Ophrydiidae?

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D0c
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Joined: Mon Nov 30, 2020 9:13 pm
Location: England

Ophrydiidae?

#1 Post by D0c » Fri Apr 16, 2021 1:39 pm

I’ve spent the last few days trying to decide what genus these critters belong to, and I’m still struggling to be honest and need help.

They were all from the same sample of pond water that contained decaying leaves. There were about 20 of them but they were all solitary, apart from the pair in the video below.

Can anyone tell me why some have a skirt of cilia around the bottom of the cell and some do not have this. Are they a different species?

I’ve narrowed it down to the following three. I thought it could be Ophrydium but these are colonial and often have zoochlorellae within them so I don’t think it’s Ophrydium. I then looked at Ophrydiopsis which is similar to the above but are solitary. Unfortunately I cannot find any info about this species. It could be a Gerda species similar to the one I found a little while ago. Gerda I think has a peristomial disc which is raised above the rim of the peristome which I think we see here.

With cilia skirt:

Video 1 - https://www.flickr.com/photos/154534235 ... datetaken/
Video 2 - https://www.flickr.com/photos/154534235 ... datetaken/
Video 3 - https://www.flickr.com/photos/154534235 ... datetaken/
Video 4 - https://www.flickr.com/photos/154534235 ... datetaken/

Without cilia skirt:

Video 5 - https://www.flickr.com/photos/154534235 ... datetaken/
Video 6 - https://www.flickr.com/photos/154534235 ... datetaken/
Video 7 - https://www.flickr.com/photos/154534235 ... datetaken/
Video 8 - https://www.flickr.com/photos/154534235 ... datetaken/
Leitz SM-Lux

Bruce Taylor
Posts: 986
Joined: Fri Sep 04, 2015 11:34 am

Re: Ophrydiidae?

#2 Post by Bruce Taylor » Fri Apr 16, 2021 4:28 pm

A really nice observation! An ophrydiid, certainly. The ones with posterior skirts of cilia are transforming into their migratory forms (i.e. becoming "telotrochs"). As it grows this "posterior ciliary wreath", the cell changes shape and its mouth closes up. Then, the sessile peritrich swims away to a new location.

We can rule out Ophrydiopsis, because the genus no longer exists. :D In his revision of Ophrydiidae, Guhl transferred the one species in that genus, O. concava, to Scyphidiella. That leaves Ophrydium and Gerda. Colonial ophrydiids are assigned to Ophrydium, and the rest go to Gerda. Unfortunately, we can't really establish whether a critter has a colonial lifestyle on the basis of a few observations, because it is not uncommon to encounter solitary specimens of Ophrydium. We see at least one closely associated pair, so that hints at a possibly colonial custom for these guys.

I haven't seen a source that lists a raised peristomial disc as a generic character for Gerda. Am I missing something? :) As I recall, your previous Gerda glans was easy to ID because of its rather bulbous posterior (an oddity of the species). This one is slender, like most Ophrydium, but also like the nominal species Gerda sigmoides or G. vernalis (the validity of which has been rejected by some workers, including Esteban et al., 2002). Without doing a lot more digging, I would just put it in Ophrydiidae. However, if you want to go deeper, a good place to start is Guhl's revision (in German, I'm afraid): https://www.sciencedirect.com/science/a ... 6585800154

D0c
Posts: 267
Joined: Mon Nov 30, 2020 9:13 pm
Location: England

Re: Ophrydiidae?

#3 Post by D0c » Fri Apr 16, 2021 5:19 pm

Thanks Bruce

I got the information source from the following websites:

https://www.nies.go.jp/chiiki1/protoz/m ... /gerda.htm
https://www.youtube.com/watch?v=8DYSQqSQwcI

The ophrydiid in the video does look like mine and he calls it a Gerda. I have discovered there is so much incorrect information and identification on the web.

I'm going to read up on this and delve a little deeper hopefully to genus level, I've kept the samples so can see if i can find more and make better observations.
Leitz SM-Lux

Bruce Taylor
Posts: 986
Joined: Fri Sep 04, 2015 11:34 am

Re: Ophrydiidae?

#4 Post by Bruce Taylor » Fri Apr 16, 2021 7:55 pm

Ah, OK. That description of Gerda, with the mention of a raised peristomial disk, is from Colin R. Curds's big book of British freshwater ciliates (published before Guhl's revision, which is why he retains Ophrydiopsis). He also mentions a raised peristomial disk for Ophrydium, so it isn't a useful way to distinguish the genera. The video is by Michel-Marie Solito de Solis, a lovely person, a fine artist and composer, and an enthusiastic amateur protistologist. I see he's quoting Curds, as well, probably via the same NIES site you consulted. The taxonomic echo-chamber of the internet. :D

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