Study #2: Test 3: Chordates

Question 1

Evidence that echinoderms were ancestors of chordates

Answer 1

Deuterostomes (2nd opening to gut is mouth while anus develops from blastopore)
Enterocoelous development of embryo
Bilateral symmetry of larvae

Question 2

Phylum Hemichordata Distinguishing features

Answer 2

1. Soft bodied, worm-like marine animals
2. Dorsal tubular nerve cord (significance: spinal cord in later animals)
3. Pharyngeal slits (opening between digestive tract to outside)Significance?: used for feeding then developed into future gills for breathing

Question 3

Features defining Chordates

Answer 3

1. Notochord: flexible rod extends dorsal length of body; 1st to appear in embryo; axis for muscle attachment; replaced by vertebrae in future vertebrates
   2.Tubular nerve cord: runs dorsal to notochord; forms brain anteriorly; formed by infolding of ectoderm
   3.Pharyngeal Pouches/Slits: filter feeding; some Chordates modify gills for gas exchange; embryo features in terrestial vertebrates
   4 Endostyle or Thyroid gland: ventral or under pharynx; secretes mucus to trap food in filter feeder chordates; transforms into thyroid gland in other chordates
   5.Postanal tail: elongation of body past anus; good for propulsion in lower chordates; coccyx in humans

Question 4

Features defining Subphylum Urochordata- tail chordates (tunicates or sea squirts)

Answer 4

1. Tunic: tough body wall (protection from predators)
2. Adults: sessile; juvenile: free-swimming
3. Adults: pharyngeal gill slits used for FEEDING not breathing; endostyle (secretes mucus)
4. Juvenile urochordata have ALL the chordate characteristics
5. Body plan: 2 siphons (oral, atrial) permit water to circulate thru out body)
6. all are marine

Question 5

Features defining Subphylum Cephalochordates (lancelets, amphioxus)

Answer 5

1. All 5 chordate characteristics as adults: notocord (significance: develops into vertebrae), tubular nerve cord, pharyngeal slits, endostyle, postanal tail)
2. Shallow, sandy ocean bottom dwellers
3. Notocord used for burrowing
4. Has fins, but weak swimmers; if swim use metameric muscles below
5. Oral hood at front with buccal cirri used for feeding
6. Oral hood at back with a mouth leading into pharynx, with many pharyngeal slits for feeding
7. Blocks of metameric muscles along body (also found in fish); allows for rhythmic contracting to flex body and swim like a fish;