Origins of Animals Flashcards
What is an animal?
Metazoans that eat, move, and possess collagen.
Animals undergo a developmental stage called blastula, a fluid-filled ball of cells.
What is the significance of cell specialization in animals?
It differentiates eukaryotic animals from single-celled protists, allowing for a division of labor.
This includes structured gene expression.
What does Ecdysozoa refer to?
Ecdysis, the shedding process in invertebrates.
Ecdysozoa is a major clade of animals that undergo this process.
What are the evolutionary pressures that led to multicellularity?
- Division of labor
- Increased size
- Efficiency
- Predation and environmental tolerance
These pressures drive the evolution of complex multicellular organisms.
What are the hypotheses for the origin of multicellularity?
- Symbiotic
- Colonial
- Cellularization
Each hypothesis presents a different mechanism for how multicellular organisms may have arisen.
What does the colonial hypothesis suggest about multicellularity?
Unicellular organisms undergo mitosis and remain attached, leading to specialized cells.
Over time, these cells form a complex animal.
Who are the first animals identified in evolutionary history?
Choanoflagellates, which are single-celled protists with long flagella.
Choanocytes in sponges are similar to choanoflagellates.
What is the order of geological periods in the history of animal life?
- Precambrian
- Ediacaran
- Cambrian
- Ordovician
- Silurian
- Devonian
- Carboniferous
- Permian
- Triassic
- Jurassic
- Cretaceous
- Tertiary
An anagram to remember these periods is: ‘Camels Only Sit Down Carefully Perhaps Their Joints Creak Too.’
What is the Burgess Shale known for?
An explosion of biodiversity approximately 540 million years ago.
Located in Canada, it contains a vast number of organism fossils from the Cambrian period.
What were some causes of the Cambrian explosion?
- Global climate change
- Rising O2 levels
- Mass extinction
- Rapid evolutionary cascade due to predatory interactions
These factors contributed to the rapid diversification of life forms.
What are the key characteristics of Phylum Porifera?
- Sessile and immobile
- Filter feeders
- No symmetry
- No nerves or muscles
- No organs or discrete tissues
Porifera means ‘pore bearing’, reflecting their structure.
What is the structure of a sponge?
- Inner layer: choanocytes
- Outer layer: pinacocytes
- Non-cellular matrix: mesohyl
- Water flows in through Ostia
- Atrium: empty space
- Water exits through Osculum
- Spicules: made of calcite or silica
These components work together for filter feeding.
How many species of sponges exist and what are the three classes?
15,000 species divided into:
* Hexactinellida (glass sponges)
* Calcarea (calcareous spicules)
* Demospongiae (silicaceous spicules)
Hexactinellida are often found in deep water and have no cell boundaries.
