1. Acoelomate Bilateral Animals

2. Acoelomate Bilateral Animals
Consist of phyla:
Phylum Platyhelminthes
Phylum Nemertea
And others

3. Acoelomate Bilateral Animals
Simplest organisms to have bilateral symmetry
Triploblastic
Lack a coelom
Organ-system level of organization
Cephalization
Elongated, without appendages
Reproductive and osmoregulatory systems

4. Bilateral Symmetry Divided along sagittal plane into two mirror images
sagittal= divides bilateral organisms into right and left halves

5. Review Anterior= head end Posterior= tail end Dorsal= back side
Ventral= belly side

6. Bilateral animals
Bilateral symmetry = important evolutionary advancement
Important for active, directed movement
Anterior, posterior ends
One side of body kept up (dorsal) vs. down (ventral)
Cephalization and bilateral symmetry evolved together

7. Directed movement evolved with anterior sense organs cephalization
specialization of sense organs in head end of animals

8. Acoelomates lack a true body cavity
Solid body
no cavity b/w the digestive tract and outer body wall
Acoelomate
Phylum Platyhelminths
Or not shown here
Nemerterean
This is a round worm
Different Phylum

9. Architectural patterns of animals
Architectural patterns of animals. These basic body plans have been variously modivied during evolutoinary descent to fit aimals to a great variety of habitats. Ectoderm is shown in gray, mesoderm in red, and endoderm in yellow

10. Acoelomates are triploblastic
Triploblastic (3 germ layers)
Germ layer= layers in embryo that form the various tissues and organs of an animal body

11. 3 germ layers Ectoderm Endoderm Outermost germ layer
Gives rise to outer covering of animal ie. epidermis
Endoderm
Innermost germ layer
Gives rise to inner lining of gut tract

12. Mesoderm Middle germ layer b/w ectoderm and endoderm
Gives rise to various tissues/organs (ie. muscles)

13. Acoelomate animals have an organ-system level of organization

14. Acoelomate animals have an organ-system level of organization
Different organs operate together (ie. excretory system, nervous system)
mesodermal tissue gives rise to parenchyma
Digestive tract and nervous system
Organ= different tissues assembled into functional unit
Visceral- internal organs

15. Polyclad
From Red Sea

16. Phylum Platyhelminthes
Free living
Flatworms
Parasitic

17. From Atlantic ocean

18. Phylum Platyhelminthes
Flattened dorsoventrally
flatworms
34,000 species
Gastrovascular cavity (if present) has only one opening (mouth = anus)
Mostly monoecious

19. Phylum Platyhelminthes
First phylum that has an Organ systems present
derived mesodermally (parenchyma):
Muscular system
Digestive system (incomplete; gastrovascular type) (absent in some)
Nervous system
Excretory system (absent in some)
Reproductive system

20. Phylum Platyhelminthes
Organ systems absent:
Circulatory
Respiratory
Rely on diffusion

21. Phylum Platyhelminthes (cont’d)
Divided into 4 classes:
Class Turbellaria (mostly free-living flatworms)
Class Trematoda (parasitic flukes)
Class Monogenea (ectoparasitic flukes)
Class Cestoda (tapeworms)
Hymenolepsis- rat tapeworm

22. Class Turbellaria Mostly free-living flatworms
Marine (mostly) or freshwater bottom-dwellers
Predators and scavengers
First group of bilateral symmetrical animals
Planarian genus Dugesia

23. The best-known turbellarians, commonly called planarians
Have light-sensitive eyespots and centralized nerve nets
Pharynx. The mouth is at the
tip of a muscular pharynx that
extends from the animal’s
ventral side. Digestive juices
are spilled onto prey, and the
pharynx sucks small pieces of
food into the gastrovascular
cavity, where digestion continues.
Digestion is completed within
the cells lining the gastro-
vascular cavity, which has
three branches, each with
fine subbranches that pro-
vide an extensive surface area.
Undigested wastes
are egested
through the mouth.
Ganglia. Located at the anterior end
of the worm, near the main sources
of sensory input, is a pair of ganglia,
dense clusters of nerve cells.
Ventral nerve cords. From
the ganglia, a pair of
ventral nerve cords runs
the length of the body.
Gastrovascular
cavity
Eyespots
Figure 33.10

24. Class Turbellaria (cont’d)
Move by muscles, ciliated epidermis
/gastrovascular cavity

25. Class Turbellaria (cont’d)
Freshwater turbellarians adapted osmoregulatory structures
Protonephridia
protos= first
nephros= kidney
network of fine tubules running down sides of organism

26. Class Turbellaria (cont’d)
Flame cells= branch from tubules
Ciliary projections drive fluid down tubule
Tubules open to outside= nephridiopore

27. Class Turbellaria (cont’d)
nervous system with nerve ganglion
ganglion- aggregation of nervous tissue
Cephalization- cerebral ganglion= primitive brain

28. Class Turbellaria (cont’d)
Ocelli= light-sensitive eyespots

29. Turbellarian Reproduction
Reproductive and osmoregulatory systems
Asexual (fission)
transverse
Sexual
Monoecious (mostly)
Cross-fertilization

30. Other 3 classes: Class Trematoda Class Monogenea All parasitic
Class Cestoda
All parasitic
lack cilia
Have unusual body covering: tegument
Outer zone of tegument (glycocalyx)
consists of proteins and carbohydrates
aids in transport of nutrients, waste, gases
Protection against host defenses
Tegument= external covering for epithelium

31. Class Trematoda Parasitic flukes Endoparasites
Hooks, suckers, increased reproductive capacity

32. Definitive host (primary/final host)
1mm-6cm long
Complex life cycle:
Definitive host (primary/final host)
where parasite matures and reproduces (sexually) (eggs released)
vertebrate

33. Intermediate host Mollusc (ie. snail)
Hosts in which larval stages develop and undergo asexual reproduction
Results in an increase in the number of the individuals

34. Trematodes that parasitize humans
Spend part of their lives in snail hosts
These larvae penetrate
the skin and blood
vessels of humans
working in irrigated
fields contaminated
with infected human
feces.
Asexual reproduction
within a snail results in
another type of motile
larva, which escapes from
the snail host.
Blood flukes reproduce
sexually in the human host.
The fertilized eggs exit the
host in feces.
The eggs develop in
water into ciliated
larvae. These larvae
infect snails, the
intermediate hosts.
Snail host
1 mm
Female
Male 5 2 3 4
Figure 33.11
Mature flukes live in the blood vessels of the human
intestine. A female fluke fits into a groove running
the length of the larger male’s body, as shown in
the light micrograph at right. 1

35. Chinese Liver Fluke Definitive host: 2 intermediate hosts:
Infects 30 million people in eastern Asia
Lives in ducts of liver
Eats epithelial tissue, blood
Definitive host:
Humans, dogs, cats
2 intermediate hosts:
snail
fish
Adult worm is 10-25mm long and 1-5mm wide

36. Class Monogenea Parasitic flukes Mostly ectoparasites
Single host, mostly fish

37. Class Cestoda Tapeworms Endoparasites Vertebrate host 1 mm- 25m long
Live in digestive tract
1 mm- 25m long
(EWWWW!!)
Hymenolepsis- rat tapeworm

38. Tapeworm Tapeworms Are also parasitic and lack a digestive system
Proglottids with
reproductive structures
200 µm
Hooks
Sucker
Scolex
Figure 33.12

39. Class Cestoda Highly specialized Lack mouth, digestive tract
Absorb nutrients across body wall
Hooks and suckers
“head”= scolex
Hymenolepsis- rat tapeworm

40. Adult tapeworms consist of long series of repeating units= proglottids
Chain of proglottids= strobila

41. Tapeworms are monoecious (mostly) No specialized sense organs
Mostly cross-fertilization
No specialized sense organs
scolex

42. Cestodes depend on host digestion
Small molecules in host intestine, liver

43. Beef Tapeworm
Definitive host= human
Intermediate host= cattle

44. Phylum Nemertea Triplobastic, acoelamate bilateral symmetry
Unsegmented
Ciliated epidermis
Closed circulatory
usually <20cm
Marine mud, sand
Elongate, flattened worms

45. Phylum Nemertea (cont’d)
Unlike the platyhelminthes, Complete digestive tract, with anus
One-way
More efficient; allows larger growth

46. Phylum Nemertea (cont’d)
Cerebral ganglion, longitudinal nerve cords
Long proboscis used in carnivorous species
Two lateral blood vessels yet no heart
Dioecious
“two” “house”
Male and female organs in separate individuals