BIS2C: Lecture 27: Having a Diploblast

Slides by Jonathan Eisen for BIS2C at UC Davis Spring 2016
Lecture 27:
Having a Diploblast
BIS 002C
Biodiversity & the Tree of Life
Spring 2016
Prof. Jonathan Eisen
1

Where we are going and where we have been…
2
•Previous lecture:
•26: Animals and Sponges
•Current Lecture:
•27: Diploblasts
•Next Lecture:
•28: Triploblasts

Animal Diversity Topics
• Major Groups
• Diversity within Groups
• Key Features of Groups
!Body Plans, Forms and Symmetry
!Reproduction and Life Cycles
!Mobility
!Feeding
• Examples
3

Key Topics
• Monoblasts vs. diploblasts vs. triploblasts
• Ctenophore features
• Placozoan features
• Cnidarian features
• Cnidarian examples
!Coral
!Box jellies
4

Where we are …
!5Slides by Jonathan Eisen for BIS2C at UC Davis Spring 2016
Filasterea
Ichthyosporea

Animal Diversity
6

Animal Diversity
7
Diploblasts
Triploblasts
Monoblasts

In the diplontic life cycle, the
organism is diploid and the gametes
are the only haploid stage.
HAPLOID
(n)
DIPLOID (2n)
Zygote (2n)
Mature
organism (2n)
Gametes
Male (n) Female (n)
FertilizationMeiosis
Animal Life Cycle

Animal Life Cycle
HAPLOID
(n)
DIPLOID (2n) Zygote (2n)
Mature
organism (2n)
Gametes
Male (n) Female (n)
Fertilization
Meiosis
Monoblasts (1)
3
2
1

Animal Life Cycle
HAPLOID
(n)
Mature
organism (2n)
Gametes
Male (n) Female (n)
Fertilization
Meiosis
Diploblasts (2)
3
2
1

Animal Life Cycle
HAPLOID
(n)
Mature
organism (2n)
Gametes
Male (n) Female (n)
Fertilization
Meiosis
Triploblasts (3)
3
2
1
In the diplontic life cycle, the
organism is diploid and the gametes
are the only haploid stage.

Diploblasts
10

Ctenophores: Comb Jellies

Slides by Jonathan Eisen for BIS2C at UC Davis Spring 2016 12

• ~ 100 species, all marine, some in very deep environments.
• Radial symmetry, diploblastic
• The two cell layers are separated by a gelatinous mesoglea.
• Ctenes: comb like rows of cilia (for swimming & feeding)
• Very similar in outward appearance to cnidarians.
• Sticky, but not stinging, cells; called ‘lasso’ cells.
• 1 mm to 1.5 m in size

Placozoans

Chapter 31 Opener Did Placozoans Diverge at the Root of the Animal Tree?

Figure 31.17 Placozoan Simplicity

Figure 31.17 Placozoan Simplicity
• Small (2-3mm), diploblastic*, benthic, marine animals.
• 1 described species, asymmetrical
• No tissues, few specialized cells.
• Feed by phagocytosis
• Motile larvae
•Their relative ‘absence’ of morphological features may be secondarily
derived.

Cnidarians

Cnidarians: Some Key Features
• ~ 11,000 species
• Most are marine (salt water), a few aquatic
(fresh water)
• Features
!Gastrovascular cavity
!Cnidae; specialized collection of cells (prey
capture, defense)
!Muscle fibers and nerve nets for movement
!Two stage adult life cycle
!Specialized nematocysts
!Many species have microbial symbionts
24

Anthozoans: Sea anemones & sea pens

Anthozoans: Corals

Scyphozoan (Jellyfish) and Hydrozoan

Cnidaria: Cubozoa (box jellies)

The Life Cycle of Most Cnidarians Has Two Stages
• Planula: free
swimming larvae
• Polyp: sessile.
Produces medusa by
budding
• Medusa stage: free-
swimming; produce
gametes.

Feature I: Nematocysts Are Potent Weapons
Tentacles have specialized cells
with organelles called
nematocysts (a form of cnidae)
that inject toxins into prey
organisms.

Cnidarian Example I: Corals
33

Anthozoans: Corals

Anthozoans: Corals
• Colonial.
• Polyps secrete matrix of organic molecules on which they
deposit calcium carbonate, which forms a skeleton.
• Living polyps form a layer on top of a growing mass of
skeletal remains, which forms coral reefs and islands.
• Many grow in clear, nutrient-poor tropical waters.

Coral Symbiosis with Dinoflagellates
Corals contain symbiotic dinoflagellates (algae) called zooxanthellae

Clicker
What are dinoflagellates?

Clicker
What are dinoflagellates?
A. Eukaryotes in the Alveolate lineage
B. Eukaryotes in the Plantae lineage
C. A type of cyanobacteria
D. Small dinosaurs
E. The sister group to animals

•Most are marine and are important
photoautotrophic primary producers
•Mixture of pigments give them a golden brown color.
•Have two flagella, one in an equatorial groove, the
other in a longitudinal groove.
Alveolates: Dinoflagellates
41
Certium
tenue
Coral symbiont

Clicker
What is the minimum number of symbiotic events in the
history of the Dinoflagellate chloroplast?
A. 0
B. 1
C. 2
D. 3
E. 4

N
M
N M
C
44
Secondary Endosymbiosis

Dinoflagellate Kryptoperidinium foliaceum
http://onlinelibrary.wiley.com/doi/10.1111/j.1550-7408.2007.00245.x/full
45

N
M
Tertiary Endosymbiosis
46
N
M
N M
C

N
M
47
N
M
N M
C
Host
Symbiont
After a tertiary symbiosis

Cnidarians: Major Groups
Anthozoa Hydrozoa Scyphozoa Cubozoa
• ~ 11,000 species
• Most are marine (salt
water), a few aquatic
(fresh water)

Quaternary?
49
N
M
N
M
N
M
N M
C
Host
Symbiont

Symbiodinium in coral polyp (Porites porites)
50https://microbewiki.kenyon.edu/index.php/File:Hosttissuesection.png

Classes of symbiosis
Organism
Class of symbiosis A B
Mutualism + +
Commensalism + 0
Parasitism + -
52

Classes of symbiosis
Organism
Class of symbiosis A B
Mutualism + +
Commensalism + 0
Parasitism + -
53

Cnidaria Example II: Cubozoa - Box Jellies
55

Cnidaria: Cubozoa
!56
• Also called box jellies or sea wasps.
• Sting is very toxic, may cause death in humans.
• Some species with well-developed eyes.

Lecture 26: Cnidaria, Ctenophora
• Previous lecture:
! Bis2B
!  
!57

Another Cnidarian Symbiosis
!58
Some anemones form mutualisms
with clownfish; why do they not get
stung?
They have a protective
coating that prevents the
nematocysts from firing.

BIS2C: Lecture 27: Having a Diploblast

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BIS2C: Lecture 27: Having a Diploblast