The Euctenidiacea (=true gill) nudibranchs comprise the holohepatic nudibranchs (with a compact digestive gland) and have a gill formed by dendritic gill leaves. They are also generally known under the name of Doridaceans.
Peltodoris atromaculata by Enric Madrenas
These nudibranchs are characterized by having an elongated or flattened body where it is easy to differentiate the notum or back from the flanks of the body. The rhinophores could be contractile or they can be completely retracted into the head. The back of the animal can be smooth or it can be adorned with tubercles of different shaped: rounded, conical, digitiform, etc. The species of certain genuses as Jorunna, Taringa or Rostanga have spiculated tubercles that surround it forming a crown and that are known as caryophyllid tubercles.
The gill leaves surround the anal tubercle and are located in the posterior region of the back. Certain groups can contract the gills when they feel threatened (fanerobranch euctenidiaceans) or they can fully retract them into the body (cryptobranch euctenidiaceans).
Euctenidiaceans feeding is very specific, they are all carnivores, most feed on sponges but there are some species that feed on bryozoans.
Within Euctenidiacea two groups are considered with Infraorder category, the strict Doridaceans, where most species belong, and Gnathodoridacea, with only two genus and very few species of deep, cold waters.
Main Euctenidiacea groups: