A parasitic amphipod that hollows out a salp, climbs inside the empty barrel, and pushes it through the water as a nursery.
A hyperiid amphipod, transparent, with two pairs of eyes and one enormously enlarged claw. The female attacks a salp or a doliolid, eats the animal out of its own tunic, and takes up residence in the hollow barrel that is left. She grips the inside wall, beats her pleopods, and drives the barrel through the water. Her young are released inside it and stay there, fixed to the inner surface, while she feeds them and keeps the barrel clean.
This is straightforwardly where the Alien film’s design came from, and the animal is usually described that way. The more interesting point is that the barrel is not a shell or a case the amphipod builds: it is another animal’s body, emptied and reused as both vehicle and nursery, and there is nothing else quite like it.
Identifying a Phronima to species from a photograph is not reliable. Several species occur in the Indo-Pacific and they differ in details of the limbs rather than in anything visible through a housing port; Phronima sedentaria is the one usually named, and is often named wrongly.
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.
