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dwarf male

British  

noun

  1. a male animal that is much smaller, and often internally simpler, than its female counterpart. Dwarf males are commonly carried by the female, as in species of angler fish

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Example Sentences

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And if you look closely, she’s got a mate: A dwarf male is fused to her underside, essentially acting as a permanent sperm provider.

From Science Magazine