This jelly is commonly seen in Monterey Bay during spring and summer, sometimes in large groups. Growing to about four inches in diameter, a cross jelly's bell is rimmed with hundreds of fine white tentacles and is bioluminescent. Four white canals visible under the transparent bell form an obvious "X" pattern, after which the cross jelly was named.
Jelly populations naturally ebb and flow. Scientists are now wondering whether human impacts like overfishing, pollution and possibly climate changes might affect jelly populations also.
Recent studies by the Monterey Bay Aquarium Research Institute (MBARI) suggest that the cross jelly (and possibly other jelly species) can "smell" food in the water, indicating that it might actually pursue prey rather than rely on chance encounters. This might explain why cross jellies are often seen in large groups around concentrations of prey.