Platyhelminthes Flashcards
Study Slide Pack Three
1
Q
Platyhelminthes
A
- Flatworms
- Acoelomate, dorsoventrally flattened and bilaterally symmetrical
- Most hermaphroditic
- Protostome, spiral cleavage, some determinate growth
- Mesodermal layer develops into
parenchyma, a loose collection of cells - No anus, respiratory or circulatory organs
- Has excretory structures (like rotifers)
- Clear cephalization w/ central nervous system
2
Q
Platyhelminthes - Free-living Body Plan
A
- “turbellarians” – 6,500 spp. in a paraphyletic group
- Range from 1mm to 30 cm long
- Flat body enhances SA:V ratio for efficient gas exchange
- Vulnerable to desiccation
- Has hydrostatic skeleton – ciliary gliding with mucus
3
Q
Mesodermal layer develops into
parenchyma
A
A loose collection of cells
- Either 1st animal with mesoderm or secondary loss of coelomic cavity leading to acoelomate condition
4
Q
Cephalization with sensory structures
A
auricle, pits, tentacles, and centralized, ladder-like nervous system
5
Q
Ocellus –
A
inverted pigment-cup for photoreception
6
Q
Platyhelminthes - Feeding and Digestion
A
- Most are carnivorous or scavengers
- Use chemoreception to find food
- Has mouth and pharynx
- Complex intestinal system but incomplete
Simple, triclad (3 branches), polyclad (many)
Gut lined with gland cells and phagocytic cells - Waste exits the mouth
7
Q
Platyhelminthes - Osmoregulation and Excretion
A
- Protonephridia present, key to invasion of freshwater and terrestrial envs.
- Act primarily for osmoregulation
8
Q
Flame bulbs -
A
- cilia in mesh cup
- Beating cilia looks like a flickering flame
9
Q
Drain into networks of collecting tubules called
A
excretory ducts or canals
10
Q
Platyhelminthes - Regenerative Capabilities
A
- Asexual fission – common in free-living species
- Neoblasts – totipotent stem cells, make up 20% of cell pop in adults, can become or renew any cell type
11
Q
Cohort Cestoda -
A
- “tapeworms”
- Scolex – attachment to host
- Proglottids – reproductive segments of the body, 50,000 eggs
- Matures with age, embryos fill near posterior end
- Proglottids break free or burst open and release embryos in host feces
- Syncytial external covering called tegument with many folds
- No digestive tract!
- Obtain host fluids through pinocytosis or diffusion
12
Q
Cohort Trematoda -
A
- “flukes”
- Lack external cilia, rely on musculature to move or ride along host bodily fluids
- Also has a thick outer tegument
- Uses oral sucker and acetabulum (ventral sucker) to attach to host
- Feed on host fluids, tissues or gut content
Mouth leads to esophagus and then ceca (gut)
13
Q
Schistosoma mansoni
A
- Blood flukes – live in blood vessels near intestines
- 5 species infect 240 million people with schistosomiasis, or snail fever
14
Q
Nemertea
A
- ribbon worms
- Coelomate, unsegmented, flattened dorsoventrally
- Complete gut w/ protonephridia
- Unique proboscis – snapomorphy!
- Closed circulatory system, some w/ hemoglobin
- Mostly gonochoristic with spiral cleavage
15
Q
Nemertea - Body Plan
A
- Superficially resemble flatworms, with features of acoelomate and coelomates
- Share parenchyma, external cilia and mucus and protonephridia
- Centralized nervous system with ladder-like arrangement of nerves
