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The comb jelly is a marine invertebrate that swims by beating rows of cilia that resemble combs. Some species have rounded bodies and tentacles like jellyfish, but comb jellies and jellyfish belong to two separate phyla. Jellyfish are cnidarians, while comb jellies belong to the phylum ctenophora. The name ctenophora comes from Greek words that mean "comb carrying." Approximately 150 comb jelly species have been named and described to date. Examples include the sea gooseberry (Pleurobrachia sp.) and Venus' girdle (Cestum veneris).
Fast Facts: Comb Jelly
- Scientific Name: Ctenophora
- Common Names: Comb jelly, comb jellyfish
- Basic Animal Group: Invertebrate
- Size: 0.04 inches to 4.9 feet
- Lifespan: Less than a month to 3 years
- Diet: Carnivore
- Habitat: Marine habitats worldwide
- Population: Abundant
- Conservation Status: Not Evaluated
As their name implies, comb jelly bodies are gelatinous. Species that live near the water surface are transparent, but those that live deeper in the water or parasitize other animals may be brightly colored. Some species have tentacles. Most species have eight strips of cilia, called comb rows, that run the length of their body. Ctenophores are the largest non-colonial animals that use cilia for locomotion. The comb rows scatter light and produce a rainbow effect. Most species are bioluminescent blue or green and some flash light or eject a bioluminescent "ink" when disturbed. Comb jellies display a wide array of body plans. In contrast to jellyfish, comb jellies are not radially symmetrical. Most are bilaterally symmetrical, like humans. They range in size and shape from tiny (0.04 inch) spheroids to long (4.9 feet) ribbons. Some are lobe-shaped, while bottom-dwelling species resemble sea slugs.
Habitat and Range
Ctenophores live all over the world, from the tropics to the poles and from the ocean surface down to its depths. Comb jellies are not found in fresh water. They live in the ocean and in brackish bays, marshes, and estuaries.
Except for one genus that is partially parasitic, comb jellies are carnivores. They prey on other ctenophores and on zooplankton, including small crustaceans, fish larvae, and mollusk larvae. They employ a wide range of strategies to catch prey. Some use tentacles to form web-like structures, others are ambush predators, and still others dangle sticky lures to attract prey.
Although masses of comb jellies may occur, they actually live solitary lives. Ctenophores use different neurotransmitters than other animals. A comb jelly lacks a brain or nervous system, but has a nerve net. Nervous impulses direct muscles to move the animal as well as to capture and manipulate prey. It has a statolith made of calcium carbonate that it uses to sense orientation. Chemoreceptive cells near the jelly's mouth allow it to "taste" prey.
Reproduction and Offspring
Sexes are separate in a few species, but most comb jellies are simultaneous hermaphrodites. Both self-fertilization and cross-fertilization can occur. Gametes are expelled through the mouth. Fertilization often occurs in the water, but in Coeloplana and Tjalfiella, gametes are taken into the mouth for internal fertilization. Fertilized eggs develop directly into the adult form, without larval stages and without parental care. Comb jellies produce gametes as long as there is sufficient food. Some species regenerate if injured and reproduce asexually as well as sexually. Small parts of these animals break off and grow into adults. Little is known about most species, but the lifespan of those that have been studied ranges from less than a month to three years.
No ctenophore species has a conservation status. Generally, comb jellies are not considered threatened or endangered. Like other marine species, they are affected by climate change, pollution, and weather. Comb jellies are prey for several species, including the endangered leatherback sea turtle.
Comb Jellies and Humans
Unlike jellyfish, comb jellies cannot sting. While the animals are not directly used by humans, they are important for marine food chains. Some species control zooplankton which could wipe out phytoplankton if left unchecked. Invasive comb jellies, carried in ship ballast water, diminished fish catches in the Sea of Azov and Black Sea by eating fish larvae and the crustaceans that are the food source for mature fish.
- Boero, F. and J. Bouillon. Cnidaria and Ctenophora (Cnidarians and Comb Jellies). in K Rohde, ed. Marine Parasitology. Australia: CSIRO Publishing, 2005.
- Brusca, R. C. and G. J. Brusca. Invertebrates (2nd ed.). Sinauer Associates, 2003, ch. 9, p. 269. ISBN 0-87893-097-3.
- Haddock, S. and J. Case. "Not All Ctenophores Are Bioluminescent: Pleurobrachia." Biological Bulletin, 189: 356-362, 1995. doi:10.2307/1542153
- Hyman, Libbie Henrietta. The Invertebrates: Volume I, Protozoa Through Ctenophora. McGraw Hill, 1940. ISBN 978-0-07-031660-7.
- Tamm, Sidney L. "Mechanisms of Ciliary Co-ordination in Ctenophores." Journal of Experimental Biology. 59: 231-245, 1973.