1. Chapter 16 Invertebrates II
Mollusks, Arthropods, and Echniderms

2. Mollusks
Mollusks are animals such as clams, snails, slugs, and octopuses.
Phylum Mollusca has the second highest number of species. They have soft bodies.

3. Octopus
The octopus has many muscles and eight tentacles. On the lower surface of each arm is a series of suction cups which allow it to grasp items. The mouth is located under its head in the center of its arms. It hunts live food (crabs and lobsters). To move rapidly is can force water out of a muscular tube called a siphon. When frightened it can squirt a black fluid into the water to serve as a “smoke screen”, allowing it to jet away to safety.
The octopus has special cells in it’s skin that contain different-colored pigments. This allows the octopus to change colors to reflect it’s mental state or to blend in with its background.

4. Clam
The clam is a mollusk with a shell. Clams, mussels, and scallops produce two shells which are hinged together. They are called bivalves.
The clam’s soft body is covered with a thin skin called a mantle. The outside of this skin manufactures the materials that harden to become the shell. As it grows it adds layers to its shell. The oldest part of the shell is the thickest. The newest part is the thinnest.
The clam has strong muscles than can keep its shells tightly closed. When the clam moves it uses it muscular foot.
Clams are filter feeders. They have two siphons. One draws water in and the other shoots the water away to remove waste.

5. Snails
Snails have exceptionally soft bodies. They have one shell so they are called univalves.
Snails are eaten by humans = escargot.
Snails can be hosts to human liver flukes.

6. Section 2 Arthropods
Phylum Arthropoda has the most species of any animal phylum.
The insect class called Hexapoda is the largest class within this phylum. (over 800,000 species known)
They serve as pollinators, decomposers, disease carriers, and parasites.
They have exoskeletons = a hard, nonliving outer covering that supports and protects the animal. Muscles that are attached to the inside of an arthropod’s exoskeleton pull to move it.

7. Insects Insects typically have three sections:
Head, thorax, and abdomen
Three pairs of legs (six total)
Even caterpillars have three pairs the rest are not real legs.
Most have two pair of wings but can have one or none.
Compound eyes: Thousands of small sections which make the image look like a mosaic.

8. Grasshopper Grasshoppers have blood and a heart.
Blood = fluid tissue made up of cells floating in liquid. Function = to carry substances to and from all parts of the body.
Heart = muscular organ that pumps blood to all body cells.
Grasshopper has a small tubular heart located just under its exoskeleton on the back upper side.
Blood goes in through two slits. When the heart contracts, the slits close and the blood is pumped forward through an artery. Arteries are blood vessels that carry blood away from the heart. The artery is the grasshopper’s only blood vessel.
As the grasshopper’s blood passes over the organs it picks up and deposit things where they go. It has an open circulatory system since the blood does not remain in the blood vessels.
The respiratory system of the grasshopper consists of the spiracles and the tracheas. This is how it gets air.
The excretory system: wastes are filtered out of the blood and collected by thread like Malpighian tubules. Then the wastes pass into the intestine and out of the grasshopper’s body.

9. Incomplete Metamorphosis
Metamorphosis for insects = a change in body
Molting = to shed the old exoskeletons and replace them with new ones.
Insects with a life cycle that is incomplete metamorphosis start as eggs and go through a series of molts in which they progressively larger.
Exp. Cicadas, grasshoppers, cockroaches
Each time an insect with incomplete metamorphosis molts it gets a little bigger but the appearance is the same.

10. Complete Metamorphosis
This involves a life cycle with four stages:
Egg, larva, pupa, and adult.
Example: Butterfly
Egg…larva=caterpillar…pupa=chrysalis…adult=butterfly
Each time an insect with complete metamorphosis molts, it passes from one stage to another.

11. Echinoderms Starfish and sea urchins are called echinoderms.
Starfish are supported by hard, flat plates bound together by tough tissues and muscle fibers just under the skin. Some have spines that stick up through the epidermis (skin) which are used for protection.
The starfish has radial symmetry.
Starfish can regenerate arms (rays) if lost to a predator.
Movement comes from a water-vascular system which is
made up of tiny tube feet on the bottom of each ray. They function as suction cups to pull it forward.
Favorite food = clams
The starfish pries the clam open just a bit with its suction cups and then it inserts its stomach inside out inside the clam shell and digests the soft body of the clam. Then it withdraws its stomach and goes to look for another meal.