The young starlet sea anemone forms tentacles by cell division, migration, and shape changes.
The starlet sea anemone Nematostella vectensis is shown at three stages of development from left to right, a planula larva, a juvenile, and a primary polyp. During these early stages, the starlet anemone elongates from 275 to 650 mm in length—about the size of a grain of salt. In the planula larva, one can just see the tentacle buds as slight thickenings. These groups of cells continue to divide and then each cell becomes taller than wide in shape, resulting in the four protuberances seen at the top of the juvenile. As cell division and specialization continues, four functional tentacles emerge that the primary polyp uses to feed. Additional tentacles are progressively added to produce an adult anemone with 16 to 18 tentacles, which it uses to capture and eat prey.
Image courtesy of Matt Gibson, PhD, Stowers Institute for Medical Research, Kansas City, Missouri, USA
These three different animals were each fixed as a larva, a juvenile, and a primary polyp. Different color stains were used to see various structures in cells: actin (red), microtubules (green), and nuclei (blue). The stained animals were viewed using a confocal microscope.