Phylum Hemichordata Phylum Chordata 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 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

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.

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.

Invertebrate Chordates Tunicates – 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

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

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

Phylum Chordata Subphylum 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

Phylum Chordata Subphylum Cephalochordata, the Lancelets

Phylogenetic relationships of animal phyla

Characteristics of Major Animal Phyla