My own area of expertise is microbiology
I can only imagine how difficult it my be to keep up with taxonomy within microbiology! I guess there is a lot of work to be done there, and seeing as the traditional taxonomy was based on morphology, there must be lots and lots of mistakes for microbes.
A lot of time, we don't even bother with species, and instead use something called an OTU (operational taxonomic unit), which is essentially us just giving up and saying they're different because of some % difference in their DNA (usually 3% or more in part of the DNA sequence which codes for their 16S rRNA).
Oh, that's very interesting! It makes a lot of sense though; the traditional taxonomy does not fit very well to the diversity of the microbes.
In terms of macrobiology, DNA is doing the same thing. As you've pointed out, they've settled a longstanding debate in six-gilled sharks, but that's not the only case. My favorite example is when they discovered multiple species of lemurs based on DNA evidence - the lemurs appear otherwise identical even to trained researchers in the lab.
This is really cool! I wonder how many more examples of this we will find in the next decades; surely there will be a lot of species that will be divided into several new species.
Thanks again for leaving a great comment, @effofex!