Almost all underwater guides are using common names like “Spanish Dancer, False Pyjama Sea Slug, Three Striped Phyllidia” etc. These common names cause some problems:.

Nobody can be sure, of which animal you are really talking (even in the same language there are regional differences concerning the meaning). But what is more important: more than 95 % of the sea slugs don’t have “common” names. The authors are forced to create them. 

The results: different authors create different names. So you find pretty often in different uw-guides different names for the same species. Animals get “real common names” if they are of interest to many people: maybe as food, maybe because they are very pretty, maybe because they have a very significant behavior, maybe to increase the sexual power – but who on earth is interested in sea-slugs?

Scientific names:
Scienstist solve this problem in using Latin names.
The scientific name contents: Genus Species  Author, Year of description – genus and speciesname are written italic. This is just like using name and prename, in the genus Acteon are many species, Acteon variegatus, Acteon siebaldii, Acteon tornatilis etc.

Some examples:
Bulla ampulla  Linnaeus, 1758
means Linnaeus published in 1758 a description of an animal which he named ampulla, in this description he placed it in the genus Bulla. In many cases this first placement later turns out to be wrong – this is shown by putting author and year in brackets.

Armina semperi (Bergh, 1861) [Pleurophyllidia]
means Bergh published in 1861 a description of an animal which he named semperi and placed it in another genus than Armina, where this one is now placed. Whenever I know the original genus name, I add it in square-brackets:[Pleurophyllidia].

Sometimes authors publish their work together, this is also reflected the name :

Acanthodoris pilosa (Abildgaard in Mueller, 1789) [Doris] 
means in the publication of Mueller of the year 1789 was a section, in which Albildgaard described the species pilosa, placing it in the genus Doris.
Adalaria loveni (Alder & Hancock, 1862) [Doris] 
means Alder and Hancock published the description together in 1862. They named this species loveni and placed it in the genus Doris.
Chromodoris cf. africana  Eliot, 1904
cf. is an abbreviation from a Latin word (confer) and means ‘refer to’ or ‘compare with’, here it means it could possibly be Chromodoris africana or perhaps something closely related, or at least similar in appearance.
Platydoris sp. A  Genus: Bergh, 1877
sp. is an abbreviation from a Latin word (species) and means it is an undescribed species of the genus Platydoris which was established by Bergh in 1877. The letter A is to seperate it from other undescribed Platydoris sp. 

Taxonomy:
If you look at Select by taxonomy you will easily see the hierarchical structure of tanonomy starting with 
Class:  GASTROPODA
Subclass:  OPISTHOBRANCHIA 
(this is what is treated at this website as sea-slugs),
followed by Orders etc. – I think this needs no further comment.

Biology:
I strictly recommend to visit Bill Rudman’s Sea Slug Forum! 
Just use the search button to find what you are looking for.