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Chapter 28
Simple Invertebrates
28-1: Sponges
 Domain: Eukarya
 Kingdom: Animalia
 Phylum: Porifera
General Characteristics
 No symmetry
 No tissues / organs
 Cells can recognize other cells
 Reorganize when separated
 Sessile: do not move as adults
 Diameter ranges from 1cm to 2m
Body Characteristics
 Ostia: Pores on outer wall
 Osculum: Large hole for water to exit
 Choanocytes: cells with flagella that line
internal cavity
 Move water through body cavity
 Trap food particles and digest
 Also called Collar Cells
 Amoebocytes: cells that move around in
sponge body to transport nutrients / wastes
Pore cells = Ostia
Collar cell = choanocyte
Sponge Feeding
Sponge “Skeletons”
 Most have Spicules: tiny needles made
of calcium carbonate or silica
 Some sponges have spongin: flexible
protein fibers
3 Classes of Sponges
1. Calcareous Sponges
•
Skeletons made of
calcium carbonate
spicules
2. Glass Sponges
•
Spicules made of silica
3. Demosponges
•
Skeletons made of
spicules and spongin
Asexual Reproduction
 Can regenerate when cut into pieces
 Fragmentation
 Budding: smaller individuals grow off
sides of larger individual
 Form gemmules: when living conditions
become too poor, amoebocytes encase
in protective shells to survive
Sexual Reproduction
 Most sponges are hermaphrodites
 Sperm released into water
 Sperm cells from another sponge enter
through pores
 Larvae develop from fertilized eggs and
swim away
Sponge Defenses
 Sponges are soft (easily eaten)
 Sponges are sessile (can’t swim away)
 Protect selves by producing chemicals
 These chemicals have been used by
humans for
 Antibiotics
 Pain killers / Sedatives
 Cancer treatments
28-2: Cnidarians
 Two body forms:
 Medusa: free-floating umbrella-like
 Polyp: tubelike and attached at base
 Polyps are sessile…
 Attach to floor / object with Basal Disk
 Both show radial symmetry
 Tentacles surround mouth
 Enters into gastrovascular cavity
2 layers of cells
 Ectoderm on outside
 Endoderm on inside
 Mesoglea: layer of “jelly” between the 2
layers
 Cells arranged into tissues
Cnidocytes
 Cnidocytes: Stinging cells on tentacles
 Contain Nematocysts: small, barbed
harpoons
 Some nematocysts have deadly toxin, some
with chemicals to just stun
 Used for defense and to spear prey
 Tentacles pull food into mouth
3 classes
 Hydrozoans
 Ex: Hydra, Portuguese-Man-of- War
 Scyphozoans
 Ex: Jellyfish
 Anthozoans
 Ex: Sea Anemones, Corals
Hydrozoans
 Most are Colonial
 Life cycle includes both polyp and
medusa forms
 Live in freshwater and marine
 Freshwater example: Hydra
 Marine hydrozoans are among most toxic
(deadly to humans)
Hydra: freshwater
Hydrozoans
 Most of life is individual polyp
 Stick to surfaces with sticky secretion
from basal disk (bottom)
 Can glide on basal disk or tumble
Reproduction in
Hydrozoans
 Most capable of sexual reproduction
 Some are hermaphrodites
 Can reproduce asexually also
 budding
Scyphozoans
 “True” Jellyfish
 Can be small (thimble-sized) to extremely
large (queen-sized mattress)
 Go through polyp stage at some point in
life cycle
Anthozoans
 Corals and Sea Anemones
 Have symbiotic algae living in cells to help
provide energy
 Sea Anemones are soft-bodied
 Corals secrete calcium carbonate outer
skeletons
 Only top layer is alive, rest is old skeletons of dead
corals
 Build up into reefs
28-3: Flatworms &
Roundworms
Flatworms
Flatworms
 Phylum Platyhelminthes
 More complex than sponges and
cnidarians




Have middle tissue layer
Tissues organized into organs
Bilateral symmetry
Cephalization
Since they are flat…
 Each cell close enough to outside to get
O2 and release CO2
 Gastrovascular cavity branched and
close to all tissues (nutrients to cells
easily)
 Still have just 1 opening
3 classes
1. Turbellaria:



Free-living
Most marine
Freshwater: Planaria
Planarian Feeding
 Use muscular tube
that extends from
center of GVC
 Called Pharynx
 Eat small protists or
dead / dying animals
Planaria Reproduction
 Attach posterior end to rock, pull apart
into 2
 Regenerate
 Sexually reproduce by exchanging sperm
with another planarian
 Hermaphrodites
2. Cestoda
 Parasitic
 Commonly called Tapeworms
 Hooks and suckers on head to attach
inside host’s intestine
 Absorb nutrients from host
 Produce proglottids: string of rectangular
body segments that break off in
reproduction
 Can grow to be 40 ft. long
3. Trematoda
 AKA “Flukes”
 Parasites:
 Live in host (endoparasites)
 Live on host (ectoparasites)
 Ex: Schistosoma
 Disease: Schistosomiasis
•Enter
through skin
(hookworm)
and burrows
to blood
vessels to lay
eggs
•Block blood
vessels
(internal
bleeding and
liver damage)
Roundworms
 Phylum Nematoda
 Have pseudocoelom
 Simplest animals with one-way digestive
tract (mouth and anus!)
 Most microscopic
 One square yard of forest soil can have 3
million nematodes
Pseudocoelom
 “False” body cavity
 Filled with fluid to act as simple
respiratory and circulatory systems
 O2, CO2, nutrients flow through body
Can be human parasites…
 Ascaris lumbricoides
 Infects lungs, gall bladder,
pancreas
Trichinella spiralis
Infects muscles
Elephantitis: blockage of
lymph system by
nematode
•enters through skin in
water