1. Hemichordata Invertebrate Chordates

2. Evolutionary Perspective
Echinoderms, Hemichordates, and Chordates are most likely derived from a common (yet undiscovered) ancestor, since they all share deuterostome characteristics.

3. What characterizes a chordate?
A dorsal tubular/hollow nerve cord
A notochord
Pharyngeal slits or pouches
Postanal tail

4. Which are shared by both Chordates and Hemichordates?
Pharyngeal slits
Most have a dorsal (sometimes hollow) nerve cord.
This shows that evolutionary ties b/w Hemichordates and Chordates are closer than b/w echinoderms and either of these phyla.

6. Hemichordates Hemichordata means “half chord”
Includes: Acorn worms and Pterobranchs
Live in or on marine sediments

7. 5 Characteristics of Hemichordates
Marine, deuterostomes w/bodies in 3 segements-proboscis, collar, and trunk
Ciliated pharyngeal slits
Open circulatory system
Complete digestive tract
Dorsal (sometimes hollow) nerve cord

8. Class Enteropneusta
Acorn worms-named so b/c of the proboscis at the anterior end
75 species, cm usually
Most occupy U-shaped burrows along the sandy shore-line
Cilia and a mucous-covered proboscis assist in feeding

9. Class Pterobranchia Name means “wing or feather gills”
Around 20 species-Rhabdopleura
Small mm, often living in secreted tubes in asexually produced colonies
Proboscis is sheild-like and secretes the tube
Found mostly in deep oceans of the Southern hemisphere
Use cilia on arms/tentacles to filter and transport food to mouth

11. Phylum Chordata Bilateral symmetry, deuterostomes
Notochord, pharyngeal slits or pouches, dorsal nerve chord, and postanal tail present at some point during development
Presence of endostyle (produces mucous) or thyroid gland
Complete digestive tract
Ventral, contractile blood vessel (heart)

12. Notochord-a supportive rod extending most of body length
Pharyngeal slits-series of openings along pharyngeal region. Invert chordates use for filter feeding. Some chordates for gas exchange.
Dorsal hollow nerve cord-runs along length of body, associated w/development of complex sensory systems
Postanal tail- extends posterior to the anus

13. SubPhylum Urochordata
Marine animals; some species are solitary, others are colonial.
Sessile adults, but motile during the larval stages
Possess all 5 chordate characteristics as larvae
Settle head first on hard substrates and undergo a dramatic metamorphosis (e.g., tail, notochord, muscle segments, and nerve cord disappear)

14. SubPhylum Urochordata cont.
Adult body covered by an outer envelope or tunic; composed of proteins, salts, and cellulose
Tunic encloses a basket-like pharynx, that is perforated by gill slits
Tunicates are filter feeders; Oral siphon (mouth)-plankton is trapped in a sheet of mucus and cilia later direct the food-laden mucus to the stomach
Water leaves the animal via an excurrent siphon

15. SubPhylum Cephalochordata- 45 species
“Head chord”
Exclusively marine, tadpole-like animals (up to 5cm)
Although they are capable of swimming, they usually are buried in the sand with only their anterior end being exposed
World’s oceans in shallow waters clean sands

16. All chordate characteristics are present throughout their life history
SubPhylum Cephalochordata cont.
All chordate characteristics are present throughout their life history
They are filter feeders: inside of the oral hood is lined with cilia -wheel organ
These cilia, plus cilia in the pharynx help generate a water current
Water and suspended food particles pass through the oral hood, equipped with projections called cirri that strain larger particles
Feed by secreting a mucous net across the gill slits to filter out food particles that are present in the water.