aporobranchia

from The Century Dictionary.

• noun In Latreille's system of classification, an order of Arachnida having no apparent respiratory apparatus, by which the Pycnogonidæ alone were distinguished from other arachnidans: synonymous with Podosomata of Leach's system.
• noun In De Blainville's system of classification, an order of his Paracephalophora, containing the pteropods, which are divided into the Thecosomata and Gymnosomata. Also Aporobranchiata.