The Cnidarians

These flashcards cover key concepts and details about the phylum Cnidaria, including characteristics, life cycles, and ecological roles.

What are the defining characteristics of the phylum Cnidaria?

1) Secretion of complex intracellular organelles called cnidae (nematocysts); 2) planula larvae in the life cycle.

What percentage of cnidarian species live in marine environments?

More than 99% of cnidarian species are marine.

What are the two main body forms of cnidarians?

The two body forms are the medusa form (jellyfish) and the polyp form.

What is a characteristic feature of cnidarians regarding their tissue structure?

Cnidarians have a basic radial symmetry and possess only two layers of living tissue: the epidermis and the gastrodermis.

What is the function of the mesoglea in cnidarians?

The mesoglea is a gelatinous layer located between the epidermis and gastrodermis.

What unique organelles do cnidarians secrete for capturing prey?

Cnidia, including nematocysts, are unique organelles secreted by cnidarians.

What is the primary limitation of the cnidarian digestive system?

Cnidarians lack an anus; all undigested food material exits through the same opening used for ingestion.

What type of diet do cnidarians primarily have?

Cnidarians are primarily carnivorous, although some species also feed on phytoplankton.

How do some cnidarians obtain additional nutrients?

Many species obtain nutrients through symbiotic relationships with unicellular algae.

What is the role of cnidae in cnidarians?

Cnidae function in food collection, defense, and locomotion.

What is unique about the nervous system of cnidarians?

Cnidarians possess a network of nerve cells but no central nervous system.

What are the two networks of nerve cells found in cnidarians?

A slow-conducting network and a fast-conducting nerve network.

What do cnidarians lack in terms of respiratory structures?

Cnidarians lack gills and respiratory structures; gases diffuse across all exposed surfaces.

What is the significance of the class Scyphozoa?

Class Scyphozoa includes true jellyfish, with a defining characteristic of asexual replication by strobilation.

How do scyphozoan jellyfish swim?

They swim by contracting muscles and utilizing the mechanical properties of the mesoglea.

What is a strobilation in the life cycle of scyphozoans?

Strobilation is the process where the body column of a scyphistoma subdivides transversely to form ephyrae.

What is the primary characteristic of the class Cubozoa?

Cubozoans have a cube-like body, and their rhopalia bear complex, lensed eyes.

What differentiates the class Hydrozoa from other cnidarian classes?

Hydrozoans generally have a more pronounced polyp form compared to the medusa form.

What unique operational feature do some hydrozoans exhibit?

Some hydrozoans can reverse their ontogeny and revert to the polyp stage from the medusoid stage.

What are the key characteristics of anthozoans?

Anthozoans lack a medusa stage, are predominantly marine, and can reproduce both sexually and asexually.

How do anthozoans contribute to reef building?

Many anthozoans, such as corals, secrete calcium carbonate skeletons and play a significant role in reef structures.

What is the ecological relationship between corals and zooxanthellae?

Zooxanthellae provide energy-rich compounds through photosynthesis, while corals offer protection and organic waste for the algae.

What is the impact of ocean acidification on coral reefs?

Ocean acidification threatens coral growth and stability, affecting recruitment and survival rates of coral larvae.