Mollusks, Arthropods, EchinodermsMollusks, Arthropods, Echinoderms

Mollusks• Soft-bodied invertebrates• Have bilateral symmetry• Usually have one or two shells with

organs in a fluid filled cavity• Most live in water• Many different species

Mollusks’ Body Plan• Mantle

– Thin layer of tissue that covers the body organs

• Mantle cavity (between soft body and mantle)– Contains the gills that are used to breathe

by exchanging oxygen and carbon dioxide in the water

• Open Circulatory System– Most mollusk have this– Moves blood through vessels and into

open spaces around body organs

Mollusks’ Body Plan• Have a well developed head with a

mouth and some sensory organs• Underside is a muscular foot

– Moves by making rhythmic contractions

Classification of Mollusks• Classified into three common

groups based on shell presence, type and foot type– Gastropods– Bivalves– Cephalopods

Gastropods• Largest group of mollusks• Usually have a single shell• Use a radula (a tongue-like organ

with rows of teeth) to get food• Have foot glands that secrete a

layer of mucus for sliding• Includes snails, conchs, and

garden slugs

The Radula

Obtaining Food

• Some gastropods are herbivores. These include animals that eat only plants.

• Other gastropods are carnivores. These include animals that eat only other animals.

Bivalves• Have a hinged, two-part shell• To open or close their shell they either

contract or relax their muscles• Includes clams, oysters, scallops, &

mussels• Well adapted for water

– Clams can burrow in sand– Mussels attach themselves to a solid surface– Scallops escape predators by rapidly opening

and closing their shell

Pearls

Cephalopods• Most specialized and

complex mollusks.• Include squid, octopuses,

and chambered nautiluses.• Have a well developed

head and many tentacles for capturing prey.

• Closed circulatory system– Moves blood through the

body in a series of closed vessels like humans.

• Use jet propulsion to move at speeds of 6 m/s.

Origin of Mollusks• Mollusk fossils date to more than

500 million years ago• Some species of mollusk, like the

chambered nautilus, have changed very little from their ancestors

• Today’s mollusks are descendants of ancient mollusks

Value of Mollusks• Provide food for people and other

animals• Many people make their living raising or

collecting mollusks to sell• Shells can be used for jewelry and

decoration• Pearls are produced by several species

of mollusks most are made by pearl oysters

Negative Effects of Mollusks

• Land slugs and snails can damage plants

• Certain species of snails are hosts for parasites that can infect humans

• Bacteria, viruses, and toxic protists can become trapped in these animals because they are filter feeders—eating them could result in sickness or even death

Arthropods• Characteristics

– Largest group of animals– Have jointed appendages which

include legs, antennae, claws and pincers

– Have bilateral symmetry, segmented bodies, exoskeletons, a body cavity, a digestive system with two openings and a nervous system

– Most have separate sexes and reproduce sexually

Origin of Arthropods• Some fossils are more than 500 million

years old• Scientist hypothesized that arthropods

probably evolved from an ancestor of segmented worms because they have body segments

• The hard exoskeleton and walking legs allowed arthropods to be among the first animals to live successfully on land

Value of Arthropods• A source of food• Agriculture would be impossible

without bees and other insects to pollinate crops

• Useful chemicals are obtain from some arthropods

• Important part of ecological community

Arthropods• Body Segments

– Bodies of these animals are divided into segments similar to segmented worms

– Some have many segments, others have segments that are fused together to form body regions

• Exoskeleton– A hard outer covering that supports and

protects the internal body and provides places for muscle to attach.

– Doesn’t grow as the animals does, it is shed and replaced during a process called molting

Crustaceans• Have one or two pair of antennae

and mandibles, which are used for crushing food.

• Most live in water, but some live in moist environments on land—such as pill bug.

• Have five pair of legs, first pair of legs are claws for catching and holding food.

Crustaceans• Swimmerets are appendages on

the abdomen which help in movement and are used in reproduction; also force water over the gills used in O2 and CO2 exchange

• If a crustacean loses an appendage it can regenerate it

Arachnids• Scorpions

– Have sharp, poison filled stinger at the end of abdomen.

– Have a well-developed appendages which they can grab their prey.

• Spiders– Can’t chew their food, release enzymes into

prey to digest it—then suck the predigest liquid into its mouth.

– Have book lungs where O2 and CO2 are exchanged.

Arachnids• Mites & Ticks

– Most are parasites– Ticks have specialized mouthparts to

remove blood from the host.– Ticks often carry disease such as

Lyme disease.

Centipedes & Millipedes• Have long bodies and many segments,

exoskeleton, jointed legs, antennae and simple eyes.

• Found in damp environments• Reproduce sexually• Make nests for eggs and stay with them

until they hatch.• Centipedes are predators• Millipedes feed on decaying plant

matter.

Insects• Have three body regions• Head

– Has a pair of antennae, eyes and a mouth

• Thorax– Three pairs of legs and one or two

pairs of wings if present are attached here

• Abdomen– Where reproductive structures are

found

Insects• Have an open circulatory system that

carries digestive food to cells and removes wastes

• Insect blood doesn’t carry O2 instead air enters and exits through openings called spiracles found on the abdomen and thorax

• Are the only invertebrate animals that can fly

Insects & Food• Feed on a number of things have

different mouth parts to obtain food• Grasshoppers and ants have large

mandibles for chewing• Butterflies and honey bees have

siphons for lapping up nectar• Aphids and mosquitoes have mouth

parts that are adapted for piercing into plants or other organisms

Metamorphosis• A series of changes that an insect goes

through• Two types

– Complete• Includes stages of egg, larva, pupa, and adult• Ex. Butterflies, bees, flies

– Incomplete• Includes stages of egg, nymph, adult• The nymph form molts several times before

becoming an adult• Ex. Grasshoppers, crickets

Insects success• Insects are extremely successful

based these reasons– Tough flexible, waterproof

exoskeleton– Ability to fly– Rapid reproduction cycles– Small sizes

• Insects have other adaptations that allow them to be successful

Controlling Insects• Not all arthropods are of value

some are pests that carry disease or can damage crops

Controlling Insects• Common ways to control insects

– Insecticides, but these also kill non-harmful insects

– Biological controls• Types of bacteria, fungi, and viruses can

be used to control insects• Natural predators being released to kill

the harmful insect• Some how interfere with reproduction of

the particular insect

Echinoderms• Characteristics

– Have an endoskeleton covered by a thin, bumpy or spiny epidermis

– Radial symmetrical—allowing them to sense food, predators and other things in the environment from all directions

– Have mouth, stomach, intestines– Feed on a variety of plants and animals– Have no head or brain, but have a nerve

ring that surrounds the mouth– Also have cells that respond to light and

touch

Water-Vascular System• A characteristic unique to echinoderms• Allows them to move, exchange CO2

and O2, capture food, and release wastes

• It is a network of water-filled canals with thousands of tube feet connected to it.

• Tube feet—hollow, thin walled tubes that ends in a suction cup.– As pressure in the tube feet changes the

animal is able to move along by pushing out and pulling in its tube feet

Characteristics of Echinoderms• Echinoderms, such as this sea star, have a water

vascular system that helps them move and catch food.

Types of Echinoderms• Sea Stars

– Echinoderms with at least 5 arms arranged around a central point

– Uses tube feet to open shells of prey, once open pushes its stomach into shell and uses an enzyme to digest it

– Reproduce sexually– Can repair themselves by

regeneration

Types of Echinoderms• Brittle Stars

– Have fragile, slender, branched arms that break off easily

– This adaptation allows them to survive

– They can regenerate broken off body parts

– Use flexible arms for movement and tube feet to get food into their mouths

Types of Echinoderms• Sea Urchins & Sand Dollars

– Disk or globe-shaped animals covered in spines

– Spines help in movement and in burrowing

– Also can protect them from predators – Sea Urchins have five tooth like

structures around their mouth

Types of Echinoderms• Sea Cucumber

– Soft bodied echinoderms– Have a leathery covering– Have tentacles around their mouth

and rows of tube feet on their upper and lower surfaces

– When threatened, they may expel their internal organs which will then be regenerated in a few weeks

Value of Echinoderms• Feed on dead organisms in the

marine environment• Help recycle material• Used for food• Possible sources of medicine• Sea stars can help control the

population of other organisms

Origin of Echinoderms• Date back more than 400 million years

ago• Earliest echinoderms had bilateral

symmetry as adults• Scientists hypothesize that echinoderms

more closely resemble animals with backbones than any other group of invertebrates– Have similar embryos that develop similar

to vertebrates– Complex body systems