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By Autumn Erwin
Geographic Range
Craspedacusta sowerbyi is a freshwater jellyfish occupying all continents, although quite rare in Africa (Smith 1998). It was first taxonomically recorded in England, in 1880. The United States did not report Craspedacusta sowerbyi until 1908. As of February 8, 2000, this organism was reported in 43 out of 50 states. With increased interstate and intercontinental travel, the translocation of Craspedacusta sowerbyi into new habitats continues (Davis 1998).
Biogeographic Regions:
nearctic 
(native ); neotropical (native ).
Habitat
Craspedacusta sowerbyi is a fresh-water Cnidarian and has been found in a variety of water environments: freshwater lakes, reservoirs, man-made impoundments, water-filled gravel pits, rock quarries, algae-filled ponds, and rivers. However, despite its ecological diversity, Craspedacusta sowerbyi seems to favor calm water to the rough water characteristic of most rivers (Pennak 1989, Peard 2000).
Aquatic Biomes:
lakes and ponds; rivers and streams.
Physical Description
(0.11 to 0.18 oz; avg. 0.14 oz)
This organism shares many of the same traits characteristic of most jellyfish. It is a white or green gelatinous creature, with 99% of its body made of water (Peard, 2000). This organism lacks a head, a skeleton, contains no special organs for respiration or excretion (Davis, 1998).
The freshwater jellyfish is dimorphic, alternating between both a polyp and medusa morph (Johnson, 1999). The mature medusa stage resembles a bell shape. It also contains the manubrium, four radial canals, and one circular canal, typical of most jellyfish.
The diameter of the circular canal is anywhere from 5 to 22mm. It bears string-like tentacles, arranged in sets of three to seven. The tentacles are solid and vary in length. Tentacles, with nematocysts, aid in capturing food and serve as a type of protection against predation. At the base of their tentacles, jellyfish have eyespots. These are used in detecting light and dark, providing another means by which to find food and escape predation (Davis 1998).
This organism can move in any direction by pulsating contractions along its bell surface. The bell margin is made up of statocysts while the velum is made of nematocysts, which are in abundance around the mouth. This is helpful when the jellyfish is killing its prey, helping to draw the prey into the jellyfish's mouth (Pennak 1989).
The Craspedacusta swerbyi contains a velum atypical of other jellyfish. This structure is a thin, shelf-like structure that extends inward from the ring canal of the bell. There is a hole in the velum by which the manubrium extends upward toward the mouth. This structure is unique to this species (Peard, 2000).
Reproduction
Craspedacusta sowerbyi reproduce asexually in the polyp form, via budding. They can form three different types of buds: polyps, frustules, or medusa buds. The polyp bud grows and develops while still attached to the original polyp. The frustule bud develops into a frustule; they are only able to travel a short distance before devloping into a new polyp. The medusa bud reproduces sexually via fertilized eggs, which develop into planula larva. These larva settle onto underwater surfaces (plant roots, rocks, and tree roots) where they develop into polyps (Peard 2000).
Sexual reproduction is relatively rare in this form of jellyfish. Most populations are strictly male or female (Peard, 2000). The rarity of sexual reproduction is beneficial to populations wanting to limit genetic variation, in which changes in morphology could be detrimental to their continuing existence. In addition, it eliminates the hassle of finding a mate in order to be able to reproduce (Johnson 1999).
Scientists are still learning about the larvae and the conditions affecting the dispersal of this organism. Correlation studies have demonstrated a relationship between increased travel distance of the larvae and increased polyp feeding. It is believed that increased polyp feeding increases the energy stores of the frustules, allowing them to travel greater distances (Peard 2000).
The polyps can be distributed in nonmotile ways as well. During winter months, polyps contract and become dormant, as to survive the cold temperatures. These polyps, also known as podocysts, can be transported by aquatic plants, aquatic animals, or birds' feet to new areas of dispersal. As winter ends, and conditions become more favorable, the podocysts mature back into polyps (Peard 2000).
Behavior
Freshwater jellyfish can be spotted during the summer and fall months, with August and September being peak months. Warm water temperatures and an abundance of food cause a proliferation of this species (Peard 2000).
Jellyfish tend to lie on the bottom of shallow waters; they generally conserve their energy for efforts of capturing food or escaping predation (Pennak 1989).
Food Habits
The diet of the freshwater jellyfish consists primarily of zooplankton, which range in size from 0.2 to 2.0 mm in size. It uses its nematocysts located on tentacles to sting and paralyze prey before scooping it into its mouth (Pennak, 1989).
Economic Importance for Humans: Negative
An overpopulation of this species can decrease the oxygen level in the freshwater community, causing other organisms to die out. When oxygen levels are low, fish are often one of the first species to suffer (Johnson 1999). This can be globally destructive as a large population of the world depends on fish for food (Kottak 2000).
Economic Importance for Humans: Positive
Freshwater jellyfish are eaten in some countries; however, they are not a main source of food (Berkley 2000).
Conservation Status
Freshwater jellyfish are unpredictable in their appearance within bodies of water. They may appear in large numbers one year, not appear the next, and come back several years later (Peard 2000). Thus, populations are difficult to predict.
Despite this unpredictability, conservation within the United States, and around the world, does not appear to be an issue. Craspedacusta sowerbyi remain the most populated jellyfish in the United States (Davis 1998).
Other Comments
Craspedacusta sowerbyi possess cnidocytes with nematocysts, otherwise known as stinging cells. Unlike other jellyfish, the nematocysts of freshwater jellyfish are unable to penetrate human skin (Peard 2000). Therefore, freshwater jellyfish are unable to produce the painful sting caused by most marine jellyfish.
Freshwater jellyfish are hard to raise in an aquarium. If you choose to try raising one, here are a couple of things to keep in mind: 1) make sure that you have a filtration system that will not suck up the jellyfish (sponge filters are not recommended); 2) do not use a tank that has a strong current; 3) jellyfish can kill small fish with their stinging cells; 4) jellyfish require a constant supply of food (brine shrimp or Daphnia are suggested) (Peard 2000).
Fossil records date this organism back to the Pre-Cambrian era (Smith 1998).
Information about Craspedacusta sowerbyi is incomplete. Researchers continue to study this organism. The University of Pennsylvania is currently involved in an in-depth study of this creature (Peard 2000).
Contributors
Autumn Erwin (author), Southwestern University.
Stephanie Fabritius (editor), Southwestern University.
