A small clear barrel bound by complete muscle hoops, pumping water to swim and to feed.
A small transparent barrel, open at both ends, encircled by eight complete rings of muscle that show as fine bands down its length. It is regularly logged as a salp. The separation is the muscle: a doliolid’s bands are complete hoops that go right round the body, a salp’s are incomplete and do not close on the underside, and doliolids are the smaller of the two.
Doliolids are tunicates and feed as salps do, by pumping water through the body and straining phytoplankton from it on a sheet of mucus. The life cycle is more complicated than a salp’s and involves a stage that is not free-living at all: the sexual generation produces a tadpole larva, which becomes a nurse that carries developing buds on a long dorsal projection, and these are released in turn. A single individual can generate very large numbers in a short time when food allows, and doliolid swarms appear and disappear over days.
On a blackwater dive they are numerous and mostly ignored, which is fair enough on their own account. They are worth a second look for the same reason salps are: hyperiid amphipods hollow them out and ride inside the empty tunic.
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.
