Phylum Arthropoda

General Arthropod Characteristics

• Coelomate, Triploblastic
• Protostome (Ecdysoan)
• Cephalization
• Open circulatory system
• Tagmatization
• Exoskeleton made of Chitin
• Jointed appendages
• Molting (ecdysis)
• Live in almost all habitats on the earth
• Estimates of 30-100 million species! (mostly insects)

+ Arthropod Relatives are Phylum Onychophora (velvet worms), Phylum Lobopodia (The walking cactus) and Phylum Tardigrada (water bears)

Classification
Subphylum Trilobitomorpha (extinct)
Subphylum Chelicerata- arachnids, horseshoe crabs
Subphylum Mandibulata
+ Class Crustacea
+ Class Insecta (in Superclass Hexapoda)
+ Class Myriapoda – millipedes, centipedes

Three major functions of the Exoskeleton:
• Protection from predators
• Prevention of desiccation
• Locomotion (attachment sites for muscles)

Sclerotization: Hardening of the procuticle after molting (also called tanning)

Sclerites: Different segments or body parts covered by exoskeletal plates

Joints are places that are thin and flexible

Diversity of Appendages– legs, wings, antennae, mouthparts, etc

+ Ecdysis is controlled by the hormone ecdysone

+ Nerves and Muscles: Arthropods have striated muscle

Subphylum Chelicerata

+ Class Arachnida (Scorpion)

Arachnids: human skin mites (forehead, eyelashes)

Subphylum Mandibulata
+Class Crustacea

Includes lobster, banded coral shrimp, and barnacles

+ There are also copepod crustacean

+ Copepodos are extraordinarily abundant members of the zooplankton: key components of marine and aquatic food chains

Subphylum Mandibulata
Class Insecta (Superclass Hexapoda)

Includes;  beetle (Order Coleoptera), grasshopper, dragonfly, feather louse etc

Some Insect features
• Most diverse animal group
• Most abundant (especially ants and termites)
• In tropical rainforests, insects can constitute 40% of
the total animal biomass.
• reproduce rapidly, short life cycles
• metamorphosis- can exploit different resources at
different stages
– hemimetabolous (nymphs, adults)
– holometabolous (larvae, pupae, adults)

More Insect features
• Important as pollinators
• Co-evolution with flowering plants
• Transmitters of major world diseases
• Major agricultural pests
• Eusociality in some groups
• Important in food chains
• Can fly!

Subphylum Mandibulata
+Class Myriapoda

Order Diplopoda (millipedes)

Order Chilopoda (Centipedes)