There are Four major phyla of worms

    Phylum Platyhelminthes: The flatworms

    Phylum Nemertea: Ribbon worms

    Phylum Nematodes: Roundworms

    Phylum Annelida: Segmented worms

   Phylum Platyhelminthes

    Characteristics

    -Bilateral symmetry

     -Unsegmented 

    -They have a central nervous system

        -Simple brain (Aggregation of nerve cells in the brain)

    -Has an actual mesoderm (middle layer) making them a triploblastic animal, having 3 layers.

    -No anus. They do not have a complete digestive track. They have one opening where food enters and waste exits. 

    -They have a flat body shape

            -Their flat body shape allows oxygen and water to enter their body due to diffusion and osmosis. They do not have osmoregulatory organs. 

    -Flatworm anatomy is very simple. The flatworms have an organ called protonephridia. The protonephridia is a series of folds that absorb small molecules. In this manner they act like simple kidneys.

   -The flatworm has a pharynx in the middle of its body. It uses the pharynx as both a mouth and an anus.

    -20,000 known species

Class Turbellaria

    -Most common marine species are from the class turbellarians

        -The turbellarians are free living (not parasites) carnivores

Phylum Nemertea

    Characteristics

     -They are triploblastic

     -They have bilateral Symmetry 

    -They have a complete digestive tract with mouth and anus

    -They are ribbon shaped

    -They have a simply circulatory system 

    -They have a large Proboscis

            -A proboscis is a long feeding tube that sticks out of the mouth. On nemertean worms the proposcis has a sharp spear like end that can puncture the flesh of an animal and then be used as a straw to eat the animal.

    -There are about 900 species of nemertean worms.

Phylum Nematoda

Nematode Characteristics

     About 80,000 species have been described

     -They are Triploblastic

     -They have bilateral Symmetry 

     -They are round in shape

     -They have an Ecdysis, a tough cuticle that molts (molting as they grow) similar to insects.

     -Complete digestive tract. They have a mouth and an anus

          -Mouth usually surrounded by lips that have sense organs

     -Body wall only has longitudinal muscles

     -Do not posses cilia or flagella in anyway (even their sperm is amoeboid)

-Nematodes are mostly parasitic. 

            -This means that they infect a host. Usually they will live inside another animal and live off of it.

    -Round

Class discussion:

Lets talk about how Anisakis works

-At risk if you eat Sashimi or Ceviche

 Phylum Annelida

    -They are Segmented

    -They are Triploblastic

    -They have bilateral Symmetry 

   -Closed circulatory system (Meaning they have veins)

About 22,000 species

    -Has a pair of Parapoda on each segment

        -Sharp bristles called setae

    -Gills

Sandcastle Worms are a type of Polychaete

These are worms that build honeycomb like structures out of sand to live in. These worms and their structures can be found all over the California tide pools. 

    Christmas tree worms (a type of polychaete)