Phylum Arthropoda

“jointed” “foot”

80% of all animals are arthropods…..

76% of those are insects…..www.onacd.ca

Major Classes of Arthropods

Above left: Subphylum Myriapoda, Class Chilipoda: includes the centipedes

Lower Right: Subphylum Hexapoda, Class Insecta: includes all 6 legged insects

Above: Subphylum Myriapoda, Class Diplopoda: includes the millipedes

Above Left: Subphylum Chelicerata Class Arachnida: includes the spiders, mites and scorpions

Lower right: Subphylum Crustacea, Class Malacostraca: includes the lobsters, crab and shrimp

Above: Subphylum Crustacea, Class Maxillopoda: includes the barnacles

Shared characteristics of Arthropods• Coelomate and bilaterally symmetrical• Jointed appendages• Exoskeleton of chitin secreted by the epidermis• 3 body regions (head, thorax, and abdomen)• Respiration by body surface, gills, trachea, or book lungs• Open circulatory system• Sensory organs are well-developed: compound eyes, tympanum

(drum-like ear) antenna (touch, smell, chemical reception)• Complete digestive systems with mouth, specialized organs and

anus• Dioecious: fertilization is usually internal• Developed nervous system with dorsal brain connected by a

ring and double ventral nerve cords• Found in marine, freshwater, terrestrial and aerial environments

Let’s take a closer look at a few different Classes of Arthropods

Class Insecta• Exoskeleton made of chitin• Have a head segmented into

6 with sensory antennae and compound eyes

• Have a thorax with attached segmented legs and possibly wings

• Have an abdomen with 11 segments which houses most of the digestive, respiratory, excretory and reproductive systems

• Insects respire through a system of internal tubes and sacs that lie directly next to the circulatory system,therefore the circulatory system does not need closed vessels

• Most insects hatch from eggs which are fertilized by sexual reproduction (see ladybugs at top right)

• Insects molt as they grow in size (undergo metamorphosis)

Class Maxillopoda : The Barnacles

The Barnacle Life CycleIncludes 2 larval stages

1. NAUPILUS• spend their time floating

around in the current, eating and molting

• last approx. 2 weeks

2. CYPRID• strong swimmer• Settles in a safe, productive

environment• Cements itself headfirst to

surface and undergoes metamorphosis into a barnacle

• As the cyprid metamorphosizes it develops 6 hard armor plates around its body

• The adult barnacle has feathery legs that protrude to capture food and gametes when spawning

• Barnacles are hermaphroditic

Famous Barnacle Fact:

Barnacles have the largest penis to body size ratio of any species in the animal kingdom

Class Malacostraca : The Crustaceans

• Head and thorax are often fused into cephalothorax

• Head includes 6 segments with antennules, antennae and mouthparts with appendages called maxillipeds

• 8 thoracic segments• Cephalothorax is

almost completely covered by a carapace

• 6 abdominal segments often used for swimming

• Eyes are compound stalked or sessile (stalked eyes allow the crustacean to pull them in for protection or see in many different directions)

• 5 pairs of walking legs, some with modified pincers

• 2-chambered stomach

• Centralized nervous system

Spiny King Crab

Hermit Crab

Above: Pacific White Cleaner Shrimp

Left: Decorator Crab: will cover its body in algae etc. in order to camouflage itself with its surroundings

Above: Lobster

Pair of Lobster Prawn

Spiny Lobster Hermit Crab

Ecological Roles of Arthropods

• Pollination• Production of honey,

wax, and silk• Recycle biological

materials to aid in producing topsoil

• Form symbiotic relationships with other organisms (see left)

• Part of food chain

Burrowing shrimp and Goby fish living in Symbiosis

• shrimp cleans and digs a burrow where they both live

•When danger approaches, the goby fish touches the shrimp with its tail to warn it (shrimp is blind) and both hide in the burrow

The Largest living Arthropod!

is the Japanese Spider Crab with a leg span of 4 meters and a weight of 20kg.

This crab has a life expectancy of 100 years.