Homalozoon multinucleatum

I first began seeing these about 12 years ago, in the Mer Bleue.  They looked very much like Homalozoon, but were quite small and had a single, centrally located contractile vacuole. Since then, I’ve also encountered them in a bog pool in Chisasibi, in the Eeyou Istchee region of northern Quebec.

When I first encountered the morphotype, I sent an inquiry to a leading expert on haptorids, the late Wilhelm Foissner, who told me there was a “realistic chance it is a new species.” However, a couple of months ago, I noticed a very brief entry in Foissner et al., 1995 (the fourth volume of their “ciliate atlas”) concerning “H. multinucleatum DRAGESCO (nur I kontraktile Vakuole in Körpermitte).”  This is almost certainly the species I’ve been seeing. It must have slipped Foissner’s mind when he wrote to me.

The original description is in: Dragesco, J. (1966b): Cilies libres de Thonon et ses environs. – Protistologica, 2: 59-95.  Unfortunately, digitized copies of articles in Protistologica (if they exist at all) are not available to me. 

It is a haptorid, with an oral bulge and an arsenal of toxicysts arranged in a fan-shape.  It is reminiscent of the common Homalozoon vermiculare, however, this ciliate is much smaller (130 µm, on average), and has a single contractile vacuole, located near the center of the cell. If the vacuole were more posterior, I would take it for a Spathidiid. However, the location of the CV is very atypical for that group. Macronucleus is nodular.

From an ombrotrophic marsh attached to Mer Bleue sphagnum bog. Collected in early May, 2013.

Length on average ~130 µm