01:119:115 Lecture 34: chapter34
15 Feb 2018
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Document Summary
It is composed of large, fluid-filled cells encased in fairly stiff, fibrous tissue. In all chordate embryos, a series of pouches separated by grooves forms along the sides of the pharynx. In most chordates, these grooves (known as pharyngeal clefts) develop into pharyngeal gill slits that allow water that enters the mouth to exit without continuing through the entire digestive tract. In contrast, nonchordates have a digestive tract that extends nearly the whole length of the body: the chordate tail contains skeletal elements and muscles. It provides much of the propulsive force in many aquatic species. Lancelets are suspension feeders, feeding by trapping tiny particles on mucous nets secreted across the pharyngeal slits: ciliary pumping creates a flow of water with suspended food particles into the mouth and out the gill slits. Living craniates have a set of derived characters.
