Planula

The planula or Planulalarve is a larval form of cnidarians (Cnidaria). It is formed by gastrulation of the blastula , has two layers ( ectoderm and endoderm ) and ciliate. The mouth (blastopore) is usually closed again immediately after formation. The planula feeds on plankton (planktotroph) or yolk (lecithotroph). The flagellation is not uniform everywhere, in the larvae of the crust anemones (Zoanthidea) it is limited to a longitudinal strip. The planula continues to rotate and, after a planktonic stage of a few days to several weeks , attaches itself to a solid surface with its aboral pole and forms an adhesive disc. This is followed by the formation of the mouth, if not already present, and the tentacles , the metamorphosis to the polyp . With the Hydrozoa (Hydrozoa) and the cylinder roses (Ceriantharia) the tentacles already form during the planktonic phase. The resulting Actinula and Arachnactis larvae are initially free-swimming polyps and only later come to life on the ocean floor . In medusa-like hydrozoans without a generation change, the planula flattens out on its mouth surface and the edge of the flattened region becomes a medusa bell.

source

• Volker Storch, Ulrich Welsch: Systematic Zoology Pages 54-55, Fischer, 1997, ISBN 3-437-25160-0