BIS2C: Lecture 28: Lophotrochozoans

Slides by Jonathan Eisen for BIS2C at UC Davis Spring 2016
Lecture 28:
Triploblasts-Protostomes I:
Lophotrochozoans
BIS 002C
Biodiversity & the Tree of Life
Spring 2016
Prof. Jonathan Eisen
!1

Where we are going and where we have been…
•Previous lecture:
•27: Diploblasts
•Current Lecture:
•28: Triploblasts: Protostomes:
Lophotrochozonas
•Next Lecture:
•29: Triploblasts: Protostomes:
Ecdysozoans
!2

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

Lophotrochozoans
• Key Features of Lophotrochozoans
• Major Groups
• Diversity within Groups
• Examples
!Molluscs
!Annelids
!4

Animal Diversity
!5

Animal Diversity
Diploblasts
Triploblasts
Monoblasts
!6

Animal Diversity
Monoblasts
!7

Animal Diversity
Diploblasts
!8

Clicker
!9Slides by Jonathan Eisen for BIS2C at UC Davis Spring 2016

Clicker
Placozoans are really simple. Why don’t we place them at
the base of the animal tree? Why do we believe the
molecular phylogeny?
A. Molecular phylogeny is more prone to homoplasy
B. Appearances can be deceiving.
C. Organismal complexity always increases over
evolutionary time
D. Sequences cannot undergo convergent evolution

Animal Diversity
12
Triploblasts

Animal Diversity
13

Slides by Jonathan Eisen for BIS2C at UC Davis Spring 2016 14

Lophotrochozoa
!15

Lophotrochozoa
Lophotrochozoa
A lophophore circular or U-
shaped ring of hollow, ciliated
tentacles around the mouth. It
Lophophorates
!16

Lophotrochozoa
Lophotrochozoa
A trochophore is a
specialized, free-swimming
larval stage. Moves and pulls
in food by beating a band of
cilia.
!17

Lophotrochozoa
Lophotrochozoa
Zoa = Animal

Lophotrochozoa

A Few Summaries for Your Enjoyment …

Figure 32.6 Flatworms Include Both Parasites and Free-Living

Figure 32.7 Rotifers and Gastrotrichs

Figure 32.7 Rotifers and Gastrotrichs (Part 2)

Figure 32.8 Ribbon Worms

Figure 32.9 A Brachiopod’s Lophophore

Figure 32.10 Phoronids

Lophotrochozoa

Not JUST for your enjoyment …

Mollusks
• Most diverse group of Lophotrochozoans
•~90,000 species, both aquatic and terrestrial.

Mollusks: Main Features
• Bilaterally symmetrical (secondary asymmetry), coelomate
protostomes
• Reduced coelom
• Open or closed circulatory system
• Body plan: mantle, foot, and visceral mass
• Mouth with a radula (lost in some groups)

Mantle
• Fold of tissue along the dorsal surface that covers the visceral
mass and encloses the mantle cavity.
• Secretes the shell (when present).

Foot
• Large, ventral muscle mass.
• Used for locomotion, burrowing, and feeding.
• Modified as a siphon (bivalves) or tentacles (cephalopods).

Visceral Mass
•Central mass that encloses digestive, circulatory, excretory, and
reproductive organs.

Radula
• Rasping organ used for feeding.

A Few Summaries for Your Enjoyment …

Chitons
Chitons: 1,000 species.
Eight overlapping calcareous plates,
surrounded by a girdle, protect the
organs and muscular foot.
Most are marine omnivores that
scrape rocks with a radula.
They cling tightly to rock surfaces
with the large, muscular foot.

Gastropods
Gastropods: snails, slugs,
nudibranchs, limpets,
abalones; 85,000 species.
Most move by gliding on the
foot, but in a few species it is
a swimming organ.
Nudibranchs and slugs have lost
their shells. Many are toxic
and have brilliant colors for
warning (aposematic
coloration). Others have
camouflaged coloration.
Land snails and slugs are the
only mollusks that live in
terrestrial habitats.
The mantle tissue is modified
into a highly vascularized
lung.

Bivalves
Bivalves: clams, oysters,
scallops, mussels; 30,000
species.
Have hinged, two-part shells.
Many use the foot to
burrow into mud or sand.
Feed by bringing water in the
incurrent siphon and
filtering food particles with
large gills; water exits
through the excurrent
siphon.

Not JUST for your enjoyment …

Mollusk Example: Cephalopods
• Cephalopods: squids,
octopuses, nautiluses; 800
species.
• Excurrent siphon modified to
eject water pulses allowing “jet
propulsion.”
• Head with complex sensory
organs. Eyes are comparable to
those of vertebrates.
• Head has arms and/or tentacles
(modified from food) used for
predation and movement.
• Most retain a small internal shell
for internal support.
• Octopuses completely lost
shells
• Many intelligent w/ complex
communications

Cephalopods: Vision
• Single lens eye, very similar to vertebrates

Cephalopods: Outward Appearance Modification I

Cephalopods: Outward Appearance Modification II

Annelids
• ~ 19,000 species, marine
and terrestrial
• The coelom in each
segment is isolated from the
coelom in other segments.
• A separate nerve ganglion
controls each segment.
• Most have a thin, permeable
body wall that serves for
gas exchange; restricted to
aquatic or moist habitats.
.

Annelid Example: Pogonophorans (Bearded Worms)

Hydrothermal Vent
50Slides by Jonathan Eisen for BIS2C at UC Davis Spring 2016
(Image from Dive and Discover, WHOI)
Deep Ocean Seawater
Seafloor

Scientists Expected Little Life There
• No light
• Very high pressure
• Low temperatures
• Very little food
• New seafloor

http://nationalgeographic.org/media/deep-sea-hydrothermal-vents/

Teeming Ecosystem

Clicker
Tubeworm symbionts fix carbon dioxide using energy and
electrons from hydrogen sulfide (H2S).
This makes them
A. Chemolithoheterotrophs
B. Chemoorganoheterotrophs
C. Chemoorganoautotrophs
D. Chemolithoautotrophs
E. None of the above

Component Different Forms
Energy source Light
Photo
Chemical
Chemo
Electron source
(reducing
equivalent)
Inorganic
Litho
Organic
Organo
Carbon source Carbon from C1
compounds
Auto
Carbon from
organics
Hetero
Forms of nutrition (trophy)
Three main components to “trophy”

Tubeworm Anatomy
No Mouth
No Digestive Tract
No Anus
Basic Tubeworm Anatomy
But how can
they eat with no
mouth, gut, or
anus?

Colleen Canavaugh

Filled with Bacteria
Basic Tubeworm Anatomy
Dr. Colleen Cavanaugh used microscopy
techniques in 1981 and discovered billions
of bacterial cells packed inside the
tubeworm’s trophosome.
1011 bacteria per gram of trophosome!!
Plume
Trophosome

Pogonorphorans
Pogonophorans live in tubes of chitin.
Digestive tract has been lost.
They take up dissolved organic matter from
the substrate and have endosymbiotic
bacteria in a specialized organ called the
trophosome.
Hemoglobin in the tentacles imparts red
color.

Pogonophoran's
Pogonophorans were discovered in the
twentieth century in the deep oceans.
Largest are up to 2 meters long and live near
deep hydrothermal vents.
The endosymbiotic bacteria fix carbon using
energy from the oxidation of H2S.

Whale Fall Worms
• Chemoautotrophs related to beard worms with similar
features (no gut).
• Live on ‘whale falls’ the decaying remains of whales.
• Bacteria are able to metabolize bone and lipids.

http://video.nationalgeographic.com/video/hydrothermal-vents

Figure 32.11 Annelids Have Many Body Segments (Part 1)

Figure 32.11 Annelids Have Many Body Segments (Part 2)

BIS2C: Lecture 28: Lophotrochozoans

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