Animals - Protostomes

Chapter 29

Characteristics of Protostomia:

Based on embryonic development Spiral cell arrangement – early cell

divisions are diagonal to the polar axis Determinate cleavage – each cell’s fate is

fixed very early Blastophore develops into the mouth

Platyhelminthes: Flatworms

The largest group of acoelomate worms Contain a mesoderm Have tissues organized into organs Bilaterally symmetrical Flat, ribbon-like body Have a highly branched gastrovascular cavity Dissolved substances move through the body by

diffusion Most do not have a respiratory or circulatory system

Planaria

Marine Flatworm

Tapeworm

Fluke

Nematodes: Roundworms

Pseudocoelomates – fluid movement acts as a simple circulatory system

Have a one-way digestive tract

Ascaris

Trichinella

Hookworms

Mollusks: Soft-bodied Animals

Snails, slugs, oysters, clams, scallops, octopuses, squid A larval stage called a trochophore Second largest phylum of animals Found in almost all marine, freshwater and land

ecosystems Three major classes: 1. Gastropods2. Bivalves3. Cephalopods

Gastropod means ‘stomach-foot’

Bivalve means ‘two-shells’

Cephalopods – ‘head-foot’ squid, chambered nautilus, octopus

Annelids – Segmented Worms

Coelomates 2/3rds are marine Each segment contains digestive, excretory, circulatory

and locomotor organs and is separated from other segments by septa

Some segments also contain areas responsible for specific functions such as reproduction, feeding or sensation

A primitive brain – the cerebral ganglion – is located at the anterior end, with a nerve cord that runs the length of the body

Marine Tube Worms glue grains of sand together to make their tubes

Marine Feather Duster Tube Worms

Earthworms are hermaphrodites but don’t fertilize their own eggs

Leeches can be useful medicinally

Arthropods – jointed legged animals All have jointed appendages – legs,

antennae, and mouth parts The largest group of animals – more

arthropods than all other groups combined Divided into two groups: those with jaws

and those with fangs or pincers

Three body parts – head, thorax, abdomen

Cephalothorax – combines head and thorax with a separate abdomen

Arthropods must molt their exoskeletons as they grow

Spider fangs

Some arachnids have pincers

Centipedes – 1 pair of legs/segment

Millipedes – 2 pairs of legs/segment

Isopod

Shrimp

Lobster

Crabs

Crayfish

Barnacles