Phylum Arthropoda

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

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”

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

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

Arthropod Diversity

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)

Crustacean Diversity Ostracod Water flea Copepod Fairy shrimp Fish louse

Barnacles are Crustaceans!