Ch. 28 – Simple Invertebrates
Section 28.1Sponges
Sponges were once classified as plants
Asymmetrical
Lack tissues and organs
Cell recognition makesthem animals
The Simplest Animals
Sponges belong to Phylum Porifera System of pores
Ostia Pores that let water into sponge
Oscula Pores that let water exit Larger than ostia
Sessile
The Simplest Animals
Prevent sponge body from collapsing on itself
Composed of spicules Tiny needle composed of silica or calcium
carbonate
Some sponges contain spongin Flexible protein fiber
Sponge Skeletons
3 Types of Sponges Based on Their Skeleton Calcareous
Spicules composed of calcium carbonate
Glass Spicules made of silica
Demosponge Spongin
Types of Sponges
Can reproduce asexually Regenerate when cut into pieces Commonly reproduce by shedding fragments
Also reproduce sexually Hermaphrodites
Reproduction
Section 28.2Cnidarians
Phylum Cnidaria Jellyfish
Sea anemone
Hydras
Corals
Medusa Umbrella-shaped
Polyp Tubelike
Both have radial symmetry Cells arranged into tissues
2 Body Forms
Characteristic specific to Cnidarians
Stinging cells found on tentacles
Nematocyst Barbed harpoon within cnidocytes Some contain deadly toxins
Cnidocytes
Most primitive cnidarians
Life cycle contains polyp and medusa stages
Some found in freshwater Hydra
Use basal disk to attach to objects
Marine Hydrozoans More complex than freshwater forms Form colonies
Reproduction Sexual and asexual reproduction Some species are hermaphrodites
Hydrozoans
True jellyfish
Range in size from a few cm to several feet in diameter
Medusas
Reproduce sexually
Scyphozoans
Anthozoans Largest class of
cnidarians
Polyps
Brightly colored sea anemones and corals
Tubelike body topped with tentacles
Reproduce sexually and asexually
Sea Anemones Feed on fish that swim
near their tentacles Reproduce asexually by
pulling self in half
Corals Found in colonies Stonelike outer skeleton
of calcium carbonate Only outer layer of coral
is alive
Section 28.3Flatworms and Roundworms
Largest group of acoelomate worms Tissues organized into organs Bilateral symmetry Belong to phylum Platyhelminthes
Turbellaria Cestoda Trematoda
Flatworms
Most are marine flatworms
Freshwater flatworms Planaria
Have ability to be cut in half andregenerate
Reproduction method
Turbellaria
Parasitic tapeworms Attach themselves to the intestinal wall of host Proglottids
String of rectangular body sections May reach 40 ft. long
Commonly infect humans when they eat infected meat that is undercooked.
Cestoda
Largest flatworm class Parasitic worms called flukes Endoparasites contain tegument preventing them
from being digested by host Suck body fluids from host using pharynx Lake itch
Burrows under skin
Trematoda
Common canine parasites
Members of phylum Nematoda
Pseudocoelom
Long, cylindrical bodies
Roundworms
Trichinella spiralis common roundworm that infects humans
Causes trichinosis Commonly occurs due to eating undercooked
pork
Roundworm Infection
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