Strobilation 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 f ...

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

cnidarian 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, ...

s and helminths. This mode of reproduction is characterized by high offspring output, which, in the case of the

parasitic Parasitism is a close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The ent ...

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 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'') reproduces both sexually and by strobilation. This latter process occurs during the colonial polyp stage and produces either polyps or juvenile

Medusae Jellyfish, also known as sea jellies or simply jellies, are the medusa-phase of certain gelatinous members of the subphylum Medusozoa, which is a major part of the phylum Cnidaria. Jellyfish are mainly free-swimming marine animals, althoug ...

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'', 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; it has symbol I and atomic number 53. The heaviest of the stable halogens, it exists at standard conditions as a semi-lustrous, non-metallic solid that melts to form a deep violet liquid at , and boils to a vi ...

, 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

cestode 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 co ...

s, 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 segments is a

proglottid Cestoda is a Class (biology), 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. T ...

. As they mature, proglottids are disposed in the

feces 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 ...

of the host.

References

{{Reflist Reproduction in animals Scyphozoa