BIOL 101 Lecture Notes - Lecture 15: Hemichordate, Tunicate, Thyroid
Document Summary
Deuterostomes: the invertebrates that led to vertebrates, phylum echinodermata: sea urchins, sea stars, etc, phylum hemichordata: acorn worms, phylum chordata: Craniata (vertebrates: synapomorphies of hemichordates and chordates. Dorsal hollow nerve cord: forms from a folding of ectoderm tissue. Pharyngeal gill slits or pouches (at some life stage): originally used as a filter-feeding mechanism, lined with cilia. Hemichordata: acorn worms, small, marine, sedentary or sessile, construct burrows in sand, unique proboscis: projection off the head used to open and close mouth, ancestral characteristics: Fibrous rod that lies below the nerve cord. Ventral fold of tissue along the bottom of pharynx. Eventually becomes thyroid gland (contains iodine: urochordata: Incurrent (leads to mouth) and excurrent siphons (near the anus) Atrium: where the water flows out from the pharynx to the excurrent siphon. Myomeres: chevron-shaped muscle segments attached to notochord. Digestive cecum: becomes the liver in higher chordates, purifies body fluids. Small, marine animals, shallow sandy habitats, burrow posterior end in sand.
