Several sources list etymologies for algal names, for instance “Introduction to the Algae, 2nd ed.” (1985) by Bold and Wynne. For protozoans and other groups they are harder to find, and in fact many were never given an explicit etymology, but many are fairly clear from common Greek and Latin elements.
The words I have given are thus meant to represent the root rather than an exact form, and when the same one appears in both Greek and Latin I’ve mostly preferred the former. To make it clear how they relate and avoid using an alphabet that might be unfamiliar, the following transliteration is used:
|α = a||β = b||γ = g||δ = d|
|ε = e||ζ = z||η = ē||θ = th|
|ι = i||κ = k||λ = l||μ = m|
|ν = n||ξ = x||ο = o||π = p|
|ρ = r||σ, ς = s||τ = t||υ = y, u|
|φ = ph||χ = ch||ψ = ps||ω = ō|
|ʽ = h (rough breathing mark)|
Note names usually adapt suffixes -on to -um, -os to -us, and sometimes -ē to -a when they are not replaced entirely. They also typically change k to c and the diphthongs (vowel pairs) ai to ae, ei to i, oi to oe, and ou to u, as well as g to n before g, k, x, or ch.
When genera are instead named after a person they are usually at least mentioned in the original source. There are also a few cases where the roots are less obvious or otherwise deserve further comment:
1. Nostoc were named by the 16th century physician Paracelsus, who said they seemed as if blown from nostrils of planets. Potts (1997) thus explained the name as a mix of Old English nosþyrl and German nasenloch, both meaning nostril. The overlap seems odd, though, and I wonder if a root like tóch, sticky, might not be as likely.
2. Coleps looks like it should be from Greek kōlēps, the bend of the knee. However neither the meaning nor gender fits with the genus, as pointed out in a review by Foissner et al. (2008). Nitzsch had introduced the name without any explanation, but they propose Latin colum, strainer or sieve, as a possible source.
I could also imagine that kōlēps might be used in place of related kōlea or kōlē, thigh or ham, which refer to both the body part and cut of meat. At least today hams are often tied or scored in a regular pattern, which if common then could have been a fair analogy for colepid armour.
3. Euplotes is related to Greek plōs, swimmer, and plōtos, floating, though they mostly move by crawling. Ehrenberg originally named them Euploea or “Nachenthierchen” with the single species E. charon, referencing the mythical barque or ferry of Charon, so I have preferred the latter form.
4. Simulium could be from Latin simulare, to copy or feign, or simulus, a diminutive form of snub-nosed. I do not know enough to guess which Latreille might have meant. Either can be found in books without much justification, and I have tentatively favoured the former only for seeming to have been popular first.
5. Chydorus was introduced without comment by Leach. I have found two suggested roots: Greek doros, wallet, in “Composition of Scientific Words” by Brown (1956) and hydōr, water, in the “Encyclopædic Dictionary” (1881) ed. Hunter. However these leave the odd prefix chy- unexplained.
Leach and others named many crustaceans after figures in classical myth or history, not always with obvious reasons. Here the closest sounding is Cheidōros, Herodotus’s name for the river Gallikos drunk dry by the Persian army. This was even written Chydorus in a few older dictionaries so seems like a plausible source.
6. Moina was not explained by Baird but he did say he named Bosmina for a daughter of Fingal, who is from the works of Ossian by James Macpherson, then supposed to be a Gaelic epic. These poems also have a Moina, the ill-fated wife of Fingal’s uncle, so I think it is reasonable to assume this genus was likewise named for her.