BIOL 111 Lecture Notes - Hirudin, Clitellum, Seta

• School: McGill University
• Department: Biology (Sci)
• Course: BIOL 111
• Professor: Multiple

Document Summary

Multicellularity has evolved more than once in the evolutionary. Bilateral symmetry evolved at d (protostomes and deuterostomes) The first triploblasts (3 layers of cells) also evolved at d. Protostomes and deuterostomes split in the cambrian period. Animals have cleavage (huge ball of cells from one cell) in embryonic development: Protostomes: blastopore becomes mouth and second opening becomes anus (worms) Deuterostomes: blastopore becomes anus and second opening becomes mouth (humans) Digestive tract evolved at d although arrow worms and lophotrochozoans lost it through evolution and only has a digestive cavity. Advantages of digestive tract: specialization of gut regions, sequential food processing, continuous operation. One difference between the three groups of worms is body cavity (coel = cavity) No coelom (no body cavity) solid except for gut space flatworms, (cnidarians diploblasts) Mesoderm lines the outside of the coelom. Mesoderm lines entire cavity as a peritoneum". A coelom provides hydrostatic support, locomotion, storage, space for organ development, isolation of digestive tract.