Chapter 28
Simple Invertebrates
Section 1: Sponges
Section 2: Cnidarians
Section 3: Flatworms and Roundworms
Section 1
Sponges
Objectives:
•Summarize the general features of sponges.
•Describe how sponge cells receive nutrients.
•Describe how a sponge's body is structurally
supported.
•Distinguish between sexual and asexual
reproduction in sponges.
Section 1
Sponges
The Simplest Animals
•Sponges Sponges lack symmetry and tissues.
Sponges are sessile filter feeders that draw sea water
through pores into an internal cavity, trapping tiny
aquatic organisms.
•Protistan Ancestors Ancient choanoflagellates may
be the ancestors of sponges.
Section 1
Sponges
Sponge Diversity
•Sponge Skeletons The sponge’s supportive skeleton
is composed of soft spongin fibers, hard spicules, or a
combination of both.
Section 1
Sponges
Reproduction
•Reproduction Sponges that reproduce sexually are
usually hermaphrodites. Sponges also reproduce
asexually.
Section 2
Cnidarians
Objectives:
•Describe the two cnidarian body forms.
•Summarize how cnidocytes function.
•Summarize the life cycle of Obelia.
•Compare three classes of cnidarians.
•Compare asexual and sexual reproduction in
cnidarians.
Section 2
Cnidarians
Two Body Forms
•Body Forms Cnidarians are radially symmetrical,
with bodies made up of tissue. Their body form may
be a medusa or a polyp.
•Cnidocytes Cnidocytes are stinging cells found in
the tentacles of cnidarians. Harpoon-like nematocysts
are located within the cnidocytes.
•Extracellular Digestion Digestion begins
extracellularly in the gastrovascular cavity.
Section 2
Cnidarians
Hydrozoans
•Freshwater Hydrozoa Freshwater hydras are
abundant and attach to rocks or water plants by means
of a sticky secretion.
•Marine Hydrozoa Marine hydrozoans are more
complex than freshwater hydrozoans and often form
colonies.
•Reproduction in Hydrozoans Most hydrozoans are
colonial organisms that reproduce asexually, though
many forms can also reproduce sexually.
Section 2
Cnidarians
Scyphozoans
•Characteristics Jellyfish are active predators, and
some have extremely potent toxins within their
nematocysts. Jellyfish spend most of their lives as
medusas and usually reproduce sexually.
•Jellyfish Relatives Jellyfish are related to the
cubozoans or box jellies.
Section 2
Cnidarians
Anthozoans
•Sea Anemones Sea anemones and corals have thick,
stalklike polyp bodies. Their life cycle includes no
medusa form.
•Corals Coral polyps live in colonies called reefs.
Section 3
Flatworms and Roundworms
Objectives:
•Compare the three classes of flatworms.
•Summarize the life cycle of a blood fluke.
•Describe the body plan of a roundworm.
•Summarize the life cycle of the roundworm Ascaris.
Section 3
Flatworms and Roundworms
Flatworms
•Turbellaria Most flatworms, such as planarians and
marine flatworms, are free-living.
•Cestoda Tapeworms are intestinal parasites that
absorb food directly through their skin.
•Trematoda Flukes are endoparasitic flatworms.
They have a protective covering called a tegument
that keeps them from being digested by their host.
Section 3
Flatworms and Roundworms
Roundworms
•Roundworm Infections Roundworms have a
pseudocoelom and a one-way gut. Most are freeliving, but some are animal parasites.