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Chapter 7

Chapter 7. Phylum Hemichordata Phylum Chordata. Phylum Hemichordata. Characteristics: Rare group, but these worms seem to span a gap between invertebrates and more advanced chordate animals

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Chapter 7

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  1. Chapter 7 Phylum Hemichordata Phylum Chordata

  2. Phylum Hemichordata • Characteristics: • Rare group, but these worms seem to span a gap between invertebrates and more advanced chordate animals • Acorn worms share some features with chordates including pharnyngeal gill slits and a nerve cord that is similar to the chordate notochord • Acorn worms are deposit or suspension feeders and use proboscis for feeding • Acorn worms have larvae that resemble those seen in echinoderms • 90 known species www.discovery.com

  3. Phylum Cordata(the inverts) • Subphylum Urochordata - tunicates • Subphylum Cephalochordata – lancelets • Chordates have several common features that are seen at least during some portion of the life. • Lancelets are the only chordates that possess all the common features as adults.

  4. Phylum Chordata • Characteristics: • Notochord – flexible support rod between nerve cord and gut • Tubular nerve cord • Muscular pharynx (gut) • Gill slits • Post-Anal Tail • Ventral heart • Note: no backbone. In vertebrates, notochord is surrounded or replaced by the vertebral column.

  5. Invertebrate ChordatesTunicates – Subphylum Urochordata, Class Ascidiacea • Characteristics: • Commonly called “sea squirts” because most filter feed via an incurrent siphon and “squirt” water out an excurrent siphon after the water has been filtered (Exception: Predatory tunicate) • Larvae has chordate characteristics that are not seen in adults- only pharynx remains • Called tunicates because of thick outer covering called a tunic • Larvae are free swimming after fertilization occurs in open water- mass reproduction - see Fig. 7.51 • Adults normally live attached to boats, docks, reefs, or other hard substrate • All 3000 known species are marine

  6. Tunicates • A A B Figure 7.51 A. Clavelina picta, colonial ascidian. B. tadpole larva of ascidians exhibits all the distinguishing characteristics of chordates.

  7. B A Figure 7.52 A. Cliona intestinalis, shallow water sea squirt. B. Adult tunicate

  8. Phylum ChordataSubphylum Cephalochordata, the Lancelets • Characteristics: • 23 species • Very small, only up to 3 inches long • Live in shallow marine waters as filter feeders • Body shows segmented muscle tissue • Notochord attached to the muscles • Gills are used to filter food, not in respiration • Only invert chordate to possess all chordate features as an adult

  9. Phylum ChordataSubphylum Cephalochordata, the Lancelets

  10. Phylogenetic relationships of animal phyla

  11. Characteristics of Major Animal Phyla

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