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Cnidarians and Ctenophores
Characteristics
• All carnivorous
• Contain a jelly-like layer between epidermis and
gastrodermis called mesoglea
• Single opening (mouth/anus) to gastrovascular cavity
where food & water enter & wastes leave; called twoway digestive system
• Have a oral surface (mouth/anus) and an aboral surface
(opposite)
Characteristics
• Have tentacles around mouth to pull in water &
capture food
• Have a simple nerve net with to help with
movement & senses
Characteristics
• Sessile members include corals, sea anemones, &
sea fans
• Motile members include jellyfish and Portuguese
man-of-war
• Have radial symmetry as adults
Characteristics
• Contain stinging cells called cnidocytes in their
tentacles that contain coiled stingers called
nematocysts that can shoot out & paralyze prey
Cnidocyte
with
nematocyst
Trigger hair
coiled
thread
Undischarged
Discharged
Body Plan
• have 2 basic body forms: polyp and medusa
Body Plan
• polyp forms are usually sessile with upright
tentacles arranged around the mouth at the top
(oral) and with a thin layer of mesoglea
• Polyps are the asexual stage
• Corals, hydra, & sea anemones exist in the polyp
form as adults
Body Plan
• Medusa forms are usually free-swimming, bellshaped animals with tentacles that hang down
around the mouth
• Medusa are the sexual stage
• Jellyfish & Portuguese man-of-war are medusa form
as adults
Gastrovascular Cavity = Blue
Gastrodermis = Green
Epidermis = Black
Mesoglea = Red
Body Plan
• Some cnidarians are dimorphic or go through both
polyp & medusa stages in their life cycle
• planula larva – free-swimming, flattened, ciliated,
fertilized egg
• strobila – the chain of segments of the larva of a
jellyfish, each segment of which gives rise to a freeswimming medusa.
• ephyra – swimming stage of medusa after detaching
from strobila
Body Plan
• Some are solitary (Hydra) others are colonial
(corals)
• Three classes include Hydrozoa (hydra), Scyphozoa
(jellyfish), & Anthozoa (sea anemones & corals)
Class Hydrozoa
• sessile hydra (exists only as polyps)
• Portuguese man-of-war (exists as colony of polyps
& medusa)
• Group of cells called basal disk produces sticky
secretion for attachment & can secrete gas bubbles
to unattach & let hydra float
Class Hydrozoa
• Hydra also move by somersaulting (tentacles bend
over to bottom as basal disk pulls free)
• Tentacles pull food into gastrovascular cavity where
enzymes digest it
• Reproduce asexually by budding during warm
weather & sexually in the fall
• Hermaphrodites that release sperm into water to
fertilize eggs of another hydra
http://youtu.be/-UI531GMRTM
Class Hydrozoa
Polyp Forms
Hydra littoralis
Medusa Forms
Obelia
Portuguese man-of-war
(Physalia physalis)
Class Scyphozoa
• Includes bell-shaped jellyfish
• Medusa stage is dominant in the life cycle
• tentacles may be meters in length & carry poisons
that cause severe pain or death
• Have both asexual polyps & sexual medusa stages in
their life cycles
Class Scyphozoa
Cyanea capillata
(Lion’s Mane)
Class Scyphozoa
Aurelia aurita
(Moon Jellyfish)
Class Scyphozoa
Cephea cephea
(Cauliflower Jellyfish)
Class Scyphozoa
Olindias formosa
(Flower Hat Jellyfish)
Class Scyphozoa
Chrysaora fuscescens
(Pacific Sea Nettle)
Class Anthozoa
• Called "flower animals"
• Some anemones in the Pacific Ocean live
symbiotically with the clownfish sharing food &
protecting each other
• Sea anemone is a sessile, polyp-form that uses its
tentacles to paralyze fish and the only solitary form
Class Anthozoa
Stony Corals (Branching Coral and Doming Coral)
Class Anthozoa
Soft corals
Class Anthozoa
Gorgonians
(Sea Whips and Sea Fans)
Class Anthozoa
Sea Pens
Class Anthozoa
Sea Pansies
Phylum Ctenophora
• Includes comb jellies
• Have eight rows of fused cilia called "comb rows”
and is the largest animal to move by cilia
Phylum Ctenophora
• Lack cnidocytes but have cells sticky cells called
colloblasts that bind to prey
• Colloblasts located on two ribbon-like tentacles
Have sensory structure called apical organ to detect
direction in the water
• Most are hermaphrodites (make eggs & sperm)
• Produce light by bioluminescence
Phylum Ctenophora
Chironex fleckeri
(Sea Wasps)
Phylum Ctenophora
Pleurobrachia
(Sea Gooseberry)
Phylum Ctenophora
Box Jellyfish
Monster Quest: Killer Jellyfish
1. How did the Nomura jellyfish affect the power
plant?
2. Describe the physical characteristics of the
jellyfish.
3. Name one theory why the Nomura jellyfish took
over the sea of Japan.
4. KEY FACT
5. KEY FACT
6. KEY FACT
7. KEY FACT