Lecture Fifteen - Animal diversity I

Question 1

How does the development from a zygote work?

Answer 1

Blastula -> Gastrula -> Life stages.

Diploblastic - 2 germ layers - ectoderm and endoderm.

Triploblastic - 3 germ layers - mesoderm added.

Question 2

What are the points of agreement for the relationaships between phyla?

Answer 2

All animals share a common ancestor.

Sponges (porifera) are the odd ones out.

All other animals (Eumetazoa) have tissues.

Most animal phyla belong to the monophyletic clade “bilateria.”

Question 3

Draw and explain the diversity tree of animals.

Answer 3

Metazoa (e.g. porifera).

Eumetazoa.

• Radial (e.g. cnidaria).
• Bilateral.

Bilateria.

• Protostomes and Deutrostomes.

Protostomes.

• Ecdysozoa -> Pseudocoelomates (e.g. nematoda) and Coelomates (e.g. arthripoda).
• Lophotrochozoa -> Acoelomates (e.g. flatworms) and Coelomates (e.g. annelids).

Deutrostomes (e.g. chorates).

Question 4

What are sponges, and what makes the weird?

Answer 4

From lineage of Metazoa.

Believed to have evolved from choanoflagelates, due to similar collar cells and homologous sequences of DNA.

Sedentary animals.

Mostly marine (some fresh water).

Cell aggregates:

• Several cell types.
• No true tissues.
• Lack organs = no muscles or nervous system.
• No symmetry.
• Free exchange between cells of nutrients, waste and gasses.

Suspension feeders - water flow by cilia.

Sequential hermaphrodites.

Lack organ systems due to the free exchange between cells and the environment (thin layer of cells so that all cells are in contact with outer environment).

Sponge anatomy:

Hollow case:

• Spongocoel.
• Pours.
• Osculum.

Connective material:

• Mesophyl (spoungin/collagin).

Specialised cell types:

• Collar cels.
• Amoebocytes.

Question 5

What are phylum cnidaria? (Jelly fish, corals and anemones).

Answer 5

Eumetazoans.

Radial symmetry.

Body plan:

• Sac like bodies.
• Tentacles.
• Gastroventricular cavity (mouth and gut but no anus).

Two forms:

• Sessile polyps (fixed to surface, stationary).
• Mobile medusa (sexual phase, can move).

Two layers (diploblastic):

• Epidermis (ectoderm).
• Gastrodermus (endoderm).

Carniverous:

• Tenticles around mouth.
• Defence and prey captured, hair trigger, stinging thread, toxins.

Move by compression of muscles against water, which cannot be compressed, thus acts as a sort of skeleton.

Question 6

Describe a Cnidarians life cycle.

Answer 6

1) Male and female medusa produce haploid egg and sperm.
2) After fertilizatio, zygote developes into a free floating larval stage.
3) When larvae finds its substrate, it attaches ad developes into a coral like structure that contains both feeding polyps and reproductive polyps.

Polyps typically cluster to form colonies.

4) Polyp reproduces asexually via mitosis, forming offspring in the form of medusa.

Question 7

What are the basic features of animals?

Answer 7

Symmetry (bilateral or radial).

Cephalisation (development of sensory features at the front of the body).

Body cavity (coelom).