Assertion: krill's source | /r/HasProperty | encyclopædia britannica].
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Source sentences:
text: Mussels open their shells and draw in food, filtering food particles over their gills, while clams use mucus on their gills to catch plankton as they push water in and out of their siphons [source: Chesapeake Quarterly]. A worm called Chaetopterus has a bag of mucus that strains the food out of water; when the bag is full, the worm eats it and starts a new bag [source: Encyclopædia Britannica].