January 28, 2018
Chapter 10 and 11
Platyhelminthes
(triploblastic
acoelomates)
and Molluscs
Body plans review
Porifera to Annellida….
Figure 10.1 Lophotrochozoan Relationships.
Evolutionary
Perspective
• Platyhelminthes are protostomes and
lophotrochozoans
• Protostomes display spiral
cleavage, mouth develops from
blastopore
• Lophotrochozoans share:
• a lophophore, horseshoe
shaped structure used in
feeding
• OR a trochophore larval form
Platyhelminthes:
General
Characteristics
•
•
•
•
•
•
Flattened dorsoventrally
Triploblastic, acoelomate
Bilaterally symmetrical unsegmented worms
Incomplete gut
Cephalized - they have a “head”
Usually monoecious - “one house”; complex
reproductive organs
• Mesodermally derived tissue includes a loose
tissue called parenchyma
• First animals we encounter that have an organ
system of organization rather than just tissues
Phylum
Platyhelminthes
• The phylum is divided into four
classes
• The Turbellaria consist of
mostly free-living
flatworms
• The Monogenea are
parasitic
• The Trematoda are
parasitic
• The Cestoidea are
parasitic
Class Turbellaria
• Free-living flatworms in fresh and salt
water
• 3,000 species
• Includes the well-known Planaria (genus
Dugesia)
• Most active carnivores – a few eat
vegetation
• Amazing powers of regeneration – you
can cut one in half and it will become
two flatworms!
Figure 10.3 Phylum Platyhelminthes: Class Turbellaria.
• Ocelli present (simple eyespot) and
usually negatively phototactic
• Movement using both cilia and
muscular contractions
• They are able to detect food by
chemical means (chemosensory)
•
Several kinds of digestive tracts – see
fig. 10.5 – they usually begin the
digestion process outside the body
• Respiration is achieved by diffusion - no
gills or lungs or anything like that
• Waste removal also accomplished by
diffusion
Class Monogenea (flukes)
•
•
•
•
•
One egg = one adult
Mostly ectoparasites on the gills of fishes
A few found on frog bladders
One lives in the eye of a hippo…..
They are usually very species specific and site specific in
their attachment and do not have multiple host species
• Opisthaptor is used for attachment
• Flukes—mostly parasites of
vertebrates
• Medically important human
parasites
• Chinese liver fluke
• Sheep liver fluke
• Schistosome flukes (blood
flukes)
• Usually very small, up to 6 cm
• An incomplete digestive tract
is present
• Most are monoecious
Class Trematoda
• The outer body layer is a
tegument (continuous layer of
fused cells)
Figure 10.12 Class Trematoda: Subclass Digenea.
Figure 10.13 Chinese Liver Fluke Clonorchis sinesis.
Trematode parasites and amphibian
deformities
• Cestodes, or tapeworms,
are gut parasites of
vertebrates
Class Cestoidea
• Two unique adaptations
characterize the group:
• Lack a mouth and
digestive tractabsorb
nutrients across body
wall
• Most consist of a series
of repeating units called
proglottids
• each has one or
two complete sets
of reproductive
structures
Figure 10.17 Life
Cycle of the Beef
Tapeworm,
T. saginatus.
Phylum Nemertea –
Proboscis Worms
• About 900 species of proboscis worms that are
mostly marine
• Mostly live in mud and sand
• Complete digestive tract
• More advanced “circulatory” system than
platyhelminths
• Dioecious
• Some can be more than 30 m long!!
Figure 10.25
Phylum
Nemertea.
Phylum Cycliphora
• Newest phylum to be named!
• Live on mouthparts of claw lobsers
• One of the most recently
described phyla
• Members of this phylum live
on the mouthparts of the
claw lobster
• Attach via an adhesive
disc on the end of an
acellular stalk
• Very tiny animals
Phylum Cycliophora
Figure 10.26 Phylum Cycliophora.
• Characteristics:
• Body is made of 2 parts
• Calcareous shell
• Bilateral symmetry
• Trochophore larvae
• Open circulatory system
radula present and used to
scrape food
Chapter 11 - Molluscs
Movement is
accomplished
with a large
foot
The radula
moves
similar to
the treads
on an army
tank and
serves to
pick up food
• Snails, limpets and slugs
• 35,000 species
• Largest and most varied
group of molluscs
Class Gastropoda- the
stomach foot
• Gas exchange involves the
mantle cavity (notice the
little gill)
• Open circulatory system
• Hydraulic skeleton
• Have photo and
chemoreceptors
• Can be dioecious or
monoecious
Gastropods
Class Bivalvia
• Clams, oysters, mussels, and scallops
• Many are edible
• Some cam make pearls!
• Small, translucent, freeswimming
• Swim using ring of cilia
• Veliger has large, ciliated
lobes: velum
• Swimming, feeding, gas
exchange
Bivalve life cycle
• Bivalves pull food inside the
shell for digestion
• Open circulatory system
• Nerves = 3 connected
ganglia, some have
photoreceptors complete
with retina!
• Most bivalves have 2 sexes
with external fertilization the
norm
Bivalve Internal Structure
• Most complex of the
molluscs
• Most modern cephalopods
do not have a shell
• Shell is internal in cuttlefish
Class Cephalopoda
Introduced Bivalvia
Two families have been introduced from Europe – the Asian clams and the zebra and quagga mussels
http://www.fws.gov/midwest/mussel/images/zebra_mussels_on_native2_620.jpg
Reproduction
in Bivalvia
•
•
•
•
•
•
Mostly dioecious
Mostly external fertilization
Many brood the developing young
Trochophore and veliger larval stages
Glochidium is a larval stage in some species
The mussel in our area uses a “lure” to attract a
fish, then the glochidium attach to the fish
where they continue to develop and then fall
off as “minature clams”
Movement
• Predators that hunt by sight
• Have jaws with radula
• Muscular digestive tract
• Closed circulatory system
• The most sophisticated
nervous system of all
invertebrates!
• Excellent vision- similar to
that of a cat
• Two sexes- internal
fertilization
Feeding, Digestion,
Reproduction
• Eggs area attached to
substrate
• Brain to body ratio the
largest of all invertebrates,
fish, and amphibians
• They can learn via
observation
• They can be trained- to a
degree
Intelligence
The amazing cuttlefish!
• Live in shallow marine
habitats
• Important food to many
Native people
• Crawl along like a snail and
can grip tightly to rocks
• Eat algae
• Two sexes and external
fertilization
Class PolyplacophoraChitons
• 300 species of burrowing
marine animals
• Head and foot extend from
one end of the shell
• Gas exchange across the
mantle helped by water flow
through the shell
• Separate sexes
• External fertilization
Class Scaphopoda – tooth
and tusk shells
• One undivided arched shell
• They have a foot, a radula,
and gills
• Two sexes
• Most of the life history is still
unknown
• 25 species have been
described
Class Monoplacophora
• These animals are
threatened by invasive
species and diminished
water quality
• Do not form strong
attachments to substrate
and can be removed easily
• Important food resource
traditionally
Montana Native Mussels