In all languages but English, this exists only to hold Category:Vertebrates, and even for English, this is its only subcategory. Moreover, Category:Vertebrates also has Category:Animals as a parent, which makes this intermediate category quite useless. As for English, it contains names of chordates that aren't vertebrates, but maybe they can be subdivided into several subspecies, or be placed in Category:en:Fish.
As I've mentioned elsewhere, some of the facts you state here aren't true. There are Portuguese entries for non-vertebrate chordates and I'm sure most of the major world languages have terms for them (see, for instance, w:nl:Zakpijpen), but marine biology isn't a priority for most editors. Tunicates are chordates, but not fish. Sharks are vertebrates- their vertebrae are made of cartilage, but they're vertebrae. Only hagfish could be considered fish but not vertebrates, and there are recent DNA studies that suggest they're really vertebrates that have lost their vertebrae. More to the point, "Fish" is a polyphyletic taxon with marginal taxonomic validity: it includes the closest living relatives of the tetrapods and much more distantly-related taxa, so to be taxonomically correct it would have to include the tetrapods. As a taxonomically-invalid category, we shouldn't be worried about a minor exception to it (if it is one). Even if we were, that would mean Category:Chordates would be the best parent category, unless we were to create a category for craniates- and that would only include fish and tetrapods. There aren't a lot of non-vertebrate chordates, but it's nice not to have them lost in Category:Animals- so Keep. Chuck Entz (talk) 18:36, 29 May 2017 (UTC)Reply
a colony of golden star tunicates After a few hours work, I've been able to expand the English category to 30 entries- most of which were already there, but not categorized. And, just in case anyone doubts me when I say tunicates aren't fish, here's a picture. Chuck Entz (talk) 21:23, 29 May 2017 (UTC)Reply
