Planula

A planula is a ciliated, free-swimming larval stage in the life cycle of many cnidarians. It typically settles on a surface and develops into a polyp.

Cnidarian embryonic development: The development of cnidarians from fertilized egg through embryonic and larval stages. The planula emerges from this developmental sequence after embryonic cleavage and gastrulation.
Cnidaria: An animal phylum that includes jellyfish, corals, sea anemones, and hydras. Planulae are characteristic larval stages of many members of this phylum.
Coral recruitment: The addition of young corals to a population through larval settlement and subsequent survival. Coral planula settlement is the first step in recruiting new individuals to a reef.
Obelia: A genus of colonial hydrozoans with alternating polyp and medusa stages. Its sexual medusae produce planulae that develop into new colonies.
Gastrulation: An embryonic process that reorganizes cells into germ layers and establishes the body plan. Gastrulation produces the layered organization present in a planula.
Medusa (cnidarian): A free-swimming cnidarian body form, usually bell-shaped, that commonly reproduces sexually. In many cnidarian life cycles, medusae produce the eggs or sperm that precede planula development.
Coral reef restoration: Interventions intended to help damaged coral reefs recover ecological structure and function. Restoration projects can use knowledge of planula settlement to support coral recruitment.
Aurelia: A genus of scyphozoan jellyfish commonly known as moon jellies. Aurelia planulae settle and develop into the polyp stage called a scyphistoma.
Cilia: Microscopic cell-surface projections that can move fluid or propel cells. Beating cilia propel many planulae through the water.
Cnidocyte: A specialized cnidarian cell that contains a capsule used for prey capture or defense. This defining cell type distinguishes the phylum whose life cycles include planulae.

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