BIS2C: Lecture 29: Triploblasts: Protostomes: Ecdysozoans I

Slides by Jonathan Eisen for BIS2C at UC Davis Spring 2016
Lecture 29:
Triploblasts:
Protostomes:
Ecdysozoans I
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:
•28: Triploblasts: Protostomes:
Lophotrochozonas
•Current Lecture:
Ecdysozoans I
•Next Lecture:
Ecdysozoans II

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

Ecdysozoa
• Key Features of Ecdysozoa
!Molting
• Major Groups
• Key Features of Key Groups
• Focus on
!Nematodes
!Tardigrades
4

Animal Diversity
5
Diploblasts
Triploblasts
Monoblasts

Animal Diversity
6
Triploblasts

Animal Diversity
7

Animal Diversity
8

Ecdysozoans
9

Slides by Jonathan Eisen for BIS2C at UC Davis Spring 2016 10

Ecdysozoan Feature #1: Cuticle and Molting
11

• Ecdysozoans have a cuticle, secreted by
the epidermis.
• For animal to grow, cuticle must be shed,
or molted, and replaced with a larger one
(a process known as ecdysis).
• Molting evolved ~500 mya, apparently only
once. All ecdysozoans have a single
common ancestor.
12

13

• In some wormlike ecdysozoans, the cuticle
is thin and flexible.
• A thin cuticle allows gas and water
exchange but restricts animal to moist
habitats.
• In arthropods, the cuticle is an exoskeleton,
thickened by proteins and chitin, a
waterproof polysaccharide.
• The exoskeleton restricts movement and
gas exchange; new mechanisms for these
functions evolved. 15

A Few Summaries for Your Enjoyment …
16

Ecdysozoans
17

Ecdysozoans

Wormlike Marine Ecdysozoans
19
Priapulids Kinorhynch Loriciferan

Wormlike Marine Ecdysozoans
• Priapulids:
!Unsegmented, three-part body plan
!Burrow in soft sediments
!Capture prey with a toothed, muscular pharynx that is
everted through the mouth
• Kinorhynchs:
!Microscopic
!Body has 13 segments, with separate cuticular plates that
are molted
!Feed by ingesting sediments through their retractable
proboscis
• Loriciferans:
!Minute
!Not discovered until 1983
!Body is covered by six plates (lorica = “corset”)
20

Ecdysozoans
21

Horsehair Worm Larvae Are Parasitic
22

Horsehair Worms
• Horsehair worms: very thin; up to a meter
in length; most are freshwater.
• Larvae are internal parasites of insects and
crayfish.
• Adult has no mouth and a reduced gut.
Some may feed only as larvae; others
continue to grow and molt, and may be
absorbing nutrients from the environment.
23

Horsehair Worms
• Horsehair worms: very thin; up to a meter
in length; most are freshwater.
• Larvae are internal parasites of insects and
crayfish.
• Adult has no mouth and a reduced gut.
Some may feed only as larvae; others
continue to grow and molt, and may be
absorbing nutrients from the environment.
• WHATEVER YOU DO - DO NOT - DO NOT
GOOGLE “HORSEHAIR WORM VIDEO”
24

Not Just for Your Enjoyment …
25

Ecdysozoans
26

Ecdysozoans
27

Clicker
Which of the following would make the
most sense to add to the UC Davis
Department of Nematology and
Entomology?
A: Plants
B: Vertebrates
C: Echinoderms
D. Annelids
E. Cnidarians
28

Clicker
Which of the following would make the
most sense to add to the UC Davis
Department of Nematology and
Entomology?
A: Plants
B: Vertebrates
C: Echinoderms
D. Annelids
E. Cnidarians
29

Animal Diversity
30

Ecdysozoans
31

Nematodes (roundworms)
!32Slides by Jonathan Eisen for BIS2C at UC Davis Spring 2016
Name from Greek:
nematos (thread)
eidos (form)

Thick,
multilayered
cuticle

Pharynx, a muscular
organ at the anterior
end, moves materials
through the gut.

Gas and nutrient
exchange occurs
through the cuticle and
the gut wall, which is
only one cell thick.

Mouthparts
modified for
specialized tasks

Brain

• Extremely abundant and universally
distributed.
• >25,000 species described.
• Includes scavengers, parasites, predators
• Many are microscopic; the largest is 9 meters
long—a parasite in placentas of female
sperm whales.
• Reduced musculature and digestive system
(pseudocoelom)
38
Nematode Features

• Caenorhabitis elegans is used as a model
organism in genetics and developmental
biology research.
• It is easy to cultivate, matures in three days,
and has a fixed number of body cells.
39
Nematode Example: C. elegans

Clicker
From an evolutionary point of view, which
of the following is the best candidate for a
model organism to compare with humans
A. C. elegans (Nematode)
B. Fruit fly (Arthropod)
C. Giant squid (Cephalopod)
D. Earthworm (Annelid)
E. All are equally good
40

Clicker
From an evolutionary point of view, which
of the following is the best candidate for a
model organism to compare with humans
A. C. elegans (Nematode)
B. Fruit fly (Arthropod)
C. Giant squid (Cephalopod)
D. Earthworm (Annelid)
E. All are equally good
41

Animal Diversity
42
Triploblasts

• Whatever you do  
 
DO NOT - I REPEAT DO NOT- GOOGLE -
GIANT NEMATODE SLITHERING DEAD
SPIDER
44

Root-Knot Nematodes
45
• Meloidogynes nematodes infect root systems of plants
• The nematodes cause galls where juvenile worms develop

• WARNING THE NEXT FEW SLIDES
COULD GROSS PEOPLE OUT
46

Nematode Example: Filarial Diseases
47
• Caused by several different parasitic nematodes and
transmitted by mosquitoes
• Infect lymph nodes, which can then get blocked. This leads to
edema (swelling) and other problems.

Nematode Example: Filarial Diseases
48
HOW CAN WE TREAT THESE DISEASES?

Opisthokonts
Opisthokonts
Fungi
Animals
Choanoflagellates
Shared derived traits of clade?

Anti fungal drugs
50
http://www.slideshare.net/drjankiborkar/antifungals-14155209

!51
Filasterea
Ichthyosporea
Microsporidi
Chytrids
Zygospore
Arbuscular
Sacfungi
Clubfungi
Dik
It’s Always More Complicated III

!52
Filasterea
Ichthyosporea
Microsporidi
Chytrids
Zygospore
Arbuscular
Sacfungi
Clubfungi
Dik
Humans & Nematodes Much Closer than Humans and Fungi
HumansNematodes

http://www.worldbank.org/en/news/video/2014/06/30/treating-river-blindness-
and-other-neglected-tropical-diseases

2015 Nobel Prize in Medicine
54

But …
55

Wolbachia
56
http://www.theatlantic.com/science/archive/2015/10/ivermectin-nobel-drugs-elephantiasis-filariasis-nematodes-wolbachia/
409306/
Ed Yong

The avermectins that Campbell and Ōmura
discovered, and especially their most potent
member ivermectin, can control the symptoms
of these diseases by killing the larval
nematodes. But they aren’t cures, because
they don’t damage the astonishingly sturdy
adults. And since these worms can live for a
decade, and can release thousands of new
larvae every day, their hosts must resign
themselves to years of regular treatments.
http://www.theatlantic.com/science/archive/2015/10/ivermectin-nobel-drugs-
elephantiasis-filariasis-nematodes-wolbachia/409306/

Filarial Nematodes Permanently House Wolbachia
58

And unfortunately, this means that killing the
worms would make everything much worse,
because they’d release all their Wolbachia in
their death throes. “You get exploding nodules,
and scrotal inﬂammation,” he told me. “You don’t
want that. You want to kill the worms slowly, and
it’s hard to think how you’d do that with an anti-
nematode drug.”

What Would You Use to Kill Wolbachia?
60

Ecdysozoa
61

Tardigrades
62

Tardigrades (aka water bears)
• Fleshy, unjointed
legs
• Use a fluid-filled
body cavity as a
hydrostatic skeleton
• Extremely small
• No circulatory or gas
exchange systems
• Live in marine sands
and on water films
on plants
63

• When water films dry up, tardigrades lose
water and shrink to form a dormant state
that can last at least a decade.
• Tardigrades have been found at densities
as high as 2 million / m^2 of moss.
66
Tardigrades

Velvet worm
67

Onychophorans (velvet worms)
• Live in leaf litter in the humid tropics
• Thin, flexible cuticle
• Use fluid-filled body cavity as a hydrostatic
skeleton
• May look similar to arthropod ancestors
68

Figure 32.19 A Trilobite Fossil
69

BIS2C: Lecture 29: Triploblasts: Protostomes: Ecdysozoans I

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