Rows of beating cilia that split a torch beam into running bands of colour; not a jellyfish and it does not sting.
Eight rows of fused cilia — the combs — run down the body and beat continuously to drive the animal along. Each comb plate scatters light as it moves, so a torch beam is broken into a band of colour that appears to run along the row. It is diffraction, not bioluminescence, and it stops when the light does, which is worth knowing before writing it up as glowing.
Comb jellies are not cnidarians and are not jellyfish. They have no stinging cells and cannot hurt a diver. Many hunt instead with colloblasts, adhesive cells on a pair of trailing tentacles that stick to small prey and are reeled in; others, the lobate forms, hold two broad muscular lobes open and close them around whatever drifts inside. They are voracious for their size and eat copepods, larvae and other gelatinous animals, including each other.
On a blackwater dive they are among the commonest things in the beam and are usually swum past. They are worth stopping for on two counts: the comb rows are one of the few genuinely unphotographable-looking things that photograph well, and the transparent body frequently has a passenger — an amphipod, a juvenile fish or a larval crab sheltering inside the bell, which is a considerably better picture than the jelly alone.
The phylum is large and identification from a photograph is rarely possible below the level of the broad body form: ovoid with long tentacles, lobate, or the flat ribbon-shaped Cestum that is unmistakable at any size. Logging one as Ctenophora, with the form noted, is the accurate record.
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.
