| 单词 | book gill | 
| 释义 | > as lemmasbook gill   book gill  n. Zoology (in aquatic arachnids) any of several pairs of external gills that each contain numerous fine lamellae; also called gill book.Now only found in horseshoe crabs, book gills are thought to be ancestral to book lungs. ΘΚΠ the world > animals > invertebrates > phylum Arthropoda > order Xiphosura or Merostomata > 			[noun]		 > genus Limulus > member of > parts of > respiratory organ book gill1897 1897    T. J. Parker  & W. A. Haswell Text-bk. Zool. I. xi. 621  				External appendages or gills (book-gills). 1960    D. C. Braungart  & R. Buddeke Introd. Animal Biol. 		(ed. 5)	 379  				Arthropods having four pairs of legs; tracheae, book-lungs, or book-gills. 2002    G. M. Eberhart Mysterious Creatures I. 125/1  				Ancestors of the True scorpions..were once primarily aquatic and were equipped with organs called book gills. < as lemmas | 
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