water spider

noun

a Eurasian spider, Argyroneta aquatica, that spins a web in the form of an air-filled chamber in which it lives submerged in streams and ponds
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

Examples from the Web for water spider