they were once described as separate species.
Empty and half-eaten salps are worth checking. Hyperiid amphipods hollow them out and live inside the tunic, and a barrel with a passenger is a better subject than the salp on its own.
Ratings are per location: 1 means found on most dives that look for it, 5 means a handful of records. Where enough dives have been logged the figure is calculated from them; otherwise it is an editorial estimate, and says so. We publish habitat and destination, not the dive site.
