Chapter 28Arthropods and Echinoderms

Arthropods

“organism with a tough exoskeleton, jointed appendages and a segmented body”

Learning Targets 28.1

•Identify the defining features of arthropods.

•Describe the important trends in arthropod evolution.

•Explain growth and development of arthropods

Exoskeleton

•Exoskeleton made of chitin (a carbohydrate)

•Can be tough and hard or soft and leathery

•Some have dozens of segments while others have only 3

•Tough exoskeleton requires joints between segments and appendages to move

Feeding

•Display all types

•Mouthparts are modified to fit feeding behavior

Respiration

•Aquatic arthropods use gills

•Horseshoe crabs use book gills

•Spiders use book lungs

•Terrestrial arthropods use tracheal tubes (supplies O2 by diffusion-muscles contract tube)

Book Gills/Lungs

•Several sheets of tissue are layered like pages in a book (increases SA)

Internal Transport

•Open circulatory system

•Blood travels through heart to arteries to smaller vessels to sinuses and back to heart

Excretion

•Terrestrial - excrete N waste through malpighian tubes (remove waste from blood and add to feces)

•Aquatic - N waste removed by diffusion across gill surfaces

•Some have glands near antenna

Response•Well developed nervous system (All

arthropods have a brain)

•Large compound eyes (may have more that 2000 separate lenses!)

•Some smell w/ antennae and use hair on legs to taste

•Well developed hearing (ears in strange places like behind leg)

Movement

•Use well developed muscular system that is controlled by its nervous system which pulls and pushes against exoskeleton

Reproduction

•Terrestrial arthropods have internal fertilization

•Some Aquatic arthropods have external fertilization

Growth and Development•Tough exoskeleton protects but does not

grow and must be shed (suit of armor)

•Molting – arthropod sheds entire exoskeleton and produces larger one

–(most molting involves metamorphosis which uses molting hormone)

•Digests and eats/new skeleton is soft for up to a day

2 Types of Development

•Complete

•Incomplete

Complete Metamorphosis

•4 stages – egg, larva, pupa and adult

•Involves interaction b/t molting hormone and juvenile hormone

Incomplete metamorphosis

•Young look like adults without wings or sex organs

•Gain these through gradual molts

28-2 A tour of Arthropods“Trilobites, Chelicerates, Crustaceans

and Uniramians”

Learning Targets 28.2

•Explain how arthropods are classified

•Identify the distinguishing features of the three subphyla of arthropods.

I. TrilobitesII.Chelicerae

a)Class Merostomataa)Horseshoe Crabs

b)Class Arachnidaa)Spidersb)Mites and Ticksc)Scorpions

III.CrustaceaIV.Uniramians

a)Centipedesb)Millipedesc) Insects

I. Trilobites•Now extinct

•Hundreds of lenses in eye

•Divided into many segments each with a walking leg.

II. Chelicerates•Chelicerates have mouthparts

called chelicerae and two body sections and nearly all have four pairs of legs.

Ex) Horseshoe crabs, spiders, ticks and scorpions

•2 part body

–1) Cephalothorax (contains legs, brain, mouth, eyes)

–2) abdomen (most of internal organs)

•Specialized mouth parts = chelicerates and pedipalps

•No antennae found in other arthropods

Used to grab prey Contain fangs

which are used to stab and paralyze

prey

A. Class MeristomataI. Horseshoe crab (Not so much a crab at all!)•Not dangerous

•Tail for plowing through sand

•Lysate in blood is used to test purity of medicines

B. Class Arachnida

•Spiders, mites, ticks, scorpions, and daddy long legs

•4 pair of walking legs on cephalothorax

•In addition they have chelicerae (sucking and biting) and pedipalps (holding prey)

1. Spiders•All are carnivores

•Capture prey by pouncing or spinning webs with spinnerets (on abdomen)

•Usually feed on insects (chelicerae-paralyzing venom-enzymes digest-suck)

•Produce protein - silk

Interesting facts about spiders webs:

•Whether or not they spin webs they produce silk

•Spider silk is stronger than steel.

•Web spinning spiders can spin webs almost as soon as they hatch!

Sydney funnel web spider

The Brown recluse

“The culprit”

“The effects”

Day 3

Day 4

Day 5

Day 6

Day 9

Day 10

C. Ticks and Mites•Parasitic on plants/animals

•Chelicerae are needlelike to pierce host (some have large teeth to hold onto host)

•Pedipalps have claws for digging and holding

•Other examples of Mites: Causing itching and painful rashes in Humans and animals

–Chiggers

–Mange

–Scabies

•Ticks can transmit bacteria that causes disease

–Rocky Mountain spotted fever

–Lyme Disease

D. Scorpions

•Predator in which pedipalps are modified into claws

•Poisonous tail to sting (enough venom to feel like wasp sting)

Their appendages may contain a claw or swimmerets

III. Crustaceans

•Typically have two pairs of antennae, two or three body sections and chewing mouthparts called mandibles.

•Ex) crabs, shrimp, lobster and crayfish

•Hard exoskeleton (CaCO3)

•2 pair of antennae (feelers)

•Appendages with 2 branches

•(may be legs, claws or mouthparts,gills)

•Mouthparts called mandible (usually for biting/grinding)

•Typically have head, thorax and abdomen

•Some may have cephalothorax

•Crayfish, water flea, crabs, lobsters, shrimp, barnacles

IV. Uniramians

•Largest subphylum of animals

•Single pair of antennae

•Appendages with only a single branch

Learning Target 28.3

•Identify the distinguishing features of insects.

•Describe two types of development in insects.

•Explain what types of insects form societites.

A. Centipedes•Lacks waterproof exoskeleton

•Wormlike body composed of many leg bearing segments

•Typically all Carnivores

•All body segments except 1st and last have a pair of appendages

continued

•Pair of poison claws in head region for killing prey

•15-170 pairs of legs

B. Millipedes

•Eat dead and decaying plant material

•Each body segment contains two pair of appendages

C. Insects

•3 part body (head, thorax, abdomen)

•3 paired appendages on the thorax

•Many have two pair of wings and a pair of antennae

Responses to Stimuli 

Insects use a multitude of sense organs

1. Compound eyes detect changes in color and movement.

2. receptors for taste and smell on their mouthparts, and also on their antennae and legs.

3. Many insects also have well-developed ears. Some located in odd places Ex) behind the legs in grasshoppers

Adaptations for Feeding 

• three pairs of appendages used as mouthparts, including a pair of mandibles.

•These mouthparts can take on a variety of shapes,

Movement and Flight 

• Insects have three pairs of legs, for walking, jumping

•Many insects can fly using two pairs of wings made of chitin

Metamorphosis  

•The growth and development of insects usually involve metamorphosis, which is a process of changing shape and form.

•Insects undergo either incomplete metamorphosis or complete metamorphosis.

Insects and Humans

•Many insects are known for their negative effects. ex) Termites, moths, bees and wasps, locusts,

mosquitoes.

•Insects also contribute enormously

• Agriculture would be very different without pollination.

• One third of the food you eat depends on plants pollinated by animals, including insects.

Insect Communication•Insects communicate using sound, visual, chemical, and other types of signals.

•Pheromones are specific chemical messengers that affect the behavior or development of other individuals of the same species.

Insect Societies

•Ants, bees, termites, and some of their relatives form complex associations called societies.

• A society is a group of closely related animals of the same species that work together for the benefit of the whole group.

•Castes are individuals which are specialized to perform particular tasks, or roles.

Communication in Societies 

• sophisticated system of communication is necessary for the functioning of a society.

•Honeybees communicate with complex movements as well as with pheromones.

•Worker bees convey information about the type, quality, direction, and distance of a food source by “dancing.”

* Two types of dances

1. The round dance indicates that food is fairly close to the hive.

2. The waggle dance indicates that food is farther away.

Moth has feathery antenna and butterflies are knobbed

Echinoderms

Echino means spiny and dermis means skin “spiny skinned animals”

Learning Targets 28-4

•Identify the distinguishing features of echinoderms

•Describe the functions carried out by the water vascular system of echinoderms

•Compare the different classes of echinoderms

What is an Echinoderm?•Spiny skin

•Internal skeleton (endoskeleton made of CaCo3)

•Water vascular system

•Tube feet (cuplike suction)

•Most adult echinoderms exhibit 5-part radial symmetry

•Echinoderms have a two sided body

–Oral Surface (mouth side)

–Aboral Surface

Form and Function in Echinoderms

•A unique feature of echinoderms is their water vascular system.

•A system of internal tubes which are filled with fluid, that carries out many essential body functions in echinoderms, including respiration, circulation, and movement.

•The water vascular system opens to the exterior at the madreporite.

•Echinoderms filter water in and out through the madreporite.

•it connects to a ring canal that forms a circle around the animal’s mouth. From the ring canal, five radial canals extend along body segments, allowing water move throughout the entire body.

•Attached to each radial canal are hundreds of tube feet.

•A tube foot is a structure that operates much like a suction cup.

•Hundreds of tube feet acting together create enormous force, allowing echinoderms to “walk” and even to pull open shelled prey such as clams.

Feeding

•Many different feeding styles

–filter feeders, detritus feeders, herbivores or carnivores

•Some such as star fish can be predators of bivalves (tube feet open shell, stomach comes out of mouth and uses enzymes to digest clam)

Respiration/Circulation/Excretion

•Use water vascular system b/c they have a large surface area exposed to water

•Some have small skin gills

•Solid waste leaves through anus. Everything else is transported by the water vascular system

Response•Do not have highly organized

nervous system (No brain)

•Enough sensory cells to taste and smell

•Most can detect light, gravity and chemicals released by potential prey.

Movement

•Use tube feet

•Use water vascular system like a hydraulic device

Reproduction•Reproduce by external fertilization.

•Separate sexes

–Eggs produced in ovaries and sperm produced in testes.

•Indirect development (larva has bilateral symmetry)

Groups of EchinodermsThere are 7000 species of

echinoderms!•Classes include:

–Sea Urchins

–Sand Dollars

–Brittle stars

–Sea Cucumbers

–Sea Stars

–Sea Lillies

–Feather Stars

Sea Urchins and Sand Dollars

Echinoidea = sand dollars and sea urchin

Brittle Stars

•Ophiuroidea = brittle stars

•Long thin flexible arms

•Move in darkness

•Found on coral reefs

•Can shed an arm when trying to defend themselves!

http://www.aquasafari.com/maps/VillaB3.jpg

Sea Cucumbers

•Holothuriodea = sea cucumbers (most are detritus)

•Found deep in water

•Secrete a sticky substance that glues predator to keep it from moving

Sea Cucumber

Sea Stars (Star Fish)

•Asteroidea = starfish

•most are carnivores feeding on bivalves

•Common to us b/c they live in shallow waters

Sea Lilies and Feather Stars

•Crinoidea = sea lilies and feather stars (filter feeders)

•Many arms

Ecology of Echinoderms

•Sea urchins help control the distribution of algae and other forms of marine life.

•Sea stars are important carnivores that help control the numbers of other organisms such as clams and corals.

•A major threat to coral reefs is the sea star called the crown-of-thorns.