Planula (from lat. Planus - flat) is the larval stage in the life cycle of the intestinal cavity (including jellyfish ). This organism is oval in shape, up to 1-1.5 mm in size, with a rounded front end and bilateral symmetry [1] .
The planula is an organism made up of two types of cells: the outer cover ( ectoderm ) is formed by flat cells with cilia, due to the beating of which the larva moves in the water column; inside the planula there is a mass of less differentiated cells ( endoderm ) that surround the rudimentary intestinal cavity [1] .
The planula can have a mouth opening and resort to self-feeding (like coral polyps ), or have no mouth and no food (as in the Hydroid class).
Due to the planktonic lifestyle, as well as the ability to actively move, the planula plays a significant role in the dispersal of its species, especially in cases when there are no other mobile forms in the life cycle of this species ( Anthozoa , some Hydrozoa ). The lifespan of planulae can vary in different species from several hours to 15-20 days. After a period of active swimming, the planula settles to the bottom and develops into a polyp , or into a jellyfish (in those taxa where the polyp stage is reduced in the life cycle) [2] .
In some species (for example, in the Scyphoid class), the planula after formation from a fertilized egg may not lead a free lifestyle, but remain attached to the maternal jellyfish.
In some cases (for example, in the order of the Narcomedusa of the Hydroid class), the planula is capable of asexual reproduction by budding , but usually each planula gives rise to only one adult organism (jellyfish or polyp).
Notes
- ↑ 1 2 Planula - Brockhaus and Efron Encyclopedic Dictionary (Rus.) , Gufo.me. Date of appeal September 3, 2018.
- ↑ Planula . bse.sci-lib.com. Date of appeal September 3, 2018.
Links
Literature
- Planula // Great Soviet Encyclopedia : [in 30 vol.] / Ch. ed. A.M. Prokhorov . - 3rd ed. - M .: Soviet Encyclopedia, 1969-1978.