Arthropods and Their Relatives

• Characteristics

– Exoskeleton (external covering made of CHITIN)– Molts or sheds exoskeleton to grow

– Jointed appendages - Groups very often named in relation to number or type of feet.

– Tend to undergo metamorphosis or pass through a number of distinct growth stages during their lives

– Tendency toward High degree of cephalization, especially in Class Insecta

Arthropods• Relative abundance.

– 3/4 of all known species of animals are arthropods.

– More known species of arthropods than known species of plants and animals combined. Great diversity in form and habitat.

Major Groups of Arthropods

• Subphylum Trilobita - all forms extinct (believed) perhaps some of earliest arthropods

• Subphylum Chelicerata - First pair of appendages form chelicera or pincher-like structures used for feeding. 4 pair of walking legs, no antennae. The Arachnida is the only important parasitic group.

Major Groups of Arthropods

• Subphylum Crustacea - mostly aquatic, most have gills, two pair of antennae. Biramous appendages, meaning limbs have more than one branch. Also have mandibles. Some are parasitic but we will not cover them.

• Subphylum Uriramia – single branch or uriramous appendages, mandibles, one pair of antennae

Major Groups of Arthropods

• Diplopoda - Millipedes - two pair of legs per body segment

• Chilopoda - Centipedes - one pair of legs per body segment

• Insecta - 3 pair of legs on adults, many with wings, most important group

Metamorphosis• Simple or gradual

– three changes• egg• nymph

– 3-5 instars

• adult

– adults and nymphs • eat same food

Metamorphosis• Complex or complete

– four changes• egg• larva• pupa• adult

– larvae and adults• eat different food

– larvae are destructive

Fundamental External structure

• Insects– 3 body regions

• head• thorax• abdomen

– 3 pair legs attached to thorax– 1 pair antennae– wings usually present in adult state.

Fore WingHind WingAntennae

Jumping Leg

Cerci

OvipositorSpiracles Walking Legs

Palps

Mouth

Simple Eye

Compound Eye

Abdomen HeadThorax

Circulatory System• Closed circulatory system• Well developed heart pumps blood• Heart is long and narrow• Arteries branch into blood vessels

and return blood to the heart via veins – cool, just like us!

Excretion• Recall the Nephridia in Annelids

• The Malphigian Tubules in Arthropods collect nitrogenous wastes in the tubules from blood

• Wastes are concentrated (like a kidney does.) Why concentrated?

• Excreted out anus

Book Gills – folded Gills increase SA for Respiration

Horseshoe Crab

Respiratory System

• Gills or lungs, as you’ll see on the next slide

• Organism is too large to rely on surface area. That is, the internal volume is too great to be supplied with oxygen from a minimal SA.

Book Lungs are Characteristic of Arachnids

Sensory Adaptations

• Well developed nervous system

• Compound eyes with many lenses give Mosaic Vision or multi-images

Ultravision – Seeing in the UV Spectrum

The Compound Eye

Each crystalline eye generates an image. All

images together generate a mosaic effect

Simple Eye (Ocelli)• Do not form the picture• Just gather light• Tell whether it’s light or dark

Exoskeleton of Chitin and

Muscles attach on

Inside

How do You Grow Larger if you Skeleton is on the

Outside?

Molt, or shed the

outer covering

External structure of Subphylum Chelicerata, Class Arachnae

• Chelicerates have specialized mouthparts called chelicerae – think of the hooked grabbers!

• Arachnids (spiders and mites)– 2 body regions

• Cephalothorax• abdomen

– usually 4 pair legs – no wings– no antennae

Chelicera = Fangs, for example, on a Spider

Chelicerates Include the Horseshoe Crab

Body of ArachnidsThe Spider Body

A spider's body is divided into two parts:

Cephalothorax - Fused head & thorax. The legs are locatedon the cephalothorax

Abdomen - Similar to that of insects..

                                                                                       

Other Members of Phylum Arachnida (4 Pairs of Walking

Legs)

1. Spiders2. Ticks and Mites3. Scorpions

Nature Says Don’t Bug Me with the Colour Red!

How Nature Says Do Not Touch