Polypstage

Polypstage refers to the polyp phase in the life cycle of certain cnidarians, a phase in which the organism is typically sessile or slow-moving, with a tube- or vase-shaped body, an oral opening at the top surrounded by tentacles, and a gastrovascular cavity used for digestion and nutrient distribution. This stage often serves feeding and growth, and in many species it reproduces asexually by budding to form new polyps or colonies. In species with alternation of generations, the polyp stage can give rise to a separate reproductive stage, such as a medusa.

In hydrozoans, the polyp stage frequently forms colonies containing distinct specialized polyps, including feeding polyps and reproductive zygophores or gonophores. The colony can persist and expand through asexual budding, while sexual reproduction may occur in specialized polyps to release free-swimming larvae. In scyphozoans (true jellyfish), the life cycle typically includes a sessile polyp stage known as a scyphistoma, which can undergo a process called strobilation to produce juvenile medusae (ephyræ) that grow into free-swimming adults. In anthozoans (anemones and corals), the polyp is the dominant and often sole life stage; medusae are absent in most groups. Sexual reproduction produces planula larvae that settle to form new polyps, while asexual budding and colony formation contribute to reef-building corals and other colonial organisms.

The term polypstage is commonly written as two words, “polyp stage,” but it may appear as a single word in some databases or literature. The concept is central to understanding the diverse life cycles of cnidarians and their ecological roles, from solitary hydras to massive coral reef systems.