Platyhelminthes - triploblastic (ectoderm, endoderm, mesoderm)
- level of organization - organs, no organ systems
- body symmetry - bilateral
- alimentary structures - 1-hole sac gut, no digestive cavity
- acoelomate - lacking body cavity (no fluid-filled space involving mesoderm)
- Class Turbellaria - flatworms, aka “Planaria”
- mostly found in freshwater
- eyespots - light-sensitive pigmented cups
- simple nervous system
- pharynx in middle of body leads to branched gastrovascular cavity
- extracellular/intracellular digestion in gastrovascular cavity
- hermaphroditic but not self fertilizing
- asexual reproduction through regeneration
- Class Tremetoda - parasitic flukes
- can live inside/outside of hosts
- no epidermis, covered in epicuticle
- attaches to host w/ suckers, nutrients absorbed directly
- mostly hermaphroditic, can self-fertilize, but some dioecious (separate male/female)
- Class Cestoda - tapeworms
- mostly endoparasites (living inside host)
- attaches to host w/ scolex
- proglottid - segmented units, each is hermaphroditic; ones farthest away from scolex are largest, carry eggs
- no epidermis, covered in epicuticle
- nutrients absorbed directly (no digestive enzymes/cavity)
- regeneration possible only if scolex still attached to host
- tapeworms can self-fertilize
Nematoda - pseudocoelomates (have body cavity between mesoderm/endoderm)
- level of organization - organ systems
- body symmetry - bilateral
- alimentary structures - 2-hole sac gut
- holds internal organs
- triploblastic
- no flagella/cilia, covered in cuticle
- no circulatory system
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