Invertebrate Phylogeny

Question 1

How many invertebrate phyla are there?

Answer 1

35 (or so)

Question 2

Which is the most species rich phyla?

Answer 2

Arthropods

Question 3

Which is the most abundant phyla?

Answer 3

Nematodes

Question 4

What is classical animal phylogeny based on?

Answer 4

4 major splits in body plan

Question 5

What is the 1st split in traditional animal phylogeny? What splits off at this step?

Answer 5

Parazoans (no true tissues)
or
Eumetazoa (all other animals).
Splits off Porifera (sponges).

Question 6

What is the 2nd split in traditional animal phylogeny?

Answer 6

Radial symmetry (split two ways)
or
Bilateral symmetry (split one way, associated with cephalisation)

Question 7

What is cephalisation?

Answer 7

Development of a head.

Question 8

What is the 3rd split in traditional animal phylogeny?

Answer 8

No body cavity (Acoelomate)
or
Cavity partially lined with mesoderm (Pseudocoelomate)
or
cavity completely lined with mesoderm (Coelomate)

Question 9

Give an example of an acoelomate.

Answer 9

Platyhelminthes - flatworms

Question 10

What is the disadvantage of not having a body cavity?

Answer 10

Reduced flexibility, body essentially solid.

Question 11

What is the 4th split in traditional animal phylogeny?

Answer 11

Protosomes
or
Deuterostomes

Question 12

Give examples of phyla which are protostomes.

Answer 12

Molluscs, annelids, arthropods.

Question 13

Give examples of phyla which are deuterostomes.

Answer 13

Echinoderms, chordates.

Question 14

What makes an organism a protostome?

Answer 14

Cleavage spiral and determinate. Different origins of coelom to deuterostomes. Fate of blastophore - mouth is formed first, then anus.

Question 15

What makes an organism a deuterostome?

Answer 15

Cleavage radial and indeterminate. Different origins of coelom to protostomes. Fate of blastophore - first forms anus, then mouth.

Question 16

Which of the factors used in traditional animal phylogeny are useful nowadays and which are not?

Answer 16

GOOD - radial vs bilateral symmetry, fate of blastophores
BAD - Body cavities
CONTESTED - Splitting of sponges first. Some still think sponges should split first, others do not.

Question 17

What is new animal phylogeny based on?

Answer 17

Sequencing of SSU-rRNA.

Question 18

Are “worms” a phylogenetic group?

Answer 18

No, just a body plan but can be unrelated.

Question 19

How can the relatedness of species to one another be determined?

Answer 19

Sequencing gene order and lining them up to see similarity. Rearrangements in gene order seem rare and hard to undo, so animals that share mutations are likely closely related.

Question 20

What is an example of a phyla that looks like a worm, but isn’t?

Answer 20

Pentastomida (parasite worms) look like worms, but are crustaceans.

Question 21

What is an example of a group that are protostomes, but develop like deuterostomes?

Answer 21

Penis worms

Question 22

How can modern phylogeny be further split after the fate of blastophores?

Answer 22

Ecdysozoans or not.
Includes arthropods and nematodes that both shed cuticle periodically with growth (ecdysis).

Question 23

What is ecdysis and what phyla do this?

Answer 23

Shedding of cuticle periodically with growth. Done by arthropods and nematodes.

Question 24

What are the closest living relatives of vertebrates?

Answer 24

Tunicates (sea squirts) (disproves inverts as a separate group)

Question 25

Are invertebrate phyla comparable in terms of described species groups?

Answer 25

No - arthropods are most species rich by far.

Question 26

Are invertebrate phyla comparable in terms of numbers of organisms in groups?

Answer 26

No - nematodes most abundant by far. Likely that there are lots of undescribed species. Some phyla only have 1 species in the group.

Question 27

Which phylum only has 1 species in the group? What is the name of the species?

Answer 27

Placazoa - Trichoplax adhaerens.