rotifers-mollusks-arthropods - Phylum Rotifera(about 1,800...

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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 complicated structures. [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 diploid) - 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):
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- usually external, but sometimes internal (squid). - some have lost shell (octopus) Some other features: - many have a radula (scraping tongue) - recognizable internal organs - their exact relationship to other animals is still debated. Have a larval form (trochophore) very similar to that of annelids, but lack any kind of segmentation. Very diverse group - 8 classes - of which we’ll just look at five (book lists four in table 33.3, p. 678): - Briefly - Scaphopods, or “tusk shells” [this class is not in the text]. - look like a very small elephant tusk (in lab!)
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rotifers-mollusks-arthropods - Phylum Rotifera(about 1,800...

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