• 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:

choanocyte

amoebocyte

pinacocyte

• 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

4) Cubozoans dominant medusa form; include tropical box jelly fish & sea wasps

Sea wasp (class Cubozoa)

Box jelly fish(class Cubozoa)