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Lecture 12

Lecture 12 - Nematods and Annelids.docx

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Biology (Sci)
BIOL 111
Suzanne Gray

• continuous operation October 13 th intestine stomach phNEMATODES AND ANNELIDS anus mouth Development of the digestive tract enables:  Specialization of gut regions  Sequential food processing  Continuous operation How does a complete digestive tract develop? second opening digor tractavity first opening (blastopore) Two ways to develop a diststive tract: 1. Protostomes (1 mouth):  Blastopore  mouth 3  New opening ndnus 2. Deuterostomes (2 is mouth)  Blastopore  anus  New opening  mouth  Example: Humans Protostome animals: Ecdysozoans: have an external covering secreted by epidermis that must be shed in order to grow Lophotrocozoans: have one of the following characteristics (some animals may have lost it secondarily or that it is only present in some groups)  Lophophore: ciliated feeding/gas exchange structure  Trocophore: a ciliated free-living larval form (on the top and a band around the middle Difference in body cavities:  There are three different body plans with respect to body cavities  Greek root of coelom = cavity 1. Acoelomate: a. No coelom b. Solid except digestive space 2. Pseudocoelomate: a. False coelom b. Mesoderm lines the outside of coelom c. Example: Nematoda October 13 th NEMATODES AND ANNELIDS 3. Coelomate: a. Mesoderm lines the entire cavity as a “peritoneum” (lining derived from mesoderm) b. Example: Humans; peritoneum attaches are organs and keeps them in place 2 Ways to Make a Coelom: Coelem isolates the gut from body movement, provides a hydrostatic skeleton that can assist in support and movement, storage reservoir for gametes and waste, provides space for organ development. 1. Schizocoely: a. Splitting within the mesoderm b. Protosomes 2. Enterocoely: a. Mesoderm forms pockets from gut b. Deuterostomes Phylum Nematoda:  Roundworms  Ecdysozoan (molting animal)  Thick, flexible cuticle; allows diffusion of gases, must live in moist habitat  Pseudocoelomates  Longitudinal muscles; move by thrashing  Tapered posterior end  Blunt anterior end Phylum Nematoda • bilaterally symmmetrcall • triploblastic • fluid-filled body No respiratory or caviy -hydrostatic cicuatoy ystem skeleton • complete digestive tract Nematoda Diversity:  ~25,000 species (est. 1,000,000)  Terrestrial (moist soil) or aquatic  Free-living (scavengers, pNematoda diversityitic  Extremely abundant  Poster Child: C. elegans- “white rat” of geneticists and developmental biologists • ~25,000 species (est. 1,000,000)  Dr. Heikimi and col•eat rrestrial (moist soil) or aquaticmutated, resulted in nematodes to live ~6x their normal life span • rfee-living (scavengers, predatory) or parasitic  Worms used energy m•reextremely abundanted & swam at a slower pace • C. elegans - “whe attofgenetcstss and developmental biologists efficiently and fed & swam at a slower pace October 13th NEMATODES AND ANNELIDS Nematodes are important part of food web of soil Most nematodes are scavengers and predators but some are parasitic  Infect protists, plants & animals
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