1. Phylum Arthropoda

2. Arthropod Classifications
Four main lines, which most zoologists recognize as 4 distinct subphyla (some list these as Classes)
1. Trilobita - extinct trilobites
2. Chelicerata - horseshoe crabs, spiders, ticks, mites, and some extinct groups
3. Crustacea - crabs, lobsters, shrimps, barnacles
4. Uniramia - insects, centipedes, millipedes

3. The Arthropod Exoskeleton
Epidermis secretes an external skeleton called the exoskeleton
Advantages of possessing an exoskeleton:
strong support
muscles can attach to and pull against it
protection…against predators, and infection
prevents internal tissues from drying out, esp. on land
Dis-Advantages :
does not grow as the animal does – must “molt”

4. Gills
Many aquatic arthropods (crabs and lobsters) - folds of tissue with a large surface area

5. Reproduction
Sexes are separate; fertilization is external in aquatic forms, internal among the terrestrial forms

6. Arthropod Diversity

7. Abdomen is also highly variable, but it is primitively large
SubPhylum Crustacea
Abdomen is also highly variable, but it is primitively large
Groups with a well-developed abdomen usually possess six pairs of appendages: Five pairs of structures called swimmerets
Open circulatory system (no blood vessels)

8. Crustacean Diversity Ostracod Water flea Copepod Fairy shrimp
Fish louse

9. Barnacles are Crustaceans!