Planula
Larval form of certain aquatic animals
A planula is the free-swimming, flattened, ciliated, bilaterally symmetric larval form of various cnidarian species and some species of ctenophores (such as in genus Lampea), which are not closely related to cnidarians. Some groups of nemerteans also produce larvae that are very similar to the planula, which are called planuliform larva. In a few cnidarian clades, like Aplanulata and the parasitic Myxozoa, the planula larval stage has been lost.
01Development
The planula forms either from the fertilized egg of a medusa, as is the case in scyphozoans and some hydrozoans, or from a polyp, as in the case of anthozoans.
Depending on the species, the planula either metamorphoses directly into a free-swimming, miniature version of the mobile adult form, or navigates through the water until it reaches a hard substrate (many may prefer specific substrates) where it anchors and grows into a polyp. The miniature-adult types include many open-ocean scyphozoans. The attaching types include all anthozoans with a planula stage, many coastal scyphozoans, and some hydrozoans.
02Feeding and locomotion
The planulae of the subphylum Medusozoa have no mouth, and no digestive tract, and are unable to feed themselves (lecithotrophic), while those of Anthozoa show more variation and can be both lecithotrophic, parasitic or feed on plankton or detritus.
Planula larvae swim with the aboral end (the end opposite the mouth) in front.
Sources and credits
This article is adapted from the Wikipedia article “Planula”, written by its contributors and licensed under CC BY-SA 4.0. Fathomly has changed the layout, removed citation markers, navigation and maintenance notices, and adjusted punctuation. This adapted version is shared under the same license. For references, see the original article.
Images, from Wikimedia Commons:
- Planula.jpg by Jccardenas13; Elizabeth Lee, CC BY-SA 4.0
- Clytia Four stages in the development of the planula.jpg by MacBride, E. W., Public domain
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