Cydippida is an order of

comb jellies Ctenophora (; ctenophore ; ) 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 (commonly referred to as "combs"), an ...

. 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 pharynx (plural: pharynges) is the part of the throat behind the mouth and nasal cavity, and above the oesophagus and trachea (the tubes going down to the stomach and the lungs). It is found in vertebrates and invertebrates, though its struc ...

. The order is not

monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...

, that is, more than one common ancestor is believed to exist.

Anatomy

Cydippids have bodies that are more or less rounded, sometimes nearly spherical and other times more cylindrical or egg-shaped; the common coastal "sea gooseberry," '' Pleurobrachia'', has an egg-shaped body with the mouth at the narrow end. From opposite sides of the body extends a pair of long, slender tentacles, each housed in a sheath into which it can be withdrawn. Some species of cydippids have bodies that are flattened to various extents, so that they are wider in the plane of the tentacles. The tentacles are typically fringed with tentilla ("little tentacles"), although a few genera have simple tentacles without these side-branches. The tentacles and tentilla are densely covered with microscopic

colloblast 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 ...

s that capture prey by sticking to it. These are specialized

mushroom A mushroom or toadstool is the fleshy, spore-bearing fruiting body of a fungus, typically produced above ground, on soil, or on its food source. ''Toadstool'' generally denotes one poisonous to humans. The standard for the name "mushroom" is t ...

-shaped cells in the outer layer of the epidermis, and have three main components: a domed head with

vesicles Vesicle may refer to: ; In cellular biology or chemistry * Vesicle (biology and chemistry), a supramolecular assembly of lipid molecules, like a cell membrane * Synaptic vesicle ; In human embryology * Vesicle (embryology), bulge-like features o ...

(chambers) that contain adhesive; a stalk that anchors the cell in the lower layer of the epidermis or in the mesoglea; and a

spiral In mathematics, a spiral is a curve which emanates from a point, moving farther away as it revolves around the point. Helices Two major definitions of "spiral" in the American Heritage Dictionary are: In addition to colloblasts, members of the genus ''

Haeckelia ''Haeckelia'' is a genus of ctenophores belonging to the family Cydippida. The species of this genus are found in Europe and Northern America. Species: *''Haeckelia beehleri'' *''Haeckelia bimaculata'' *''Haeckelia filigera'' *''Haeckelia ...

'', which feed mainly on

jellyfish Jellyfish and sea jellies are the informal common names given to the medusa-phase of certain gelatinous members of the subphylum Medusozoa, a major part of the phylum Cnidaria. Jellyfish are mainly free-swimming marine animals with umbrella- ...

, incorporate their victims' stinging

cnidocyte A cnidocyte (also known as a cnidoblast or nematocyte) is an explosive cell containing one large secretory organelle called a cnidocyst (also known as a cnida () or nematocyst) that can deliver a sting to other organisms. The presence of this ce ...

s into their own tentacles — some cnidaria-eating

nudibranch Nudibranchs () are a group of soft-bodied marine gastropod molluscs which shed their shells after their larval stage. They are noted for their often extraordinary colours and striking forms, and they have been given colourful nicknames to matc ...

s similarly incorporate cnidocytes into their bodies for defense. The tentilla of ''

Euplokamis ''Euplokamis'' is a genus of ctenophores, or comb jellies, belonging to the monotypic family Euplokamidae, Euplokamididae. Despite living for hundreds of millions of years in marine environments, there is minimal research regarding ''Euplokamis'' ...

'' differ significantly from those of other cydippids: they contain

striated muscle Striations means a series of ridges, furrows or linear marks, and is used in several ways: * Glacial striation * Striation (fatigue), in material * Striation (geology), a ''striation'' as a result of a geological fault * Striation Valley, in Ant ...

, a cell type otherwise unknown in the comb jellies; and they are coiled when relaxed, while the tentilla of all other known ctenophores elongate when relaxed. ''Euplokamis tentilla have three types of movement that are used in capturing prey: they may flick out very quickly (in 40 to 60 milliseconds); they can wriggle, which may lure prey by behaving like small planktonic worms; and they coil around prey. The unique flicking is an uncoiling movement powered by contraction of the

. The wriggling motion is produced by

smooth muscle Smooth muscle is an involuntary non-striated muscle, so-called because it has no sarcomeres and therefore no striations (''bands'' or ''stripes''). It is divided into two subgroups, single-unit and multiunit smooth muscle. Within single-unit mus ...

s, but of a highly specialized type. Coiling around prey is accomplished largely by the return of the tentilla to their inactive state, but the coils may be tightened by smooth muscle. There are eight rows of combs that run from near the mouth to the opposite end, and are spaced evenly round the body. The "combs" beat in a

metachronal rhythm A metachronal rhythm or metachronal wave refers to wavy movements produced by the sequential action (as opposed to synchronized) of structures such as cilia, segments of worms, or legs. These movements produce the appearance of a travelling wave. ...

rather like that of a

Mexican wave The wave (known as a Mexican wave or stadium wave outside of North America) is an example of metachronal rhythm achieved in a packed stadium when successive groups of spectators briefly stand, yell, and raise their arms. Immediately upon str ...

. From each balancer in the statocyst a ciliary groove runs out under the dome and then splits to connect with two adjacent comb rows, and in some species runs all the way along the comb rows. This forms a ''mechanical'' system for transmitting the beat rhythm from the combs to the balancers, via water disturbances created by the cilia.

Families

Cydippida contains 11 families: *

Aulacoctenidae ''Aulacoctena'' is a monotypic genus of ctenophores Ctenophora (; ctenophore ; ) comprise a phylum of marine invertebrates, commonly known as comb jellies, that inhabit sea waters worldwide. They are notable for the groups of cilia the ...

Bathyctenidae Bathyctenidae is a family of ctenophores belonging to the order Cydippida. The family consists of only one genus: ''Bathyctena'' Mortensen, 1932. References

Tentaculata {{ctenophore-stub ...

Cryptocodidae Cryptocodidae is a family of ctenophores Ctenophora (; ctenophore ; ) 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 sw ...

Ctenellidae Ctenellidae is a family of ctenophores belonging to the order Cydippida 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 ...

Dryodoridae Dryodoridae is a family of ctenophores belonging to the order Cydippida 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 ...

Euplokamididae ''Euplokamis'' is a genus of ctenophores, or comb jellies, belonging to the monotypic family Euplokamididae. Despite living for hundreds of millions of years in marine environments, there is minimal research regarding ''Euplokamis'', primarily d ...

Haeckeliidae Haeckeliidae is a family of ctenophores belonging to the order Cydippida. Genera: * ''Haeckelia ''Haeckelia'' is a genus of ctenophores belonging to the family Cydippida. The species of this genus are found in Europe and Northern America. ...

Lampeidae Lampeidae is a family of ctenophores belonging to the order Cydippida. Genera: * '' Gastropodes'' * '' Lampea'' Stechow, 1921 * ''Lampetia In Greek mythology, Lampetia ( grc, Λαμπετίη, translit=Lampetíē or grc, Λαμπετία, ...

Mertensiidae Mertensiidae is a family of ctenophores belonging to the order Cydippida. Genera: * '' Callianira'' Péron & Lesueur, 1808 * '' Charistephane'' Chun, 1879 * '' Gastrodes'' Korotneff, 1888 * ''Mertensia ''Mertensia'' is a genus of flowering p ...

Pleurobrachiidae Pleurobrachiidae is a family of ctenophores belonging to the order Cydippida. Genera: * ''Hormiphora'' L.Agassiz, 1860 * ''Minictena'' C.Carré & D.Carré, 1993 * ''Moseria (ctenophore), Moseria'' Ghigi, 1909 * ''Pleurobrachia'' Fleming, 182 ...

Pukiidae Pukiidae is a family of ctenophores belonging to the order Cydippida 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 ...

There are additionally

incertae sedis ' () or ''problematica'' is a term used for a taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertainty ...

genera including '' Duobrachium''.

References

{{Taxonbar, from=Q151079 Tentaculata Animal orders

Anatomy

Families

See also

References