Updated by: Arabinda Naik
Obelia is a genus of hydrozoans that exhibits a complex life cycle with both polyp and medusa stages.
Bell or Umbrella: The medusa of Obelia has a bell-shaped or umbrella-like structure, which is the main body part of the medusa. This bell is typically transparent or translucent and can vary in size depending on the species. It is often gelatinous in nature.
Radial Symmetry: Like other cnidarians, the medusa of Obelia displays radial symmetry, which means it can be divided into equal halves in any plane passing through the central axis. This symmetry allows for efficient movement in the water column.
Tentacles: Around the lower edge of the bell, there are multiple long, slender, and often numerous tentacles. These tentacles are equipped with specialized cells called cnidocytes that contain stinging structures known as nematocysts. These nematocysts are used for capturing and immobilizing prey.
Mouth: In the center of the bell's underside, there is a mouth. The mouth leads to a gastrovascular cavity, where digestion takes place. The medusa of Obelia is a carnivorous organism that feeds on small planktonic organisms and other tiny prey in the water.
Sensory Structures: Medusae typically have sensory structures like rhopalia (sensory bulbs) located around the edge of the bell. These structures help the medusa detect changes in its environment and respond to various stimuli.
Manubrium: Extending downward from the center of the bell, there is a structure called the manubrium. The manubrium contains the mouth and helps in directing prey toward the mouth for ingestion.
Gonads: Medusae are the reproductive stage in the life cycle of Obelia. Depending on the sex, medusae can have gonads within their bell. These gonads produce gametes (sperm or eggs) for sexual reproduction.
Jet Propulsion: The medusa of Obelia, like other jellyfish and medusae, is capable of jet propulsion for movement. By contracting their bell-shaped bodies, they expel water to propel themselves through the water.