Strobilisation or transverse fission is a form of

asexual reproduction Asexual reproduction is a type of reproduction that does not involve the fusion of gametes or change in the number of chromosomes. The offspring that arise by asexual reproduction from either unicellular or multicellular organisms inherit the ...

consisting of the spontaneous transverse segmentation of the body. It is observed in certain cnidarians and

helminth Parasitic worms, also known as helminths, are large macroparasites; adults can generally be seen with the naked eye. Many are intestinal worms that are soil-transmitted and infect the gastrointestinal tract. Other parasitic worms such as ...

s. This mode of reproduction is characterized by high offspring output, which, in the case of the parasitic tapeworms, is of great significance.

Strobilation in cnidarians

*The process starts with preliminary morphological changes. In particular, the cnidarian's tentacles tend to be reabsorbed. *Neck-formation: transverse constrictions appear near the upper extremity of the animal. A strobilating polyp is called a strobila while the non-strobilating polyp is called a scyphistoma or scyphopolyp. *Segmentation: the number of constriction sites increases and migrates down the body length, transforming the body into a sequence of disks. The fissures intensify until the initial body is divided into equally spaced, separate segments. The oral end of the polyp becomes the oral end of the ephyra. *Metamorphosis:

neurosecretory Neurosecretion is the storage, synthesis and release of hormones from neurons. These neurohormones, produced by neurosecretory cells, are normally secreted from nerve cells in the brain that then circulate into the blood. These neurohormones are sim ...

products of the two previous processes now disappear. Neck-formation and segmentation are only separated for clarity purposes. In reality, the two processes are simultaneous, with segmentation to release new ephyras occurring at the upper end while neck formation spreads further down the body. Usually, a portion of the animal remains adhered to the substrate and regenerates the body.

Examples

*The

moon jellyfish ''Aurelia aurita'' (also called the common jellyfish, moon jellyfish, moon jelly or saucer jelly) is a species of the genus '' Aurelia''. All species in the genus are very similar, and it is difficult to identify ''Aurelia'' medusae without genet ...

(''Aurelia aurita'') reproduces both sexually and by strobilation. This latter process occurs during the colonial polyp stage and produces either polyps or juvenile Medusae called ephyra. Strobilation tend to occur at specific periods, typically early spring. As ephyra size remains constant regardless of the polyp size, larger polyps produce more numerous ephyras. *Some scyphozoans, such as ''

Nausithoe aurea ''Nausithoe aurea'', also known as the ''Nausithoe maculata'', is a species of crown jellyfish found off the southeastern coast of Brazil. The central disc has been measured to be 10.5 mm. ''N. aurea'' is transparent with yellow and brown ...

'', cnidarians also strobilate in their solitary polyp form, producing either ephyra or planuloids. Strobilation does not happen periodically, but is thought to be induced by external stimuli, such as

iodine Iodine is a chemical element with the Symbol (chemistry), symbol I and atomic number 53. The heaviest of the stable halogens, it exists as a semi-lustrous, non-metallic solid at standard conditions that melts to form a deep violet liquid at , ...

, light regime, temperature, or food availability.

Induction in laboratory conditions

Strobilation is successfully induced in laboratory conditions by intensive feeding and temperature lowering, and also by the effect of artificial compounds.

Strobilation in helminths

In cestodes, the whole body except for the head and the neck undergoes strobilation continuously, reflecting the important role reproduction plays in the parasitic mode of life. The strobilating section is called strobila, or scolex, and each of its segment is a

proglottid 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, known as tapeworms. Their bodies consist of ...

. As they mature, proglottids are disposed of in the

feces Feces ( or faeces), known colloquially and in slang as poo and poop, 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 large intestine. Feces contain a rela ...

of the host.

References

{{Reflist Reproduction in animals Scyphozoa