BIOL 2001 Lecture Notes - Lecture 8: Hydrostatic Skeleton, Oligochaeta, Peristomium
12 Nov 2018
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Include 2 classes each with a different body plan: 1-class errantia: free-living worms with a polychaete body plan. (e. g bristleworms) 2-class sedentaria: sedentary tube or burrow dwelling worms with a. Growth is by metamerism which includes the addition of segments at teloblastic growth zone. Normally, oldest segment is just behind peristomium and youngest segment is just in front of pygidium. volume of coelomic uid inside each segment is constant (hydrostatic skeleton) because of septa. Growth by being constructed of a linear series of repeating parts called metamere (body segment, or somite) and each being formed in sequence in the embryo, from anterior to posterior. An extracellular matrix secreted by the epidermis which does not molt and does not contain cells and is mainly composed of chitin. Involves extending the body, anchoring it to a surface with four pairs of setae (stiff hairlike or bristlelike structure) on each segment, and wavelike peristaltic contractions of the circular muscles.
