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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.
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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
Nematodes: Roundworms • Pseudocoelomates – fluid movement acts as a simple circulatory system • Have a one-way digestive tract
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: • Gastropods • Bivalves • Cephalopods
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
Earthworms are hermaphrodites but don’t fertilize their own eggs
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
Cephalothorax – combines head and thorax with a separate abdomen
