Section 29.3 (Exam 2) Flashcards
The Root of the Animal Tree Provides Clues to Early Animal Diversification
What are the two major bilaterian goups?
Protostomes and Deuterostomes
What are some bilaterian synapomorphies?
Anterior-posterior axis
Triploblastic
Centralized nervous system
Name the 6 members of the non-bilaterian groups. (Monoblastic and diploblastic as well.)
Glass sponges
Demosponges
Calcareous sponges
Ctenophores
Placozoans
Cnidarians
What are the characteristics of sponges?
Monoblastic, asymmetrical
Some specialized cells, but no true organs
They have spicules as skeletal elements
Mostly marine and filter feeders
Built around a water canal system
Made of choanocytes
What are the three types of sponges
Glass sponges
Demosponges
Calcareous sponges
Glass sponges and demosponges have spicules made of _______________.
silicon dioxide
Calcareous sponges have spicules made of __________________.
calcium carbonate
Describe the sponges water canals. How is water brought in? How does it help sponges eat food?
Water is brought into canals by beating choanocyte flagella. Choanocytes then capture food particles from this water.
The body plan of sponges is an aggregation of _____________________________.
cells around a water canal system
How do sponges reproduce?
Asexually through budding and fragmentation.
They can also reproduce sexually by releasing their gametes (sperm and egg) into the water, and the water carries them to one another.
Can sponges self-fertilize?
Sponges cannot self-fertilize.
What are Ctenophores also known as?
comb jellies
What are some characteristics of ctenophores?
Radially symmetric, diplobastic
Two cell layers separated by a gelatinous mesoglea
Complete gut
Have ctenes
Ctenophores may have been the earliest lineage to split from other animals. Which other group were ctenophores thought to be closely related to?
Cnidarians
What are ctenes?
comb-like rows of cilia
How do ctenophores move?
They move through the water by beating the cilia of their ctenes.
How do ctenophores feed?
Ctenophores have feeding tentacles. These tentacles have cells that discharge an adhesive which can capture prey.
What do ctenophores eat, and where do they live?
Ctenophores feed on planktonic organisms.
They are all marine.
What are the characteristics of Placozoans?
4 distinct cell types, diploblastic
Their mature stage is asymmetrical
No mouth, gut, or nervous system
Placozoans were once thought to be the sister group of all other animals, but this isn’t supported by _____________________.
phylogenetic analyses
Placozoans aspects of structural simplicity may be secondarily derived. What does this imply?
Placozoan ancestors were more complex.
What are the 3 groups of cnidarians?
Anthozoans (sea anemones, sea pens, and corals)
Scyphozoans (jellyfish; all marine)
Hydrozoans
What are some common characteristics of cnidarians?
Mostly marine
Gut is blind, with one opening, also functions as a gastrovascular cavity
Incomplete gut; Two-staged life cycle
Tentacles have nematocysts
What is the function of a gastrovascular cavity in cnidarians?
digestion, circulation, gas exchange, and as a hydrostatic skeleton
Why is the cnidarian gut considered incomplete?
It only has one opening
What are the two stages of the cnidarian life cycle?
Polyp and medusa
How do polyps reproduce?
They produce male or female medusae asexually via budding of the mature polyp.
How do medusa reproduce?
They produce polyps sexually.
What does the fertilized egg of cnidarians develop into before becoming a polyp?
A free-swimming ciliated larva called a planula
What is a planula?
A free-swimming ciliated larva
How does a planula become a polyp?
The planula, or free-swimming ciliated larva, settles to the ocean floor and grows into a polyp.
Cnidarian tentacles have nematocysts. What are nematocysts?
Specialized cells that inject toxins into prey organisms. These cells also have a stylet, or a barb, that keeps them anchored to the prey.
Which organisms are considered anthozoans?
Sea anemones, sea pens, and corals.
Name a characteristic of sea anemones that they don’t share with all other anthozoans.
They are solitary
Name a characteristic of sea pens that they don’t share with all other anthozoans.
They are colonial with two types of polyps.
What are the two types of polyps that sea pens have?
Primary polyps that anchor in the sediments
Secondary feeding polyps that are produced by budding
Name some characteristics of corals.
sessile; colonial
polyps secrete matrix of organic molecules, aids in skeleton formation
living polyps form on top of skeletal remains of other corals
How do coral skeletons form?
Coral polyps secrete a matrix of organic molecules on which they deposit calcium carbonate, which forms a skeleton.
How are coral reefs formed?
Living polyps form a layer on top of a growing mass of skeletal remains, which forms coral reefs and islands.
Where do corals grow?
Shallow, nutrient-poor, tropical waters.
How can corals survive in nutrient-poor and shallow waters?
Endosymbiotic dinoflagellates live within them. All they need for energy is sunlight.
Why do coral reefs need clear surface water?
If the surface of the water is obstructed, the corals will not receive enough sunlight for their dinoflagellates to produce enough energy.
Why are coral reefs threatened by rising CO2?
Increasing ocean temperatures and ocean acidification. (decreasing pH)
Why is increasing ocean temperatures and ocean acidification bad for corals?
Ocean warming causes coral bleaching.
Acidification can cause calcium carbonate skeletons of corals to dissolve.
Why is excess nitrogen in runoff bad for corals?
It can lead to overgrowth of algae, which can suffocate corals—eutrophication
Which organisms are considered scyphozoans?
jellyfish
Name some characteristics of scyphozoans.
All marine
Medusa stage dominates, individuals can be male or female
Fertilized egg becomes planula
What are some characteristics of hydrozoans?
Polyps usually dominate, but some have only medusae
Mostly colonial, connected polyps share one gastrovascular cavity
Some polyps specialized for feeding, other produce medusae
How do the medusae in a hydrozoan develop?
Asexually within an enlarged secondary reproductive polyp.
