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