polyp and medusa

Introduction

CE5

Polyp and medusa stages in the life cycle of Obelia, representative of the phylum Cnidaria

polyp and medusa, names for the two body forms, one nonmotile and one typically free swimming, found in the aquatic invertebrate phylum Cnidaria (the coelenterates). Some animals of this group are always polyps, some are always medusae, and some exhibit both a polyp and a medusa stage in their life cycle. The polyp is a sessile, or nonmotile, organism; well-known solitary polyps are the sea anemone and the freshwater hydra. The medusa, when free swimming, is popularly known as a jellyfish.

Sections in this article:

Introduction
Colonial Species
Reproduction
Anatomy

See more Encyclopedia articles on: Zoology: Invertebrates