Cnidarians: An Overview

Cnidarians are a group of invertebrate animals that include jellyfish, sea anemones, corals, and hydroids. They are known for their distinct features such as tentacles with stinging cells and a radial body symmetry.

Key Characteristics of Cnidarians:

• Radial symmetry: Cnidarians have a body plan that is radially symmetrical, meaning it can be divided equally along multiple planes.
• Tentacles with cnidocytes: Cnidarians have specialized stinging cells called cnidocytes on their tentacles, which they use for defense and capturing prey.
• Two body forms: Most cnidarians exhibit two body forms - the polyp form (typically sedentary) and the medusa form (typically free-swimming).
• Gastrovascular cavity: Cnidarians have a central digestive cavity with a single opening, which functions for digestion and nutrient distribution.

Types of Cnidarians:

There are several major groups of cnidarians, including:

• Jellyfish: Free-swimming medusae with trailing tentacles.
• Sea Anemones: Sedentary polyps with a cylindrical body and stinging tentacles.
• Corals: Colonial polyps that secrete calcium carbonate skeletons, contributing to coral reef formation.
• Hydroids: Small, colonial polyps found in marine and freshwater environments.

Reproduction in Cnidarians:

Cnidarians can reproduce both sexually and asexually. They typically have a complex life cycle involving both polyp and medusa stages. Reproduction can occur through budding, fragmentation, or the release of gametes for sexual reproduction.

Ecological Importance:

Cnidarians play a crucial role in marine ecosystems. Coral reefs, formed by colonial cnidarians, support diverse marine life and contribute to coastal protection. Additionally, cnidarians serve as a food source for various marine organisms.

Study Guide:

1. Describe the radial symmetry exhibited by cnidarians.
2. Explain the function of cnidocytes in cnidarians.
3. Compare and contrast the polyp and medusa body forms in cnidarians.
4. Identify the major groups of cnidarians and their respective characteristics.
5. Discuss the role of cnidarians in marine ecosystems and their ecological significance.

[Cnidarians] Related Worksheets and Study Guides:

• Sponges, Cnidarians and WormsScience • Sixth Grade
• Invertebrates - Animals without BackbonesScience • Fourth Grade
• Mollusks, Arthropods and EchinodermsScience • Sixth Grade