Platycoely

Platycoely is a term used in biology to describe a type of symmetry in organisms, specifically in their body plans. The term is derived from the Greek words "platy," meaning broad or flat, and "koilos," meaning hollow or concave. Platycoely refers to a body plan where the organism has a broad, flat, or concave shape, often with a central cavity or hollow space.

This type of symmetry is commonly found in various invertebrate phyla, such as the Cnidaria (jellyfish, corals, and sea anemones), Ctenophora (comb jellies), and some members of the Platyhelminthes (flatworms). In these organisms, the body plan is typically bilateral, meaning it can be divided into two mirror-image halves along a central axis. However, the overall shape of the body is broad or concave, giving it a distinct platycoelous appearance.

The central cavity in platycoelous organisms often serves as a digestive or circulatory space, allowing for efficient nutrient distribution and waste removal. This body plan is an adaptation that provides structural support and facilitates the organism's mode of life, whether it be predation, filter feeding, or sessile attachment to surfaces.