Strobilation
Encyclopedia
Strobilation or transverse fission is a form of asexual reproduction
consisting of the spontaneous transverse segmentation
of the body. It is observed in certain cnidarians and helminths. This mode of reproduction is characterized by high offspring output, which, in the case of the parasitic tapeworms, is of great significance.
It is to be noted that 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.
of the host.
Asexual reproduction
Asexual reproduction is a mode of reproduction by which offspring arise from a single parent, and inherit the genes of that parent only, it is reproduction which does not involve meiosis, ploidy reduction, or fertilization. A more stringent definition is agamogenesis which is reproduction without...
consisting of the spontaneous transverse segmentation
Segmentation
Segmentation may mean:*Market segmentation, in economics and marketingBiology*A process of morphogenesis that divides a metazoan body into a series of semi-repetitive segments*Segmentation , a series of semi-repetitive segments...
of the body. It is observed in certain cnidarians and helminths. 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: The two previous processes involve neurosecretory products, which now disappear.
It is to be noted that 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
Substrate (biology)
In biology a substrate is the surface a plant or animal lives upon and grows on. A substrate can include biotic or abiotic materials and animals. For example, encrusting algae that lives on a rock can be substrate for another animal that lives on top of the algae. See also substrate .-External...
and regenerates the body.
Examples
- The moon jellyfish (Aurelia aurita) reproduces both sexually and by strobilation. This latter process occurs during the colonial polypPolypA polyp in zoology is one of two forms found in the phylum Cnidaria, the other being the medusa. Polyps are approximately cylindrical in shape and elongated at the axis of the body...
stage and produces either polyps or juvenile medusaMedusaIn Greek mythology Medusa , " guardian, protectress") was a Gorgon, a chthonic monster, and a daughter of Phorcys and Ceto. The author Hyginus, interposes a generation and gives Medusa another chthonic pair as parents. Gazing directly upon her would turn onlookers to stone...
e called ephyraEphyraEphyra may refer to:* The city of Kichyro, later known as Ephyra.* Ephyra, one of the Oceanids* Ephyra, one of the Nereids* Ephyra, a stage of the life cycle of jellyfish* Efyra, a village and an archeological site in Elis, Greece...
. 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 scyphozoaScyphozoaScyphozoa is a class within the phylum Cnidaria, sometimes referred to as the "true jellyfish".The class name Scyphozoa comes from the Greek word skyphos , denoting a kind of drinking cup and alluding to the cup shape of the organism....
ns, such as Nausithoe aureaNausithoe aureaNausithoe aurea is a species of scyphozoan found off the southeastern coast of Brazil. The central disc has been measured to be 10.5 millimetres. N. aurea is transparent with yellow and brown spots located around the gonads. N. aurea can reproduce either asexually by strobilation or sexually...
, 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 iodineIodineIodine is a chemical element with the symbol I and atomic number 53. The name is pronounced , , or . The name is from the , meaning violet or purple, due to the color of elemental iodine vapor....
, 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. As they mature, proglottids are disposed of in the fecesFeces
Feces, faeces, or fæces is a waste product from an animal's digestive tract expelled through the anus or cloaca during defecation.-Etymology:...
of the host.