Cnidaria and Ctenophora Chapter 7 Zoology Phylum Cnidaria

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Cnidaria and Ctenophora Chapter 7, Zoology

Cnidaria and Ctenophora Chapter 7, Zoology

Phylum Cnidaria Pronounced (ny-dar'e-a). Name means “like or connected with nettles”. Approximately 9, 000

Phylum Cnidaria Pronounced (ny-dar'e-a). Name means “like or connected with nettles”. Approximately 9, 000 species. All aquatic; mostly marine, a few freshwater. All have radial symmetry. All have two germ (true tissues) layers (diploblastic); the ectoderm and endoderm. Polymorphism, two body types; polyp and medusa.

Phylum Cnidaria The name is derived from the many stinging cells that they bear

Phylum Cnidaria The name is derived from the many stinging cells that they bear called Cnidocytes usually have stinging organelles called nematocysts. The nematocysts function as weapons that deliver powerful toxins to kill, paralyze, or injure their prey and/or their enemies.

Cnidocytes and Nematocysts

Cnidocytes and Nematocysts

Ecology of Cnidarians Found mostly in shallow, warm equatorial/tropical marine habitats. Hydra and Sea

Ecology of Cnidarians Found mostly in shallow, warm equatorial/tropical marine habitats. Hydra and Sea Anemones often live symbiotically on mollusk and crab shells. Jellyfish (medusa) are mostly found in open ocean (pelagic) zones and open lake (limnetic) zones. • Corals play an important role in the ecology of coral reefs by building reefs and providing a habitat for other marine organisms.

Dimorphism (Polymorphism) Cnidarians exhibit polymorphism, meaning they have two different body types. The sedentary

Dimorphism (Polymorphism) Cnidarians exhibit polymorphism, meaning they have two different body types. The sedentary or sessile type that lives attached to the ground surface are called Polyps. The mobile type that floats is called a Medusa.

Description of Polyp Body Form Cylindrical or tubeshaped body. Mouth is surrounded by tentacles.

Description of Polyp Body Form Cylindrical or tubeshaped body. Mouth is surrounded by tentacles. Mouth leads to the gastrovascular cavity. The aboral end is attached to the ground. Sea Anemone in the Polyp Body Form

Asexual Reproduction in Polyps There are three different types of asexual reproduction used by

Asexual Reproduction in Polyps There are three different types of asexual reproduction used by polyps. Budding – A round ball of tissue forms on the side of the polyp and develops into an adult polyp. Fission – When an adult polyp splits in half and develops into two identical adult clone polyps. Pedal Laceration – When a piece of tissue is torn from the base of the polyp and develops into a new polyp.

Polyps Budding

Polyps Budding

Budding Colonies In certain species of cnidarians, if buds stay attached to the polyps,

Budding Colonies In certain species of cnidarians, if buds stay attached to the polyps, a cnidarian colony may form. These budding colonies can share food through a common gastrovascular cavity. Different polyps in a colony that specialize and perform a variety of specific tasks are called zooids. Gastrozooids aid in feeding. Dactylozooids aid in defense. Gonozooids aid in reproduction.

The Portugese Man-of-War Example of colonies of zooids in a common cnidarian

The Portugese Man-of-War Example of colonies of zooids in a common cnidarian

Description of Medusa Medusa are the free-swimming or floating body form of a cnidarian.

Description of Medusa Medusa are the free-swimming or floating body form of a cnidarian. Medusa are bell-shaped or umbrella-shaped. The mouth of the medusa (oral side) faces downward and is surrounded by tentacles. Both the polyp and medusa have a jelly-like fluid in the center of their bodies called mesoglea. The mesoglea is much thicker in medusa making them buoyant, giving them the name jellyfishes.

Medusa

Medusa

Cnidarian Movement Colonial polyps are usually stationary. Solitary polyps can move slowly along the

Cnidarian Movement Colonial polyps are usually stationary. Solitary polyps can move slowly along the surface of the ground by secreting mucus and sliding along their base. Medusa can move freely by contracting their body and by excreting water out their mouth.

Cnidarian Life Cycles Life cycles of cnidarians can be complex, but in general life

Cnidarian Life Cycles Life cycles of cnidarians can be complex, but in general life begins in the form of a larva called a planula. The planula settles and develops into an adult polyp. Depending on the type of cnidarian, the polyp can remain a polyp for life (like sea anemones and corals) or the polyp may develop into a medusa (like a jellyfish). Eventually becoming sexually mature and releasing gametes (sex cells) that will unite to form a zygote. The developing zygote will form into a planula. Many cnidarians have both polyps (asexual stage) and medusa (sexual stage) for a part of their life.

Typical Cnidarian Life Cycle

Typical Cnidarian Life Cycle

Typical Cnidarian Life Cycle

Typical Cnidarian Life Cycle

Cnidarian Digestion The tentacles draw the prey into the mouth. Digestion begins in the

Cnidarian Digestion The tentacles draw the prey into the mouth. Digestion begins in the gastrovascular cavity. Digestive enzymes are secreted in the gastrovascular cavity and the food is broken down into smaller pieces. After the food is broken down, nutrients get absorbed by the cells lining the gastrovascular cavity. Eventually the waste is expelled out the mouth.

Cnidarian Tissues The body of a cnidarian consists of three parts, but these are

Cnidarian Tissues The body of a cnidarian consists of three parts, but these are derived from only two (tissues) germ layers. The outer epidermis (derived from ectoderm) The inner gastrodermis (derived from the endoderm) And the middle mesoglea (not a germ or tissue layer)

Cnidarian Cells Cnidarians posses a variety of cells lining or embedded in the epidermis

Cnidarian Cells Cnidarians posses a variety of cells lining or embedded in the epidermis and gastrodermis. Nutritive-muscular cells – provide support and structure with a hydrostatic skeleton; additionally they also function as digestive cells (found in the gastrodermis). Gland cells – secrete digestive enzymes (gastrodermis). Epitheliomuscular cells – provide a protective covering and muscular movement. Contracts tentacles. (epidermis). Interstitial cells – stem cells that can develop into a variety of other cells including cnidocytes, sex cells, buds, nerve cells etc. (found in the epidermis).

Cnidarian Cells Cnidocytes are the cells that make up the main defense mechanism for

Cnidarian Cells Cnidocytes are the cells that make up the main defense mechanism for cnidarians. The cnidocytes contain little spines attached to a coil called nematocysts that function as weapons and can injure or paralyze their prey and/or enemies. There are three types of nematocysts; Those that penetrate and inject poison (penetrants), those that entangle prey (volvents), and those that secrete a sticky adhesive substance (glutinants)

Nematocysts

Nematocysts

Cnidarian Nervous System No central nervous system (i. e. brain) in Cnidarians. All of

Cnidarian Nervous System No central nervous system (i. e. brain) in Cnidarians. All of the sensory and nerve cells are connected via a nerve net which is a complex network of cells that are able to communicate and respond to each other.

Cnidarian Senses Some Cnidarians also have some basic sensory cells that are connected to

Cnidarian Senses Some Cnidarians also have some basic sensory cells that are connected to their nerve net. Statocysts provide equilibrium and balance. Ocelli are photosensitive and detect light.

Class Hydrazoa (hi-dro-zo'a) Name means “water serpent animal”. Most Hydrazoa live in marine environments

Class Hydrazoa (hi-dro-zo'a) Name means “water serpent animal”. Most Hydrazoa live in marine environments and most also live in colonies. Some Hydrazoa are solitary and live in freshwater. Most commonly polyps reproduce asexually and medusa reproduce sexually Examples of genera include; Hydra, Obelia, Physalia,

Hydra and Obelia Hydra are freshwater cnidarians that are solitary and exist in the

Hydra and Obelia Hydra are freshwater cnidarians that are solitary and exist in the polyp body form Obelia often live in colonies and exist in both the polyp and medusa body form Solitary Hydra on left and Obelia colony on the right

Physalia (Portugese Man-of-War) Exist as both medusa and polyp forms. These Hydrazoans form floating

Physalia (Portugese Man-of-War) Exist as both medusa and polyp forms. These Hydrazoans form floating colonies. The nematocysts secrete a powerful neurotoxin that can inflict painful stings. • This portugese man-ofwar is actually a colony of hydrazoans.

Class Scyphozoa (si-fo-zo'a) Name means “cup animal” Includes most of the large common jellyfish

Class Scyphozoa (si-fo-zo'a) Name means “cup animal” Includes most of the large common jellyfish Solitary animals Scyphozoans are all marine Polyp stage is often absent Scyphozoans have a bell-shaped medusa filled with an enlarged mesoglea and they lack a velum. The velum is a circular membrane surrounding the cap of a medusa that aids in swimming. Examples of Scyphozoans genera include; Aurelia, Cyanea, Cassiopeia, and Rhizostoma

Aurelia and Cyanea Aurelia on top “moon jellyfish”. Feeds on plankton caught in mucus

Aurelia and Cyanea Aurelia on top “moon jellyfish”. Feeds on plankton caught in mucus on its umbrella Cyanea capillata on bottom. Called “Sea blubber” by fishermen. Aka Giant jellyfish or Lion's mane jellyfish) with a bell diameter of 2 meters and tentacles that can reach 60 - 70 meters long (about 200 feet long!).

Class Cubozoa (ku'bo-zo'a) Name means a “cube-shaped animal”. All marine Solitary animals. Very little

Class Cubozoa (ku'bo-zo'a) Name means a “cube-shaped animal”. All marine Solitary animals. Very little is known about the life cycle of cubozoans. Medusa are the primary body form. The bell-shaped medusa have a square or cube-shaped cross section. Examples of cubozoa include; Carybdea, Tripedalia, Chironex, and Chiropsalmus

Class Cubozoa Box Jellyfish (Carybdea marsupialis)

Class Cubozoa Box Jellyfish (Carybdea marsupialis)

The Sea Wasp Box Jellyfish (Chironex fleckeri) Stings are very painful, dangerous and sometimes

The Sea Wasp Box Jellyfish (Chironex fleckeri) Stings are very painful, dangerous and sometimes fatal. Found in the waters of Australia.

Class Anthozoa (an-tho-zo'a) Name means “flower animal”. All polyps, no medusa. All marine, some

Class Anthozoa (an-tho-zo'a) Name means “flower animal”. All polyps, no medusa. All marine, some colonial, some solitary. Found all over the world, in deep, shallow, tropical and polar seas. Very diverse group of cnidarians. Three different subclasses. Zoantharia – Sea anemones and hard corals Ceriantipatharia – Tube anemones and thorny corals Octocorallia – Soft and horny corals such. Corals with an octomerous (eight-part symmetry) arrangement.

Class Anthozoa Subclass Zoantharia Sea Anemones and Hard Corals

Class Anthozoa Subclass Zoantharia Sea Anemones and Hard Corals

Class Anthozoa Subclass Ceriantipatharia Tube Anemones and Thorny Corals

Class Anthozoa Subclass Ceriantipatharia Tube Anemones and Thorny Corals

Class Anthozoa Subclass Octocorallia Soft and horny corals Octocorallians are octomerous meaning they usually

Class Anthozoa Subclass Octocorallia Soft and horny corals Octocorallians are octomerous meaning they usually have an arrangement of eight tentacles arranged around the mouth.

Phylum Ctenophora (te-nof'o-ra) Name means comb bearing. Ctenophorans are called “comb jellies”. All marine,

Phylum Ctenophora (te-nof'o-ra) Name means comb bearing. Ctenophorans are called “comb jellies”. All marine, less than 100 species known. Live mostly in warm, tropical waters. Eight rows of comblike plates lined with cilia used for locomotion. Radial symmetry like Cnidarians. Most Ctenophores do not have nematocysts like Cnidarians. Instead they use sticky glue-like cells called colloblasts to capture prey. Comb jellies are also bioluminescent.

Ctenophora (Comb Jellies)

Ctenophora (Comb Jellies)