Leidy’s comb jellyfish-like organisms that have a lobed, oval shaped and transparent body, with four rows of  “cilated” combs that run along the body vertically.  Leidy’s glow blue-green when disturbed. Unlike cnidarians (marine invertebrates such as anemones, jellyfish, and corals that have stinging cells).  Leidy’s comb jelly doesn’t sting. Leidy’s is a major carnivorous predator of edible zooplankton pelagic fish eggs and larvae, and has been associated with crashes in fishery populations when introduced in new locations.

Leidy’s comb jelly are native in temperate to subtropical inshore waters of North and South America, and are common in southern New England in late summer to early fall, with occasional sightings in the winter. In the 1980’s this species was unintentionally introduced in the Black Sea via ballast water where it ate eggs and larvae of pelagic fish, causing a dramatic drop in fish populations, notably the commercially important anchovy, by competing for the same food sources.  In 1999, the species  was introduced in the Caspian Sea, resulting in a depletion of 75% of the zooplankton and affecting the entire food chain of the lake.  By 2006 the species spread throughout the Mediterranean basin and the northwestern Atlantic and the Baltic Sea.

One look-alike to the comb jellyfish is Beroe forskali, the comb jelly predator. The difference between a comb jellyfish and common jellyfish is that Leidy’s comb jelly does not have stinging cells and are bell shaped with no tentacles.  Other jellyfish have a dome shape with hanging tentacles.