Uroleptus musculus

[janvangastel]

I found a new (for me) hypotrich and I think it is Uroleptus musculus. It has a tail like U. caudatum and U. piscus, but smaller and its body is a little wider. With a length of 153 microns it is also smaller then the two others. In 'Fresh water biology' by Hildrew and Townsend a length between 180 and 230 microns is mentioned and the species is not mentioned at all in 'Ciliated protozoa' by Bick. Kahl gives a length between 130 and 200 microns and 153 microns is well within this range. Kahl also mentiones a peristoma of 1/3 body length and a length/width ratio of about 3:1, which is in line with this specimen. As far as I can see it has also the cirri on the body surface in the right place.

[Bruce Taylor]

A very nice record of an interesting ciliate.

I have a couple of comments, as usual (please let me know if I'm being a nuisance!). First, size of a single specimen is a weak character. For instance, a recent divider might be below the normal size range for the mature population. Also, there is often quite a bit of regional variation in the size ranges for a given morphospecies.

As for this critter...it is very true that the cell is shaped, overall, like Uroleptus (perhaps more like U. gallina than U. musculus, with those caudal cirri). However, you've done a terrific job of showing the midventral cirri, and I don't see the two closely spaced "zigzag" rows that would put this in genus Uroleptus. Unless I am seeing this wrongly (see your video at 0:21 and 1:41), I think your creature only has a single midventral row:

Single midventral row.jpg (28.29 KiB) Viewed 2639 times

Classically, that would make this an amphisiellid, but the old morphological definitions are coming apart and I don't think that single midventral row is enough to put this in Amphisiellidae (that family has been shown to be a "polyphyletic", and therefore not a natural group). For comparison, researchers have described a brackish-water Strongylidium with a fairly similar appearance (and distinct caudal cirri): https://www.researchgate.net/figure/Str ... _235398331 Genetically, their new species groups with the erstwhile amphisiellid Pseudouroleptus, which is interesting.

In any case, without a midventral complex (double row), it cannot be Uroleptus. So, unless I am misinterpreting your video, I don't think there's enough information here to be sure of a genus-level identification. Hypotrichs, grrr!

[KD Arvidsson]

Very nice close-up and video Jan //KD

[Bruce Taylor]

After watching the video again, I think the 2 rows of the midventral complex are briefly visible at 0:24! Which would mean this is Uroleptus after all, and I apologize for any confusion caused by my preceding comments. I can't explain why only one midventral row is visible at 0:21 and 1:41, but I suppose the second row is simply out of focus, for some reason.

[janvangastel]

Hi Bruce,
Yes, that's the place where I had seen the two rows. And I think I also see them between 1.42 and 1.46.
Thanks again for your detailed comments. They are not a nuisance at all, the contrary. I learn a lot from your comments and they motivate me to look at all the possible details of a specimen when trying to ID them.

About the species name: I couldn't find U. gallina in Kahl. Has the name been changed?

[Bruce Taylor]

Kahl would have regarded Uroleptus gallina (a historic species, recorded by Otto Mueller in 1785 under the name Trichoda gallina) as a synonym of Uroleptus musculus. It's redescribed in Foissner et al., 1991 (first volume of their "ciliate atlas").

I wouldn't attempt to assign a species to this single specimen. U. gallina is generally smaller than U. musculus sensu Foissner et al. 1991 (they give a size range of 180-230 um for the latter, a typical length of 110 um for the former). But as I note above, size is mostly useful when you have numerous specimens to compare. Also, there are significant features that are difficult to see, such as the transverse cirri (often quite inconspicuous in Uroleptus), and the paroral membranes. And it needs to be said again...species itself is often a questionable concept, with ciliates! It may even be that both species are part of species complex...a continuum of "musculus-like" Uroleptus with regional variations, etc.

[janvangastel]

Thanks Bruce. I Will delete the species name