Strobilisation or transverse fission is a form of
asexual reproduction 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 animals found both in Fresh water, freshwater and Marine habitats, marine environments, predominantly the latter.
Their distinguishing feature is cnidocyt ...
s and
helminth
Parasitic worms, also known as helminths, are large macroparasites
Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adap ...
s. 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 on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson ha ...
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
Substrate may refer to:
Physical layers
*Substrate (biology), the natural environment in which an organism lives, or the surface or medium on which an organism grows or is attached
** Substrate (locomotion), the surface over which an organism lo ...
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