Cnidarians Overview

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Questions and Answers

Which of the following are general characteristics of cnidarians? (Select all that apply)

Stinging tentacles (correct)
Soft bodied (correct)
Carnivorous (correct)
Fast swimmers

What type of symmetry do cnidarians exhibit?

Radial

Cnidarians do not have specialized tissues.

False (B)

What does the word 'cnidaria' derive from?

The Greek word 'cnid', which means stinging nettle. Signup and view all the answers

What are the cells called that sting?

Cnidocytes Signup and view all the answers

How do cnidocytes function?

They contain stingers called nematocysts that catch prey and protect against predators. Signup and view all the answers

What are nematocysts connected to?

A long thread that entangles the prey. Signup and view all the answers

What effect can the poison from cnidarians have?

Paralyze an organism Signup and view all the answers

How many species of cnidarians are there?

More than 9,000 Signup and view all the answers

What type of environment do cnidarians live in?

All are aquatic, most are marine, and some are benthic. Signup and view all the answers

What does 'marine' mean?

Salt water Signup and view all the answers

What does 'benthic' mean?

Bottom of the ocean Signup and view all the answers

Describe the digestive system of a cnidarian.

Cnidarians are basically a sac with a gastrovascular cavity (stomach), and most feed on prey that comes into contact with their tentacles. Signup and view all the answers

What type of digestive system do cnidarians have?

They have an incomplete digestive system. Signup and view all the answers

Describe an incomplete digestive system.

A single opening that serves as both mouth and anus for ingesting food and excreting waste, surrounded by tentacles. Signup and view all the answers

Describe the respiratory system of cnidarians.

The presence of a larger inner cavity makes it possible for cells to exchange gases directly with the surrounding water by the process of diffusion. Signup and view all the answers

Describe diffusion.

The movement of materials from an area of high concentration to an area of low concentration until equilibrium is reached. Signup and view all the answers

Cnidarians require gills, lungs, or tracheae.

False (B) Signup and view all the answers

Describe the nervous system of cnidarians.

They possess a nerve net and simple receptors to help with movement and senses. Signup and view all the answers

What can many cnidarians do after being attacked?

Regenerate lost parts Signup and view all the answers

Match each cnidarian form with its description:

Polyp = Asexual reproduction and sessile, contains little mesoglea Medusa = Sexual reproduction and motile, contains lots of mesoglea Signup and view all the answers

What are the four major classes of cnidaria?

Anthozoa, Hydrozoa, Scyphozoa, Cubozoa Signup and view all the answers

Describe Anthozoa.

It means flower animals; true corals, anemones, sea fans; bottom dwelling polyps, growing in shallow waters for proper lighting; they have symbiotic relationships; polyp deposits lime from their exoskeleton which builds up slowly to form coral reefs. Signup and view all the answers

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Study Notes

General Characteristics of Cnidarians

Soft-bodied and carnivorous animals
Equipped with stinging tentacles
Considered the simplest form of animal life
Exhibit radial symmetry

Cnidocyte Functionality

Stinging cells called cnidocytes contain nematocysts, which are specialized stingers
Nematocysts catch prey and provide protection from predators

Species and Habitat

Over 9,000 species of cnidarians exist
Habitats include all aquatic environments; primarily marine, with some residing on the ocean bottom (benthic)
Marine environments are characterized by saltwater

Digestive and Respiratory Systems

Cnidarians possess an incomplete digestive system, featuring a single opening for ingestion and waste excretion
Gastrovascular cavity acts as both stomach and site for nutrient absorption
Gas exchange occurs directly by diffusion, eliminating the need for specialized respiratory organs like gills or lungs

Nervous System and Regeneration

Nervous system includes a nerve net and simple receptors for basic movement and sensory functions
Many cnidarians can regenerate lost parts after being attacked

Life Forms and Reproduction

Exist in two forms: polyp (sessile, asexual reproduction) and medusa (motile, sexual reproduction)
Asexual reproduction commonly occurs through budding, leading to genetically identical colonies
Sexual reproduction is external; gametes unite in water to form swimming larvae that eventually settle and transform into polyps

Movement Mechanisms

Polyp movement involves a basal disk that secretes a sticky substance for attachment and gas bubbles for detachment
Hydras exhibit somersaulting movement, while medusas employ jet propulsion

Major Classes of Cnidarians

Four main classes: Anthozoa, Hydrozoa, Scyphozoa, and Cubozoa

Anthozoa Class

Commonly referred to as "flower animals"
Includes true corals, sea anemones, and sea fans
Typically bottom-dwelling and thrive in shallow waters, reliant on light for symbiotic relationships with algae
Coral polyps deposit lime from their exoskeletons, contributing to the formation of coral reefs over time