sentences:  Cryptobranch dorid nudibranchs (previously known as the taxon Cryptobranchia), are nudibranch sea slugs within the clade Doridacea.These slugs are called "cryptobranch," meaning "hidden gill", because they are able to retract their gills into a gill pocket, in contrast to nudibranchs in the traditional group phanerobranchs (or Phanerobranchia), which taxon is probably paraphyletic (in other words, composed of more than one evolutionary lineage).A.