Cyclostomata
Cyclostomata
1. (subphylum Ectoprocta, class Gymnolaemata) An order of bryozoans in which the colony is made up of thin-walled, finely perforate, calcareous tubes. The aperture of each individual is rounded, without any covering. Reproduction and larval development take place in a single, enlarged individual called an ‘ovicell’. The order appeared in the Ordovician and exists at the present day.
2. The group that comprises the jawless fish, the most primitive of living vertebrates, characterized by the absence of jaws and paired fins, by a series of gill pouches rather than gill slits, by a cartilaginous skeleton without proper vertebrae, and by never having more than two semicircular canals. The taxonomic status of the term ‘Cyclostomata’ is somewhat confused: at various times it has been ranked as an order, superorder, subclass, and class. The extant orders usually included are the lampreys (Petromyzoniformes) and the hagfish (Myxiniformes) but there is now considerable doubt whether they are closely related to each other; the hagfish may be a sister group to other vertebrates.
1. (subphylum Ectoprocta, class Gymnolaemata) An order of bryozoans in which the colony is made up of thin-walled, finely perforate, calcareous tubes. The aperture of each individual is rounded, without any covering. Reproduction and larval development take place in a single, enlarged individual called an ‘ovicell’. The order appeared in the Ordovician and exists at the present day.
2. The group that comprises the jawless fish, the most primitive of living vertebrates, characterized by the absence of jaws and paired fins, by a series of gill pouches rather than gill slits, by a cartilaginous skeleton without proper vertebrae, and by never having more than two semicircular canals. The taxonomic status of the term ‘Cyclostomata’ is somewhat confused: at various times it has been ranked as an order, superorder, subclass, and class. The extant orders usually included are the lampreys (Petromyzoniformes) and the hagfish (Myxiniformes) but there is now considerable doubt whether they are closely related to each other; the hagfish may be a sister group to other vertebrates.
More From encyclopedia.com
Terebratulida , Terebratulida (terebratulids; class Articulata) Order of Brachiopoda with punctate shells, rounded hinge lines, functional pedicle, deltidial plates,… Order , Order
Few notions have both so rich a heritage of meaning and so clear an application to all fields of knowledge as does order. There are many myths… Rhynchonellids , Rhynchonellida (rhynchonellids; class Articulata) Order of brachiopods (Brachiopoda), with rostrate shells, a functional pedicle, and a delthyrium pa… Salmoniformes , Salmoniformes (subclass Actinopterygii, superorder Protacanthopterygii) An order of bony fish that have a single dorsal fin which, like the pelvic fi… Anglerfishes , Lophiiformes (subclass Actinopterygii, superorder Paracanthopterygii) An order of marine, bottom-dwelling fish that have a relatively large head, wid… Diplostraca , Conchostraca (clam shrimps; class Branchiopoda, order Diplostraca) Suborder of branchiopods called ‘clam shrimps’ because the body is almost or compl…
About this article
Cyclostomata
All Sources -
You Might Also Like
NEARBY TERMS
Cyclostomata