Biology 20: Diversity of LifeInvertebrates – Teacher Notes

Invertebrates

Phylum Mollusca (Snails, Bivalves, Octopus, Squid)

The word “Mollusca” means soft

Bilateral symmetry

Soft body with internal or external shell

Have a muscular foot for movement - can be modified into arms or tentacles

Breathe through gills or lungs located below a protective layer called the mantle

The mantle forms the shell in some species and also protects the body organs

Visceral mass protects the internal organs

All mollusks except bivalves contain a rasping, tongue-like radula for scraping food.

The circulatory system consists of a three-chambered heart and open-flowing system except for octopus & squids which have a closed circulatory system.

Reproduction is sexual even in hermaphroditic forms. Mollusks go through a free swimming larval stage called the trochophore.

Classified according to their foot and shell. Three major classes of mollusks: 1. Gastropods (snails, slugs)

shell-less or single shelled move by a muscular foot attached to their belly snails without shells are called slugs

Biology 20: Diversity of LifeInvertebrates – Teacher Notes

2. Bivalves (clams, oysters) have two shells hinged together by a ligament muscles open and close the shells siphons circulate water containing food and oxygen through

the bivalve gills extract the oxygen from the water move by jet propulsion muscular foot can be extended from the shell for movement or

anchoring. 3. Cephalopods (octopi, squid)

soft-bodied , head is attached to foot foot is divided into tentacles with sucking disks most have beaks, tentacles and jaws and are active predators small internal shells or no shell at all the most intelligent of all invertebrates use siphons to move by jet propulsion.

Representative Mollusks:

a) Snailso Gastropod meaning it walks on its bellyo Most snails are marine and have gills to breatheo Land snails have an air hole for breathingo Snails can be very large. The helmet snail can be as big as 15 pounds!

b) Squido Marine animals o Blast clouds of ink when threatenedo Translucent body, can be iridescent, and can

change colorso Are the fastest swimmers among the

invertebrates – some “flying squid” have been known to leap out of the water at speeds of 20 mph

o The giant squid is the largest cephalopod. It can be up to 60 meters in length and has been known to eat whales.

Biology 20: Diversity of LifeInvertebrates – Teacher Notes

Phylum Arthropoda (Insects, Spiders, Crustaceans)

The word “Arthropoda” means jointed

Hard exoskeleton which is usually composed of substance called chitin

Go through periodic ecdysis (molting) as they shed or molt their exoskeleton

Have specialized body segments (head, thorax, cephalothorax, & abdomen)

Have jointed appendages such as legs, antenna, and mouthparts

Have an open circulatory system (blood is pumped out of blood vessels into the body)

Further classified according to their type of appendages

Major Group Characteristics ExamplesCentipedes Have flat bodies with segments. Each body segment

has one pair of legs. Has 1 pair of antennae.Centipedes

Millipedes Have round bodies with many segments. Each body segment, except the first four, has two pairs of legs. Has 1 pair of antennae.

Millipedes

Crustaceans Have two main body parts, two pairs of antennae, large claws, and four pairs of legs. Most live in water. Have gills for gas exchange.

Lobsters, shrimp, crabs, and crayfish

Arachnids Have two body sections and four pairs of legs. Have book lungs for gas exchange.

Spiders, scorpions, ticks

Insects Have three body sections and three pairs of legs. Some have wings.

Ants, lady bugs

Biology 20: Diversity of LifeInvertebrates – Teacher Notes

Arthropods make up the largest phylum in the animal kingdom.

Why have they been so successful?a) First true walkers

b) Have adapted for all environments – land, water, and air

c) Exoskeleton provides protection

d) Exhibit social behavior (e.g. colonies of ants and their related hierarchy,

communication between bees)

Arthropods have both a helpful and harmful relationship with humans.

Helpful Pollinate plants Act as decomposers Eat things harmful to humans Produce materials (e.g. honey, silk)

Phylum Echinodermata (Starfish, sand dollars, and sea cucumbers)

The word "echinoderm" means spiny skin

Radial symmetry with five arms that extend from a middle body section

Have an endoskeleton made up of spines

Adults have no head or brain and move by extendable tube feet.

Have a water vascular system made up of a system of canals that help the organism feed and move. This hydraulic water system is strong enough to help starfish open clam shells.

Harmful Damage crops Vectors of diseases Compete with humans for

food and shelter

Biology 20: Diversity of LifeInvertebrates – Teacher Notes

Skin gills are used for respiration and waste removal.

Can reproduce asexually by regeneration whenever parts are dropped or by fragmentation

Can reproduce sexually with external fertilization

Representative Echinoderm:

a) Starfisho Have 5 arms set off from a central disk and their mouth located on

the underside or oral surfaceo Are active marine predatorso Consume clams by turning their stomach inside out and sticking it

into the clam shell to digest the clam