zoology Zoology ()The pronunciation of zoology as is usually regarded as nonstandard, though it is not uncommon. is the branch of biology that studies the Animal, animal kingdom, including the anatomy, structure, embryology, evolution, Biological clas ...

, 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 Phyl ...

: 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 mesoth ...

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 most 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, it r ...

or, as in the

Anthozoa Anthozoa is a subphylum of marine invertebrates which includes the sea anemones, Scleractinia, stony corals and Alcyonacea, soft corals. Adult anthozoans are almost all attached to the seabed, while their larvae can disperse as part of the plank ...

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

Vertebrates

vertebrates Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, ...

, a

mesentery The mesentery is an organ that attaches the intestines to the posterior abdominal wall in humans and is formed by the double fold of peritoneum. It helps in storing fat and allowing blood vessels, lymphatics, and nerves to supply the intestines ...

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 divid ...

. 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 animals found both in freshwater and marine environments, predominantly the latter. Their distinguishing feature is cnidocytes, specialized cells that th ...

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 Mesoglea refers to the extracellular matrix found in cnidarians like coral or jellyfish that functions as a hydrostatic skeleton. It is related to but distinct from mesohyl, which generally refers to extracellular material found in sponges. Descr ...

sandwiched between two layers of

gastrodermis The gastrodermis is the inner layer of cells that serves as a lining membrane of the gastrovascular cavity The gastrovascular cavity is the primary organ of digestion and circulation in two major animal phyla: the Coelenterates or cnidarians (inc ...

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

, 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 ''Acontia'' is a genus of moths of the family Noctuidae. The genus was named by Ferdinand Ochsenheimer in 1816. ''Eusceptis'', ''Pseudalypia'' and ''Spragueia'' are sometimes included in the present genus, but here they are tentatively treated ...

which are armed with

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 (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 ...

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 polyp (zoology), polyps and have a cylindrical body crowned by an oral di ...

, 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 for ''something that encloses''; plural septa) is a wall, dividing a cavity or structure into smaller ones. A cavity or structure divided in this way may be referred to as septate. Examples Human anatomy * Interatri ...

, 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 of the order (biology), order Actiniaria. Because of their colourful appearance, they are named after the ''Anemone'', a terrestrial flowering plant. Sea anemones are classifi ...

s, order

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

, 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 coral Alcyonacea, or soft corals, are an order of corals. In addition to the fleshy soft corals, the order Alcyonacea now contains all species previously known as "gorgonian corals", that produce a more or less hard skeleton, though quite different f ...

s, order

Alcyonacea Alcyonacea, or soft corals, are an order of corals. In addition to the fleshy soft corals, the order Alcyonacea now contains all species previously known as "gorgonian corals", that produce a more or less hard skeleton, though quite different f ...

, 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