Arthropods

Body Symmetry: bilaterally symmetrical

Segmentation: metamerism, appendages

Organization:

Coelom: triploblastic coelomates, though coelom reduced; most of body cavity is hemocoel

Body Plan:

 

Digestion: Tube-within-a-tube plan; complete

 

Excretion: Paired glands analogous to nephridia in annelids

• Some with malpighian tubules:

 

Outer covering/Skeleton:

 

Versatile exoskeleton made up of cuticle

·         Chitin:

 

·         Calcium salts:

 

·         Molting:

 

Movement: complex muscular system

 

Temperature Regulation: exothermic but with physiological and behavioral mechanisms for generating and/or dissipating heat

 

Respiration: body surface via diffusion, gills, tracheae, or book lungs

• Tracheae

 

• Book Lung

 

Circulatory System: open system with dorsal contractile heart, arteries, and hemocoel

 

Nervous System: organization similar to annelids (dorsal brain, double nerve cords); many with well developed sensory organs

·         Complex behavior patterns

 

Reproduction: usually dioecious, internal fertilization

v  Some parthenogenic

v  Metamorphosis:

1.      Complete

 

2.      Incomplete

 

v  Growth with molting:

 

Types of Arthropods

1. Trilobites

·         All extinct but well represented in fossil deposits

·         Hard exoskeleton capable of rolling into ball

·         One pair of antennae

·         Four pairs of appendages

·         Indistinct mouthparts

·         Compound eyes

 

 2. Chelicerates

·         Pair of chelicerae:

·         Most with pair of pedipalps

·         Usually with four pairs of walking legs attached to cephalothorax

·         Most suck liquid food from prey

·         No appendages on head, no wings

o   Horseshoe crabs

§  Body covered by exoskeletal shields

§  Horseshoe-shaped carapace , broad abdomen ending in telson

§  Book gills

o   Sea spiders

§  Marine

§  Ovigers

§  Suck in soft-bodied prey with proboscis

o   Arachnids

§  Primarily terrestrial

§  Incomplete metamorphosis

§  Spiders

·         Cephalothorax and abdomen connected by pedicel

·         Chelicerae modified into fangs used to inject venom into prey

·         Many use silk to capture food and encase eggs

o   spinnerets

·         Numerous (usually 8) simple eyes, often depend on setae for senses

·         Book lungs

·         Pedipalps are often sexually dimorphic.

§  Harvestmen

·         Not spiders

·         Fused cephalothorax

·         Fangs but no venom

·         No silk glands

§  Ticks and Mites

·         Fused cephalothorax

·         Spend at least one part of life cycle as parasites

o   Can be problematic as disease transmitters

·         Characterized by capitulum

·         Ticks usually larger than mites

§  Scorpions

·         Pedipalps modified into large pincers

·         Abdomen with 12 distinct segments

·         Abdomen ends with stinger.

·         Females bear live young, carry them on back.

·         Glow under UV light!

 

3. Crustaceans

·      Hard, crusty exoskeleton made of chitin

·      Most live in marine/aquatic environments

·       Two pairs of antennae

One pair of mandibles

Two pairs of maxillae

Usually one pair of appendages on each body segment

·         Appendages usually biramous (2 main branches)

·       Branchiopods

·         Legs flattened and leaflike—used for respiration

·         Includes fairy and brine shrimp (no carapace), tadpole shrimp (carapace forms large dorsal shield), clam shrimp (carapace is bivalve), and water fleas (carapace covers entire body but not head)

Copepods and krill

o   Small crustaceans

o   Live in water and feed on algae

·         Barnacles

o   Thick, heavy shells, reduced head region

o   Sedentary

·        Isopods

o   Includes terrestrial pillbugs and freshwater/marine forms

o   Roll into a ball for protection, no carapace, compressed laterally

·         Decapods

o   Include lobsters, crabs, crayfish, hermit crabs, and shrimp

o   Thorax bears five pairs of walking appendages: first pair is often modified into pincers

o   Gills

o   Rostrum on anterior portion of cephalothorax

o   Large, sometimes broad carapaces

o   Open circulatory system

o   Some with well developed nervous systems

o   Modified swimmerets for sperm transfer

 

4. Uniramians

·         Appendages are unbranched

·         Mandibles and one to two pair of maxillae are present.

·         Only one pair of antennae

·       Centipedes

·         Many body segments, each with a pair of walking legs

·         Carnivorous: poison claws that inject venom into prey and strong mandibles for chewing

·         Millipedes

·         Each of four thoracic segments bears one pair of legs; abdominal segments have two pairs of legs

·         Harmless herbivores

·         Insects

·         Adapted for life on land

·         3 body regions:

·         Head

 

·         Thorax

 

·         Abdomen

 

·         Light exoskeleton

·         Usually two pairs of wings

·         Complete digestive and excretory systems

·         Crop, gizzard, stomach, gastric ceca

 

·         Malpighian tubules

 

·         Respiratory system

·         Spiracles

 

·         Tracheae

 

·         Circulatory system

·         Heart and hemolymph

 

·         Reproduction

·         Male with penis to transfer sperm for internal fertilization

·         Female deposits fertilized eggs into ground with ovipositor

 

·         Complete/incomplete metamorphosis

·         Diapause:

 

·         Behavior and Communication

 

o   Beneficial Insects

 

 

o   Harmful Insects