Cnidaria & Ctenophora

Characteristics - Include Hydras, jellyfish, sea anemones & corals -Radially symmetrical Two basic forms:

Polyp: Cylindrical form which attach bases (Sessile) Hydras, anemones Medusa: Bell-shaped, mouth down version of the polyp. Moves freely

Polyp

Freshwater

Marine

Medusa

Body Plan

• They have tissue layers

• Outer layer of cells - the

epidermis

• Inner gastrodermis, which

lines the gut cavity or

gastrovascular cavity

(gastrodermis secretes

digestive juices into the

gastrovascular cavity)

• In between these tissue layers is a

noncellular jelly-like material

called mesoglea

Movement & Nervous System

• The cnidarian body is capable of some kind of

coordinated movement

• Both the epidermis and the gastrodermis possess

nerve cells arranged in a loose network - nerve net

(plexus), which innervate primitively developed

muscle fibers that extend from the epidermal and

gastrodermal cells

• Stimulus in one part will spread across the whole

body via the network

Movement & Nervous System

Nutrition

• Cnidarians are carnivores

• hydras and corals consuming plankton

• sea anenomes & jellyies consuming small fish & clams

• Use tentacles to capture prey and direct it toward the mouth

• Digested in the gastrovascular cavity where gland cells secrete enzyme

that digest prey.

• The gastrovascular cavity exists as 1 opening for food intake and the

elimination of waste. IN one cavity; OUT the same cavity

• There is no system of internal transport, gas exchange or excretion; all

these processes take place via diffusion

Cnidocytes

• Prey capture is enhanced by use of specialized stinging cells called cnidocytes located in the outer epidermis.

• Each cnidocyte has a modified cilium - cnidocil, and is armed with a stinging structure called a nematocyst.

• The undischarged nematocyst is composed of a long coiled thread

• When triggered to release, either by touch or chemosensation, the nematocyst is released from the cnidocyte and the coiled thread is inverted

• Some nematocysts function to entangle the prey; others harpoon prey and inject a paralyzing toxin

Cnidocytes

• Nematocyst Animation: Feeding Tentacles

– http://vimeo.com/37431528

• Nematocyst Animation: Fighting Tentacles

– http://vimeo.com/37432287

Portuguese Man O' War

Box Jellyfish

Reproduction

• One of the most amazing adaptations is the ability of some

cnidarians to regenerate lost parts or even a complete body

• Asexual reproduction is common with new individuals

being produced by budding

• Sea anenomes engage in a form of asexual reproduction

called pedal laceration (pieces break off and regenerate

new clones)

• Fertilization is external, with the zygote becoming a

elongated, ciliated, radially symmetrical larva - planula

larva

Life Cycle

Cnidarian Taxonomy

Class Hydrozoa: The Hydras

• Can be found in freshwater; most are

marine

• Live solitary or colonial lives

• Life cycle includes both asexual polyps

and sexual medusa stages; or neither or

both.

• Freshwater hydras are found in ponds and

streams

• Mouth opens to the gastrovascular cavity

• The life cycle is simple: eggs and sperm

are shed into the water and form fertilized

eggs; planula is by passed with eggs

hatching into young hydras

• Asexual reproduction via budding

Colony – Budding were bud stays attached to main stalk. Adding more and more.

Class Hydrozoa: Hydra

Colony: Tubularia crocea

Class Hydrozoa: Hydra

Colony: Tubularia crocea

Class Hydrozoa cont.

Life Cycle of Obelia

• Gonozooids release free swimming medusae

• Zygotes become planula larvae, which eventually settle to become polyp colonies

• The medusae of

hydroids are smaller

than those of

jellyfishes (C.

Scyphozoa)

• Also, the margin of

the bell projects

inward forming a

shelf-like velum

Class Hydrozoa Cont…

Portuguese Man O' War • Actually a floating colony of four

different polyps which are connected by tissues.

• Body polyp consists of a nitrogen-filled bladder which floats on top of the water.

• Reproductive polyp

• Feeding polyp

• Defense polyp - tentacles that are typically 10 m (30 ft) in length but can be up to 50 m (165 ft), which contain toxic nematocysts.

Class Scyphozoa: The Jellies

• Typical “Jellyfish”

• Umbrella-shaped bell (medusa) and trailing tentacles. The bell can pulsate for locomotion, while stinging tentacles can be used to capture prey.

• Contain massive amounts of mesoglea (95-96% water)

• Bell –

• Manubrium - stalk-like structure hanging down from the centre of the underside, will reach out for prey then grabs it with its mouth

• Velum – shelf-like inward fold that increases water jet flow

• Statocysts ( gravitational detectors or balance sensory )

• Ocelli – photoreceptor cells

• Hydrostatic skeleton – based on water filling up cavaties.

• Radial Canal – aid in moving food from stomach

• Rhopalia - sensory structors

• Gonads - sexual gland

• Tentacles –

• nematocysts

• ~+500 million years, oldest tissued organism.

Class Scyphozoa: The Jellies

• Gametes develop in gastrodermis of

gastric pouches; eggs and sperm are shed

through mouth

• Fertilized eggs develop into a planula

larva; settles on substrate and develops

into a polyp - scyphistoma

• Scyphistoma produces a series of polyps

by budding - strobila

• The polyps undergo differentiation and

are released from the strobila as free

swimming ephyra

• Ephyra matures into an adult jellyfish

Scyphozoan Life Cycle - Aurelia

Class Cubozoa: Box Jellies

• Similar in form to scyphozoans

• Box-shaped medusa allows it to move more rapidly than other jellyfish.

• Four corners of the bell contains a cluster of 15 tentacles up to 3 meters long covered with millions of cnidocytes

• Four eye-clusters with twenty-four eyes, complete with retinas, corneas and lenses.

• Tests have shown that they have a limited memory, and have a limited ability to learn

• Diet that consists of fish, worms, and crustacean arthropods.

• Mostly found in the Indo-Pacific, but some species are found many other areas of the world

• Chironex fleckeri -One of the most venomous creatures in the world.

• Strong toxin, causes immediate, extreme pain

• Death can occur 3-20 min after a sting

Class Cubozoa: Irukandji jellyfish

• Carukia barnesi

• Extremely venomous jellyfish that inhabit

marine waters of Australia

• Bell about 5 mm - 10 mm wide and four

long tentacles, which range in length from

just a few centimeters up to 1 meter.

• Nematocysts are in clumps, appearing as

rings of small red dots around the bell and

along the tentacles

• Venom is very powerful, 100 times as

potent as that of a cobra

Class Anthozoa: Anemones • Do not have a medusa stage in their development.

ONLY Polyp

• Instead, they release sperm and eggs that form a

planula, which attaches to some substrate on which

it grows

• They attach to shells, rocks, timber, etc. by pedal

discs; some burrow in mud or sand.

• Most anemones can glide slowly on pedal discs;

some can swim with limited ability.

• A crown of tentacles (nematocysts) surrounds the

flat oral disc.

• A slit-shaped mouth leads into a pharynx.

• The siphonoglyph is a ciliated groove that creates

the water current into the pharynx.

• Currents carry in oxygen and remove wastes, and

maintain fluid pressure for a hydrostatic skeleton.

• When in danger, water is rapidly expelled through

pores as the anemone contracts to a small size.

• Most harbor symbiotic algae; some have a

mutualistic relationship with clown fish.

Class Anthozoa: Anemones

Class Anthozoa: Corals

Coral Polyps

Scleractinian Corals

•Also known as true or stony corals.

•They are miniature sea anemones that

live in calcareous cups they have

secreted.

•A sheet of living tissue forms over the

coral surface, connecting all

gastrovascular cavities.

Coral Reefs

•Living plants and animals are limited to

the top layer above the calcium carbonate

deposits.

•These corals require full salinity of

seawater and warmth and light, limiting

them to waters between 30 degrees north

and south.

Fringing Reefs

Barrier Reefs

Atolls

Phylum Ctenophora: Comb Jellies

• 8 comb rows

• Have colloblasts: sticky ends that are used to capture prey

• Catch food with tentacles

• Bioluminescent

• All marine

• Most are pea-size to

golf ball-size