OK, here's one that went the other way. Show of hands, everyone who's heard of NGC 4569. Messier heard of it and labelled it 90. It's what van den Bergh has called an anemic spiral, right in the core of the Virgo cluster, with truncated H I distribution and smooth outer arms. Its nucleus is so compact that Humason, Mayall, and Sandage though it was a star, and picked some emission region that probably belongs to an adjacent galaxy for their redshift measurement in the classic paper. Here's a composite image from some old Lowell BVR data:
In fact, it's almost as blueshifted as galaxies come - something like 800 km/s. And the nuclear spectrum looks a whole lot like an A-type star. This once gave me a moment of hair raising on the back of the neck, noticing that its not even a typical aging starburst because the Balmer absorption lines are too narrow for main-sequence stars. The thing is loaded with supergiants, and the central star cluster is so compact that HST didn't even properly resolve it with WFPC2. I'm not convinced I ever worked out just what history gives such a phase, but I did notice that when people were grabbing Kennicutt's spectral atlas from my ftp site, they would notice NGC 4569 in there as well and casually mention that they thought it was interesting and had grabbed it just for grins.