pectinibranchiata

from The Century Dictionary.

• In Cuvier's classification, the sixth order of gastropods, divided into three families, Trochoides, Capuloides, and Buccinoides.
• An order of prosobranchiate gastropods, having comb-like gills formed of one (rarely two) longitudinal series of laminæ on the left side of the mantle over the back of the neck.

from the GNU version of the Collaborative International Dictionary of English.

• noun plural (Zoöl.) A division of Gastropoda, including those that have a comblike gill upon the neck.