Chp 7

• Rotifers (Rotifera)


  Microscopic and near-microscopic pseudocoelomate animals
• Rotifers


  • Common, small (most <1 mm), mainly aquatic animals
  • Mostly free-living and found in freshwater environments; some are parasites; some terrestrial
  • Corona - ciliated, food-gathering organ at tip of head (filter-feeders)
  • Body=coronoa+ trunk+ foot (these end by one, two or many toes)
  • Feet contain pedal glands whose secretion is used for anchorage
  • Sometimes called "wheel animals" because of appearance of beating cilia
  • True digestive tract with mouth, modified pharynx called mastax, short esophagus and intestine that open in the cloaca at the end of the trunk
  • Two salivary glands open in the mastax and two digestive glands open in the stomach
  • Hydrostatic skeleton with rudimentary circulatory system
  • Excretion by protonephridia that join in a bladder and open in the cloaca
  • Separate sexes and internal fertilization; some species with parthenogensis – development of unfertilized eggs
• Rotifers


  • Free swimming and truly planktonic
  • Move by inchworming along a substrate
  • Sessile, living inside tubes or gelatinous holdfasts that are attached to a substrate
• Rotifers are an important part of the freshwater zooplankton, being a major food source and with many species also contributing to the decomposition of soil organic matter
• Rotifers eat particulate organic detritus, dead bacteria, algae, and protozoans
• Like crustaceans, rotifers contribute to nutrient recycling
• Rotifers are used in fish tanks to help clean the water, to prevent clouds of waste matter
• Rotifers affect the species composition of algae in ecosystems through their choice in grazing
• About 2200 species of rotifers have been described
• The phylum Rotifera is divided into three classes: Seisonidea, Bdelloidea and Monogononta
• One example in the class Bdelloidea


  • Genus Philodina