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Download Animals - Protostomes
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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 1. 2. 3. 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 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
