Life in an ‘Organic pond’

Life in an ‘Organic pond’ – Part 2

TCIS Outreach | Sat, Nov 09, 2019, 10:46 PM

Let’s explore more of the life in an ‘organic’ pond, continuing with the same water sample that we investigated for the last post .

I now noticed a larva, about 5 mm long, swimming in the water. It was moving very fast, but I patiently followed it with a dropper and was finally able to pick it up and place it on a glass slide. I imaged it under my Foldscope with an iPad.

While observing the legs of the larva under the foldscope I noticed little round or bell-shaped organisms attached to both legs by stalks. Periodically the stalks contracted, while cilia beat continuously around the mouth-end of the organisms. These are surely the beautiful Vorticella sp.!

From other posts on microcosmos (by @damontighe and @akshathanayak ) I had learnt that Vorticella live on mosquito larvae and Ambiphyra sp. on fish gills ( @manup ). These relationships might be any one of mutualism, commensalism or parasitism . When I focused on this larva’s abdomen I saw tracheal gills on both sides, with the lovely vorticella swinging from them!

In this video you see the breathing of the larva with fanning movements of its gills. At the same time, the Vorticella cilia are working away, profiting from the rapid water currents. Imagine how the vorticella hold fast near the gills amidst this flurry of movement!

The larva that I observed has external gills, three tails and no wriggling movement, so it is definitely not a mosquito larva! I thought it may be a nymph of a Damselfly or a Mayfly. It looks long and slender, like a Damselfly nymph, but the external gills are on the abdomen, not at the tip of the abdomen. So I guessed it may be a nymph of Mayfly. Here is a nice guide that I consulted.

Still wondering about this I returned to the pond to confirm, and there I noticed an underdeveloped insect on grass, without wings but with a long slender abdomen, like a Damselfly. I saw dragonflies flying over the pond, but I didn’t see any Mayflies near or above the pond water. I still don’t know, what could be this larva?

Next I collected some water from another corner of the pond, where there was a fish swimming around. I collected filaments of algae, which included Cyanobacteria, Spirogyra sp. and Zygnema sp. .

Then I noticed that one of the filaments was non-uniform in thickness, and with a clear outer layer of cells. I scanned along the length of this filament with the foldscope… and surprise!! At the other end of the filament were six leaf-shaped tentacles! This is is no algae, it’s a Hydra sp.!

Long ago in my college days I had seen only pink (stained) Hydra in permanent slides. Now for the first time in my life I saw a live Hydra! Thank you foldscope! But why is this Hydra green in colour?

Wikipedia clarified for me that this must be Hydra viridissima which has a symbiotic relationship with the green algae Chlorella vulgaris . What a flexible body it has! At the same moment that I was observing, it contracted its body and looked just like a green lotus with a stalk!

At first I saw only the column of its body stretched in search of food. Later I saw it was stretching out its tentacles to almost half of its body size.

The Hydra’s feeding is quite interesting. It has biting cells called nematocysts. These cells release toxins when the Hydra touches its prey, to paralyse it. Finally its tentacles catch the prey and push it into its mouth. I actually watched a Hydra trying to paralyse its prey (a rotifer) but luckily for the prey it managed to escape!

Later on I saw one colourless Hydra with four tentacles. It is Hydra vulgaris . Enjoy its dance!

I kept watching the Hydra hoping to see its budding but then… something else interesting happened. A Chaetogaster was engaged in weight lifting! It looked as if it way trying to hoist a dumbell-shaped weight, but it failed. What are those weights? Are they ciliates attacking the Chaetogaster or is the Chaetogaster attacking them?

I tried to video the drama unfolding before me. As it was a long scene I took two videos. Was this one big ciliate? Can any one help figure out this mysterious event? All around the main action, large ciliates were rushing around and diatoms were shining brightly.

Such memorable experiences! I want to continue my work on water samples for the wonderful experiences that these tiny creatures are giving to me and to my friends.

Cheers,

Ashalatha

with Jayashree and Chandrika