Doridoidei are a group of marine heterobranch gastropod molluscs traditionally associated with sea slugs. They are soft-bodied animals, generally without an external shell in the adult stage, and are characterised by a great diversity of body shapes, colours and external structures. The group includes some of the best-known nudibranchs and many species that are relatively easy to observe during dives.
Doridoidei mainly inhabit marine benthic environments, from shallow waters to considerable depths. They can be found on rocky substrates, among algae, on sponges and other sessile organisms, or in other habitats on the seafloor. The group has a very broad distribution and occurs in tropical, subtropical, temperate and cold seas. Their diversity is particularly notable in areas with a wide variety of benthic habitats.
One of their most distinctive characteristics is the presence of a well-developed dorsal mantle, which may bear tubercles, papillae, keels or other structures that give each species a distinctive appearance. A branchial plume, consisting of gills arranged around the anus, is usually present at the posterior end of the body. This plume may be retractable, and its shape and arrangement are important characters for identification. The head bears rhinophores, sensory structures involved in detecting chemical stimuli in the surrounding environment.
Most Doridoidei are carnivorous and feed mainly on other sessile organisms. Sponges constitute an important part of the diet of many species, although some doridoideans also consume other invertebrates, such as bryozoans, cnidarians or ascidians. Their radula is adapted to this type of feeding and shows considerable variation among species. In many cases, the association with the organism on which they feed is an important element in understanding their ecology.
Doridoidei display an extraordinary diversity of body shapes and colour patterns. Some species have vivid colours and contrasting patterns, while others show colouration that allows them to blend into the substrate or the organism on which they live. In some species, mantle structures may contribute to camouflage or defence. Some may also incorporate or accumulate chemical compounds obtained from their prey, which can provide a defensive function against predators.
From an evolutionary perspective, Doridoidei are one of the most important groups of nudibranchs for understanding the diversification of marine heterobranchs. Anatomical and molecular studies have helped revise the relationships among different families and genera and have shown that some groups traditionally considered closely related do not always share as simple an evolutionary history as previously thought. The combination of different body forms, feeding strategies and defensive adaptations reflects the remarkable evolutionary diversification of nudibranchs.
Doridoidei therefore form a particularly diverse and conspicuous component of the sea slug fauna. Their variety of body forms, colours, feeding strategies and relationships with other organisms makes them a group of great taxonomic, ecological and evolutionary interest. Careful observation during dives, particularly of the organisms on which they live and feed, is essential for detecting smaller or cryptic species and improving knowledge of their distribution and diversity.
The taxonomy of Doridoidei according to WoRMS is:
Species of Doridoidei recorded from the Mediterranean Sea or the Iberian Peninsula:
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