BIO2231 Lecture Notes - Lecture 14: Ascaris Lumbricoides, Nematode, Eumetazoa
Lecture 14 - Nematoda and other Pseudocoelomates
Phylum Nematoda (roundworms)
Pseudocolomates
• Body cavity that isn’t new
• A clade that wasn’t to be
• A body cavity bounded on only
one side by mesoderm
• Molecular phylogenies do not
support pseudocoelomates as
monophyletic clade
• Formed directly from blastocoel
• Eucoelomate are annelids
Features
• Metazoa → eumetazoa → bilateria → protostomes → ecdysozoa
• Body covered with protective cuticle - needs to moult
• Digestive system with mouth and anus
• Eutely - cell constancy
• Muscles all run longitudinal
• Contain excretory canal on lateral side
Habitat
• Freshwater, marine and terrestrial
• Interstitial - live in between things
Locomotion
• Lack cilia
• Only have long longitudinal muscles
• Muscles act by bending the elastic cuticle against high pressure of
pseudocoleom
• Creates poorly directed sinusoid ‘thrashing’ movement
• With sufficient resistance of environment leads to ‘snake like’ movement
Feeding and Digestion
• Majority: parasititc
• Variety
o Detrivores, parasites, predators, microscavengers
• Piercing mouthparts for individual cells
• Specialised gut - cuticle lined pharynx, pumping oesophagous
Respiration
• No circulatory or gas exchange structures
• Rely on diffusion since so small
• Efficient in harnessing aerobic and anaerobic metabolic pathways are present
Parasitic Nematodes within Humans
• Ascaris lumbricoides
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Document Summary
Pseudocolomates: body cavity that isn"t new, a clade that wasn"t to be, a body cavity bounded on only one side by mesoderm, molecular phylogenies do not support pseudocoelomates as monophyletic clade, formed directly from blastocoel, eucoelomate are annelids. Locomotion: lack cilia, only have long longitudinal muscles, muscles act by bending the elastic cuticle against high pressure of pseudocoleom, creates poorly directed sinusoid thrashing" movement, with sufficient resistance of environment leads to snake like" movement. Feeding and digestion: majority: parasititc, variety, detrivores, parasites, predators, microscavengers, piercing mouthparts for individual cells, specialised gut - cuticle lined pharynx, pumping oesophagous. Respiration: no circulatory or gas exchange structures, rely on diffusion since so small, efficient in harnessing aerobic and anaerobic metabolic pathways are present. Phylum nematomorpha (horsehair worms: similar to nematodes, long and slender, key feature: vestigial gut, absorbance, larvae parasites of arthropods, adults in freshwater, are pseudocelomates and lophotrochozoa, bilaterally symmetrical, triploblastic, protostomes, spiral cleavage, molecular characters.
