Battery of Gun Cells in Haptoglossa mirabilis One of the gun cells has been fired and you can see the everted hypodermic with the infective sporidium at its tip. The fungus has missed its target or the sporidium would be inside the body of the rotifer or nematode under attack (click here). The one-celled thallus grows until it nearly fills the body cavity of the host (click here).
Mechanism of Action of Gun Cell in Haptoglossa
1.Haptoglossa mirabilis produces biflagellate zoospores that swim around for a while, then lose their flagella and produce a spherical cyst.
2. The cyst germinates to produce the gun cell (for detailed diagram click here )
3. The gun cell is anchored to the substrate or floating debris by the sticky mucilaginous base.
4. A harpoon-shaped projectile is housed inside the barrel of the gun cell (click here)
5. When a rotifer or nematode touches the tip of the gun cell it fires.
6. The projectile is shot through the muzzle of the gun cell.
7. The projectile blows a hole through the animal's epidermis.
8. The fungus everts a hypodermic-like syringe through the hole into the animal's body. The protoplasm and nucelus of the fungus are pumped throught the hypodermis using the osmotic power of the swollen basal part of the gun cell.
9. The soft tip of the hypodermic swells up to form a spore-like structure (sporidium).
10. The animal, reacting to the injection winces and swims off and the now mature sporidium breaks off and is released into the body cavity of the host nematode or rotifer.
11. Feeding on the host's nutrientas, the sporidium enlarges rapidly and to form a single-celled thallus that may completely fill the body cavity of the host.
12. The host dies and the parasite produces exit tubes to the exterior through which the zoospores escape.
Note: The entire process from # 6 - #11 takes place in about 1/10th sec.
What's in a Name
More than fifty years ago I was listening to a lecture in Botany at the University of Glasgow on Botany from an exceptional lecturer ('Sammy' Williams) who described to us a 'saprophytic' liverwort that had been recently found in Scotland although it had originally been described years before in Europe. This liverwort grew under the ground and was a yellowish white. It had no chlorophyll, so it was not photosynthetic and clearly must have received its carbohydrate energy from a source other than the sun. Nowadays, we know that this miraculous plant was in a mycorrhizal association with a fungus that was also mycorrhizal with a photosynthetic plant. So, in fact, the liverwort was getting its energy indirectly from the plant through the fungal hyphal system. It was probably getting mineral nutrients from the fungus and in effect was parasitic on both the fungus and the photosynthetic plant. It is the liverwort equivalent of the Ghost Plant Monotropa uniflora (Ericaceae) click here.
At any rate the liverwort was called Cryptothallus mirabilis (the miraculous liverwort with the hidden thallus). It is commonly called 'Ghostwort' ! At the time I remember thinking that it was well-named. Not only did the name trip easily from the tongue, it also neatly and clearly described the organism. I thought 'mirabilis' was an excellent descriptive epithet.
Over the years in my work on soil fungi and endoparasitic fungi of nematodes, rotifers and amoeba, I discovered and described many new species of fungal parasites of microscopic animals (amoebae, rotifers, nematodes, copepods, tardigrades, ciliates etc.). I never found anything remarkable enough to use the decriptive name mirabilis; at least not until I found the remarkable fungus I described as Haptoglossa mirabilis.
Thank you 'Sammy' Williams!
For a great lecture and a great species name for my Haptoglossa
Micrograph from MycoAlbum CD