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