Fun with plurals

A learned reader corrected me on a recent post on another blog, which I titled "The amazing story of a bacteria." Bacteria is plural, he wrote, and bacterium is singular.

I knew that, and all the dictionaries will tell you that. However, my ear told me that using the singular would sound like a reference to just one of the little buggers, and I was referring to a species. So it sounded right to use the plural. Technically speaking, I suppose my friend was right.

However, I did find a few references that suggest otherwise. Here's a question posed at a place called Physics Forums.

When you say species of cat, you say exactly that, cat, not cats, the singular, don't you? There seems to be a mixture when it comes to bacteria. Some sources say species of bacteria, others speices of bacterium. Would you say "How many species of cats are there?" or "How many species of cat are there?" It seems, when it comes to bacteria, the plural is used in this case.... Peculiar! Anybody got any ideas??? 

Here's one answer.

I suppose it's because Bacteria is the name of the family (or in this case domain) which is normally given as a plural. So you would say - how many species of the family Felidae are there. But bacteria is also used as a singular in everyday speech anyway. Plus this is English - there aren't any rules, well there are but you are allowed to make up your own anyway. 

Another:

Species is both singular and plural, so it depends. If you are asking about a species of cat, then you're talking about one species. If you ask about species of cats, then you're asking about more than one species. Though, biologists are more typically going to ask about species of felids.

And here's something I found on the pages of John Lindquist, who is on the instructional Laboratory Staff, Department of Bacteriology, University of Wisconsin-Madison. Bear with me. I'll never post on this again. Lindquist:

To refer to members of a given genus in the plural sense, using Bacillus, Micrococcus and Mycobacterium as examples, one cannot change the genus name directly to a plural form. Bacilli, Micrococci and Mycobacteria would be improper. To get around the problem, one can write such as the following: "species of Bacillus," "isolates of Micrococcus," "strains of Mycobacterium." If the genus names were to be reduced to common forms (made into conventional English words, not capitalized, italicized or underlined), then plural alteration would be valid, as follows: bacilli, micrococci, mycobacteria. Use the term "bacilli" with caution; this term (depending on context) can mean rod-shaped cells in general or members of the genus Bacillus more specifically. [Emphasis mine.]

I have no idea what that means, so I'm going with the guy who wrote, "This is English - there aren't any rules, well there are but you are allowed to make up your own anyway."

I'll also go with Samuel Clemens, my final arbiter on everything, who said:

"I like the exact word, and clarity of statement, and here and there a touch of good grammar for picturesqueness."

And added for good measure:

"I am almost sure by witness of my ear, but cannot be positive, for I know grammar by ear only, not by note, not by the rules. A generation ago I knew the rules--knew them by heart, word for word, though not their meanings--and I still know one of them: the one which says--but never mind, it will come back to me presently."

That's me. The rules were drilled into me in the eighth grade by Miss Schindler (who had taught my father) and in the 12th grade by Miss Whitton (who had taught my father), and somehow I know them but not by name, and like Mr. Clemens, I can't remember how I got into all this in the first place.