A new Hypotrich to ID

[NachoBen]

Here again searching help to ID a new freshwater critter.

Since its features are clear, it should be easy to ID, but I do confess that I still haven't become used to this difficult group.



Thank you everyone for any hint.

[Bruce Taylor]

Since its features are clear, it should be easy to ID

You might think so. We don't see the arrangement of ventral cirri clearly, but other features put it in the family Oxytrichidae. It is a compact cell, somewhat elongate, with two macronuclear nodules, enlarged, trailing transverse cirri, long marginal cirri (very long in the posterior), 3 prominent caudal cirri (important). A few dorsal bristles are glimpsed occasionally. I don't think it is Tetmemena (cell too slender and somewhat soft-looking), so that would likely put it in Oxytricha sensu Berger, 1999. Unfortunately, that genus has been split on the basis of features that are quite difficult to resolve without stains and sustained observation of a whole population (e.g. number of micronuclei and the behaviour of dorsal kineties during cell division). So, some historic species previously in Oxytricha are now in Monomicrocaryon and Quadristicha. We don't see micronuclei or dorsal ciliature here, and the undulating membranes (paroral and endoral) are also unclear. We don't see species characters that are so distinctive that we can bypass genus ID. So, that leaves us at family-level ID: Oxytrichidae.

[NachoBen]

Well, as far as we can go for now, problem solved (or this what I might think! ).

Thank You very much once again, Bruce!