BISC 120Lg Lecture Notes - Lecture 14: Burgess Shale, Ecdysis, Aysheaia
Document Summary
Bisc 120: general biology: organismal and evolutionary biology- lecture 14: United by molecular data and the trait that all these organisms have to undergo some form of ecdysis which is the shedding of the external coat (exoskeleton / cuticle) as they grow. Species-rich clade, contain more species that protists, fungi, plant, and animal groups combined. Thus, they are a very successful group that has thrived everywhere on earth. Non-segmented pseudocoelomates that were only recently classified as ecdysozoans. Cylindrical bodies covered with a tough outer collagenous cuticle. To grow, shed old cuticle and secrete a new one. Complete digestive tract but no circulatory system; fluid in pseudocoelom transports nutrients. No heart or sophisticated way of moving food; it is moved only by their thrashing. Intestine runs the length of the organism. Separate sexes, hermaphrodites or both, with internal fertilization. Can produce zygotes that are extremely resistant to harsh conditions. Females can lay a lot of eggs!