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Lecture 17 � Coelomate Protostomes � Mollusks

Lecture 17 � Coelomate Protostomes � Mollusks...

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Lecture 17 – Coelomate Protostomes – Mollusks A. Introduction - These are considered the higher invertebrates, which of the protostomates include: 1) Mollusks – clams, oysters, snails 2) Annelids – earthworms 3) Arthropods – insects, shrimp - The highest invertebrates also include one deuterostomate: the echinoderms (such as sea stars) 1. Mollusks, Annelids, Arthropods 2. Coelom – separation, hydrostatic skeleton, transport, space - How do you define a true coelom? 1) it forms within the mesoderm, and therefore it would have to be completely lined with mesoderm (mesoderm = muscle) - What are the advantages? 1) Separation – the outer body wall is completely separated from digestive tract (its capable of movement on its own) 2) Hydrostatic skeleton – not the case with us; annelids have this and they use the muscles squeezing against this to move 3) Transport – if its fluid-filled, its bathing the organs on the inside and is helping provide nutrients and perform waste 4) Space – provides space for the organs to function (such as the mediastinum for the heart) 3. Terrestrial – body covering, respiratory surface, reproduction, exoskeleton - Insects, spiders, and earthworms have moved to land - When you move to land you need to prevent 1) Desiccation
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2) Support To do these, there is an exoskeleton (with chitin; lobsters and crayfish) or a cuticle Respiratory surface – if the organism is aquatic there are external gills; a land organism has internal lungs or tracheal tubes Reproduction – internal fertilization (to prevent drying out), fish lay eggs on floor but land organisms can’t do that; young have to develop inside the
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