Download Animals - Protostomes

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
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Platyhelminthes: Flatworms
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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
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Ascaris
Trichinella
Hookworms
Mollusks: Soft-bodied Animals
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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:
Gastropods
Bivalves
Cephalopods
Gastropod means ‘stomach-foot’
Bivalve means ‘two-shells’
Cephalopods – ‘head-foot’
squid, chambered nautilus, octopus
Annelids – Segmented Worms
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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
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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