The aeolidaceans differ from other nudibranchs by their sleek body and the presence of groups of papillae, called cerata, on the back and sides of the body. Aeolidaceans are usually colorful, specially on the dorsal papillae. The head has, on the front, the oral tentacles, long and thin, and the rhinophores on the top, which can be smooth or have lamellae or warts.
Dondice banyulensis by Enric Madrenas
The digestive gland is highly branched and its branches, in the form of hollow conduit, enter inside of each cerata. In many species, the end of the digestive gland on each cerata expands, forming a spherical small bag called cnidosac that is communicated with the outside through a pore, the cnidopore, located on the tip of the cerata. They breath through the skin (cutaneous respiration) because they lack gills, so they use the cerata for gas exchange. Radula is narrow, with a row of teeth (monoseriate radula) or 3 teeth in each row (triseriate radula); generally a pair of chitinous jaws are found in the anterior part of the buccal bulb. Genital and anal orifices are located to the right of the body. The foot may differentiate, in its anterior zone, a pair of propodial palps, shaped short and triangular. Aeolidaceans prey mainly on Cnidarians: polyps of hydrozoans, jellyfish and anemones. This specialization provides these nudibranchs food as well as a defense mechanism of great biological interest because they are able to use for self-defense the stinging capsules (or cnidocysts) from their prey. For still unknown reasons, these cnidocysts are not triggered nor digested by the digestive juices of nudibranch, so they pass through the ramifications of the digestive gland until they reach the cnidosacs on the tip of the cerata, where they are stored. These cnidocysts can be expelled to the outside by contact with the potential predator, they are triggered and perform their defensive action. Some species have specialized in feeding on fish eggs, cirriped crustaceans or even other species of nudibranchs. The aeolidaceans are usually found on hydroid colonies, often the same species that serves them as food, and tend to lay their spawn there as well, usually in the form of a ribbon wrapped in various ways. At other times they can be found below stones, near anemones, even at very shallow depths, or can be found wandering on the rock walls abundant with algae and invertebrates.
The updated taxonomy of Aeolidaceans is as follows
- Parvorder Aeolidida
- Superfamily Aeolidioidea Gray, 1827
- Family Aeolidiidae Gray, 1827: includes about 10 genus currently accepted, among them, the following have species in European waters: Aeolidia Cuvier, 1797, Aeolidiella Bergh, 1867, Berghia Trinchese, 1877, Cerberilla Bergh, 1873, Limenandra Haefelfinger & Stamm, Spurilla 1968 Bergh, 1864.
- Family Facelinidae Berg, 1889: a large family that includes six species subfamilies and 33 genus distributed worldwide, of which the following have species in European waters: Algarvia Garcia-Gomez & Cervera, 1990, Antonietta Schmekel, 1966 Calorie Trinchese, 1888, Cratena Bergh, 1864, Facelina, Aler & Hancock, 1855, Facelinopsis Pruvt-Fol, 1954, Dicata Schmekel, 1967, Dondice Marcus, 1958, Favorinus M.E. Gray, 1850, Pruvotfolia Tardy, 1969, Rolandia Pruvot-Fol, 1951.
- Family Glaucidae Gray, 1827: monogeneric family with a single genys Glaucus Forster, 1777 and two pelagic nudibranch species, geographically spread, that live floating below the surface film of water and prey on jellyfish. Glaucus atlanticus Forster, 1777 is cosmopolitan and has been quoted in the waters of the Iberian Peninsula.
- Family Piseinotecidae Edmunds, 1970: family with a single genus Piseinotecus Er. Marcus, 1955 and only 4 species, of which 3 are found European and Iberian waters.
- Family Pleurolidiidae Bern, 1966: only one genus Protaeolidia Baba, 1955 with a single Pacific species P. atra Baba, 1955.
- Family Unidentidae Millen & Hermosillo, 2012: a very recently described family with a single genus so far Unidentia Millen & Hermosillo, 2012, with a single species living in the Mexican Pacific coast.
- Superfamily Fionoidea Gray, 1857
- Family Calmidae Iredale & O’Donoghue, 1923: a single genus Calma Alder & Hancock, 1855 and two species, C. glaucoides (Alder & Hancock, 1854) and C. gobioophaga Calado & Urgorri , 2002, both living on the coasts of the Iberian Peninsula and specialized on preying litoral fish eggs.
- Family Eubranchidae Odhner, 1934: from the 8 accepted genus only one Eubranchus Forbes, 1838 is found in Iberian waters.
- Family Fionidae Gray, 1857: This family has a single genus Fiona Alder & Hancock [in Forbes & Hanley], 1853 with a single species Fiona pinnata (Eschscholtz, 1831) which has a characteristic pelagic life, living on drifting floating objects and feeding on cirriped crustaceans of the genus Lepas.
- Family Pseudovermidae Thiele, 1931: monogeneric family with a single genus Pseudovermis Périaslavzeff , 1891 and 16 known species with only one P. artabrensis Urgorri, Cobo & Besteiro, 1991 living in Iberian waters. All species of this family are of very small size and have their body modified to live in the marine interstitial environment.
- Tergipedidae Family Bergh, 1889: of the 8 genus of this family, only the following have representatives in European and Iberian waters: Catriona Wickworth, 1941, Cuthona Alder & Hancock, 1855, Tenellia A. Costa, 1866 and Tergipes Cuvier, 1805.
- Superfamily Flabellinoidea Bergh, 1889
- Flabellinidae Family Bergh, 1889: from the 7 genus currently accepted, only three are found in European waters: Flabellina Gray, 1833, Calmella Eliot, 1910 and Cumanotus Odhner, 1906.
- Family Notaeolidiidae Eliot, 1910: a single genus Notaeolidia Eliot, 1905 with three species living in Antarctic waters: N. depressa Eliot, 1907, N. gigas Eliot, 1905 and N. schmekelae Wägele, 1990.
- Superfamily Aeolidioidea Gray, 1827
Aeolidacean species recorded in the Mediterranean Sea or around the Iberian Peninsula: