BIO 2135 Chapter DigiDiv: Platyhelminthes
7 Feb 2017
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Platyhelminthes
- Flat, in part because they are acoelomate
- Triploblastic; endoderm, mesoderm, ectoderm
- Mouth connects with an incomplete gut
- Bilaterally symmetric
- Cephalization → paired eyespots that detect light + anterior brain coordinates sensory
input from the eyes
- Protonephridia: osmoregulatory organs, removes accumulated intercellular-space water
- Most are monoecious (both male and female sex organs)
Class Turbellaria
- Free living, marine, freshwater, terrestrial
- Dual gland adhesive system → can stick in place; one gland secretes cement, the other
dissolves the glue when they want to become mobile again
- Mouth located on the ventral surface
- Simplest digestive tract = mass of phagocytic cells that ingest food
- Most complex = hollow gut that branches through the body
- Flame cells:
filters fluids that accumulate between cells (in spaces in mesodermal
parenchyma)
Class Monogenea
- Ectoparasites that only have one host their whole life
- Suckers (prohaptor) and hooks (opisthaptor) on their ventral surface
- Tegument:
the outer covering of parasitic flatworms
- Incomplete gut with two branches
- Eggs undergo initial development in the host, ciliated larvae (oncomiracidium) is released
Class Trematoda
- Complex life cycle; two or more hosts
- Leaflike
- Acetabulum:
oral sucker surrounding the mouth + a midventral sucker
- Eggs hatch free from host → miracidium (ciliated) finds intermediate host (mollusc) →
sporocyst, filled with huge numbers of redia (larval amplification) → redia filled with
cercaria (larval amplification again), which are released and swim to find the host
- Syncytial tegument
increases surface area (with microvilli)
- Incomplete gut, 2 branches
- Protonephridia connect to form a single posterior nephridiopore
- As many as 3 lateral nerve cords
- Flukes
find more resources at oneclass.com
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Document Summary
Cephalization paired eyespots that detect light + anterior brain coordinates sensory input from the eyes. Most are monoecious (both male and female sex organs) Dual gland adhesive system can stick in place; one gland secretes cement, the other dissolves the glue when they want to become mobile again. Simplest digestive tract = mass of phagocytic cells that ingest food. Most complex = hollow gut that branches through the body filters fluids that accumulate between cells (in spaces in mesodermal. Ectoparasites that only have one host their whole life. Eggs undergo initial development in the host, ciliated larvae (oncomiracidium) is released. Suckers (prohaptor) and hooks (opisthaptor) on their ventral surface. Incomplete gut with two branches the outer covering of parasitic flatworms. Complex life cycle; two or more hosts. Protonephridia connect to form a single posterior nephridiopore increases surface area (with microvilli) As many as 3 lateral nerve cords. Proglottids: anterior, anchors the tapeworm in the intestine.
