UNIT 3: Worms + Arthropods

Trait first appeared in Platyhelminthes

Bilateral symmetry

Classes of Platyhelminthes

Cestoda (Tapeworms), Tubellaria (Flatworms)

Importance of bilateral symmetry

Allows for cephalization, which means you have a head and centralized nervous system

Symmetry of sponges and cnidarians

Sponge: None Cnidarians: Radial

Trait first appeared in nematoma

First complete digestive tract + body cavity

Importance of body cavity and digestive tract

Body cavity: Development of more complex systems, Digestive tract = separate mouth and anus

3 benefits of nematodes, one harmful

Tells us about soil, helps plants grow, is a natural pesticide. Destroys some plants

Trait that first appeared in Annelida

First real coelom

Classes of Annelida

Oligochaeta (Earthworm), Hirudenea (Leech)

Coelom + Function

Surrounds and contains digestive tract and other organs, circulates nutrients; hydrostatic skeleton

Cutaneous respiration

Breathe through skin

Leeches and what they release

Segmented parasites, releases anticoagulants and anesthesia

First trait that appeared in Arthropoda

Jointed appendages

All arthropods have these four traits

Segmented body, exoskeleton, compound eyes, antennae

Arachnids

No antennae, cephalo and abdomen, book lungs

Insects

One antennae, head thorax abdomen, tracheal tubes

Crustacean

2 antennae, cephalo and abdomen, gills