- Byname:
- Comb Jelly
- Related Topics:
- sea gooseberry
- sea walnut
- lobed comb jelly
- Cydippida
- cat’s-eye
ctenophore
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What is a ctenophore?
A ctenophore is a marine invertebrate in the phylum Ctenophora, also known as comb jellies, sea walnuts, or sea gooseberries. They possess vertical ciliary combs on their surfaces, giving the phylum its name, which comes from the Greek ctene, meaning "comb," and phora, meaning "bearer".
Most comb jellies are small, but the Venus's girdle can grow to over 1 meter. They inhabit marine environments worldwide, particularly near shorelines. Ctenophores swim freely, using their comb rows for movement, and are mostly carnivorous, feeding on small planktonic animals. They have a primitive nerve network and lack an excretory system. Ctenophores are hermaphroditic, with gametes released for external fertilization.
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Where do ctenophores live?
Ctenophores are marine invertebrates found in almost all ocean regions, especially in surface waters near shores. Though most have restricted distributions, at least two species (Pleurobrachia pileus and Beroe cucumis) are cosmopolitan.
Most ctenophores float freely, but some creep or are parasitic. They are frequently found in vast swarms, especially in bays, lagoons, and other coastal waters.
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What do ctenophores look like?
Ctenophores, also known as comb jellies, are marine invertebrates that derive their name from the comb-like rows of cilia they use for swimming. Most comb jellies are colorless, but some, like Beroe cucumis, are pink, and the Venus's girdle (Cestum veneris) is violet.
Most of the roughly 90 species are spherical or oval-shaped, featuring a statocyst (a sensory organ) at one end and a mouth at the opposite end. They possess eight comb rows that extend from the statocyst and function as organs for movement. Ctenophores swim with the mouth facing forward. More primitive species have long, branched tentacles covered in colloblasts, which secrete a sticky substance to capture prey. Many comb jellies are bioluminescent, producing brilliant displays of bluish or greenish light at night.
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How do ctenophores move in the water?
Ctenophores, also known as comb jellies, are marine invertebrates that move using rows of cilia called comb plates. These plates run along the length of their bodies. The cilia beat in coordinated waves, with the effective stroke directed toward the statocyst (a sense organ), which is at the opposite end of the mouth. This motion propels the ctenophore through the water, typically with the mouth facing forward. Most comb jellies are free-floating, but some can creep or are parasitic.
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What do ctenophores eat and how do they catch their food?
Ctenophores, also known as comb jellies, are carnivorous marine invertebrates that eat planktonic animals, including young fish, larval crabs, clams, oysters, and copepods.
Most ctenophores have a pair of long, branched tentacles used for capturing food. These tentacles are equipped with colloblasts, unique adhesive cells that secrete a sticky substance to which prey adheres upon contact.
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How are ctenophores different from jellyfish and other similar sea creatures?
Ctenophores, also known as comb jellies, share a resemblance to cnidarian medusa (jellyfish), but they possess distinct characteristics. Unlike jellyfish and other cnidarians, ctenophores lack stinging cells (nematocysts). Instead, they use adhesive cells called colloblasts, found only in ctenophores, to capture prey.
Ctenophores possess a primitive nervous system known as a nerve net, similar to jellyfish; however, they are more highly evolved due to the presence of a definite mesoderm. Ctenophores also have biradial symmetry and fundamental differences in embryological development compared to cnidarians. They use cilia arranged in comb rows for locomotion, and most are bioluminescent, displaying brilliant bluish or greenish light.
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ctenophore, any of the numerous marine invertebrates constituting the phylum Ctenophora. The phylum derives its name (from the Greek ctene, or “comb,” and phora, or “bearer”) from the series of vertical ciliary combs over the surface of the animal. The body form resembles that of the cnidarian medusa. Various forms of ctenophores are known by other common names—sea walnuts, sea gooseberries, cat’s-eyes.
Though comb jellies are, for the most part, of small size, at least one species, the Venus’s girdle, may attain a length of more than 1 m (3 feet). One parasitic species is only 3 mm (1/8 inch) in diameter. Some ctenophores live in somewhat brackish water, but all are confined to marine habitats. They live in almost all ocean regions, particularly in surface waters near shores. At least two species (Pleurobrachia pileus and Beroe cucumis) are cosmopolitan, but most have a more restricted distribution.
Apart from a few creeping and parasitic species, ctenophores float freely suspended in the water. They are frequently swept into vast swarms, especially in bays, lagoons, and other coastal waters. Except for one parasitic species, all of them are carnivorous, eating myriads of small planktonic animals. When abundant in a region, ctenophores consume most of the young of fish, larval crabs, clams, and oysters, as well as copepods and other planktonic animals that would otherwise serve as food for such commercial fish as sardines and herring. In turn, however, comb jellies are themselves consumed by certain fish.
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Natural history.
Ctenophores are hermaphroditic; eggs and sperm (gametes) are produced in separate gonads along the meridional canals that house the comb rows. In most ctenophores, these gametes are released into the water, where fertilization and embryonic development take place. In Pleurobrachia and in other Cydippida, the larva closely resembles the adult, so that there is little change with maturation. Most ctenophores, however, have a so-called cydippid larva, which is ovoid or spherical with two retractable tentacles. The metamorphosis of the globular cydippid larva into an adult is direct in ovoid-shaped adults and rather more prolonged in the members of flattened groups. Only the parasitic Gastrodes has a free-swimming planula larva comparable to that of the cnidarians.
Form and function.
Most ctenophores are colourless, although Beroe cucumis is pink and the Venus’s girdle (Cestum veneris) is delicate violet. The colourless species are transparent when suspended in water, except for their beautifully iridescent rows of comb plates. Most of the comb jellies are bioluminescent; they exhibit nocturnal displays of bluish or greenish light that are among the most brilliant and beautiful known in the animal kingdom.
Most of the nearly 90 known species of comb jellies are spherical or oval, with a conspicuous sense organ (the statocyst) at one end (aboral) of the body and a mouth at the other end (oral). The eight comb rows that extend orally from the vicinity of the statocyst serve as organs of locomotion. Each comb row is made up of a series of transverse plates of very large cilia, fused at the base, called combs. When the cilia beat, the effective stroke is toward the statocyst, so that the animal normally swims oral end first. The more primitive forms (order Cydippida) have a pair of long, retractable branched tentacles that function in the capture of food. The tentacles are richly supplied with adhesive cells called colloblasts, which are found only among ctenophores. These cells produce a sticky secretion, to which prey organisms adhere on contact.
The mouth leads into a tubular pharynx, from the aboral end of which arises a complex, branched series of canals that make up the digestive tract. Since this structure serves both digestive and circulatory functions, it is known as a gastrovascular cavity. Ctenophores have no true anus; the central canal opens toward the aboral end by two small pores, through which a small amount of egestion can take place.
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Gonads develop as thickenings of the lining of the digestive canals. The nervous system is a primitive nerve network, somewhat more concentrated beneath the comb plates. It is similar to the cnidarian nervous system. There is no trace of an excretory system.
The outside of the body is covered by a thin layer of ectodermal cells, which also line the pharynx. A second thin layer of cells, constituting the endoderm, lines the gastrovascular cavity. Between the ectoderm and the endoderm is a thick gelatinous layer, the mesoglea. Because it contains not only many mesenchymal cells (or unspecialized connective tissue) but also specialized cells (e.g., muscle cells), the mesoglea forms a true mesoderm. In this respect the comb jellies are more highly evolved than even the most complex cnidarians.
Classification.
Ctenophores and cnidarians were formerly placed together in the phylum Coelenterata. Modern authorities, however, have separated the cnidarians and ctenophores on the basis of the following ctenophore characteristics: (1) the lack of the stinging cells (nematocysts) that are characteristic of cnidarians; (2) the existence of a definite mesoderm in the ctenophores; (3) fundamental differences in embryological development between the two groups; and (4) the biradial symmetry of ctenophores. It is, however, generally thought that ctenophores and cnidarians share a common evolutionary ancestor.