BIOL 111 Lecture Notes - Oligochaeta, Hirudin, Nephridium

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13/10/11
Development of digestive tract enables:
1. specialization of gut regions
2. sequential food processing
3. continuous operation (multiple tasks at once)
Gastrulation occurs = development of gut cavity
Blastopore forms then second opening forms
1. Protostomes (1st is mouth)
a. blastore mouth
b. new opening anus
2. Deuterostomes (2nd is mouth)
a. Blastopore anus
b. New opening mouth
Protostomes:
1. Lophotrocozoans: have one of the characteristics:
- lophophore: ciliated feeding/gas exhange structure
- trocophore: ciliated free living larval form
- unsure about rise of these two forms, perhaps common ancestor had both
and some lost one
2. Exdysozoans:
- have external covering secreted by epidermis that must be shed in order for
animal to grow
Presence /type of body cavities (coelom) differentiate protostomes:
1. Pcoelomate: no coelom, solid digestive space (ex. Flat worms)
a. mesenchyme: unspecialized cells derived from mesoderm
2. Pseudoceloemate: false coelom (ex nematodes)
a. mesoderm lines the outside of coelom
3. Coelomate
a. Mesoderm lines entire cavity (peritoneum)
i. Lining derived from mesoderm
2 ways to make a coelom:
1. Schizocoely:
a. Splitting within the mesoderm form ceolom
b. In protostomes
2. Enterocoely:
a. Mesoderm forms pochets from guy
b. In deuterostomes
Phylum nematoda: Roundworms
- Blunt anterior end/tapered posterior end
- Ecdysozoans diffusion of gas across thin flexible cuticle
o Live in moist habitats to help with diffusion of gases across
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