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

Where we are going and where we have been…

•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

Key Topics

• Monoblasts vs. diploblasts vs. triploblasts

• Ctenophore features

• Placozoan features

• Cnidarian features

• Cnidarian examples !Coral !Box jellies

Where we are …

!5Slides by Jonathan Eisen for BIS2C at UC Davis Spring 2016

Animal Diversity

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

HAPLOID (n)

DIPLOID (2n) Zygote (2n)

Monoblasts (1)

Animal Life Cycle

HAPLOID (n)

Diploblasts (2)

Animal Life Cycle

HAPLOID (n)

Triploblasts (3)

In the diplontic life cycle, the organism is diploid and the gametes are the only haploid stage.

Diploblasts

Ctenophores: Comb Jellies

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

Ctenophores: Comb Jellies

• ~ 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

• 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

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

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

Certium tenue

Coral symbiont

Clicker

What is the minimum number of symbiotic events in the history of the Dinoflagellate chloroplast?

Clicker

What is the minimum number of symbiotic events in the history of the Dinoflagellate chloroplast?

Secondary Endosymbiosis

Dinoflagellate Kryptoperidinium foliaceum

http://onlinelibrary.wiley.com/doi/10.1111/j.1550-7408.2007.00245.x/full45

Tertiary Endosymbiosis

N MN M

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?

N MN M

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 + -

Classes of symbiosis

Organism

Class of symbiosis A B

Mutualism + +

Commensalism + 0

Parasitism + -

Cnidaria Example II: Cubozoa - Box Jellies

Cnidaria: Cubozoa

• 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 !

Another Cnidarian Symbiosis

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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