Biodiversity 2: Parazoa and Radiata Flashcards
What does ‘animals are monophyletic’ mean?
It means they have a single common ancestor
What was the first key branch point in animal evolution?
Gastrulation results in at least 2 tissue layers (endoderm.ectoderm) vs no gastrulation
→ Separates Parazoa (sponges) from everything else
Why are parazoa very unspecialsed?
Because they are neither radially or bilaterally symmetrical
What was the second key branch point in animal evolution?
Radial vs bilateral symmetry
→ separates Radiata (e.g jellyfish) from Bilateria
Describe Radiata
- Have oral/aboral side
- Dipoblastic (2 tissue layers)
Describe Bilateria
- have anterior/posterior and dorsal/ventral sides
- triploblastic (3 tissue layers)
What was the third key branch point in animal evolution?
Patterns of cleavage, coelom formation and mouth/anus formation
→ separates protosomes and deutrostomes
Give some examples of Protostomes
mollusks, annelids, arthropods
What are protostomes patterns of cleavage?
Spiral and determinate
When is cell fate determined in protostomes?
Cell fate determined early in development
Which phylums are deuterostomes?
Chordata, echinoderms
What are deuterostomes patterns of cleavage?
Radial and interdeterminate
When is cell fate determined in deutrostomes?
Cell fate is not determined early = early cells can develop into any cell type
Describe deutrostomes coelom formation
Folds of archenteron form coelom
What is the function of the coelom?
protects organs, allows organ growth
Describe protostomes coelom formation
Solid mass of mesoderm splits to form coelom
Describe the fate of the blastopore in protostomes
Mouth forms first from the blastopore, anus 2nd
Describe the fate of the blastopore in deutrostomes
Anus forms first from the blastopore, mouth 2nd
What was the fourth key branch point in animal evolution?
Division of protostomes
→ Separates Lophotrochozoa and Ecdysozoa
Describe Lophotrochozoa larvae
Have a crown of cilia (lophophore) on their trochophore larva
What are the differences that separate the Lophotrochozoa and Ecdysozoa?
Lophotrochozoa - have specific type of larvae (with a lophophore)
Ecdysozoa - shed their exoskeletons (ecdysis)
Which phylum belongs to the sub-kingdom Parazoa?
Porifera (sponges)
Describe the Parazoa
Asymmetrical → lack a body axis
No gastrulation
= No true tissues
Describe the porifera (sponges)
Simple body plan
Lack muscles, nervous system, organs
Sessile → don’t move and feed passively
Some specialised cells
Describe how the Porifera feed.
- Water drawn into central space (spongocoel) through pores (porocytes) in the sponge wall
- Drawn in through the action of flagella
- Water passes out through top of sponge (osculum)
- Choanocyte (specialised feeding cells) line spongocoel
- Amebocytes distribute food to rest of the sponges cells
Porifera contain amebocytes. What is their other role, aside from food distribution?
Amebocytes also secrete calcium or silica spicules = form sponge framework, gives rigidity
Describe the radiata
Radial symmetry
Diploblastic (2 tissue layers)
Which phylum belongs to the sub-kingdom Radiata?
Cnidaria (hydras, jellyfish, sea anemones, corals)
Describe Cnidaria
Simple form → most ingest food into a blind sac with a gastrovascular cavity
Mouth = anus
Polyp (mouth up) or medusa (mouth down)
No brain, but simple nerve network → can detect stimuli
Contractile bundles of microtubules act like muscles
What are the two forms in Cnidaria?
Polyp (mouth up) or medusa (mouth down)
- Sometimes a species will have both forms at different life stages
What is the gastrodermis in Cnidaria?
Gastrodermis = absorbs food
What is the mesoglea in Cnidaria?
Mesoglea = jelly
In Cnidaria, what are the tentacles covered in?
cnidocytes
What is the function of cnidocytes?
Used for defence and prey capture
Nematocyst triggered = wraps around prey and injects venom
- Diverse, some have spines/no spines, some have
long threads that stick to prey or entangle small animals
What are the 4 groups of Cnidaria?
Anthozoans, Scyphozoans, Cubozoans, Hydrozoans
Describe the anthozoans
Anemones & corals
- Polyp stage only
- On the whole, sessile
Describe the scyphozoans
True jellyfish
- Medusa form dominates (might be a polyp when young)
- Free swimming
Describe cubozoans
Box jellyfish
- Larval polyp stage v different to ‘true jellies’
- Umbrellas cuboid = more streamlined, can move rapidly (7 km/hr)
- Nervous system more developed, complex eyes on rims of bells
- Can see points of light = active predators
- Many are poisonous (Indo-Pacific Sea wasp is most poisonous)
Describe the hydrozoans
Hydra, Portuguese Man o’ War, Immortal jellyfish
- Most are colonies of animals
- Some have only medusae / polyps
