Loaches (Botiidae) were previously considered a group among the family Cobitidae; in 2002 T.T. Nalbant argued persuasively that the Botias were a sufficiently distinct monophyletic group to rank as a family themselves: Botiidae.
About Botiine species in general. Some familiar Botia species were separated off by Maurice Kottelat in 2004, as Yasuhikotakia. The botiine fishes within the family Botiidae, the core group, are all high-backed flat-bellied bottom feeders, mostly quite nocturnal and shy, some more aggressive than others, often more or less territorial— and charming. After cichlids and catfishes, loaches have the most dedicated fans among fish-keepers. Keeping social Botias singly, or cranky loners in company, or, worse, trying to keep "one of each kind" together can all lead to trouble. Be cautious about mixing Botiine species and give the sociable ones some company, and they won't fail you.
Many Botia have a characteristic fright reaction, which sends them all flocking together and jammed into a narrow space. This panicky shoaling is especially typical of young or half-grown individuals— as our aquarium fishes tend to be when we find them at the LFS. If there's a survival value in the behavior, it might be that the group together gives the appearance of a single larger fish, or perhaps of a few larger fishes huddling together. The whole shoal may be passed over by a predator who would in fact have been able to swallow any one of them. If that is so, and there is survival value in the huddling instinct, the behavior would tend to get genetically magnified with each succeeding generation. Loaches that don't have this fright reaction would tend to get picked off first and fail to live long enough to pass on their own DNA.
Some Botia communicate excitement and aggressiveness with clearly audible clicks. Stéphan Reebs remarks (in Fish Behavior in the Aquarium and in the Wild), "Acoustical advertisement seems common in fishes that spend a lot of time hidden in crevices and holes"; though his examples are marine fishes, his observation certainly applies to Botia (Yasuhikotakia) modesta. I announce food for mine with some loud tongue clicks; curiosity gets the better of them, and they dash out of their hidey-holes under roots.
Loaches are "scaleless," that is, their scales are greatly reduced in size and embedded deep within the skin. They are more sensitive to certain medications, such as malachite green. So medicate them with care.
Links. One of the best websites devoted to a group of fishes, as good as the best of the cichlid sites, is Jeff Shafer's "Loaches On-Line," fairly touted as the "greatest international grouping of practical experience with Loaches to be found on the Internet" and the source of hands-on expertise that was published as Loaches: Natural History and Aquarium Care (2008). There's lots more about loaches at Jeff and Cassi Dietsch's "Loach Reference Page". Steven Grant's two-part article "Fishes of the genus Botia in the Indian region" is archived at Loaches-on-line. Mike Ophir is a name you probably already know if you're interested in loaches: his web page devoted to loaches is gone, but he's the author of many loach articles.