Metazoan Origins

Question 1

What is the hypothesised origin of metazoans?

Answer 1

From a colonial flagellate

Question 2

Why did multicellularity evolve?

Answer 2

Increased oxygen and predation

Question 3

What are some main features of the phylum Porifera?

Answer 3

Simple structures (no tissues, no organs)

Most are filter feeders

Most are marine but some are freshwater

Question 4

Why can sponging by advantageous for Porifera?

Answer 4

Can be a way of distribution - sometimes undergo fragmentation during sponging

Question 5

Give two examples of species in the phylum Porifera?

Answer 5

Barrel sponge

Breadcrumb sponge

Question 6

What are the different parts of a sponge? What are their roles?

Answer 6

Pinaccoytes - cover the outside

Incurrent pores are in the pinacoderm

Porocyte - where water enters

Osculum - where water leaves

Choanocyte - generates current (via flagella) throughout the sponge

Mesohyl - sticks cells together (contain myocytes that contract when sponge wants the oscula to close)

Amoebocyte - moves around and digests food ( these are totipotent)

Spicule - makes the sponge less edible (can be made from calcium carbonate, sponging filaments or silicate)

Question 7

What makes the glass sponge unique?

Answer 7

75% of tissues are syncitial (no cell boundaries so cells are connected)

Have large spicules made from silicate

Osculum cannot close

Question 8

What shape are most sponges?

Answer 8

Leuconoid shape

Question 9

What was Wilson’s experiment? What did he discover?

Answer 9

Put sponge through sieve and it regenerated

Took two sponges and mashed them together and put them through the sieve and it formed two different sponges

Discovered that sponges have self-recognition

Question 10

What ways do sponges reproduce?

Answer 10

Asexual - via budding or gemmules (dormant cluster of embryonic cells produced by sponges for development in favourable conditions)

Sexual - most heramphrodite but often cross-fertilised (sperm expelled via osculum and engulfed by choanocytes and transferred to the egg)

Question 11

What are the features of gemmules?

Answer 11

Tend to be found in freshwater sponges

Have ameobocytes on the inside (totipotent)

Have microphyle (hole on top)

When conditions improve, ameobocytes leave through microphyle and forms sponges