Author:
Qjure
Book:
Qjurious
Type:
Info
Chapter:
4-220.00.00
Ctenophora
English: Comb jellies.
Name: from the Greek kteis, comb and phero, carry.
Members: 100 to 150 valid species, possibly 25 that have not been fully described and named.
Region: worldwide.
Habitat: marine.
Zoology
Animals; few millimeters to 1.5 m.
Motion: swimming with combs, groups of cilia; largest animals that swim by cilia.
Nervous: decentralized nerve net rather than a brain.
Body: mass of jelly, with one layer of cells on the outside and another lining the internal cavity; layers are two cells deep; decentralized nerve net; water flows through the body cavity for digestion and respiration.
Food: microscopic larvae, rotifers, small crustaceans; can eat ten times their own weight in a day.
Reproduction: most are hermaphrodites; fertilization is generally external, platyctenid eggs are fertilized inside their parent bodies and kept there until they hatch; young are generally planktonic and in most species look like miniature cydippids, gradually changing into the adult shape as they grow; young beroids are miniature beroids with large mouths and no tentacles; young platyctenids live as cydippid-like plankton until they reach near-adult size, but then sink to the bottom and rapidly metamorphose into the adult form.
Taxonomy
Some authors combined ctenophores and cnidarians in one phylum, Coelenterata, as both groups rely on water flow though the body cavity for both digestion and respiration. Recent authors classify them in separate phlya.
Ctenophores in the evolutionary family tree of animals has long been debated, and the majority view at present, based on m
Molecular phylogenetics show that cnidarians and bilaterians are more closely related to each other than either is to ctenophores, their common ancestor was cydippid-like. Modern groups appeared relatively recently. Evidence indicates that the cydippids are not monophyletic, because all the other traditional ctenophore groups are descendants of various cydippids.
Clades
Tentaculata (with tentacles)
Cydippida, egg-shaped animals; egg-shaped bodies; a pair of long, retractable tentacles fringed with tentilla, litte tentacles, covered with colloblasts, sticky cells that capture prey.
Lobata, with paired thick lobes.
Platyctenida, flattened animals that live on or near the sea-bed; most lack combs as adults, and use their pharynges as suckers to attach themselves to surfaces.
Ganeshida, with a pair of small lobes round the mouth, but an extended pharynx like that of platyctenids.
Cambojiida
Cryptolobiferida
Thalassocalycida, with short tentacles and a jellyfish-like "umbrella".
Cestida, ribbon-shaped and the largest ctenophores.
Nuda (without tentacles).
Order Beroida and family Beroidae
Genus Beroe (several species)
Genus Neis (one species)