Freshwater Jellyfish

Common Name - Freshwater Jellyfish

Category - cindarians

ScientificName - Craspedacusta sowerbyi

Kingdom - Animalia

Phylum - Cnidaria

Class - Hydrozoa

Order - Hydroida

Family - Olindiidae

Genus - Craspedacusta

Species - sowerbyi


Description - Medusa form is umbrella or bell-shaped, jellyfish in appearance, normally dime to nickel-sized; clear to translucent with milky velum fringe and gonads. Fringe consists of nematocysts (stingers) and numerous tentacles (50 - 500) which are used for capturing prey. Swims in undulating or dancing fashion, up and down or even sideways. Hydroid or polyp stage is similar in appearance to the more well-known hydras except it is absent tentacles, and is normally found in colonies that are 2mm to 8 mm long.

Size - Medusa form (jellyfish form) is 0.20 - 0.87 inch (5 - 22 mm) in diameter

Ecological Role - Basically unknown. May impact zooplankton, possibly even ichthyoplankton populations during periods of abundance.

Fun Facts - Unlike their marine counterparts (the true jellyfish), freshwater jellyfish are incapable of inflicting damage to humans as their nematocysts cannot penetrate our skin. Ward and Whipple (1918) reported the first United States occurrence in the wild to be numerous specimens found in a creek near Frankfort, Kentucky, by Professor H. Garman in September of 1916. Freshwater jellyfish differ from the true marine jellyfish in that they possess a velum, or skirt, which forms a shelf on the interior margin of the fringe of the medusa form.

Food - Hydroid or polyp stage moves slowly across substrate feeding on small invertebrates. Medusa or jellyfish stage feeds on zooplankton. Prey is stunned by nematocysts.



Breeding - Sexual and asexual. Medusa release eggs and sperm into the surrounding water. The zygotes develop into planula larvae, which eventually settle to the bottom and develop into polyps. Polyps reproduce by budding, either through the formation of polyp buds, frustule buds (small cigar-shaped larvae that crawl on the bottom and develop a new polyp), or medusa buds, which develop into the familiar jellyfish form. In the United States, sexual reproduction is thought to be quite rare since most medusas found during periods of abundance are of one sex.


Habitat - Ponds, lakes, slow-moving streams and rivers, old quarries.

Kentucky Distribution - Only one species known in Kentucky and most of the United States, except coastal areas. Probably statewide, but rarely observed. Occurrence is very sporadic and unpredictable. May be numerous in some water bodies in some years, absent in successive years. Normally observed in the medusa or jellyfish stage and this is normally found in the late summer or early fall.

Life Cycle

Life Span

Life Stage


Seasonal Changes


Status - Rare, occasionally found in abundance for a short period




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Diagnosis and Control

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