Transcript Sea anemone - Cloudfront.net

• Phylum Porifera: Sponges
have  specialized cells
but no tissues; no
symmetry
– Sponges are the most 
primitive animals on Earth
• 570 million year old fossils
• Closely related to a  group
of protists
– Sponges share common
characteristics:
• Sessile  do not move
• Reproduce both  sexually &
asexually
• They are  filter feeders
– Sponges have several types of specialized
cells:
• Pinacocytes  thin and leathery cells that form a
sponge’s outer layer
• Choanocytes  “collar cells,” form the inner layer
of a sponge
– Cells have flagella surrounded by a collar of tiny hairlike
structures called  microvilli
– These cells pull water through the sponge by beating
their flagella  trapping food particles in their mucus.
• Ameobocytes  mobile cells found in the jellylike
material between the 2 cell layers
– They  absorb & digest food particles caught by their
collar cells
– Transport  oxygen & waste in the sponge
• Internal organization of a sponge:
pinacocyte
choanocyte
amoebocyte
• Phylum Cnidaria: Cnidarians are the 
oldest existing animals that have
specialized tissues; radial symmetry
– Cnidarians have 2 body forms:
• Polyps  cylindrical tubes with mouth and
tentacles facing upward (example – coral)
• Medusas  umbrella-shaped with their mouth and
tentacles on the underside (example – freeswimming cnidarians such as jellyfish)
– Cnidarians reproduce both  sexually &
asexually
• Polyps reproduce asexually by  budding,
producing genetically identical offspring
• Medusa reproduce sexually by  releasing
gametes into the water
– Fertilized egg develops into a free-swimming larva called
a  planula
– The planula then develops into the  polyp stages
• Many cnidarian species  alternate between
these two body forms
Feeding
polyp
Reproductive
polyp
Medusa
bud
ASEXUAL
REPRODUCTION
(BUDDING)
Portion of
a colony
of polyps
Haploid (n)
Diploid (2n)
Gonad
Medusa
Egg
SEXUAL
REPRODUCTION
Sperm
FERTILIZATION
Zygote
1 mm
Key
MEIOSIS
Developing
polyp
Mature
polyp
Planula
(larva)
– Cnidarians are made up of  2 tissue
layers separated by mesoglea (noncellular jelly like material)
• Outer tissue layer has 3 cell types:
– Contracting cells  cover the surface of the
cnidarian & contain muscle fibers
– Nerve cells  interconnect & form a network
over the entire animal (they do not have brains)
– Cnidocytes  specialized cells that contain
stinging structures used for defense & capturing
prey.
» Found all over a cnidarian’s body but 
most are on their tentacles
» A nematocyst is a stinging structure found
in both sea anemones & jellyfish  they
contain a thin, coiled, harpoon-shaped
tubule with a poisonous barb at one end
• Gastrovascular cavity  sac-like digestive space
through which cnidarians stuff prey
– Secretes  digestive enzymes & absorbs nutrients
– Also moves  oxygenated water to internal cells
Polyp
Mouth/anus
Tentacle
Medusa
Gastrovascular
cavity
Endoderm
Body
stalk
Mesoglea
Ectoderm
Tentacle
Mouth/anus
– The four major cnidarian classes are defined
by  their dominant body form
1) Anthozoans  polyp form is dominant, there is
no medusa form; include sea anemones & coral
Sea anemone
(class Anthozoa)
2) Hydrozoans  alternate between polyp and
medusa; include fire coral, Portuguese Manof-War & hydras
Hydra
Fire coral
Portuguese Man-of-War
3) Scyphozoans  medusa form is dominant,
very short or no polyp stage; include jellyfish
Jellies
4) Cubozoans  dominant medusa form;
include tropical box jelly fish & sea wasps
Sea wasp
(class Cubozoa)
Box jelly fish
(class Cubozoa)