A planula is the free-swimming, flattened, ciliated, bilaterally symmetric larval form of various cnidarian species and also in some species of Ctenophores. Some groups of Nemerteans also produce larvae that are very similar to the planula.[1]
Development
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.[2]
Feeding and locomotion
The planulae of the subphylum Medusozoa have no mouth, and no digestive tract, and are unable to feed themselves, while those of Anthozoa can feed.[2]
Planula larvae swim with the aboral end (the end opposite the mouth) in front.[2][1]
References
- ^ a b Ruppert EE, Fox RS, Barnes RD (2004). "Nemertea". Invertebrate Zoology (7 ed.). Brooks / Cole. pp. 271–274. ISBN 0-03-025982-7.
- ^ a b c Nakanishi, Nagayasu; Yuan, David; Jacobs, David K.; Hartenstein, Volker (2008). "Early development, pattern, and reorganization of the planula nervous system in Aurelia (Cnidaria, Scyphozoa)". Development Genes and Evolution. 218 (10): 511–524. doi:10.1007/s00427-008-0239-7.