Aglantha digitale (Rocket Jelly)

Aglantha digitale earned its common name from its ability to swim rapidly through the water column, which is unusual among hydromedusae. It has two distinct modes of locomotion: a slow rhythmic swim used for routine movement and a much faster escape response triggered when it detects predators. This dual-mode swimming has made it a valuable model organism in neuroscience.

Aglantha digitale possesses a single class of large nerve fibers that can conduct both slow and fast action potentials, allowing researchers to study how one neural system controls two very different behaviors. Studies of this species, including work by researchers at the Marine Biological Association in Plymouth, have revealed mechanisms of neurotransmitter switching between slow swimming and escape swimming. Its relatively simple nervous system makes these processes easier to isolate than in more complex animals.

Aglantha digitale is found in cold and temperate ocean waters, including the North Atlantic and North Pacific, where it lives pelagically in the water column. It is a small hydromedusa, typically reaching only about one to two centimeters in bell height. Despite its small size, it feeds actively on small planktonic animals such as copepods.

Aglantha digitale is a hydromedusa, placing it in the class Hydrozoa rather than the Scyphozoa, which includes the large, familiar jellyfish like the moon jelly (Aurelia aurita). Both groups belong to the phylum Cnidaria and share traits like tentacles with stinging cells (nematocysts). However, hydromedusae like Aglantha are generally smaller and have more complex life cycles that can include both polyp and medusa stages.