Transcript Radiate Animals Phylum Cnidaria Phylum Ctenophora Radiate

Radiate Animals
Phylum Cnidaria
Phylum Ctenophora
Radiate Animals: General Characteristics
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These phyla are characterized by radial or biradial symmetry.
Their bodies are arranged around a central axis.
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Biradial symmetry means that the body can be divided
into mirrored halves ONLY along 2 planes that pass
through the central axis.
General Characteristics
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Both phyla have two well-developed germ layers
(endoderm and ectoderm).
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A third layer, mesoderm, is present in some.
General Characteristics
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They have an internal body cavity (gastrovascular cavity) with
a single opening that acts as both mouth and anus.
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Most radiates have tentacles
that aid in food capture.
General Characteristics
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Radiates have the simplest form of true nerve cells
(protoneurons), but nerves are arranged as a nerve
net, with no central nervous system.
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Radiates have the simplest form of sense organs.
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Statocysts maintain equilibrium and ocelli are
photosynthetic.
Radiates can move by muscular contractions or
ciliary comb plates, but most forms are best adapted
for floating or being carried by currents.
Phylum Cnidaria
Classes Hydrozoa, Scyphozoa, and Anthozoa
Characteristics of Cnidaria
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All are aquatic and have radial symmetry.
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Primarily sessile or floating
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More specialized than sponges
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Contain nematocysts (stinging cells) that are found in cells
called cnidocytes
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Have two body forms:
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Polyp – tubular body with tentacles; example – hydra
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Medusa – bell shaped and free-swimming; example jellyfish
Class Hydrozoa
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Representatives: hydra, obelia, and Portuguese man-of-war
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Members of this class exhibit the polyp
or medusa form. The medusa form has
a velum (ring of tissue that is found at the
base of the tentacles).
The Hydra
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Hydra are the freshwater Hydrozoa representative.
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They are typically sessile polyps.
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The normal habitat for hydra is
the underside of aquatic leaves
and lily pads in the water of ponds
and streams.
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Hydra are found throughout the
world with 16 species in North America alone.
Structure of the Hydra
Body Plan
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Its body can extend to a length of 25-30 millimeters.
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It is a cylindrical tube
with a stalk-like end
and an attachment end.
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The basal disk is the
attachment end that
contains gland cells
to allow adhesion.
Structure (continued...)
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The mouth (hypostome) opens to the gastrovascular cavity.
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Six to ten tentacles
surround the mouth:
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These are hollow
and extendable.
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They contain
nematocysts (coiled
stinging cells used to
get food and provide
protection).
Structure (continued...)
Body Wall
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Ectoderm – outer layer or epidermis; contains many types of cells
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Epitheliomuscular cells – responsible for muscular contractions
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Interstitial cells – undifferentiated stem cells that become most
other types of cells
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Gland cells – secretes an adhesive substance that aids in the
attachment process
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Cnidocytes – contain nematocysts
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Nerve cells – multipolar neurons
Structure (continued...)
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Endoderm – gastrodermis; inner layer that contains muscular,
gland, and interstitial cells
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Mesoglea – jelly-like substance
found between ectoderm and
endoderm
Processes of the Hydra
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Locomotion – floats and moves by somersaulting motion
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Response – when disturbed, it will contract and form a small
ball
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Digestion
1. Food enters the gastrovascular cavity that is lined with
gastrodermal cells.
2. Some secrete digestive enzymes that partially digest food.
3. Partially digested food is taken in by the gastrodermal cells
when digestion is complete.
Processes (continued...)
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Excretion
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Digestive wastes are expelled through the mouth.
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Metabolic wastes and carbon dioxide are
discharged into water.
Respiration – oxygen diffuses from water into cells
Processes (continued...)
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Nervous
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Contains a nerve net that consists of interconnected nerve
cells located at the base of the epidermis and
gastrodermis
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This is a primitive type of nervous system.
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It controls movement of tentacles.
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NO BRAIN!
Processes (continued...)
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Reproduction
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Asexual reproduction occurs through budding or regeneration.
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Miniature versions break off of mature organisms and grow
to maturity.
Sexual reproduction occurs when temporary gonads develop
in the autumn.
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The ovaries produce eggs and the testis produce sperm.
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The developing embryos are encased in a cyst to protect
them from harsh winters. Warm weather stimulates the
“hatching” of new hydras.
Class Scyphozoa
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Scyphozoa means “cup animal.”
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The most common representative is the jellyfish (Aurelia).
The Jellyfish
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Contains both body forms – polyp
and medusa
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Medusa form is for sexual
reproduction
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Zygote develops into a
PLANULA LARVA which
swims around and then settles
to form the polyp form
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The polyp form produces more of the medusa form
The Jellyfish
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Tentacles of the medusa have nematocysts that give humans
painful stings
Most Deadly Jellyfish
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All jellyfish contain a toxin, but some are more toxic than others.
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Many of the box jellies are considered to be more dangerous.
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Specifically, the Irukandji is considered the most deadly of the
jellyfish. (There are actually multiple species.)
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It is only one centimeter cubed at its
largest, while many are 5mm or less
in diameter.
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It’s small size makes it almost
invisible in the marine waters off
of Australia’s coast.
Class Anthozoa
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Means “flower animal”
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Common representatives are the sea anemone and coral
Class Anthozoa
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Anthozoans lack a medusa stage.
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All anthozoans are marine, found in both deep and shallow
water, and vary in size.
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Anthozoans are solitary or colonial.
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They contain a large gastrovascular
cavity that is separated by divisions
called septa, which are inward
projections of the body wall.
Sea Anemone
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The polyps of sea anemones are larger and heavier than
hydrozoan polyps
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They attach to shells, rocks, or timber by pedal discs. Some
burrow in mud or sand.
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A crown of tentacles surrounds
the flat oral disc.
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A slit-shaped mouth leads into
a pharynx.
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The gastrovascular cavity is
divided into six pairs of primary
septa.
Sea Anemone
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When in danger, water is rapidly
expelled through pores as the
anemone contracts to a small size.
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Some anemone fishes shelter in
sea anemones and have a skin
mucus that protects them from
triggering nematocysts.
Corals
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Corals display only the polyp body form.
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Coral reefs have great productivity, rivaled only by tropical rain
forests.
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Living plants and animals
are limited to the top layer
above the calcium
carbonate deposits.
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Coral reefs are suffering
from global warming and
high concentrations of
carbon dioxide.
Corals
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Coral also has a large economic value.
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When coral dies, the hard skeleton remains
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The skeletons produce coral reefs and can also
be used to create jewelry.
Phylum Ctenophora
Class Tentacula
Characteristics of Ctenophora
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Composed of fewer than 100 species, all of which are marine and
primarily found in warm waters
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All are formed from 8 rows of comblike plates that function in
locomotion
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Has a combination of radial and biradial symmetry
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Has endoderm and ectoderm, with mesoglea between
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Does not contain nematocysts, but do contain adhesive cells called
colloblasts that are used to capture prey
Class Tentacula
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Has tentacles that may or may not have sheaths into which
they retract
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Some have flattened tentacles for creeping
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Representative - Pleurobrachia
Pleurobrachia
BODY FORM
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Its body is 1.5-2 cm in diameter and has a sense organ called a
statocyst near the mouth opening.
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Its surface has 8 equally spaced bands called comb rows that
have long fused cilia called comb plates.
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Movement is accomplished by the wavelike beating of the
cilia.
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It has two tentacles that are very long and extensible that may
also be retracted into tentacle sheaths.
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The surface of the tentacles are covered with colloblasts (glue
cells) that can catch or hold small animals.
Pleurobrachia
DIGESTION
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It has a gastrovascular system that consists of a mouth, pharynx,
stomach, and a system of gastrovascular canals.
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Digestion is both extracellular and intracellular.
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Undigested waste leaves the body through 2 anal canals.
RESPIRATION and EXCRETION
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Both occur through the body surface
NERVOUS and SENSORY
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The epidermis contains numerous sensory cells that allow the
organism to be sensitive to chemicals and other stimuli.