Chapter 23: Question 1

What characteristics are shared by the three deuterostome phyla that indicate a monophyletic group of interrelated animals?

The characteristics that are shared by the three deuterosotome phyla that indicate a monophyletic group of interrelated animals are bilateral symmerty; notochord; single, dorsal and tubular nerve chord; pharyngeal pouches; endosytle (thyroid gland); postanal tail; and segmentation.

The notochord is a skeletal rod present at some stage in the life cycle. The anterior ends of the single, dorsal and tubular nerve chord is usually enlarged to form the brain. Thw pharyngeal pouches are present at some stage in the life cycle; in aquatic chordates these develop into pharyngeal slits. The endostyle is in the floor of the pharynx; it is sometimes in the form of a thyroid gland derived from the endostyle. The postanal tail projects beyond the anus at some stage but may or may not persist. The segmentation, if present, is restricted to the outer body wall, head and tail and not extending into the coelom.

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