1. Phylum Platyhelminthes
Lecture #11
Worms, Worms & Worms
Phylum Platyhelminthes
Phylum Nematoda
Phylum Annelida

2. Current Molecular Classification
Clade Lophotrochozoa:
Phylum Platyhelminthes - worms
Phylum Annelida - worms
Phylum Mollusca – clams, scallops, squids, snails etc…
Clade Ecdysozoa:
Phylum Nematoda - worms
Phylum Arthropoda – crustaceans, spiders & insects

3. Phylum Platyhelminthes
flatworms – 20,000 species
“platy” – flat
“helminth” = worm
unsegmented flatworms
novel developments (vs. Sponges and Cnidarians):
development of bilateral symmetry and three embryonic (triploblastic) tissues in these worms
development of a head-like region = cephalization
development of an excretory system = protonephridia

4. Phylum Platyhelminthes
flatworms are divided into two lineages
A. Non Parasitic
Class Turbelleria (free-living)
B. Parasitic:
Class Monogenea (ectoparasitic)
Class Trematoda (parasitic) = flukes
Class Cestoidea (parasitic) = tapeworms

5. Features common to Phylum Platyhelminthes
1. triploblastic
three germ layers: ectoderm, mesoderm and endoderm
mesoderm  muscle
2. bilateral
3. flattened body plan
thin
4. acoelomate
5. protonephridia for an excretory system
6. no circulatory or respiratory system
exchange by diffusion
7. incomplete digestive system
mouth, no anus
8. most are hermaphroditic (monoecious)

6. Features common to all flatworms
protonephridia for osmoregulation (water balance)
for the flatworms – influx of water into their bodies from their environment
this excess water is removed through protonephridia
comprised of flame cells or flame bulbs that draw the water in and expel it back to the outside

7. Class Turbellaria free-living flatworms – e.g. Planaria & Dugesia
marine and freshwater
bottom dwellers
over 4,500 species to date
less than 1 cm long in most species
free-living species are shades of black, brown and gray
larger species can be brightly colored

8. Class Turbellaria incomplete digestive system
most turbellarians are carnivorous and feed on small invertebrates or scavenge dead animals
both extracellular and intracellular
food enters the pharynx – enzymes secreted into the pharnyx for extracellular digestion
food enters the intestine where cells phagocytose smaller food particles and complete digestion intracellularly

9. tubellarians have net-like nervous system (like most flatworms)
nerve trunks that run the length of the body
neurons organized as sensory and motor and association – seen in higher order animals like humans
accumulation of neurons near the head – function as a brain
also have two auricles – have neurons for detecting chemicals
two eyespots called ocelli at the head for detecting light

10. Class Turbellaria
Asexual reproduction: reproduce asexually via transverse or longitudinal fission
regenerate the missing body regions once they separate
head regeneration:

11. Class Trematoda 8,000 species parasitic flatworms called flukes
wide, flat shape to oval or elongate
body plan: like the turbellarians in structure
large intestine that splits into two tubes
hermaphroditic
outside is covered with an organic layer of proteins + carbohydrates = glycocalyx
can help evade the host’s immune system

12. Flukes: e.g Clonorchis sinensis – liver flukes
attachment through an oral sucker that surrounds the mouth
a second sucker – acetebulum – located ventrally in the middle of the body
e.g Clonorchis sinensis – liver flukes
infects 30 million people annually – mostly in Asia
adult flukes live in the human liver – definitive host
life cycle also requires an intermediate host – usually a mollusc
e.g. Schistosoma – blood flukes
e.g. Paragonimus – lung fluke
e.g Clonorchis sinensis – liver flukes

13. Schistosoma – blood flukes
adult flukes live in the human bloodstream
dioecious – males are shorter and thicker
female is long and slender – carried in a ventral canal on the male
life cycle
1. copulation is continuous – constantly mating pairs of worms (female, smaller & thinner)
2. eggs are released in feces and releases miracidia into freshwater
3. penetrates a snail to continue it life cycle
4. larval form leave the snail and penetrate human flesh (creates a rash)
5. once in humans the larvae form adults

14. Class Cestoidea tapeworms 3,500 species
endoparasites – vertebrate digestive system
1 mm to 25m in length
nearly all monoecious
lack a mouth and digestive tract
absorb nutrients by diffusion
consist of a long series of repeating units called proglottids (repeating reproductive segments)
attachment by a scolex – holdfast that attaches the worm to its host
live in a very stable environment – intestinal tract has few variations

15. proglottids are filled with reproductive structures (male and female)
devoted to making eggs
BUT the male organs mature before the female – no self fertilization
fertilized eggs accumulate in the uterus (black under the microscope)
the further back in the tapeworm – the more mature the proglottid and the more eggs
the oldest proglottids filled with eggs = gravid proglottid
gravid proglottid breaks off from the worm and breaks open to release the fertilized eggs
the lost proglottid is remade up near the neck

16. beef tapeworm – Taenia saginata
adults live in small intestine
may reach lengths of 25 meters!!
80,000 eggs per proglottid
eggs released in human feces
egg develops and forms a 6 hooked larva called the onchosphere
intermediate host – cattle
onchospheres travel from the gut to the skeletal muscle where they encyst over long periods of time
when eaten by humans releases the worm into the human bloodstream – scolex attaches to the intestine wall of the human
oncospheres

17. Phylum Annelida characteristics: 1. segmented – into metamers
2. bilaterally symmetrical
3. coelomate
4. closed circulatory system
large vessels that function as hearts
series of vessels closed off from the tissues
circulatory fluid = blood
gas exchange by capillary beds
5. complete digestive system
mouth --> storage crop  grinding gizzard  absorptive intestine  anus
6. excretory system – pairs of nephridia in each segment
7. well developed longitudinal and circular muscles
for locomotion =

18. excretion by nephridia
filters body fluid
minerals and water reclaimed and put back into the bloodstream
wastes expelled to the outside
very similar to the vertebrate nephron

19. Phylum Arthropoda characteristics:
1. metamerism – segmentation PLUS specialization of body segments for specific functions
2. chitinous exoskeleton for support and protection
growth achieved through molting
number one reason for arthropod success
3. paired, jointed appendages
4. open circulatory system & complete digestive tract
5. metamorphosis often seen to achieve sexual maturity

20. Phylum Arthropoda 4 subphyla 1. Subphylum Chelicerata
Class Merostomata – horseshoe crabs
Class Arachnida - spiders
Class Pycnogonida – sea spiders
2. Subphylum Crustacea – 6 classes
Class Branchipoda – brine shrimp
Class Malacostraca – shrimp, lobsters, crab, crayfish
Class Maxillopoda – copepods and barnacles
3. Subphylum Hexapoda
insects
4. Subphylum Myriapoda
millipedes and centipedes

21. Subphylum Chelicerata
chelicerae
includes the spiders, mites, ticks, horseshoe carbs and sea spiders
two specialized body segments
1. cephalothorax – for sensory, feeding and locomotion
first pair of paired appendages = chelicerae (feeding)
second pair = pedipalps (feeding)
followed by paired walking legs
2. abdomen
contains digestive, reproductive, excretory and respiratory organs

22. Subphylum Crustacea crayfish, shrimp, lobsters and crabs
plus the copepods, fairy shrimp, isopods (pillbugs), amphipods and barnacles
barnacle
copepod
isopod

23. Class Malacostraca crayfish: known as a Decapod
at least ten pairs of jointed appendages
body plan: cephalothorax and abdomen
exoskeleton extends all the way around the body = carapace
abdomen takes the form of the “tail”

24. Decapod Appendages 10 pairs of appendages used for feeding and walking
Head - sensory
1. antennae
2. antennules
Thorax – feeding and walking
1  3. Maxillopeds (feeding)
4  8. Periopods (walking legs)
Abdomen - swimming
1  5. Pleopods (Swimmerets)
6. Uropod (part of telson)

25. Class Malacostraca
feeding and digestion: prey on other invertebrates, eat plant matter and scavenge dead and dying animals
1st 8 pairs of appendages are for food detection and handling
enlargened stomach – part of which is specialized for grinding
digestive gland called a hepatopancreatic gland - secretes digestive enzymes into the stomach
intestine extends from the stomach
intestine ends in an anus – important role in water and salt regulation

26. circulation: similar in all arthropods – open system
Class Malacostraca
circulation: similar in all arthropods – open system
tissues are bathed in body fluids containing oxygen binding pigments
do have a heart
respiratory: feathery gills attach to the bases of the walking appendages
water is moved over the gills for the exchange of gases between the oxygenated water and the body fluids
gills

27. Subphylum Hexapoda- Class Insecta
2 classes: Entognatha and Insecta
insect body plan:
body is divided into: head, thorax and abdomen
head bears a single pair of antennae, mouthparts (maxillae, mandibles), compound eyes and ocelli
thorax bears three pairs of legs & wings (in some insects)
locomotion: varied methods from crawling to flying

28. Class Insecta feeding and digestion:
head bears mouthparts for food handling and sensory
mandibles for chewing
maxillae for cutting
digestive tract - long, straight tube of foregut, midgut and hindgut

29. The Insect Eye ocelli + several compound eyes
ocelli = 500 – 1000 receptor cells beneath a single circular lens
compound eyes found in many adult insects
better suited for detecting movement rather than for forming an image
compound eyes consists of a few to 28,000 receptors called ommatidia – fuse into a multifaceted eye
ommatidia –light-gathering structure
covered with a cornea, contains a cone (lens)
base is a rhabdom – converts light energy into a nerve impulse

30. excretion: Malphigian tubules
open into the junction of the midgut and hindgut
ions, water and other critical materials are reabsorbed from the rectum back into the body fluid
nitrogenous wastes move into hindgut
main excretory product - uric acid

31. gas exchange : tracheae
tubes that open to the air via the spiracles along the body
spiracles lead to tracheal tubules that carry air to the muscles – gas exhange
inspiration through the thoracic spiracles and expiration through the abdominal spiracles

32. Features common to Phylum Echinodermata
1. triploblastic
2. pentaradial symmetry in adults; bilateral symmetry in larvae
3. coelomate
4. internal endoskeleton made of calcerous (bony) plates called ossicles
5. water vascular system for locomotion

33. Phylum Echinodermata approximately 7,000 species all are marine
living echinoderms are classified into 6 classes
1. Asteroidea – sea stars
2. Ophiuroidea – brittle stars and basket stars
3. Echinodea – sea urchins and sand dollars
4. Holothuroidea – sea cucumbers
5. Crinoidea – sea lilies and feather stars
6. Cocnentricycloidea – sea daises

34. Class Asteroidea sea stars about 1,500 species
live on hard substrates in marine environments
five arms radiating from a central disc
central disc has a mouth on its ventral side (oral surface)
opposite surface is the aboral surface with an anus

35. Water vascular system water-filled canals for locomotion
water enters into a ring canal through a stone canal and a sieve-like pore called the madreporite
five radial canals (or multiples) branch from the ring canal and run down each arm
extensions off of the radial canals are called tube feet
madreporite

36. extensions off the ring canals
-tube feet
extensions off the ring canals
project to the outside & have suction cups at its end
inside the body they end as a bulblike, muscular ampulla
when the ampulla contracts- forces water into the tube which then extends
contraction of tube feet back into body pulls sea star forward: locomotion