1: Metazoans

Question 1

Briefly describe the origin of metazoans

Answer 1

• Originated from colonial flagellate >800 MYA
• Single celled → multicellularity, evolved due to increased O2 & predation
• Conflict between movement and division

Question 2

Describe the Porifera

Answer 2

(sponges)
- Radiata
- Simple structure
- Successful and widespread
- Ancient group of animals → 600 MYA, perhaps even 890 MYA
- Split from rest of animals early on

Question 3

What are pinocytes in the Porifera?

Answer 3

Form pinacoderm - outer skin-like layer

Question 4

What are the ostia in the Porifera?

Answer 4

Ostia = pores
Formed from porocytes (tube shaped cells)
Allow water exchange in and out of the Osculum (large opening)

Question 5

What are the choanocytes in the Porifera?

Answer 5

Flagellated cells which line the osculum
→ generate current used for feeding

Question 6

What are the amoebocytes in the Porifera?

Answer 6

Digest food - secrete spicules

totipotent

Question 7

What do myocytes do in the Porifera?

Answer 7

Detect changes in stimuli, which alter the rate flagella beat at = feeding current changes

Question 8

Larger sponges get more complex. They can have an infolded _________ layer

Answer 8

choanocyte

Question 9

What are spicules in the Porifera?

Answer 9

Skeleton of the sponge
Can be made from calcium carbonate → hard
Can be made of silicates → like glass
Can be made of spongin (protein fibre) → spongey
Provide support
Also form of defence

Question 10

Describe how the Porifera reproduce

Answer 10

Asexual → budding or gemmules

Sexual → most sponges are hermaphrodites, but cross fertilise (produce different gametes at different times):
1. Sperm expelled via osculum & engulfed by choanocytes & transferred to egg
2. Larvae retained until blastula stage