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In the case of the tapering worm tubes " Selkirkia " , trilobites are always found with their heads directed towards the opening of the tube , suggesting that they reversed in ; the absence of any moulted carapaces suggests that moulting was not their primary reason for seeking shelter .
 Selkirkia
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Selkirkia