Final answer:
Cnidarians possess two distinct body forms, polyp and medusa, with the polyp being sessile and the medusa being motile. Some cnidarians are dimorphic, featuring both forms in their lifecycle. Both polyp and medusa forms have diploid cells and a two-layer body structure with mesoglea in between.
Step-by-step explanation:
Cnidarian Body Forms
Cnidarians exhibit two body forms: the polyp and the medusa. The polyp form, exemplified by sea anemones and corals, is sessile with a cup-shaped body and the mouth/anus opening facing upwards, surrounded by tentacles. In contrast, the medusa, which includes jellyfish, is motile and characterized by a bell-shaped body with tentacles and the mouth hanging downwards.
Some cnidarians are dimorphic, meaning they have both polyp and medusa stages in their life cycle. The polyp is generally the asexual phase, while the medusa is the sexual phase, responsible for producing gametes. Despite the differences in form and function, both polyp and medusa are diploid stages. Furthermore, many corals contribute to the creation of coral reefs by secreting an exoskeleton.
The structure of cnidarians is also notable, consisting of two tissue layers with a jelly-like substance called mesoglea between them. Additionally, cnidarians possess nematocysts, specialized cells capable of ejecting a toxin as a defense mechanism or to capture prey.
Cnidarians, such as jellyfish and sea anemones, have two distinct body forms called the polyp and medusa.
The polyp form is like a stalk with the mouth facing upward, while the medusa form is bell-shaped with the mouth and tentacles hanging down.
Polyps are usually sessile, meaning they are attached to a surface and do not move, while medusae are motile and can swim freely.