Cheilostomata
Encyclopedia
Cheilostomata, an order of Bryozoa
in the class Gymnolaemata
, are exclusively marine, colonial invertebrate animals. Cheilostome colonies are composed of calcium carbonate
and grow on a variety of surface
s, including rock
s, shells
, seagrass
and kelp
s. The colony shapes range from simple encrusting sheets to erect branching and even unattached forms. As in other bryozoa
n groups, each colony is composed of a few to thousands of individual polypide
s, which has a U-shaped gut, and no respiratory
, circulatory, or nerve system. Unique among bryozoans, cheilostome polypides are housed in a box-shaped zooids, which do not grow larger once the zooid is mature. The opening of through which the polypide protrudes is protected by a calcareous
or chitin
ous lidlike structure, an operculum
. Cheilostomes possess avicularia, which have modified the operculum into a range of mandibles (possibly for defense) or hair-like setae (possibly for cleaning).
The cheilostomes are the most abundant and varied of modern bryozoans. The classification in suborders is based upon frontal calcification and the mechanism of lophophore protrusion.
(Pyriporopsis) but diversified very slowly during the Early Cretaceous
, with only 1 family known up to the Albian
. During the Late Cretaceous, cheilostomes diversified rapidly to reach a level of more than 20 families in the Maastrichtian
. This diversification is thought to be a consequence of the evolution of a new larval type. Though the K-T Extinction Event had some impact on genetic diversity, the rapid diversification continued into the Eocene, then apparently reaching a plateau of about 50 families up to the Recent.
Bryozoa
The Bryozoa, also known as Ectoprocta or commonly as moss animals, are a phylum of aquatic invertebrate animals. Typically about long, they are filter feeders that sieve food particles out of the water using a retractable lophophore, a "crown" of tentacles lined with cilia...
in the class Gymnolaemata
Gymnolaemata
Gymnolaemata is a class of the phylum Bryozoa. Gymnolaemata typically live under seawater and grow on surfaces of rocks, kelps, and even in some cases, on animal species like fish. They are mostly marine bryozoans with cylindrical or flattened zooids. The lophophore is protruded by action of...
, are exclusively marine, colonial invertebrate animals. Cheilostome colonies are composed of calcium carbonate
Calcium carbonate
Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks in all parts of the world, and is the main component of shells of marine organisms, snails, coal balls, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural lime,...
and grow on a variety of surface
Surface
In mathematics, specifically in topology, a surface is a two-dimensional topological manifold. The most familiar examples are those that arise as the boundaries of solid objects in ordinary three-dimensional Euclidean space R3 — for example, the surface of a ball...
s, including rock
Rock (geology)
In geology, rock or stone is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic...
s, shells
Seashell
A seashell or sea shell, also known simply as a shell, is a hard, protective outer layer created by an animal that lives in the sea. The shell is part of the body of the animal. Empty seashells are often found washed up on beaches by beachcombers...
, seagrass
Seagrass
Seagrasses are flowering plants from one of four plant families , all in the order Alismatales , which grow in marine, fully saline environments.-Ecology:...
and kelp
Kelp
Kelps are large seaweeds belonging to the brown algae in the order Laminariales. There are about 30 different genera....
s. The colony shapes range from simple encrusting sheets to erect branching and even unattached forms. As in other bryozoa
Bryozoa
The Bryozoa, also known as Ectoprocta or commonly as moss animals, are a phylum of aquatic invertebrate animals. Typically about long, they are filter feeders that sieve food particles out of the water using a retractable lophophore, a "crown" of tentacles lined with cilia...
n groups, each colony is composed of a few to thousands of individual polypide
Polypide
The polypide in bryozoans encompasses most of the organs and tissues of each individual zooid. This includes the tentacles, tentacle sheath, U-shaped digestive tract, musculature and nerve cells. It is housed in the zooidal skeleton, which in cyclostomes is tubular and in cheilostomes is box-shaped....
s, which has a U-shaped gut, and no respiratory
Respiration (physiology)
'In physiology, respiration is defined as the transport of oxygen from the outside air to the cells within tissues, and the transport of carbon dioxide in the opposite direction...
, circulatory, or nerve system. Unique among bryozoans, cheilostome polypides are housed in a box-shaped zooids, which do not grow larger once the zooid is mature. The opening of through which the polypide protrudes is protected by a calcareous
Calcareous
Calcareous is an adjective meaning mostly or partly composed of calcium carbonate, in other words, containing lime or being chalky. The term is used in a wide variety of scientific disciplines.-In zoology:...
or chitin
Chitin
Chitin n is a long-chain polymer of a N-acetylglucosamine, a derivative of glucose, and is found in many places throughout the natural world...
ous lidlike structure, an operculum
Operculum (bryozoa)
In the bryozoan order Cheilostomata, the operculum is a calcareous or chitinous lid-like structure that protects the opening through which the polypide protrudes....
. Cheilostomes possess avicularia, which have modified the operculum into a range of mandibles (possibly for defense) or hair-like setae (possibly for cleaning).
The cheilostomes are the most abundant and varied of modern bryozoans. The classification in suborders is based upon frontal calcification and the mechanism of lophophore protrusion.
Evolution
Cheilostomes first appeared in the Late JurassicJurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
(Pyriporopsis) but diversified very slowly during the Early Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
, with only 1 family known up to the Albian
Albian
The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous epoch/series. Its approximate time range is 112.0 ± 1.0 Ma to 99.6 ± 0.9 Ma...
. During the Late Cretaceous, cheilostomes diversified rapidly to reach a level of more than 20 families in the Maastrichtian
Maastrichtian
The Maastrichtian is, in the ICS' geologic timescale, the latest age or upper stage of the Late Cretaceous epoch or Upper Cretaceous series, the Cretaceous period or system, and of the Mesozoic era or erathem. It spanned from 70.6 ± 0.6 Ma to 65.5 ± 0.3 Ma...
. This diversification is thought to be a consequence of the evolution of a new larval type. Though the K-T Extinction Event had some impact on genetic diversity, the rapid diversification continued into the Eocene, then apparently reaching a plateau of about 50 families up to the Recent.