Objective: Phylum Platyhelminthes, Nematoda.

Body PlanBilateral Symmetry

- Mirror image (left side mirrors right side)

Body Plan

3 Tissue Layers:

Ectoderm: body covering

Mesoderm: internal tissue (muscle)Endoderm: - Gastrovascular cavity or digestive tract

Body Cavities- Coelom- body cavity that holds organs• Acoelomate: animal that lacks a fluid filled

body cavity

Digestion

- Gastrovascular cavity: food enters and exits through this muscular sac

Major CharacteristicsMovement: - Ventral cilia- Muscles

Eyespots: detect lightNervous system: anterior clusters of nerve

cells, side flaps for sense of smell

Class Turbellaria

Example: Planarians (marine, freshwater), free-living

Class Trematoda

Example- Blood fluke, parasites

http://www.youtube.com/watch?v=uWvHvl25oXI

Class Cestoidea

Description- Parasitic

• No digestive or circulatory system• Absorb nutrients

Ex: Tapeworm!

http://animal.discovery.com/videos/monsters-inside-me-meter-long-tapeworm.html

Phylum Nematoda (Roundworms)

• Have bilateral symmetry and 3 tissue layers like flatworms

• Different from flatworms because they have:

• Complete Digestive Tract: - Opposite mouth and anus

- Digestive tube

Body Plan

Pseudocoelm:- fluid filled body cavity in direct contact with the digestive tract, worm thrashes to distribute nutrients

Diversity

• Most are free-living and decomposers

• Some are Parasites• Ex: Heartworm

http://animal.discovery.com/videos/monsters-inside-me-flesh-eating-hookworm.html

http://animal.discovery.com/videos/monsters-inside-me-lymphatic-filariasis.html

Phylum Annelida (Annelids) aka Segmented Worms

Body Plan

- Divided into sections by internal walls-

- Digestive tract, nerve cord, and main blood vessels not segmented

• Have bilateral symmetry and 3 tissue layers

Closed Circulatory System:

• Blood remains in vessels

- nutrients, oxygen, and wastes diffuse

Coelm

• True, fluid filled body cavity in contact with internal tissues

Anatomy• Pharynx: beginning of

digestive tract• Crop: stores food

temporarily• Gizzard: soil mixture is

ground up• Clitellum: flat area near

anterior end• Responsible for secreting

mucus for mating and creating cocoons for offspring

• Setae: tiny hairs on ventral side for movement

Class Polychaeta

Class Oligochaeta

• Example: Earthworms

Class Hirudinea

• Example: Leeches