Do microscopic animals like dust mites have smaller cells?
June 23, 2020 10:00 PM   Subscribe

I know that most animal cells are about the same size; an elephant just has many more cells than a mouse, say. But what about animals that are already so small you can't see them except in a microscope, like dust mites? (I know that amoebas etc are single celled organisms, I'm talking about mites which are arachnids) how can they have normal sized cells when they are practically the same size as animal cells?
posted by Pastor of Muppets to Science & Nature (5 answers total) 2 users marked this as a favorite
I’d start by looking more closely at your assumption that they are “practically the same size”. A dust mite might be ~4000 um long while a typical human cell is ~10 um across.
posted by doctord at 10:24 PM on June 23, 2020 [5 favorites]

Apparently human cell sizes span a pretty wide range. Note that neurons can be a meter long (but their chart shows volume not length)

This isn’t a direct answer to your question but all adult tardigrades of the same species have the same number of cells! (It’s “as much as” 40,000 which is somewhat less than a human’s 30,000,000,000,000 ish)
posted by aubilenon at 11:19 PM on June 23, 2020 [3 favorites]

I think the answer is definitely yes, some animals have much smaller cells. For example, Megaphragma mymaripenne is a multi-cellular wasp that is 200μm long. The linked article says it has 7,400 neurons so I would assume it has many tens of thousands of cells in total, which I think means that its cells must be a lot smaller than normal animal cells. That's all I have though. Hopefully someone else can post a more complete answer.
posted by richb at 3:58 AM on June 24, 2020 [10 favorites]

Basically there's an upper limit and a lower limit on how large or small a cell can be, based on the actual physics of how cells work, but most organisms are not working up against these bounds and so some microscopic animals manage to cram in a lot more cells (therefore smaller cells) than others.

The tardigrade (with its 40,000 cells over ~0.5mm of body length) is mentioned above, but C. elegans is 1mm long and has 959 or 1031 cells depending on its sex (XX hermaphrodites have fewer cells than XO males - here's a list of all the cells!). The largest cells (e.g. neurons in a giraffe's spinal cord, or ostrich eggs) tend to belong to larger animals, because obviously you can't fit a meters-long neuron into a spider mite body. But small animals can have quite large cells. I don't know whether a microscopic spider mite's heart, for example, is made of the same number of cells as a giant tarantula's heart (but smaller cells) or whether it has fewer cells. It could be both!
posted by mskyle at 11:13 AM on June 24, 2020 [1 favorite]

Basically there's an upper limit and a lower limit on how large or small a cell can be

Plasmodial slime molds up to 20kg have been found, which is larger than all but the chonkiest of cats. They (slime molds) have multiple nuclei but without cell walls between them and are considered single-cellar creatures.
posted by aubilenon at 12:08 PM on June 24, 2020 [5 favorites]

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