The Collaborative International Dictionary of English v.0.48:

Aspidobranchia \As`pi*do*bran"chi*a\, n. pl. [NL., fr. Gr. ?, ?,
   shield + ? gills.] (Zool.)
   A group of Gastropoda, with limpetlike shells, including the
   abalone shells and keyhole limpets.
   [1913 Webster]