Phylum Arthropoda Arthropod Classifications Four main lines which

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

Sub. Phylum 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 Copepod Fairy shrimp Water flea Fish louse

Barnacles are Crustaceans!