Presentation 2: Chordate Ancestry

Question 1

Protochordata

Answer 1

Includes Hemichordata (ex. Acorn worms and pterobranchs), Urochordata (ex. molgula and Thaliacea), and Cephalochordata (ex. lancelets or amphioxos)

Question 2

Hemichordate Larvae

Answer 2

Tonaria (similar to Bipinnaria Larva of Echinoderms)- have simple digestive system and cillia bands

Question 3

Hemichordate Segments

Answer 3

Proboscis, collar, and trunk (synapomorphy for hemichordates)

Question 4

Stomocord

Answer 4

aka pre-oral diverticulem, a projection of digestive tube into anterior system (synapomorphy for hemichordates)

Question 5

Hemichordate groups

Answer 5

Enteropneusta (acorn worms)
- solitary filter feeders with dorsal strand of nerve cells)
Pterobranchia (pterobranchs)
- small colonial moss-like creature some of which lack stomochord or dorsal nerve strand

Question 6

Chordata Synapomophies

Answer 6

1. Dorsal Hollow Nerve Cord
2. Notochord (main form of support)
3. Muscular unsegmented post-anal tail
4. Endostyle (homologous to the thyroid gland)

Question 7

Urochordate

Answer 7

Free swimming larval stage w/ all 4 chordate synapomorphies that undergoes metamorphosis to become adult. Have a thick cellulose-like tunic

Question 8

Urochordate Groups

Answer 8

1. Ascidians (molgula/sea squirts)
   - Complete metamorphosis from chordate synapomorphy containing larva to sessile adult
2. Larvacea (appendicularia)
   - Larva do not undergo metamorphosis, sex. maturity reached at larval stage and remain free swimming
3. Thaliacea
   - Lack notochord and post anal tail

Question 9

Chephalochordate (amphioxus) structures

Answer 9

Segmented V shaped myomere muscle units separated by connective tissues called myosepta
Fins: dorsal, ventral, and caudal
Metapleural folds that help keep them upright

Question 10

Amphioxous (lancelet) key anatomy

Answer 10

• Oral Hood (front)
• Oral Cirri (tentacles)
• Wheel organ (cycles water in)
• Velum (where mouth is)
• Hatchek’s groove/pit (top of vellum cirri produces mucus)
• Pharynx (where water moves through
• Notochord (main support of body)
• Nerve Chord (dorsal to notochord)
• Gill Slits (allow water to enter peripharyngeal bands)
• Pharyngeal bands (part of respiration)
• Endostyle (produced mucus)
• Midgut cecum (where mucus collects to digest nutrients)
• Gonad (ventral to midgut cecum)
• Midgut (before illeocolon ring)
• Illeocolon ring (blocks waste from exiting until after digestion)
• Atriopore (where water exits)
• Anus (where waste exits)

Question 11

Cephalization

Answer 11

Development of the head (congregation of sense organs on the anterior tip of the head)

Question 12

Evolution of free swimming vertebrates

Answer 12

• Cephalization (development of head)
• Muscle coordination (muscle system integrated with nervous system)
• Predation (either become predator or prey)