Ch.10 - Mollusks, Arthropods, and Echinoderms

Ch.10 - Mollusks, Arthropods, and Echinoderms

10.1 - Mollusks

- Mollusks are invertebrates with soft, segmented bodies that are often protected by a hard outer shell

- They also have an organ called a foot

- Most species have an open circulatory system, have gills, bilateral symmetry, and two openings in their digestive system

Biologist classify mollusks based on physical characteristics such as:

- Presence of shell

- Type of shell

- Type of foot

- Type of nervous system

Gastropods - largest group of mollusks, include snails

- Have a single shell or no shell at all

- Usually creep along on a broad foot.

Bivalves - mollusks that have two shells held together by hinges and muscles

- Includes Clams, oysters, scallops, and mussels

- Bivalves cover sand or grit lodged in their shells with a protective coat, which eventually forms a pearl

Cephalopods - An ocean-dwelling mollusk whose foot is adapted to form tentacles around its mouth

- Octopuses, cuttlefish, nautiluses, and squids

- Have large eyes and swim by propulsion

10.2 - Arthropods

The major groups of arthropods:

- Crustaceans

- Arachnids

- Centipedes and millipedes

- Insects

Arthropod characteristics are:

- Invertebrates

- External skeleton

- Segmented body

- Jointed appendages

- Bilateral symmetry

- Open circulatory system

- Two opening digestive system

- Sexual reproduction

Exoskeleton - protects the animal and helps prevent evaporation of water

- Exoskeletons cannot grow with the animal

- They are shed by molting

Arthropods have jointed appendages that give them flexibility and enable them to move

- Segments are usually distinct and specialized

Crustacean - an arthropod that has:

- two or three body sections

- five or more pairs of legs

- two pairs of antennae

- live in water and use gills

Arachnids have:

- two body sections

- four pairs of legs

- no antennae

- Ex. Spiders, mites scorpions, and ticks

Centipedes and Millipedes have:

- Two body sections

- Numerous pairs of legs

Centipedes have one pair of legs attached to each segment

- Millipedes have two pairs of legs on each segment

10.3 - Insects

Insects are arthropods with:

- three body sections

- six legs

- one pair of antennae

- usually one or two pairs of wings

The three body sections are the head, thorax and abdomen

Most insects have two large compound eyes that are keen at seeing movement

An insects thorax is the section to which wings and legs are attached

The abdomen contains many of the insects internal organs

An insects mouth parts are adapted for a highly specific way of getting food

Insects either undergo complete metamorphosis or gradual metamorphosis

Complete metamorphosis - Four stages

1. Egg

2. Larva

3. Pupa

4. Adult

- After eating and growing, the insect is enclosed in a protective covering and gradually changes into an adult

Gradual metamorphosis - no distinct larval stage

- Egg hatches into a nymph that often resembles the adult insect

10.4 - Insect Ecology

Food Chain - a series of events in which one organism eats another to obtain energy

Ecology - the study of food chains and how organisms interact

How a food chain works:

- A food chain starts with a producer

- It is then eaten by a consumer

- A decomposer breaks down waste and dead parts of other organisms

Insects play key roles in food chains because of the many different ways that they obtain food and then become food for other animals

Why are insects so important?

- Insects eat plants

- Insects are then eaten by fish, birds, and other animals

- Insects break down plant and animal material

- Humans eat insects

- Insects produce products such as honey

Two ways insects interact with other living things are:

1. Moving pollen among plants

2. Spreading disease causing organisms

Insects carry pollen and are called pollinators

- Without pollinators, some plants cannot reproduce

Harmful insects are called pests

- Pests are controlled by chemicals, traps, and other insects

- Chemicals that kill pests are called pesticides

10.5 - Echinoderms

Echinoderms are invertebrates with an internal skeleton and a system of water-filled tubes called a water vascular system

Endoskeleton - Internal skeleton

Most echinoderms use their tube feet to move and to capture food

Four major groups of echinoderms:

1. Sea stars

2. Brittle stars

3. Sea urchins

4. Sea cucumbers

Sea Stars

- Predators with five arms

- Unique feeding

- Feeds by forcing its stomach out through its mouth and between the shells of its prey

- Chemicals break down prey

- Sea star sucks out digested prey

Brittle Star

- Long slender arms with flexible joints

- Use their arms to slither along the ocean bottom

Urchins

- Have no arms

- Movable spines protect their bodies

- Have a shell of plates that are joined together

- Move by using tube feet that extend out between the spines

Sea cucumbers

- Body is soft, flexible, and muscular

- Move by using five rows of tube feet on their underside

- Use their tentacles to sweep food toward their mouths