Platyhelminthes
“Flatworms”
- Most are parasitic - (flukes and tapeworms) - Some are free living (Planaria)
- Triploblastic
- Acoelomate
- Bilateral symmetry
- Cephalization
- Hydrostatic skeleton
- Blind gut
- Asexual and sexual reproduction
- Tissue-organ level complexity
Tubellaria
Platyhelminthes 5mm-50cm Most are free living Some symbiotic Blind gut Sexual ad asexual reproduction
Cestoda
Platyhelminthes
Tapeworms
Long flat body
Scolex - Attachment to host
Stobila - Main body composed of chain of proglottids
Proglottids - reproductive units
Nearly all monoecious - Proglottids fertilized by other
Trematoda
Platyhelminthes
“Flukes”
Almost all endoparasites
Swimmer’s itch
Shistosoma - Trematoda
- Passes between snail (intermediate host) and birds (Definitive host)
Cecariae can enter skin of human
Nematoda
Triplblastic Pseudocoelomate Bilateral Cephalization Hydrostatic skeleton with fluid filled pseudocoelom Complete gut Sexual, most dioecious - Sexually dimorphic Organ-system level of biological complexity
Annelida
- Triploblastic
- Coelomate
- Bilateral symmetry
- Cephalization
- Hydrostatic skeleton
- Complete gut
- Sexual and asexual / monoecious or dioecious
- Organ-system
- Metamerism
- Many have setae
Metamerism
- Being composed of serially repeating parts; serial segmentation
- Segments are repetitive but not identical
- Allows for greater complexity in structure and function possible
- Evolved separately in classes
Effect of metamerism
Allows for greater complexity in structure and function possible
Evolved separately in classes
Pseudometamerism
Tapeworms
- Repeated segments are independent of each other
- Each contain a complete set of organs
Annelida
Descriptive terms awaiting taxonomic revision
- Polychaeta, Oligochaeta, Hirudinida
- Clitellata - Monophyletic group (subphylem)
- Characterized by a reproductive structure called the citellum
Oligochaeta
Earthworms and freshwater worms
Bear setae
Earthworm Reproduction
- Extend anterior ends from burrows and press ventral surfaces together
- Held by mucus
- Ventral setae also penetrate each other’s body
- Sperm discharged and travels along the seminal groove into seminal receptacle
- Worms separate
- Each worm secretes around its clitellum
- Mucous tube
- Tough band that forms a cocoon
- Moves along body to anterior end and collects eggs (genital pore), Albumin (skin glands), sperm (seminal receptacles)
- Fertilization occurs in cocoon
polychaeta
marine worms
- Well differentiated head
- Specialized sense organs
- Paired paddlelike appendages (parapodia)
- Chaetae (satae) on each parapodium
- No clitellum
Hirudina
- Fixed number of segments - usually 34
- No parapodia or setae
- Variable dietary strategies
- Carnivores on small insects, temporary parasite, permanent parasite
- Monoecious
- Clitellum only evident during breeding season
