Phylum Rotifera (about 1,800 species)
- most are microscopic - largest up to about 2 mm in size)
- multicellular animals, which have muscles, a complete digestive tract, and other more
[Fig., not in book, but see fig. 33.13, p. 676]
- body fluids help serve as an hydrostatic skeleton.
- rotifer => “wheel bearer”
- crown of cilia surrounding mouth.
Use this to draw in water (and food).
- food then enters jaw, which is part of the mastax (a characteristic grinding organ
of this group).
- reproduction is unusual:
- many use parthenogenesis:
- females produce more females from unfertilized eggs (but eggs are
- some, but not all, will produce degenerate males when conditions are bad.
these males live just long enough to fertilize eggs [NOTE: many
organisms use sexual reproduction when conditions are bad, and asexual
reproduction when conditions are good - WHY?].
- some are suspension feeders, others raptorial (predatory).
- other features from overhead: toe, pedal gland.
- most can detach and swim.
Phylum Molluska (about 100,000 species)
Very large, successful group, even found on land.
Clams, snails, slugs, octopus, etc.
All have a similar arrangement of body parts
[Fig. 33.15, p. 678]
1) ventrally, a muscular foot
2) a dorsal covering, the mantle
3) in between -> visceral mass, which contains internal organs
Most have a shell (derived from the mantle):