What is the etymology of the scientific term "tomont", referring to a life stage of certain parasitic organisms such as Cryptocaryon irritans?

The Oxford English Dictionary has an entry for a combining form "-ont" which is says is

< ancient Greek ὀντ-, ὄν being (see onto- comb. form). Compare German -ont. Combining with first elements of Greek origin. Formations are found from the late 19th cent.


Forming nouns denoting organisms (or cells) of a particular type, esp. protozoa at a particular stage in the life cycle.

This appears to be the source of the end part of tomont. But I can only guess about the first part. The main candidate I have been able to find so far is Greek τόμος (tomos) meaning "slice" or "piece", but I don't know exactly why this would have been used as the base of the scientific term. I'd also like to know whether the etymology is explicitly given in any source. The word seems to have existed since at least the first half of the 20th century.

1 Answer 1


"Tomont" is the dividing stage in the organizm's life cycle.

tomo-: sections; cutting. Ancient Greek τόμος (tómos, “section, slice”).

Re: OP's "… but I don't know exactly why this would have been used as the base of the scientific term," see here:

Ichthyophthirius multifiliis on Wikipedia:

Once the tomont falls to the bottom, it forms a thin cyst wall. Within that cyst wall the tomont begins to divide, creating thousands of tomites.

After it feeds within the skin or gills, the trophont falls off and enters an encapsulated dividing stage (tomont).

with -ont

Denoting an individual or cell of a specified type. ‘schizont
From Greek ont- ‘being’, present participle of eimi ‘be’.

  • Thanks for the answer! As I said in the question, τόμος does seem a likely candidate for the base for this word. If you know of any sources that can confirm this hypothesis about the formation of tomont, I would be completely satisfied with this answer. Currently, it looks like it's based on an educated guess; that's fine, but I'm hoping to get a bit more conclusive information about the origin and derivation of this term.
    – herisson
    Sep 24, 2019 at 17:27

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