Placozoa

Question 1

Where in the phylogeny by Brusca et al. are the placozoans located?

Answer 1

They are basal metazoans, grouped with sponges, jellyfish, and comb jellies but
separate from bilaterians.

Question 2

What are synapomorphies of placozoa

Answer 2

have two cell layers delimiting a space containing nucleated mesenchyme cells in an extracellular matrix.

These organisms have external digestion via temporary formation of a digestive chamber on the ventral surface

Question 3

How many placozoa species exist?

Answer 3

20+

Question 4

How do placozoa develop, eat, and move?

Answer 4

No distinct larval stage

Bacteria and algae (absorbed after external digestion)

Glides with cilia

Question 5

How do placozoa reproduce, and where do they live?

Answer 5

Mostly asexual (splitting), some sexual

Habitat is warm, shallow marine waters (rocks, seagrass, algae)

Question 6

What structures do placozoa have not found in porifera? (4)

Answer 6

cilia

defined top and bottom

contractile fiber cells

external digestion

Question 7

How many have been reported from the Marianas? How might you collect more?

Answer 7

Some found, exact number is unclear

Some collection methods might be to scrape from rocks & algae, using light traps,
and filter seawater for DNA.