Phylum Platyhelmenthes (the flatworms)

1
Phylum Platyhelmenthes (the flatworms) General
characteristics

• Eumetazoa - animals with tissue
• Bilateria - have bilateral symmetry
• Head end-cephalization
• Tail end
• Right and left side
• Top (dorsal) and bottom (ventral)
• triploblastic -ectoderm, mesoderm, endoderm.
• Protostomia - a group of animals whose mouth
  develops from the blastopore, and the mesoderm
  forms from an area near the blastopore.
• Acoelomata - They have a true mesoderm which
  fills the original blastocoel between the outer
  epidermis and digestive tract.

2
Integumentary- Rhabdites and one cell layer
epidermis in Turbellaria and usually ciliated
syncytial tegument in other classes. Skeletal -
hydrostatic Muscle - longitudinal, transverse,
and circular muscles are present. Digestive -
incomplete with intracellular and extracellular
digestion no system in Cestoda.
3
Excretory - flame cells, or excretory tubes in
Cestoda. Respiratory - no system,
diffusion Circulatory - none, diffusion. Nervous
- anterior ganglia, ventral ladder-like system
(two lateral cords with transverse cords). a
bilobed anterior ganglial mass (brain)
4
Protonephridia-a series of flame cells that aid
in excretion
5
Endocrine - hormones produced by nervous
system Reproductive - monoecious in most Well
developed reproductive organs, mostly internal
fertilization. Two of the parasitic classes have
complex life cycles Trematoda - Cestoda -
6
Class Turbellaria- 5000 species, mostly
free-living Dugesia- free living planarian
Branched gut
7
Reproduction- asexual- fission sexual -
monoecious Diversity-land planarian- Bipalium
8
(No Transcript)
9
(No Transcript)
10
Gone fission
11
(No Transcript)
12
Branched gut eyespots
13
Class Trematoda--flukes parasitic endoparasitic
ectoparasitic tegumentbody wall suckers feed
on host cells, tissue fluids, mucus (yuk!) and
blood life cycle monogenic flukes digenic
flukes
14
Opisthorchis - Human liver fluke
15
Schistosoma --- swimmers itch
16
(No Transcript)
17
Class Cestoda tapeworms Proglottids-
Head-scolex
18
Scolex
proglottid
19
Proglottid- note interconnection
20
Scolex
21
Life cycle
22
(No Transcript)
23
(No Transcript)
24
Phylum Nemertina- ribbon worms Proboscis can be
extruded to capture food
25
General characteristics- tube within a tube body
plan- a complete digestive tract Acoelomate
eversible proboscis, within a rhinocoel above the
gut feeding-stylets and toxins closed
circulator system, a single dorsal vessel with
two lateral vessels paired lateral
longitudinal nerve cords
26
asexual reproduction by fragmentation sexual
reproduction- dioecious free-swimming larva in
some marine species Advanced Features- anus clo
sed circulatory system dorsal nerve cord in
some complex excretory system in close
association with circulatory system mesodermally
derived blood vessels mesodermally
lined rhinocoel may provide links to higher phyla
27
(No Transcript)