What is a medusa?
Q: What is a medusa?
A: A medusa is a form of cnidarian in which the body is shaped like an umbrella. It can vary from bell-shaped to the shape of a thin disk, and has an upper or aboral surface called the exumbrella and a lower surface called the subumbrella.
Q: What are some features of a medusa?
A: The mouth of a medusa is on its lower surface, which may be partially closed by a membrane extending inward from the margin (called the velum). Its digestive cavity consists of the gastrovascular cavity and radiating canals which extend toward the margin; these canals may be simple or branching, and vary in number from few to many. The margin of the disk bears sensory organs and tentacles.
Q: In what classes do medusae appear?
A: Medusae appear in two classes - Hydrozoa and Scyphozoa (the common, colourful, large jellyfish) as well as Cubozoa. Except for freshwater hydrozoans like Craspedacusta sowerbyi, these are the only classes in which medusae appear.
Q: How do medusae catch their prey?
A: Medusae have many tentacles with which they catch their prey. These tentacles are long and thin and covered in venomous stinging cells (known as nematocysts), injecting poison that immobilizes small fish.
Q: What should people do if they are stung by a medusa?
A: People who are stung by a medusa should seek medical attention immediately as there have been some deaths after severe stings.
Q: How does one distinguish between polyps and medusae?
A: Polyps attach to surfaces while medusae are free-floating; species of cnidarians take each form at different phases of its life cycle.
