1: The deuterostomes: Hemichordates

Question 1

Describe the Enterpneusts (acorn worms)

Answer 1

Vary from 9 - 200 cm
Body part functions:
- Proboscis collects food
- Gill slits for respiration
- Stomochord supports heart and excretory organ
- Larval stage (tornaria) echinoderm-like
- Nerve net (concentrated in collar, can be hollow)

Question 2

Describe the Pterobranchs (sea angels)

Answer 2

Similar body struc to acorn worms
Small sessile
Body struc:
- Some have gill slits
- Simple nerve net
- Stomochord supports oral shield

Question 3

Why are the hemichordates not regarded as chordates?

Answer 3

• Lack a true notochord
• Structure and function of Pharyngeal gill slits is different (used for respiration)
• No post anal tail