Lecture 12 - What are animals?

Question 1

What is an animal

Answer 1

Multicellular eukaryote without a rigid cell wall

Motile (at some stage)

Blastula (hollow sphere of cells) in development – the way that cells divide and the fate of the blastopore are both very significant

Question 2

The first animal

Answer 2

Dickinsonia, a large animal for its time period

Question 3

The porifera phylum

Answer 3

Around 5000 species of sponge

• Mainly marine, but around 150 freshwater species
• Mainly found in tropical seas, but can account for 75% of biomass on Antarctic sea floor
• Incredibly successful

Question 4

Choanocytes

Answer 4

Contain specialised flagella

Question 5

How do sponges affect nutrient cycling in the ocean

Answer 5

Appearance of sponges alters carbon and phosphorous cycling in ocean. Anoxia supports P recycling, as bottom becomes oxygenated, P removed into sediments.

Question 6

Cladorhizidae

Answer 6

Carnivorous sponges

Question 7

Phototaxis

Answer 7

The bodily movement of a motile organism in response to light, either towards the source of light (positive phototaxis) or away from it (negative phototaxis)

Question 8

Large sponges and phototaxis

Answer 8

Cilia on photosensitive cells allow phototaxis to occur

Question 9

Ephydatia muelleri: how it deals with surrounding substances in the environment

Answer 9

This species is able to “sneeze” by ejecting waste and mucus so that substances in the environment are removed

Question 10

GABA

Answer 10

Gamma-aminobutyric acid is an amino acid that functions as the primary inhibitory neurotransmitter for the central nervous system

It functions to reduce neuronal excitability by inhibiting nerve transmission

Question 11

Reorganisation of sponges

Answer 11

Sponges can reconstitute themselves

• Break up sponge into cells
• Allow it to sit, ends up re-forming
• Odd behaviour for an animal, but based on recognition of self

Question 12

The most ancient animal

Answer 12

Sponges as most ancient lineage seems the most likely, but genetic data have suggested Ctenophores first, which would mean neurons and muscles evolved twice.

Question 13

Cnidaria: how many species are in the phylum, what is the origin of the name, what features suggest it’s more advanced than sponges and ctenophores?

Answer 13

Contain around 9000 species

“Cnidos” = nettle. Stinging nematocysts presumed to be ancestral

Seems to be more advanced than ctenophores and sponges as they have tissue level organisation

Contain a nerve net with neurotransmitters but myelin not present so synapses can go both ways

Question 14

Nematocysts: what are they?

Answer 14

Specialized cells in the tentacles of a jellyfish or other coelenterate, containing a barbed or venomous coiled thread that can be projected in self-defence or to capture prey.

Question 15

How do Cnidaria use nematocysts?

Answer 15

Nematocysts opens, revealing stylet held in place by collagen, releases with pressure of a bullet, at 2 m/sec, which fires poison (NB some coil round prey)

Question 16

Siphonophores

Answer 16

Colony organism (no alternation of generations, Identical individuals, reproduced clonally to form colony)

Components are called ‘zooids’, and are a mixture of polyps and medusas

Ocean drifters, incapable of movement by themselves

Question 17

Polyp stage in Cnidaria

Answer 17

Polyps are sessile (immobile) and asexually reproduce by budding

Question 18

Medusa stage in Cnidaria

Answer 18

Medusa reproduces sexually by producing sperms and eggs and free-swimming

Question 19

Anthozoa: what phylum does the class belong to, what species are included, and what is the anatomy?

Answer 19

Cnidaria

Sea anemonies and corals

Tentacles, mouth, pharynx, transverse muscles, longitudinal muscles (on CM), basilar muscle, complete mesentry, incomplete mesentry, pedal disc (as an anchor)

Question 20

Corals: what are they, what are they made of, and what are the challenges for corals nowadays?

Answer 20

Corals are invertebrate animals belomging to the Cnidaria phylum, they get their food from algae living in their tissues (often a unique partnership with tiny algae called zooxanthellae - the algae live within the coral polyps, using sunlight to make sugar for energy) or by capturing and digesting prey

They are made of calcium carbonate which is formed by carbon dioxide dissolving and reacting with water to form carbonic acid, which then reacts with calcium to form calcium carbonate

Subject to acidification and rising sea levels: with a lower pH, there is less carbonate available and with higher sea levels, more sediment is deposited on top of the corals, which may lead to coral smothering