Oct 6 - Animals Lecture #9

Phylum nematoda general characteristics most abundant

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Phylum Nematoda – general characteristics (most abundant in the planet) Chapter 12, Pages 222 - 234 Nemaode worms are ubiquitous! o Up to 4 million per square meter Good farmland topsoil estimated to contain billions/m2 “if all the matter in the universe except the nematodes were swept away, our world would still be dimly recognizable..” - N.A Cobb (1914) Nematodes exhibit considerable uniformity of both internal and external anatomy Long cylinder animals Typical nematode: o 1-2 mm long o Shows no external segmentation o Is tapered at both ends o Is cover by a multilayered cuticle Cuticle: o Non-cellular covering secreted by epidermis (may be lost in parasitic forms) o Provides structural resistance for high pressure hydrostatic skeleton
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Very pressurized on the inside (helps locomotions but can set up problems too) Locomotion o Internal hydrostatic pressure can be a high as 225 mm Hg (earthworm: 5-10 mm Hg) If you were to piece an earthworm, it won’t care If you pierce a nematode, it would be compromised and loses its internal pressure o Epidermis does not pocess any cilia o Nematodes possess longitudinal muscles but no circular muscles Moves like sinocodials waves (not very graceful) o Movement achieved by undulating waves, driven by alternating contractions of muscles o Muscle contraction controlled by nervous system o
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