Arthropods

Chapter 28

Animal Classification

Animals

Invertebrates

Vertebrates

SpongesCnidariansWormsMollusksArthropodsEchinoderms

Ectotherms(cold-blooded)

Endotherms(warm-blooded)

FishesAmphibiansReptiles

BirdsMammals

Arthropods -Class Arachnida-Class Crustacea-Class Insecta

28-1: Characteristics of Arthropods

Characteristics

Arthropod comes from the Greek words “arthron” – joint “pod” – foot

A typical arthropod is: Segmented A coelomate Has bilateral symmetry Has an exoskeleton

Characteristics

Appendages – any structure (a leg or an antenna) that grows out of the body of an animal

Characteristics

Arthropods are the earliest known invertebrates to exhibit jointed appendages

Joints are advantageous because they allow more flexibility and powerful movements

Arthropod Exoskeletons Provide Protection Exoskeleton is made of protein and

chitin (KI tun) Chitin is also found in cell walls of fungi The exoskeleton protects and supports

internal tissues and provides places for attachment of muscles

Arthropod Exoskeletons Provide Protection The weight of the exoskeleton limits the size

of arthropods The larger an arthropod is, the thicker and heavier

its exoskeleton must be to support its larger muscles

Why Arthropods Must Molt

Exoskeletons cannot grow, so they must be shed periodically

Molting – shedding the old exoskeleton

Before an arthropod molts, a new, soft exoskeleton formed beneath the old one

Cicada

Segmentation in Arthropods

Arthropods do not have as many segments as segmented worms

In most groups, arthropods are consisted of three segments Head Thorax Abdomen

Segmentation in Arthropods

Some arthropods have two sections Cephalothorax – A fused head and thorax Abdomen

Arthropods Have Efficient Gas Exchange Three types of respiratory structures have

evolved in arthropods: 1. Gills – Aquatic arthropods exchange oxygen

and carbon dioxide through gills

Arthropods Have Efficient Gas Exchange Land arthropods have either:

2. Tracheal tubes – branching networks of hollow air passages that carry air throughout the body

Arthropods Have Efficient Gas Exchange

3. Book lungs – air-filled chambers that contain leaf-like plates

Arthropods Have Acute Senses Movement, sound, and chemicals can be

detected with great sensitivity by antennae Antennae are also used for sound and odor

communication; can detect pheromones

Atlas moth

Arthropods Have Acute Senses Pheromones – chemical odor signals given

off by animals Some pheromones are used as scent trails

(example: the group-feeding behavior of ants) Many pheromones are important in the

mating behavior of arthropods

Arthropods Have Acute Senses Most arthropods have one pair of large

compound eyes and three to eight simple eyes A simple eye is a visual structure with only one

lens that is used for detecting light

Arthropods Have Acute Senses

A compound eye is a visual structure with many lenses

Compound eyes can detect the movements of prey, mates, or predators, and can also detect colors

Arthropods Have Acute Senses Arthropods have hairlike structures used to

detect movement Ex. Fly and flyswatter

Arthropod Nervous Systems are Well Developed The nervous system consists of a double

ventral nerve cord, an anterior brain, and several ganglia Ganglia act as control centers for the body

sections in which they are located

Arthropods Have Other Complex Body Systems Arthropods have an open circulatory system

and a complete digestive system Mouth, stomach, intestine, and anus

Arthropods Have Other Complex Body Systems Mandibles – the mouthparts of most

arthropod groups include one pair of jaws The mandibles are adapted for holding,

chewing, sucking, or biting

Arthropods Have Other Complex Body Systems Malpighian tubules –

used to excrete wastes into the intestine

Arthropods Reproduce Sexually Some species (bees,

ants, and wasps) exhibit parthenogenesis – a form of asexual reproduction in which a new individual develops from an unfertilized egg

In bees, drones are developed from unfertilized eggs

28-2: Diversity of Arthropods

About 85% of all known animals are arthropods

Diversity of All Animals

Additional informationhttp://evolution.berkeley.edu/evolibrary/article/_0_0/arthropods_intro_05

Arachnids

Spiders, scorpions, mites, and ticks belong to the class Arachnida

Spiders are the largest group of arachnids An arachnid has a cephalothorax and an

abdomen with six pairs of jointed appendages

Arachnids

Chelicerae [kuh-lis-er-uh] – the first pair of appendages located near the mouth (modified pinchers or fangs) Pincers are used to hold food, and fangs inject

prey with poison

Arachnids

Pedipalps – the second pair of appendages that are adapted for handling food and for sensing

In male spiders, pedipalps are used to carry sperm during reproduction

The four remaining appendages are adapted as legs

Arachnids

As silk is secreted, it is spun into thread by structures called spinnerets, located at the rear of the spider

Crustaceans

Crustaceans are the only arthropods that have two pairs of antennae for sensing

Some crustaceans have three body sections, and other have only two

Crustacean mandibles open and close from side to side

The blue crab has 3 body sections

Crustaceans

Class Crustacea include crabs, lobsters, shrimps, crayfishes, pill bugs, and barnacles

Most crustaceans are aquatic and exchange gases over gills

Centipedes and Millipedes

Centipedes and millipedes have tracheal tubes for gas exchange

Centipedes are carnivorous and eat soil arthropods, snails, slugs, and worms

These arthropods can bite

Centipedes and Millipedes

A millipede eats mostly plants and dead material on damp forest floors

Millipedes do not bite, but they can spray foul-smelling fluids from stink glands

Insects

Class Insecta is the largest group of arthropods

Insects have three body segments and six legs

Insect Reproduction

Insects usually mate once during a lifetime Some insects exhibit parthenogenesis Most insects lay a large number of eggs,

which increase the chances that some offspring will survive long enough to reproduce

Metamorphosis

Metamorphosis – the series of changes, controlled by chemical-substances in the animal

Two types of metamorphosis: 1. Complete metamorphosis consists of four stages:

Egg Larva – the free-living, wormlike stage of an insect Pupa – a period of reorganization in which the tissues and

organs of the larva are broken down and replaced by adult tissues

Adult

Metamorphosis

Examples: ants, beetles, flies, and wasps Complete metamorphosis is an advantage for

arthropods because larvae do not compete with adults for the same food

Metamorphosis

2. Incomplete metamorphosis – insects go through only three stages of development Egg Nymph – hatches from an egg, has the same general

appearances the adult but is smaller Adult

With each molt, it begins to resemble the adult more

Grasshoppers and cockroaches undergo incomplete metamorphosis

Picture of incomplete metamorphosis