Simple Invertebrates

Sponges, jellyfishes and coral, flatworms, roundworms, and

segmented worms too!

So what do you know about simple invertebrates?

Do you know the main characteristics of each of the five phyla?

Let’s check them out.

Phylum Porifera(Sponges)

Simplest animals of all (some of the oldest too). All are aquatic (freshwater and marine). Only two layers of cells, but no tissues or organs! Their skeletons are made of tiny spines called

spicules. Cannot move (grow attached to the bottom). Mostly filter feeders. Uses?

The mighty sponge!

Phylum Cnidaria (aka Coelenterata): Jellyfishes and Corals

More advanced than sponges. (for example, they have tissues, but still no organs).

Their body is a hollow cavity with only one opening (for food AND wastes)!

Entirely aquatic (freshwater and marine). All have stinging cells, but not all can harm people. Some are pretty nasty predators. Others filter-feed

on small particles and organisms in the water.

Medusae vs. Polyps

MEDUSAE

Ex. Jellyfishes. A medusa is free-swimming. Most are solitary. Their opening is on the

bottom of their body.

POLYPS

Ex. Corals Polyps are like an upside

down medusa. Their opening is on the top

of their body. Coral polyps are tiny and live

in huge colonies of thousands.

Corals build their “home” as the colony grows larger and larger.

Jellyfish

Most jellyfish are harmless to people, although not so to small fish and other marine organims.

Portuguese man-of-war.Look out!

Corals: beautiful colonies of polyps.

More Cnidarians: hydra and sea anemones.Is it a medusa or a polyp?

Not to confuse you, but did you know that jellyfish start their lives as polyps, but become medusae as an adult? It’s true! Here is a jellyfish life cycle.

Phylum Platyhelminthes(Flatworms)

Even more complex. Long, flat body. Clearly defined head with mouth. Some have senses, a few even have eyespots. Some move freely. Many are parasites (ex. Tapeworm). Some live in the water (fresh or marine), others live inside their

host!

Flatworms

Phylum Nematoda(Roundworms)

Another step up the ladder! Some even have a simple nervous system. Some have a digestive system that runs through the entire body

-- with two openings, one for food to enter and one for wastes to leave.

Most are parasites. Many are harmless microscopic critters that live in the soil. Also, the trichina worm (in pork), as well as hookworms and heartworms (common in pets).

Roundworms!

One teaspoon of garden soil may contain as many as 10,000 tiny nematodes (roundworms) in it!

Phylum Annelida(Segmented Worms)

Most complex worms of all. Tube-like body divided into segments. Sophisticated digestive system! (mouth, crop and gizzard,

intestine, anus) Many other specialized organs heart, blood vessels, nerve

cords, simple brains) Can move well. Some aquatic (leeches, clam worms), some terrestrial

(earthworms). Some are parasites (leeches), others are very important

decomposers (earthworms). Any other uses for annelids?

Phylum Annelida(Segmented Worms)

So NOW what do you know about the simple invertebrates?

Do you know the names of the five phyla of simple invertebrates?

Do you know the main characteristics of each of the five phyla?

Can you identify examples of animals in each of the five phyla?