• 1,000,000 + species
• “jointed appendages”
• Eumatazoan, triploblastic coelomates
• Bilaterally symmetrical protostomes
Major features of Arthropods:
1.
Evolved segmentation
2.
Exoskeleton
3.
Jointed appendages
4.
Open circulatory system
• The most biologically successful of all animals
• Well developed senses
• Prolific reproductively

• Over half of all known species belong to the arthropod phulym
• Diverse organisms
• Specialized structures (wings)
• Well adapted senses (compound eyes & antennae)
• Live in a great variety of environments (exoskeleton – not bound to water)
• aquatic & terrestrial
• High reproductive potential (quickly reproduce)
• Many lay 1,000’s of eggs during life
• Immeasurably vast ecological impact
• Food sources
• Detrivores – eat dead, decaying organisms (nature’s recyclers)
• Pollinators
• Help plant populations
• Pests
• Fleas, ticks, mosquitoes
• Agricultural pests
• “Home invaders”

• Exoskeleton – a hardened cuticle of protein and chitin
• For protection, body structure, and muscle attachment
• Prevents water loss
• Thick and hard in some areas
• Paper thin and flexible in others (jointed areas)
• Ecdysis – molting process
• Allows arthropods to grow
• Molting is energetically expensive and leaves arthropods vulnerable
• Evolved segmentation
• Fusion of segments and specialization via function of body
• Tagmata – head, thorax (chest), abdomen
• Efficient body plan (division of labor)

• Modified, specialized, and adapted for:
• Locomotion (walking legs, “tails”, wings)
• Feeding (mouthparts, pincers)
• Sensory reception (antennae)
• Defense (pincers, stingers)
• Copulation (egg and sperm deposit)

• Digestion system is complete (annelid like)
• Respiratory
• Internalized lungs or gills for diffusion of gas, despite having an exoskeleton
• Most insects have a tracheal system that is branched leading to pores along the exoskeleton (believed that this system limits the size of bugs)
• Open circulatory system
• Hemolymph is the fluid pumped by the heart through short arteries and spills into sinus spaces, called hemocoels, surrounding tissues and organs (not part of the body cavity)
• Reproductive
• Extremely prolific
• Males seek females
• Mostly egg layers

• Sensory system is highly developed and Complex
• Compound eyes (most insects)
• 1,000’s of lenses – vision looks like a tile mosaic
• Excellent at detecting motion
• Antennae (touch/vibrations and smell sensors)
• Pheromones - Chemical messages or “smells”
• Used by insects of a species to communicate with members of the same species.
• Reproduction (mate attraction)
• Trail markers (ants)
• Alarm signals (ants, bees)
• Queen – messages to colony

• Subphylum Chelicerata
• Class Merostomata (horseshoe crabs)
• Class Arachnida (spiders, scorpions, ticks, mites)
• Subphylum Crustacea
• Class Malacostraca (lobsters, crabs, shrimp)
• Class Maxillopoda (barnacles & copepods))
• Subphylum Hexapoda
• Class Insecta (beetles, butterflies, ants, etc.)
• Subphylum Myriapoda
• Class Chilopoda (centipedes)
• Class Diplopoda (millipedes)

• Examples: Crayfish, lobster, crab, aquatic isopods, rolly pollies

• Three body sections- head, chest, and abdomenusually the head and chest are fused into the
“cephalothorax.”
• Most are aquatic
• Use gills for respiration

• Examples: ants, bees, house flies

• Adult insects have 3 body parts: head, thorax, and
abdomen.
• Adult insects have 6 legs
• Adult insects have compound eyes
• Most adult insects have antennae, 2 pairs of wings, and can fly.
• Most insects have 4 stages in their life cycle: egg, larva, pupa, adult
• Have spiracles and trachea for breathing

• Examples: horseshoe crabs, spiders,

• Body consists of two main parts: a fused head and thorax
(cephalothorax) and an abdomen.
• Most live on land and breathe by means of book lungs (so called because their thin membranes are arranged like the pages of a book)
• Six pairs of appendages on the body
• the first pair are clawlike fangs near the mouth used for grasping and cutting
• the second pair serve as general-purpose mouth parts that may be modified for special functions
• the last four pairs of appendages are the walking legs

• Example: Centipedes
• Characteristics:
• 1 pair of legs per body segment
• 1 pair of poison claws/fangs underneath the head
• Antennae present
• Simple eyes
• Flatter body

• Characteristics
• Simple eyes if present, although many have no eyes
• 1 pair of antennae
• Chewing mouthparts
• Although it looks like millipedes have 2 pair of legs on each segment, closer examination shows that each body segment is actually 2 segments fused together.
• Millipedes are timid invertebrates and unlike centipedes, do not have poisonous claws so to protect themselves and to discourage predators they roll into a tight spiral and often discharge a foul smelling, distasteful
• More circular shaped body

Digestive system
Mouth-pharynx-esophagus-crop-gizzard-intestine-
Crop- stores food
Gizzard- grinds food
Digestive Gland (Gastric caeca)- makes digestive enzymes

• Open circulatory system
• Heart- on dorsal side of body
• Dorsal blood vessel leading towards and away from heart
• Blood flows out of heart towards the head, down to the ventral side of the body towards the tail and back to the heart

• Some insects have 2 tympanic membranes- These vibrate when sound waves hit it

• Honeybees
• Can see color
• four of the visual cells in each lens respond best to yellow-green light
• two respond maximally to blue light
• the remaining two respond best to ultraviolet light

• Monarch butterflies, which can migrate over 2000 miles, navigate by ultraviolet light in the sky.