Invertebrate Phylogeny Flashcards
How many invertebrate phyla are there?
35 (or so)
Which is the most species rich phyla?
Arthropods
Which is the most abundant phyla?
Nematodes
What is classical animal phylogeny based on?
4 major splits in body plan
What is the 1st split in traditional animal phylogeny? What splits off at this step?
Parazoans (no true tissues)
or
Eumetazoa (all other animals).
Splits off Porifera (sponges).
What is the 2nd split in traditional animal phylogeny?
Radial symmetry (split two ways)
or
Bilateral symmetry (split one way, associated with cephalisation)
What is cephalisation?
Development of a head.
What is the 3rd split in traditional animal phylogeny?
No body cavity (Acoelomate)
or
Cavity partially lined with mesoderm (Pseudocoelomate)
or
cavity completely lined with mesoderm (Coelomate)
Give an example of an acoelomate.
Platyhelminthes - flatworms
What is the disadvantage of not having a body cavity?
Reduced flexibility, body essentially solid.
What is the 4th split in traditional animal phylogeny?
Protosomes
or
Deuterostomes
Give examples of phyla which are protostomes.
Molluscs, annelids, arthropods.
Give examples of phyla which are deuterostomes.
Echinoderms, chordates.
What makes an organism a protostome?
Cleavage spiral and determinate. Different origins of coelom to deuterostomes. Fate of blastophore - mouth is formed first, then anus.
What makes an organism a deuterostome?
Cleavage radial and indeterminate. Different origins of coelom to protostomes. Fate of blastophore - first forms anus, then mouth.
Which of the factors used in traditional animal phylogeny are useful nowadays and which are not?
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.
What is new animal phylogeny based on?
Sequencing of SSU-rRNA.
Are “worms” a phylogenetic group?
No, just a body plan but can be unrelated.
How can the relatedness of species to one another be determined?
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.
What is an example of a phyla that looks like a worm, but isn’t?
Pentastomida (parasite worms) look like worms, but are crustaceans.
What is an example of a group that are protostomes, but develop like deuterostomes?
Penis worms
How can modern phylogeny be further split after the fate of blastophores?
Ecdysozoans or not.
Includes arthropods and nematodes that both shed cuticle periodically with growth (ecdysis).
What is ecdysis and what phyla do this?
Shedding of cuticle periodically with growth. Done by arthropods and nematodes.
What are the closest living relatives of vertebrates?
Tunicates (sea squirts) (disproves inverts as a separate group)
Are invertebrate phyla comparable in terms of described species groups?
No - arthropods are most species rich by far.
Are invertebrate phyla comparable in terms of numbers of organisms in groups?
No - nematodes most abundant by far. Likely that there are lots of undescribed species. Some phyla only have 1 species in the group.
Which phylum only has 1 species in the group? What is the name of the species?
Placazoa - Trichoplax adhaerens.
