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Valentin, I appreciate your point about the conspicuous differences between the antennae in Sphiximorpha and Ceriana. There are also large differences in the constriction & elongation of the basal portion of the abdomen between Monoceromyia and Ceriana.

To answer your question:

There are presently 4 main sub-taxa (i.e. with a large number of species) in the tribe Cerioidini: Ceriana, Sphiximorpha, Monoceromyia and Polybiomyia (as well as some other subtaxa with only one or two+ species). But there are (at least) two different opinions among those who study the tribe as to whether it's best to treat those sub-taxa as genera or subgenera...and, unfortunately, that causes a lot of confusion for many people.

Note that those who follow the "subgenus viewpoint" treat Ceriana as the single genus in the tribe Cerioidini. But that genus includes the nominate subgenus of the same name, Ceriana, as well as the other 3 subtaxa above as subgenera. So from the "subgenus point of view" both subgenus Ceriana (sensu stricto) and subgenus Sphiximorpha could still be regarded as very distinct from one another...the only difference is that the distinction is now regarded as one at the rank of subgenera rather than genera ;-)

In my opinion, simply changing the rank at which you place the subtaxa here is mostly an artificial formality that really doesn't improve understanding of the inter-relationships of the taxa, but does introduce a lot of confusion...especially when adherents of the subgenera point of view use a binomial like "Ceriana gambiana" instead of the trinomial Ceriana (Monoceromyia) gambiana.

If you're interested in more details on this topic then ... as stated in my initial comment above ... see the last five paragraphs of my (long!) iNaturalist comment here...or the remarks beginning at the 4th paragraph of my (again long) comment under this Flickr post of Sphiximorpha roederi."