phylum porifera: sponges have specialized cells but no tissues; no symmetry –sponges are the most...
TRANSCRIPT
• 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
• 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 – free-swimming 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
Feedingpolyp
Reproductivepolyp
Medusabud
Medusa
ASEXUALREPRODUCTION(BUDDING)Portion of
a colonyof polyps
1 m
m
Key
Haploid (n)Diploid (2n)
Gonad
SEXUALREPRODUCTION
MEIOSIS
FERTILIZATION
Egg Sperm
Zygote
Planula(larva)
Developingpolyp
Maturepolyp
– Cnidarians are made up of 2 tissue layers separated by mesoglea (non-cellular 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
PolypMouth/anus
Bodystalk
Tentacle
Gastrovascularcavity
Endoderm
Mesoglea
Ectoderm
TentacleMouth/anus
Medusa
– 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 Man-of-War & hydras
Portuguese Man-of-War
Hydra Fire coral
3) Scyphozoans medusa form is dominant, very short or no polyp stage; include jellyfish
JelliesJellies