Beroidae | |
---|---|
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Ctenophora |
Class: | Nuda Chun, 1879 |
Order: | Beroida Eschscholtz, 1829 |
Family: | Beroidae Eschscholtz, 1825 |
Genera | |
Beroidae is a family of ctenophores or comb jellies more commonly referred to as the beroids. It is the only known family within the monotypic order Beroida and the class Nuda. They are distinguished from other comb jellies by the complete absence of tentacles, in both juvenile and adult stages. Species of the family Beroidae are found in all the world's oceans and seas and are free-swimmers that form part of the plankton.
Some members of the diverse genus Beroe may occasionally attain a length of up to 30 centimetres (12 in), though most species and individuals are less than about 10 cm; Neis cordigera is among the largest species in the class, often exceeding 30 cm (12 in) in length. [1] The body is melon or cone-shaped with a wide mouth and pharynx and a capacious gastrovascular cavity. Many meridional canals branch off this and form a network of diverticulae in the mesogloea. There are no tentacles but there are a row of branched papillae, forming a figure of eight around the aboral tip. [2]
The sack-like body of the Beroe species may be cylindrical in cross section, or compressed to varying amounts according to species, while Neis is somewhat flattened and characterized by a pair of trailing gelatinous "wings" that extend beyond the aboral tip.
Like other comb jellies, the body wall of nudans consists of an outer epidermis and an inner gastrodermis, separated by a jelly-like mesoglea. The mesoglea has pigments that give many nudan species a slightly pink color; Neis cordigera may be yellowish or a deep orange-red.
Some nudans have a very large oral cavity, allowing them to swallow prey whole. While swimming, and particularly while pursuing prey, they close their mouths like a zipper so that they maintain a streamlined profile. The mouth is zipped closed from each end, and the edges seal shut by forming temporary inter-cellular connections. When close to the prey, the lips contract and the mouth is opened rapidly, sucking in the prey. This action is reversible and the lips can be resealed. An alternative method of feeding involves the lips spreading over the prey and the sword-shaped macrocilia lining the lips chopping off chunks. [3] The lips are sealed by the presence of adhesive strips of epithelial cells along their opposite edges. Not all species seem to have these strips which seem specifically adapted to those with wide mouths whereas species with small oral openings are able to control the opening of the aperture by more conventional means. [3]
Directly inside the mouth opening, in the lining of the gullet, can be found characteristic finger-like processes known as "macrocilia". These were first described by J.G.F. Will in 1844 and further investigated by George Adrian Horridge in 1965. He found they were complex structures composed of 2,000 to 3,000 filaments in a single, conical functional unit. Each macrocilium shows the typical eukaryote construction of nine external and two internal microtubules. The individual macrocilium is between 50 and 60 micrometres long and 6 to 10 micrometres thick, with the cilia bonded together in a hexagonal cross-sectional structure by permanent fibrils in three different planes. A system of tubules connects the basal bodies from which the macrocilia grow. [4]
The macrocilia move in unison. They are angled towards the gullet and are stacked on top of each other like roof tiles. By this arrangement they effectively grip parts of the prey in synchronized waves like a conveyor belt, transporting it to the stomach, and the throat muscles promote this process. The three-toothed tip of the macrocilia is stiff enough for it to rip the outer wall of larger prey such as other ctenophores; at the same time, proteolytic enzymes penetrate into the resulting wounds, rapidly incapacitating the victim. [4] [5]
Macrocilia also function as teeth, and can be used in the same way as the tentacles of Tentaculata.
As in other ctenophores, from the main stomach a network of channels branch through the mesogloea. Some of these have blind ends and others link up. They supply nutrients to the most active parts of the animal, the mouth, pharynx, combs of cilia and the sensory organs at the hind end of the body. Each comb plate has its own meridional canal situated directly beneath it and a ring of channels surround the mouth. [5]
At the aboral end of the animal (the opposite end from the mouth) is a statocyst, a balance organ that helps it to orient itself. Papillae surround the statocyst. Their function is unclear, but they are probably also used for sensory perception. The eight combs of cilia extend part way along the body in ribs. The combs are used in locomotion, with the cilia beating in synchronised waves to propel the animal. It usually moves with the mouth end in front, but the direction of movement can be reversed. When not actively moving, a vertical position is maintained, normally with the mouth upwards. [6]
Nudans feed on free swimming animals with soft bodies, primarily on other ctenophores, many of them larger than they are themselves. They actively hunt for prey, which they usually devour whole. Some species use their macrocilia as teeth to remove smaller chunks from their prey.
In the late 1980s the ctenophore species Mnemiopsis leidyi was introduced into the Black Sea, probably through ballast water, which led to the collapse of the local anchovy population. In 1997 another ctenophore species arrived— Beroe ovata, a predator of Mnemiopsis leidyi. The Beroe population underwent an initial explosion, until the numbers of both ctenophores stabilized. Nevertheless, both Mnemiopsis leidyi and Beroe ovata remain today in the Black Sea. The same phenomenon is occurring at the beginning of the 21st century in the Caspian Sea.
All species are hermaphrodites and reproduce sexually, having both female and male gonads. Although no detailed figures are available, it is assumed that self-fertilization is the exception among nudans. The fertilized eggs hatch into miniature versions of the adult animal, rather than distinct larval forms. They lack tentacles and are otherwise similar to the Cydippea larvae.
There are no known fossil nudans, so the phylogenetic evolution of the group by comparison with other modern ctenophores is not possible. In the traditional system, the Nuda form a class distinct from the Tentaculata, which all have at least rudimentary tentacles. This division, after provisional results of morphological and molecular studies, however, probably does not reflect the actual relationships within the ctenophores. The monophyly of Nuda is widely accepted, due to the complete lack of tentacles, and the presence of macrocilia as a common secondary feature, or synapomorphy.
There are approximately 25 species in the family Beroidae, grouped into two genera. The family and order were named in 1825 or 1829 by the German naturalist Johann Friedrich Eschscholtz.
Cnidaria is a phylum under kingdom Animalia containing over 11,000 species of aquatic animals found both in fresh water and marine environments, including jellyfish, hydroids, sea anemones, corals and some of the smallest marine parasites. Their distinguishing features are a decentralized nervous system distributed throughout a gelatinous body and the presence of cnidocytes or cnidoblasts, specialized cells with ejectable flagella used mainly for envenomation and capturing prey. Their bodies consist of mesoglea, a non-living, jelly-like substance, sandwiched between two layers of epithelium that are mostly one cell thick. Cnidarians are also some of the only animals that can reproduce both sexually and asexually.
Ctenophora comprise a phylum of marine invertebrates, commonly known as comb jellies, that inhabit sea waters worldwide. They are notable for the groups of cilia they use for swimming, and they are the largest animals to swim with the help of cilia.
Tentaculata is a class of comb jellies, one of two classes in the phylum Ctenophora. The common feature of this class is a pair of long, feathery, contractile tentacles, which can be retracted into specialised ciliated sheaths. In some species, the primary tentacles are reduced and they have smaller, secondary tentacles. The tentacles have colloblasts, which are sticky-tipped cells that trap small prey.
Lobata is an order of transparent marine invertebrates belonging to the phylum of Ctenophora in the class Tentaculata, and are commonly referred to as comb jellies or sea gooseberries. There are currently 19 extant known species in the order of Lobata. Members of Lobata exhibit a compressed body in the vertical plane and a pair of oral lobes. They are known to inhabit marine pelagic surfaces and the marine shores.
Colloblasts are unique, multicellular structures found in ctenophores. They are widespread in the tentacles of these animals and are used to capture prey. Colloblasts consist of a collocyte containing a coiled spiral filament, internal granules and other organelles.
Mnemiopsis leidyi, the warty comb jelly or sea walnut, is a species of tentaculate ctenophore. It is native to western Atlantic coastal waters, but has become established as an invasive species in European and western Asian regions. Three species have been named in the genus Mnemiopsis, but they are now believed to be different ecological forms of a single species M. leidyi by most zoologists.
Lampocteis is a monotypic genus of comb jellies, the only genus in family Lampoctenidae. The sole species in this new genus is Lampocteis cruentiventer, the bloodybelly comb jelly. This ctenophore was first collected in the Pacific Ocean off the coast of San Diego, California, in 1979. It was described in 2001. The generic name was formed from the Ancient Greek lampós and kteís ("comb"), referring to the iridescence of its "combs"; the specific epithet was formed from the Latin cruentus ("blood-red") and venter ("belly"). Two morphological differences separating it from previously known comb jellies warranted the naming of a new family for this animal. These jellies are typically found at a depth of 250-1,500 meters deep in the North Pacific Ocean.
Cydippida is an order of comb jellies. They are distinguished from other comb jellies by their spherical or oval bodies, and the fact their tentacles are branched, and can be retracted into pouches on either side of the pharynx. The order is not monophyletic, that is, more than one common ancestor is believed to exist.
Pleurobrachia bachei is a member of the phylum Ctenophora and is commonly referred to as the Pacific sea gooseberry. These comb jellies are often mistaken for medusoid Cnidaria, but lack stinging cells.
Mertensia ovum, also known as the Arctic comb jelly or sea nut, is a cydippid comb jelly or ctenophore first described as Beroe ovum by Johan Christian Fabricius in 1780. It is the only species in the genus Mertensia. Unusually among ctenophores, which normally prefer warmer waters, it is found in the Arctic and adjacent polar seas, mostly in surface waters down to 50 metres (160 ft).
Beroe, commonly known as the cigar comb jellies, is a genus of comb jellies in the family Beroidae. Beroe exhibits bioluminescence.
Beroe ovata is a comb jelly in the family Beroidae. It is found in the South Atlantic Ocean and the Mediterranean Sea and has been introduced into the Black Sea, the Aegean Sea, the Sea of Azov and the Caspian Sea. It was first described by the French physician and zoologist Jean Guillaume Bruguière in 1789.
Beroe cucumis is a species of comb jelly in the family Beroidae. It is found in the Atlantic Ocean. It was first described by the Danish missionary and naturalist Otto Fabricius in 1780.
Bolinopsis infundibulum, commonly known as the common northern comb jelly, is a species of comb jelly in the family Bolinopsidae. It is found in the northern Atlantic Ocean and was first described by the Danish naturalist Otto Friedrich Müller in 1776.
Pleurobrachia pileus is a species of comb jelly, commonly known as a sea gooseberry. It is found in open water in the northern Atlantic Ocean, the North Sea, the Baltic Sea and the Black Sea, and was first described by the Danish zoologist Otto Friedrich Müller in 1776.
Edwardsiella lineata, the lined anemone, is a species of sea anemone in the family Edwardsiidae. It is native to the northwestern Atlantic Ocean where it occurs in the subtidal zone.
Neis is a genus of nudan ctenophores. It is a monotypic genus containing the single species Neis cordigera. It occurs only near Australia. As all beroids, it is a free-swimmer that form part of the plankton.
Beroe abyssicola is a species of beroid ctenophore, or comb jelly. It is largely found in deep waters in the North Pacific Ocean, and is common in Japan and the Arctic Ocean. A predator, Beroe feeds mostly on other ctenophores by swallowing them whole. Like other ctenophores, B. abyssicola has a simple nervous system in the form of a nerve net, which it uses to direct its movement, feeding, and hunting behaviors.
Euplokamis is a genus of ctenophores, or comb jellies, belonging to the monotypic family Euplokamididae. It shares the common name sea gooseberry with species of the genus Pleurobrachia. After being originally described by Chun (1879), the family Euplokamididae was expanded by Mills (1987) due to the discovery of a new species, Euplokamis dunlapae. Further research indicated that Euplokamis should be identified from Mertensiidae due to the rows of combs and some compression. They may also be distinguished from the genus Pleurobrachia due to their more elongated shape. Additionally, various adaptations of Euplokamis have been observed such as the use of tentacles for movement/feeding, a complex nervous system, and bioluminescent capabilities. Other characteristics including a defined mesoderm, lack of stinging cells, developmental differences, and symmetry supported the reclassification of these organisms.
Beroe gracilis is a species of comb jelly in the family Beroidae. It is a free-swimming species found in the North Sea, the Atlantic Ocean and the Mediterranean Sea.
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