Transcript Bio11 Animals Lower Invertebrates Part 2

Flatworms
Planarians, Flukes, tapeworms and Nematodes
Platyhelminthes:
Flatworms
 Dorso-ventrally flattened
 Three tissue layers
 Some degree of CEPHALIZATION…Lucas!
 Sac like body plan.
 Is this good or bad?
 What might be a better option, why?
Goal for the day
 Discuss three distinct classes of phylum Platyhelminthes.
 Turbellaria: Planarians
 Trematoda: Flukes
 Cestoda: Tapeworms
 Platyhelminthes is a phylum of the kingdom Animalia.
There are approximately 20,000 different species, of
which the majority are parasitic. They live in marine,
freshwater, and damp terrestrial environments.
Platyhelminthes can be divided into four classes:
Phylum Pheatures
 Platyhelminthes are characterized as having very thin bodies between
the dorsal (back) and ventral (stomach) surfaces.
 They range in size from practically microscopic to over 20 meters long.
 Platyhelminthes have a spongy body structure because they are
acoelomates and only possess a mouth. They also lack a complete
digestive system.
 Flat worms exhibit bilateral symmetry, have no internal cavity, have
Protonephridial excretory organs rather than an anus, and have a
nervous system of longitudinal fibers.
 Flatworms do not have skeletons; however they do have an endoderm,
mesoderm, and ectoderm as well as a head region
Overview

Locomotion: have a hydrostatic skeleton, (body compartment filled with fluid). They
move mainly by contracting muscles against the hydrostatic skeleton. Flatworms have
and two layers of muscles under their skin, which assist with movement.

Respiration: lack respiratory organs, absorb oxygen through their skin by diffusion.
Respiration occurs throughout the length of the body of a flatworm.

Metabolic Waste: simple excretory system. Ammonia is excreted directly through their
skin by diffusion.

Excretory cell: "flame cell". Flame cells are hollow and have tufts of cilia; when the cilia
move, they resemble flames and force out waste products.

Circulation: They are acoelomates, meaning they lack body cavities and circulatory
organs. Circulation, like respiration, occurs through diffusion.

Reproduction: their reproductive systems are among the most complex in the animal
kingdom. hermaphroditic. One or two ovaries and numerous testes are usually present in
flatworms. Flatworms lay eggs that either hatch into tiny worms or a larval stage with
cilia.
Class Turbellaria: Planaria
 Free living and aquatic (not parasitic)
 Found in damp soils, mud, slow moving streams
Digestion and Movement
 Have Pharynx: muscular tube that acts like a mouth
 Conducts food into gastrovascular cavity (intestine).
 GVC: extends both to the anterior and posterior to
conduct nutrient throughout. (no circulatory system)
 Relies on diffusion and the body movement.
 Relies on CILIATED GLIDING for movement
 Cilia are found on ectodermal cells.
 Can also twist and tern with muscles which ‘push’ against
the MESODERM
Planaria
Get your Ganglion on.
 Posses eyes spots like our old friend clammy danny.
 Only light detectors, not actual eyes 
 These multicellular eyespots are a specialized mass of
nerve cells called a GANGLION.
 Because its located at the ANTERIOR region, and
they’re specialized, sometimes called a primitive brain.
And yeah, we’re talkin’ bout cephalization finally.
Not a ganglion…its a gang
of lions
No comment…but also
not a ganglion.
Other features
 Other features make these creatures significantly more
complex than Cnidarians:
 Cephalization
 Pair of nerves with cross branches from the eye spots
called LADDER-LIKE Nervous system
Flame Cells
 Found at the end of tubes called nephridiophores.
 Cilia beat collecting waste fluid into tubes which then
end in a pore to the outside of the organism through
nephridiopores.
Reproduction
 Hermaphrodites: ‘shed’ their sperm into the water
surrounding them through their ventral surface.
 Sperm are taken into a genital pore where ova are
fertilized
 Embryos become larvae before turning into adults.
Flukes &
Tapeworms
Trematoda and Cestoda
 Flat, and similar to
Planaria.
 Parasitic
 http://animal.discovery.
com/videos/monstersinside-me-meter-longtapeworm.html
Parasitism
 Results in two characteristics.
 How do you think a tapeworm or parasites needs and
development would different?
 1. Diminished need for specializations in: Digestion and
obtaining food, and responding to the world.
 2. Increased need for specialization for offspring
survival, transferring them to another host is ideal.
 Parasites rarely kill their hosts, why?
 Results in multi-host, polymorphic lifestyle
Parasites continued
 Tapeworms are also unique because:
 Lack cephalization. No true head
 Do have a SCOLEX: specialized hooks and suckers for
attachment to mammalian intestines
 PROGLOTTIDS or reproductive packages extend from
the scolex and have male and female sex organs. Cross
fertilization happens between tapeworms when possible.
 Scolex continuously produces immature proglottids,
which get nutrients from their environment until
developed.
Lifecycle
Nematodes
Nematodes: Roundworms

Nematodes, also called roundworms, are the
most abundant multicellular animals on Earth.
There are more than 15,000 identified species
of nematodes, and scientists are still
discovering new ones! Most nematodes are 1-5
millimeters (mm) long, but scientists have
identified a few very long nematodes, too, like
Placentonema gigantisma, an 8-meter-long
nematode found in the placenta of a sperm
whale.

All nematodes have fairly simple body plans.
These animals are tube-like in shape; have an
outer body wall, called a cuticle; and a digestive
track that runs most of the body length.
Because of this relatively simple body plan,
nematodes are sometimes described as "a tube
inside a tube.”
Decomposition

Free-living nematodes are very
important and beneficial in the
decomposition of organic
material and the recycling of
nutrients in soil. Nematode
bacterivores and fungivores do
not feed directly on soil organic
matter, but on the bacteria and
fungi which decompose organic
matter. The presence and
feeding of these nematodes
accelerate the decomposition
process. Their feeding recycles
minerals and other nutrients
from bacteria, fungi, and other
substrates and returns them to
the soil where they are
accessible to plant roots.
 Despite a simple body plan, nematodes are complex animals.
Scientific research using a variety of nematodes has been important
in understanding ecology, medicine, and basic biology. One of the
most well-studied nematodes is Caenorhabditis elegans. C. elegans
are approximately 1 mm long, are found in soils all over the world,
and feed on bacteria.
 Where can you find nematodes? Just about everywhere. They're
residents of many different habitats, including soil, plants,
freshwater, and saltwater. Some nematodes are even parasitic,
meaning they live, grow, and reproduce inside other organisms at
the expense of their host's health. Such a wide range of habitats also
means that among the various nematode species, there is a lot of
diversity in what they eat. Soil nematodes include bacterivores
(bacteria eaters), fungivores (fungus eaters), algivores (algae eaters),
and herbivores (plant eaters).
Roundworms
 No longer ventrally-dorsally flattened
 Have a tube-like intestine
 Made possible by new body cavity called a
PSDUEDOCOELOM. (*see-lum)
 Also allows for longitudinal muscles. Side to side moves.
 Flatworms are acoelomates, meaning they have NO
body cavity
 a coelom was a significant advance in animal body
structure because it repositions fluid and allows complex
tissues and organs to develop
Body plans.
Final notes
 Circulation is through diffusion: no circulatory system
 No skeletal system:
 Most excretion is through diffusion
 But complex reproductive lifecycles.
 Where do they fit in a food web?
 http://www.youtube.com/watch?v=wGj7QOP9hjk&fea
ture=related Worms are responsible for everything!