BIOL 1604 Lecture Notes - Lecture 11: Enzyme, Pinworm Infection, Wuchereria Bancrofti

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26 Feb 2017
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Phylum Nematoda
Nematodes are pseudocoelomates but they...
Have a cuticle (nonliving external layer secreted by the epidermis)
They molt!
o Ecdysozoans: animal groups whose members shed the cuticle as they grow
o Ecdysis: shedding the outer curricular layer. Regulated by the hormone ecdysone
Characteristics
Triploblastic bilateral pseudocoelomates (body cavity not entirely lined with mesoderm)
Cuticle
o Mainly composed of collagen secreted by underlying epidermis (hypodermis)
Ecdysis: molt four times during lifetime
Cuticle protects and contains the high hydrostatic pressure exerted by fluid
in the pseudocoelom
Sensory system includes papillae and setae for touch. Unique sensory amphids or
phasmids
Ring of nerve tissue with ganglia around pharynx gives rise to nerves and dorsal and
ventral nerve cords
Digestive system is complete
Excretory system may include gland cells and canals, it opens via excretory pore
No respiratory or circulatory systems
Pseudocoelom used as hydrostatic skeleton
Microscopic to several meters long
Free living (marine, freshwater, soil) and parasitic
Very abundant
12,000 (described) to 500,000 species
Body plan
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Movement
Longitudinal muscles only. No circular.
Whiplike undulations.
Feeding
Carnivorous, herbivores, omnivores, saprobes, parasites
Mouth with teeth, jaws or stylets
Muscular pharynx
Complete long digestive tract
Reproduction
Most dioecious and dimorphic: males are smaller than females
o Internal fertilization
o Parthogenesis occurs rarely
Males have 2 copulatory spicules
After fertilization, shelled zygotes or embryos are stored in the uterus until deposition
Four juvenile stages, each separated by a shedding of the cuticle
Interactions
Many nematodes are important parasites of both plants and animals
o Soybean plants, tomato plants, potatoes
Parasitic nematodes
Some have anaerobic energy metabolism
Some with free living juvenile stages and others require an intermediate host to reach the
definitive host and complete their live cycles
Human parasites
o In general larva 3 is the stage infecting humans
o High reproductive potential
o Enzyme resistant cuticle
o Resistant eggs
o Sometimes encysted larva
Ancylostoma dudodenale
Old world
hookworm
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