by Katie Bowell, Curator of Cultural Interpretation
This past week, approximately 150 people in Rye, New Hampshire were stung by the a 40lb Lion’s mane jellyfish (or “jelly,” which is the more appropriate zoological term) that washed up on shore. Lion’s mane jellies are the largest jelly species in the world, and the largest individual ever recorded was over 7 feet in diameter and had tentacles of 120 feet long. The individual who showed up in Rye was described as being the size of a trash can lid and when officials removed it from the water, some of its many tentacles broke off and continued to sting people who came into contact with them in the ocean (tentacles can remain “alive” for 3-4 days after a jelly dies).
Living in lovely, landlocked Colorado, you might think that jellies are one thing you don’t have to worry about encountering, but you’d be surprised. Meet Craspedacusta sowerbyi.
C. sowerbyi is a freshwater jelly found throughout the world. Here in Colorado, C. sowerbyi has been found in lakes and reservoirs in Jefferson and Boulder County, and its range is likely to keep expanding.
Jellies all belong to the phyllum Cnidaria (organisms that have cnidocytes – specialized cells used to capturing prey) , but there are several different classes including the Scyphozoa (the “true” jellies like the Lion’s mane), Stauroza, Cubozoa and Hydrozoa (the class C. sowerbyi belongs to). The Hydrozoa jellies differ from the true jellies by having a muscular, shelf-like structure called velum on the ventral side of the jelly that helps with propulsion through the water.
C. sowerbyi is small, only 20-25mm in diameter, but in that small space it has up to 400 tentacles, with each tentacle having thousands of cnidocytes, and each cnidocyte containing nematocysts used to sting and capture the tiny zooplankton it eats. The nematocysts inject poison into any prey they come in contact with, but don’t worry – C. sowerbyi’s nematocysts are too small to penetrate human skin.
Like all jellies, C. sowerbyi doesn’t always look like the image above. Jellies are dimorphic (having two shapes) and the organisms begin their life as a stalked, sessile polyp and then bud into a swimming medusa (the stage that looks like the jellies we’re all familiar with). For all jellies, the medusa stage is when sexual reproduction happens, with the resulting larva settling on the substrate and turning into a polyp. For C. sowerbyi, the most common form of reproduction is asexual, where the polyps bud off into more polyps. Because of that, many populations of C. sowerbyi will be all male or all female.
So the next time you’re near a calm, freshwater environment in Colorado (or almost anywhere else), take a closer look underneath the surface. You might just see a jelly.