Invertebrate Diversity and CharacteristicsSelected topics chosen from Chapters 23-24

Kingdom AnimaliaAnimals are the most physically diverse kingdom of organisms.

• Animals range in size from 25-meter-long blue whales to microscopic rotifers. • Animals are found nearly everywhere on Earth.

Each animal phylum has a unique body plan.

• Vertebrates have an internal segmented backbone.• An endoskeleton allows vertebrates to grow to large sizes.• internal• made of bone or cartilage

• Invertebrates do not have a backbone.• Invertebrates encompass most animal groups.

• Differences in body plans result from differences in the expression of Hox genes.

– Hox genes tell embryonic cells which body part to become.– Mutations in Hox genes led to the vast diversity of animal species.

head tail

headtail

fruit fly genes

human HOX-B genes

Animals are grouped using a variety of criteria.

• 3 criteria are used to categorize animals:

1. body plan symmetry2. tissue layers 3. developmental patterns

gastrovascular cavity

mouthmesoglea

oral arms

tentacles

blood vessels

brain

hearts

muscle

segmentnerve cord

mouth

digestive track

• There are 3 types of body plan symmetry.

1. bilateral symmetry: body divides equally along one planeAnimals with bilateral symmetry can be divided equally along only one plane, which splits an animal into mirror-image sides.

Animals with radial symmetry have body parts arranged in a circle around a central axis.

2. radial symmetry: body arranged in circle around a central axis (usually the mouth) 3. asymmetry: body has no general

plan or central axis. It is irregular in shape.

• Bilateral animals have three distinct layers of tissue; radial animals have only two.

– both animal types have ectoderm (outer layer) and endoderm (inner layer)

– bilateral animals have mesoderm (middle layer)

• Animals are divided into two major groups, the protostomes and the deuterostomes.– Protostomes form mouth-first, and

anus second.– Deuterostomes first form the anus

and then the mouth.

A comparison of structure and genetics reveals the evolutionary history of animals.• Protostomes and deuterostomes are the two major radiations on the animal

phylogenetic tree.

Porifera Cnidaria Platyhelminthes AnnelidaMollusca

Nematoda

ArthropodaEchinodermata

Chordata

RADIALRADIAL

NO TISSUESNO TISSUES

PROTOSTOMES

DUETEROSTOMES

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Sponges have specialized cells but no tissues.

• Sponges are the most primitive animals on Earth. • 570 million-year-old fossils• closely related to group of protists – sessile – reproduce both sexually and asexually – filter feeders

Cnidarians are the oldest existing animals that have specialized tissues.

• Cnidarians have two body forms. 1. polyps

In the polyp formof a coral, the tentaclesand mouth face upward.

2. medusas

In the medusa form of a jellyfish, the tentacles andmouth face downward.

Flatworms are simple bilateral animals. • Flatworms have a solid body and incomplete or absent gut. • There are three classes of flatworms.

Flukes: Parasites that feed on the body fluids of other animals. Larva penetrate through human skin into blood vessels to settle in human intestine. Treatable.

Tapeworms: parasites that live in vertebrate guts. Absorb nutrients from digested food by latching sucker like mouth to intestinal wall. Treatable.

Planarians: free-living, nonparasitic flatworm. Lives in ocean.

Mollusks are diverse animals. • Mollusks have a complete digestive tract

and a mantle.• A complete digestive tract has two

openings: a mouth and an anus.• Mantle is a hard shell to protect animal.

Annelids have segmented bodies.

• Segmentation refers to the repeated sections of an annelid’s body.• The coelom is a fluid-filled space completely surrounded by muscle. • There are three groups of annelids: Earthworms, marine worms, leeches

blood vessels

musclehearts

brain

mouth

digestive tract

nerve cordsegment

Roundworms shed their stiff outer skeleton as they grow.

• Roundworms are protostomes with bilateral symmetry.• Roundworms have a tough outer

skeleton called a cuticle made of chitin• Many roundworms are parasites. • Nearly every plant and animal

species are parasitized by roundworms. • hookworms• pinworms• Guinea worms

Hookworms: feed on host’s blood. Contract it by walking barefoot over contaminated soil.

The most common symptom of pinworms is an itchy rectal area. Symptoms are worse at night when the female worms are most active and crawl out of the anus to deposit their eggs. Adults live in gut of host.

Guinea worms: found in connective tissue of host. Occurs when host drinks contaminated water. Wrap worm around stick and turn it once a day. If worm breaks, it will be difficult to extract from body again.

Echinoderms have radial symmetry.

• Echinoderms have a water vascular system• a series of water-filled ring canals around central disk• canals store water used for circulation and movement • changes in water pressure extend and retract tube feet

• Echinoderms have a complete digestive system.• Some echinoderms can regenerate limbs or other body parts.• Echinoderm means “spiny skin”

tube feettube feet

Arthropods are the most diverse of all animals because they have features that are highly adapted. • Arthropods are invertebrates that share several features.

• exoskeleton (cuticle) made of chitin that will molt• jointed appendages• segmented body parts• Compound eye• External sensory organs (antennae and body hairs

– Trilobites—extinct, bottom feeders; oldest fossils date back 540 million years.

Crustaceans—live in oceans, freshwater streams, and on land

Chelicerates—specialized daggerlike mouthparts

Insects—most live on land, have six legs

Myriapods—long bodies and many pairs of legs

Arthropod exoskeletons serve a variety of functions. • Joints are made of stiff and flexible cuticle to allow

movement.• The exoskeleton is made of many layers of chitin.• hard material that protects the body• must be shed in order to grow

• Arthropods have an open circulatory system.

• Sensory organs such as antennae are made of modified cuticle.

• Most arthropods have compound eyes.

Crustaceans evolved as marine arthropods.

• two distinct body sections: cephalothorax and abdomen• one pair of appendages per segment• two pairs of antennae• exoskeleton• Carapace

• Crustaceans share several common features.

Crustacean appendages can take many forms.

•Crustacean appendages are used for a variety of functions.• collecting and manipulating food• attracting females• protection

• Appendages include claws, antennae, walking legs, swimmerets, and mandibles.

•Decapods such as lobsters and crabs have ten legs

– Barnacles are sessile filter feeders wrapped in a hard shell.

Arachnids include spiders and their relatives.

•Arachnids are a group of chelicerates that live on land.• eight legs• fanglike pincers

that inject venom• silk glands

horseshoe crabs

• Arachnids also include mites, ticks, chiggers, and scorpions.

All spiders make silk and produce venom.

Insects are the dominant terrestrial arthropods that show an amazing range of adaptations.

• Insects are in nearly every ecological niche.• Insects have a body with three parts.

• head• thorax• abdomen

abdomen

thorax head

• Some insects live independently, others live in social colonies.

Insects undergo metamorphosis. • In incomplete metamorphosis, insects look like miniature adults when they

hatch.• There are three life stages of incomplete metamorphosis.

• larva• nymph• adult nymph stage

larvae

adult

Larva

EggPupa

Adult

• In complete metamorphosis, the insect changes form entirely.

• There are three life stages of incomplete metamorphosis.– egg– larva– pupa – adult

Arthropods and humans interact in many ways by sharing many of the same resources.

• Many arthropods are herbivores that eat plants that humans depend on.• Arthropods cause millions of dollars of crop

damage.• Insecticides have unwanted side effects.

– arthropod-specific insecticides– integrated pest management (IPM) reduces pests by managing their ecology. Ex.

Use insect traps, physical barriers, or introduce natural predators.– genetically modified crops

• Scientists have developed safer insecticide alternatives.

Some arthropods can spread human diseases.

• Vectors are organisms that carry disease from one host to another.• Diseases spread by arthropods have serious effects on human populations.

– Bubonic plague is caused by a bacterium carried by fleas.– Yellow fever is caused by a virus carried by mosquitoes.– Malaria is caused by a protozoan parasite carried by mosquitoes.– West Nile virus is caused by a virus carried by mosquitoes.