Chapter 20. Cyanobacteria identification 6 (species 2 and 3)

This is mainly as an excuse to post more microscopic images of cyanobacteria, but I thought I would explain why I have started calling species 2 "possibly Lyngbya" and attempt to identify species 3.

Three filamentous cyanobacteria from a freshwater aquarium. Identified by an amateur at the genus level as;  Lyngbya (thick filaments), Jaaginema (sinuous filaments), and Romaria (short filaments).

From Chapter XIV (where I wrongly identified species 1), I know that species 1 is 2 micrometers wide because I measured some filaments under the microscope using eyepiece and stage graticules. By my calculations, depending on which photo I take measurements from, species 2 is somewhere between 8-10 micrometers. So, using the same key I used to more accurately identify species 1 in Chapter XVI, we get.

Q1. Are the filaments 3 micrometers wide or more?  A-Yes. Q2. Are the filaments cylindrical, long, sometimes constricted at the cross walls, but cells not barrel shaped or sub-spherical? A-Yes. Q3. Are the cells short, always shorter than one half the cell width? A-Yes. Then we come to the crunch. Q4. Are the filaments in vegetative state always without sheaths (if present formed only under stress)? Sheaths again! The problem is that the species 2 sample I examined in Chapter XVI  which showed clear evidence of sheaths, could have been stressed because it had sat around for a week. So I examined a fresh sample.

Filamentous and unicellular cyanobacteria from a freshwater aquarium.

No evidence of sheaths in this sample, but note the dark stripes along the filaments, it is at these necridia that the filaments fragment. I added some very small glass beads to the sample and vortexed briefly. The idea was that if I damaged the filaments I might see evidence of sheaths.

Fragmented sample of filamentous cyanobacteria from a freshwater aquarium.

It seems to me that the filaments have fragmented at the necridia. Many filaments now seem to have the remains of necridia at their end. This could happen if the filaments lacked sheaths so it doesn't tell me much.

Diatoms alongside unicellular and fragmented filamentous cyanobactera from a freshwater aquarium.

These fragments don't even have the remains of necridia at there ends. Maybe the fragmentation was too vigorous. What I really need is to slightly damage the filaments. Perhaps in the future I will find a way of doing that. But there is some evidence of sheaths here.

Fresh cyanobacteria sample from a freshwater aquarium showing evidence of sheaths.  Possibly Lyngbya.

So, if it's Q4. A-No to trichomes always without sheaths then it's Yes to "Trichomes in vegetative state always within distinct sheaths (only hormogonia and reproductive trichome segments can be without sheaths)". Q5. Do the filaments contain one trichome per sheath, forming mats? A-Yes = Lyngbya.  Of course it's possible that I have a mixture of species, some with sheaths (Lyngbya) and some without (Oscillatoria).

Possible Lyngbya filaments showing evidence of sheaths.

If you search for pictures of Lyngbya you will find some very similar images to the species 2 photos I have posted in this and other chapters.

Finally species 3. Q1. Are the trichomes less that 3 microns wide? A-Yes. Q2. Are the trichomes without sheaths or within simple, thin sheaths (when present always one trich/sheath) solitary or in mats, trichomes isopolar (both poles with same morphology)? A-Yes. Q3. Are the trichomes without sheaths, but may possess wide or diffuse mucilaginous envelopes? A-Yes. Q4. Are the trichomes straight, wavy, or irregularly coiled? A-Yes. Q5. Are trichomes mainly short, curved or irregularly coiled, usually only few celled, disintegrating , sometimes enveloped by an indistinct wide mucilaginous envelope, neighbouring cells occasionally disorganised? A-Yes (I guess) = Romaria. I can't find any photos of Romaria so I think I'm on shaky ground with this one. Correct me if I'm wrong.