Sacoglossa (also known as Ascoglossa) is a highly diverse assemblage of
opisthobranchs that are united by their specialized radular morphology.
Only one radular tooth is used at a given time and worn teeth are
stored internally in a sack. Nearly all sacoglossans are herbivores,
using their radular tooth to puncture algal cells, then sucking out the
contents. Most feed on green algae. The cells lining the digestive
gland in many species engulf functional chloroplasts derived from their
algal food. These organelles, called kleptoplastids, continue to
photosynthesize providing sugars that may be important for their host's
nutrition. At least eight families are found in Hawaii.
Medina, et. al., (2011) recovers the Siphonariidae as the sister group
to the Sacoglossa and they could be inserted as the next order under
the name Siphonariacea (or be grouped with the Sacoglossa as the Siphoglossa). However, since they haven't been traditionally
considered opisthobranchs, we've decided to leave them in the marine
pulmonate addendum, at least for now.