Phylum Nematoda The Roundworms Phylum Level Characteristics • round, not flattened • no segmentation • complete digestive system – (2 openings: mouth and anus) • -soft bodied, hydrostatic skeleton • -bilateral symmetry • No circulatory system – Nutrients and wastes diffuse through body cells Nervous System • Exhibit cephalization as they have a “head” end • In head are several ganglia or nerve bundles, no real “brain” • Have sense organs that detect chemicals given off by prey or hosts • Longitudinal muscles so movement is “snake-like” Reproduction • Sexual • Most species have separate males and females, a few are hermaphroditic • Fertilization occurs within the female • Parasitic life cycles can involve many hosts Diversity • most are free-living • found in all habitats • very successful (high # of species and large #’s of them) Diversity • parasitic round worms also infect most kinds of animals and plants • -i.e. Ascaris infects humans Ascaris Life Cycle • Adult worms live in intestines – Produce many eggs that leave in hosts feces • Feces contaminated food or water eaten by another host – Eggs hatch in intestine of new host – Young worms burrow into the walls of the intestine and enter surrounding blood vessels – Carried by blood, worms end up in lungs – Travel up air passage into throat then are swallowed – Carried back to intestines where process begins again! ascaris animation Diversity • -i.e. hookworm can enter body through bare feet Hookworm Life Cycle • Hookworm eggs hatch and develop in soil • Use sharp teeth and hooks to burrow into feet • Continue burrowing until they enter the bloodstream • Travel to lungs, coughed up and swallowed to eventually reach intestines • Adult worms dig into intestinal wall and suck blood of host http://www.youtube.com/watch?v=tGHAlmCj3DM Assignment: 1. Watch Nematoda video 2. Complete nematoda worksheet 3. Complete nematoda flash cards! Please remind me that we need to catch up on the “ecological significance” notes for the last 2 phyla!!