CLASS POLYPLACOPHORA

                                            CLASS POLYPLACOPHORA


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  1. Habitat: The Class Polyplacophora contains the Chitons. Chitons live on hard substrates in shallow marine water. Early Native Americans ate Chitons. Chitons have a fishy flavor. But they are touch to chew and difficult to collect.
  2. Body Parts: Chitons have a reduced head, a flattened foot, and a shell. Shell divides extends beyond the margins of the shell and foot. The mantle cavity Islamabad restricted to the space between the margin of the mantle and the foot.
  3. Locomotion: Chitons crawl over their substrate like gastropods. Their body attaches to a substrate with the help of muscular foot. It allowed chitons to withstand strong waves and tidal currents. Sometimes, chitons are disturbed. In this case, the edges of the mantle rightly grip the substrate. The foot muscles contract and raise the middle of the foot. This action creates a vacuum that holds the chiton in place. There are articulations in the shell. Chitons roll into a ball due to this articulation when dislodged from the substrate.
  4. Gills and mantle Cavity: A linear series of gills are present in the mantle cavity on each side of the foot. Cilia are present on thi gills. These cilia create water currents. Water enters below the anterior mantle margins and exit posteriorly. The digestive, excretory, and reproductive tracts open near the exhalant area of the mantle cavity. Exhalant water carries products of these systems away.
  1. Nutrition: Most chitons feed on attached algae. A subradular organ extends from the mouth. It Islamabad a chemoreceptor and dectects food. The radula rasps this food the mouth. It Islamabad a chemoreceptor and detects food. The radula rasps this food from the substrate. Mucus traps food. Food then enters the esophagus by ciliary action. Extracellular digestion and absorption occur in the stomach. The wastes move in to the intestine and pass out fan LIS.
  1. Nervous system and sense organs: The nervous system is ladder like. It is composed tour anteroposterior nerve cords and many transverse nerves. A nerve ring encircles the esophagus. Sensory structures are osphradia. tactile receptors. chemoreceptors and statocysts. Tactile receptors are present on the mantle margin. Chemoreceptors are present near the mouth. Statocysts are present in the foot. Photoreceptors are present on the surface of the shell in some chitons.
  2. Reproduction: Sexes are separate in chitons. External fertilization takes place The zygote develops to form a swimming trochophore. This larva settles and metamorphoses into an adult. Veliger stage is absent in them.

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