Urochordata

Question 1

intro

5 points

Answer 1

1. Highly variable body form
2. Sessile or free-living, solitary or colonial
3. Sessile or free-living, solitary or colonial [mostly benthic. Some pelagic]
4. Chordate characteristics present in larval stages
5. Exclusively marine with global distribution
   Littoral to deep sea
   Common in tropics and subtropics

Question 2

Classification [ ones focused on in this lecture]

Answer 2

Phylum: Chordata
Subphylum: Urochordata
Class: Ascidiacea, Thaliacea, Larvacea

Question 3

Key characteristics

6 points

Answer 3

1. Bilaterally symmetrical, may be lost as adults
2. Triploblastic
   Tissues, organs, and circulatory system with heart, but no excretory organs or coelomic body cavities
3. Nervous system with a hollow ‘notochord’ in free-swimming larval stages
4. Pharyngeal gill slits (like the enteropneusta)
5. U-shaped gut
6. Hermaphrodites

Question 4

Body structure

4 points

Answer 4

1. Simple epithelium
2. Body enclosed within a tunic
   Composed of tunicin fibres, amebocytes, sometimes spicules
3. Muscle bands
   Circular and longitudinal
4. Body cavity absent
   Atrium, perforated over gill-slits
   Atrial siphon

Question 5

feeding

2 points

Answer 5

1. Suspension feeders
   Rely on mucus
2. Filter feeders
   Material filtered over walls of pharynx

Question 6

Sexual Reproduction

4 points

Answer 6

1. Hermaphrodites
   Single ovary and testicle, with a duct for each
2. Internal (most colonial) and external (most solitary) fertilisation
3. Direct and mixed development
4. Free tadpole larvae (absent in thaliaceans)

Question 7

Asexual reproduction

2 points

Answer 7

1. Budding

2. Fusion

Question 8

Class Ascidiacea

4 points

Answer 8

1. Sessile, benthic species
2. Solitary or colonial
3. Incurrent and excurrent siphons directed upwards
4. Dorsal nerve cord absent in adults

Question 9

Class Thaliacea

4 points

Answer 9

1. Pelagic
2. Solitary or colonial (swap)
3. Incurrent and excurrent siphons opposite
4. No free-swimming larval stage

Question 10

Class Larvacea

4 points

Answer 10

1. Planktonic
2. Solitary
3. Notochord and muscular tail present
4. Secrete a gelatinous ‘house’
   [protection. Muscular tail makes currents to spread mucus when forming gelatinous house]