zoology Zoology ( , ) is the scientific study of animals. Its studies include the anatomy, structure, embryology, Biological classification, classification, Ethology, habits, and distribution of all animals, both living and extinction, extinct, and ...

, a mesentery is a membrane inside the body cavity of an animal. The term identifies different structures in different

phyla Phyla, the plural of ''phylum'', may refer to: * Phylum, a biological taxon between Kingdom and Class * by analogy, in linguistics, a large division of possibly related languages, or a major language family which is not subordinate to another Phy ...

: in vertebrates it is a double fold of the

peritoneum The peritoneum is the serous membrane forming the lining of the abdominal cavity or coelom in amniotes and some invertebrates, such as annelids. It covers most of the intra-abdominal (or coelomic) organs, and is composed of a layer of mesotheli ...

enclosing the intestines; in other organisms it forms complete or incomplete partitions of the body cavity, whether that is the

coelom The coelom (or celom) is the main body cavity in many animals and is positioned inside the body to surround and contain the digestive tract and other organs. In some animals, it is lined with mesothelium. In other animals, such as molluscs, i ...

or, as in the

Anthozoa Anthozoa is one of the three subphyla of Cnidaria, along with Medusozoa and Endocnidozoa. It includes Sessility (motility), sessile marine invertebrates and invertebrates of brackish water, such as sea anemones, Scleractinia, stony corals, soft c ...

, the gastrovascular cavity. The word "mesentery" is derived from the Greek ''mesos'', "in the middle" and ''enteron'', an "intestine".

Vertebrates

vertebrates Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...

, a

mesentery In human anatomy, the mesentery is an Organ (anatomy), organ that attaches the intestines to the posterior abdominal wall, consisting of a double fold of the peritoneum. It helps (among other functions) in storing Adipose tissue, fat and allowi ...

is a membrane consisting of a double fold of

that encloses the intestines and their associated organs and connect them with the dorsal wall of the abdominal cavity. In invertebrates, a mesentery is a support or partition in a body cavity serving a similar function to the mesenteries of vertebrates.

Bilateria

In bilaterally symmetrical organisms, there is often a major mesentery separating the two halves of the

. In segmented organisms such as earthworms, there are a pair of coelomic cavities in each segment. The mesothelium of the body wall is extended round the central gut to form a mesentery, a longitudinal partition in the

sagittal plane The sagittal plane (; also known as the longitudinal plane) is an anatomical plane that divides the body into right and left sections. It is perpendicular to the transverse and coronal planes. The plane may be in the center of the body and divi ...

. Above the gut is the dorsal mesentery and below the gut, the ventral mesentery. The transverse partition between the separate segments is known as a septum.

Cnidaria

In the phylum

Cnidaria Cnidaria ( ) is a phylum under kingdom Animalia containing over 11,000 species of aquatic invertebrates found both in fresh water, freshwater and marine environments (predominantly the latter), including jellyfish, hydroid (zoology), hydroids, ...

and the class

, the mesenteries are sheet-like partitions that extend from the body wall of the animal into its

gastrovascular cavity The gastrovascular cavity is the primary organ of digestion and circulation in two major animal phyla: the Coelenterates or cnidarians (including jellyfish and corals) and Platyhelminthes (flatworms). The cavity may be extensively branched into ...

. They are composed of a layer of mesogloea sandwiched between two layers of

gastrodermis Gastrodermis (from Ancient Greek: , , "stomach"; , , "skin") is the inner layer of Cell (biology), cells that serves as a lining membrane of the gastrovascular cavity in cnidarians. It is distinct from the outer epidermis and the inner dermis and ...

. They can either be "complete", joining the gastrodermis of the body wall with that of the

pharynx The pharynx (: pharynges) is the part of the throat behind the human mouth, mouth and nasal cavity, and above the esophagus and trachea (the tubes going down to the stomach and the lungs respectively). It is found in vertebrates and invertebrates ...

, or "incomplete", extending only part way into the cavity (the terms "perfect" and "imperfect" are sometimes used instead). They stretch from the pedal disc to the oral disc, and there are two perforations or ostia near the oral disc. Mesenteries are usually in pairs. The free edge of incomplete mesenteries are thickened to form glandular, ciliated bands called mesenterial filaments. The lower ends of the mesenterial filaments are elongated into acontia which are armed with

cnidocyte A cnidocyte (also known as a cnidoblast) is a type of cell containing a large secretory organelle called a ''cnidocyst'', that can deliver a sting to other organisms as a way to capture prey and defend against predators. A cnidocyte explosively ...

s (stinging cells) and can protrude through the body wall or mouth. The gonads are situated on the mesenteries alongside the mesenterial filaments.

Stony coral Scleractinia, also called stony corals or hard corals, are marine animals in the phylum Cnidaria that build themselves a hard skeleton. The individual animals are known as polyps and have a cylindrical body crowned by an oral disc in which a mo ...

s, order

Scleractinia Scleractinia, also called stony corals or hard corals, are marine animals in the phylum Cnidaria that build themselves a hard skeleton. The individual animals are known as polyps and have a cylindrical body crowned by an oral disc in which a mo ...

, have the mesenteries arranged radially in pairs which develop cyclically. The mesenteries deposit calcium carbonate which forms a stony ridge, the

septum In biology, a septum (Latin language, Latin for ''something that encloses''; septa) is a wall, dividing a Body cavity, cavity or structure into smaller ones. A cavity or structure divided in this way may be referred to as septate. Examples Hum ...

, between each pair of mesenteries and builds the

corallite A corallite is the skeletal cup, formed by an individual stony coral polyp, in which the polyp sits and into which it can retract. The cup is composed of aragonite, a crystalline form of calcium carbonate, and is secreted by the polyp. Corallit ...

, the cup in which the polyp sits.

Sea anemone Sea anemones ( ) are a group of predation, predatory marine invertebrates constituting the order (biology), order Actiniaria. Because of their colourful appearance, they are named after the ''Anemone'', a terrestrial flowering plant. Sea anemone ...

s, order

Actiniaria Sea anemones ( ) are a group of predatory marine invertebrates constituting the order Actiniaria. Because of their colourful appearance, they are named after the '' Anemone'', a terrestrial flowering plant. Sea anemones are classified in the phy ...

, have at least eight complete mesenteries and a variable number of incomplete ones near the base. The functional significance of the mesenteries in sea anemones is unclear. Their margins are involved in only a limited amount of digestion and absorption, so their chief function may be to provide support to help the animal maintain its shape. Soft corals, order

Alcyonacea Alcyonacea is the old scientific order name for the informal group known as "soft corals". It is now an unaccepted name for class Octocorallia. It became deprecated . The following text should be considered a historical, outdated way of treatin ...

, have eight primary mesenteries which alternate with the eight tentacles. The mesenteries are complete and unpaired and bear unilobed filaments.

References

{{reflist, 30em Animal anatomy