2.08.10 - A eucoelomate Ecdysozoan lineage: phylum...

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Deuterostomia Lophotrochozoa Ecdysozoa Protistan ancestor Eumetazoa Bilateria Radiata Protostomia Parazoa fundamental symmetry and number of germ layers Development patterns Cuticle presence or absence A eucoelomate Ecdysozoan lineage: phylum Arthropoda (‘jointed feet’) Porifera Cnidaria Platy- Annelida Mollusca Nematoda Arthropoda Echino- Chordata (Calcarea, helminthes dermata Silicea) triploblastic eucoelomate protostomes BY FAR the most successful animals in terms of numbers of species and ecology: > 1 million described species (mainly insects); probably 5-20 X as many not yet described (+ many fossil forms) Found in essentially all habitats, usually in great numbers • diverse in form and function Like nematodes, have an external cuticle Unlike nematodes, eucoelomate and segmented phylum Arthropoda (‘jointed feet’) Key features of arthropod body plan: Reduced coelom in adults open circulation (hemocoel) Hard external skeleton (exoskeleton; cuticle) , made of chitin (acetylglucosamine polymer) mixed with protein and varying degrees of mineralization Jointed appendages (often highly modified) Segmentation ( metamerism : serial repetition of body parts). Segments contain subdivisions of organ systems (muscles, nerve nets, etc.) Tagmosis (grouping -- sometimes fusion -- of segments into specialized units). Can obscure underlying segmentation. phylum Arthropoda (‘jointed feet’) 1. Movement requires flexible joints in appendages. Joints are thin regions of exoskeleton (the rest is usually 'armor'). Muscles connected across joints in antagonistic pairs (one to extend, one to flex). Exoskeleton provides muscle anchorage for effective movement; attachments provide variable leverage (fast or slow but powerful). Antagonistic muscles flexor extensor Joint: thin, flexible cuticle Appendage segment : thick, stiff, mineralized cuticle phylum Arthropoda (‘jointed feet’) Exoskeleton is key to arthropod success. Three attributes:
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2. Provides both support and protection . Helps arthropods move on land without buoyant support of water. Also reduces evaporation (another advantage on land) Exoskeletons preadapted early arthropods (which were aquatic) to invade land; they were among the first land animals. phylum Arthropoda (‘jointed feet’) Exoskeleton is key to arthropod success. Three attributes: Jointed legs, protection, and support are advantages of exoskeletons. But there is a big problem: Exoskeleton is largely non-living and it cannot grow. Therefore: 3. it must be molted (shed) in order for the animal to get bigger. Exoskeleton is key to arthropod success. Three attributes: phylum Arthropoda (‘jointed feet’) a. Animal reaches maximum size for current skeleton b. Most of old skeleton dissolved and reabsorbed c. Remaining part shed (animal crawls out of entire external covering and appendages -- like legs, antennae, eye surface -- plus parts of gut lining and
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This note was uploaded on 04/03/2010 for the course BIO Bio 5b taught by Professor Chappel/douhan during the Winter '10 term at UC Riverside.

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2.08.10 - A eucoelomate Ecdysozoan lineage: phylum...

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