Taenia solium tapeworm scolex with its four suckers and two rows of hooks 5262 lores

Rostellum (meaning "small beak", from the

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

' for "

beak The beak, bill, or rostrum is an external anatomical structure found mostly in birds, but also in turtles, non-avian dinosaurs and a few mammals. A beak is used for pecking, grasping, and holding (in probing for food, eating, manipulating and ...

"; pl. rostella) in

helminthology Helminthology is the study of parasitic worms (helminths). The field studies the taxonomy of helminths and their effects on their hosts. The origin of the first compound of the word is the Greek '' ἕλμινς'' - helmins, meaning "worm". In ...

in a protruding part of the anterior end of

tapeworms Cestoda is a class of parasitic worms in the flatworm phylum (Platyhelminthes). Most of the species—and the best-known—are those in the subclass Eucestoda; they are ribbon-like worms as adults, commonly known as tapeworms. Their bodies con ...

. It is a retractable, cone-like muscular structure that is located on the apical end of the

scolex Cestoda is a class of parasitic worms in the flatworm phylum (Platyhelminthes). Most of the species—and the best-known—are those in the subclass Eucestoda; they are ribbon-like worms as adults, commonly known as tapeworms. Their bodies consi ...

, and in most species is armed with hooks, the organs of attachment to the

host A host is a person responsible for guests at an event or for providing hospitality during it. Host may also refer to: Places * Host, Pennsylvania, a village in Berks County * Host Island, in the Wilhelm Archipelago, Antarctica People * ...

's intestinal wall. It is a parasitic adaptation in some cestodes for firm attachment in the

gastrointestinal tract The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the Digestion, digestive system that leads from the mouth to the anus. The tract is the largest of the body's systems, after the cardiovascula ...

and is structurally different from one species to another (or even absent is some species), thereby becoming an important diagnostic feature.

Structure

A rostellum is a knob-like protrusion at the extreme anterior end of a tapeworm, as an extension of the tegument. It is globular, spiny structure when it protrudes, and a circular hollow pit when retracted. It is structurally composed of a number of concentric rows of hooks. The number and arrangement of the hooks are species specific. The two basic types of hooks are those of the upper row, which are larger and had a projecting, rounded stout guard, and those of the lower row, which are smaller and have a flattened guard. At the base, the hooks gradually resemble the general body hairs or

microtriches Microtriches (singular microtrix) are the highly specialized microvilli covering the entire surface of the tegument of cestodes. They are fine hair-like filaments distributed throughout the surface of the body, both unique to and ubiquitous among c ...

. This shows that the hooks are modified microtriches. Electron-dense hook substance is deposited along the edges of the microthrix to form the hook blade and basal plate. The blade may be hollow or solid depending on the species. The base is connected to the underlying

cytoplasm The cytoplasm describes all the material within a eukaryotic or prokaryotic cell, enclosed by the cell membrane, including the organelles and excluding the nucleus in eukaryotic cells. The material inside the nucleus of a eukaryotic cell a ...

. Rostellum is

innervated A nerve is an enclosed, cable-like bundle of nerve fibers (called axons). Nerves have historically been considered the basic units of the peripheral nervous system. A nerve provides a common pathway for the electrochemical nerve impulses called ...

by a single bilateral pair of

ganglia A ganglion (: ganglia) is a group of neuron cell bodies in the peripheral nervous system. In the somatic nervous system, this includes dorsal root ganglia and trigeminal ganglia among a few others. In the autonomic nervous system, there a ...

, which provide

motor An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy. Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power gene ...

innervation of the anterior canal, and the circular

muscle Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives skeletal muscles the ability to muscle contra ...

s of the rostellar capsule; this connection controls the protrusion and retraction movements. The tegument lining the anterior canal and covering the apical rostellum is

syncytial A syncytium (; : syncytia; from Greek: σύν ''syn'' "together" and κύτος ''kytos'' "box, i.e. cell") or symplasm is a multinucleate cell that can result from multiple cell fusions of uninuclear cells (i.e., cells with a single nucleus), in ...

and continuous with the tegument of the scolex proper.

Function

The rostellum is an organ of attachment of tapeworms, in addition to the surrounding suckers, to the intestinal wall of the host. It is protruded during attachment, and by the use of hooks penetrates the

intestinal mucosa The gastrointestinal wall of the gastrointestinal tract is made up of four layers of specialised tissue. From the inner cavity of the gut (the lumen) outwards, these are the mucosa, the submucosa, the muscular layer and the serosa or adventitia. ...

. This is particularly important during

digestion Digestion is the breakdown of large insoluble food compounds into small water-soluble components so that they can be absorbed into the blood plasma. In certain organisms, these smaller substances are absorbed through the small intestine into th ...

of food and

bowel movement Defecation (or defaecation) follows digestion and is the necessary biological process by which organisms eliminate a solid, semisolid, or liquid waste material known as feces (or faeces) from the digestive tract via the anus or cloaca. The act ...

of the host, so that the tapeworm is not expelled along with the

faeces Feces (also known as faeces American and British English spelling differences#ae and oe, or fæces; : faex) are the solid or semi-solid remains of food that was not digested in the small intestine, and has been broken down by bacteria in the ...

References

{{Reflist, 30em

External links

Definition at Merriam-WebsterDefinition at Medical DictionaryDefinition at Academic
Cestoda Animal morphology