Green Hydra Nematocysts

gpmatthews · Post by **gpmatthews** » Wed Feb 21, 2007 11:26 am

Further to my posting ages ago (http://www.photomacrography.net/forum/v ... highlight=) here are some more detailed shots of Green Hydra nematocysts:

Shows discharged cnidoblast and the cap can be seen as well on the RH at the base of the "neck"

Showing intact nematocysts. You can see the coiled threads in the upper ones

Both images:

Microscope: Zeiss Standard GFL
Ocular: Olympus P15
Objective: Leitz x100 NPL Fluotar ICT Oel (glycerin used instead of immersion oil)
Substage: Leitz ICT, NA 0.9 (not oiled)
(DIC)
Sample from Warnham Millpond (Dipping ponds)
Kept in jar in window for ~2 wks

Although it is about sea anemones for aquarists, this page has some descriptions that fit the nematocysts in my images very well and includes details of discharge:

http://www.reefland.com/rho/0505/main4.php

beetleman · Post by **beetleman** » Wed Feb 21, 2007 5:53 pm

Those are some nasty little barbs on that thing..and some animals can inflict some very painful and deadly venom with these small spears. Really interesting photos Graham...how the heck did you isolate just one ?

Charles Krebs · Post by **Charles Krebs** » Wed Feb 21, 2007 10:21 pm

These are really excellent Graham. You have succeeded in getting great looking DIC with the 100X!

gpmatthews · Post by **gpmatthews** » Thu Feb 22, 2007 5:14 am

Thanks for the comments.

The sample was prepared as follows: I used a large circular coverslip, vaselined around the edge. A drop of water with a single hydra was placed in the slide. For most water film preps I start with the slip at an angle in contact with the drop and then lower it until level with the slide. This minimises air bubbles. In this case the coverslip was dropped squarely on top of the water drop in order to avoid a mess with the vaseline. Excess water was drawn off with some absorbent tissue, the hydra given some time to expand, and then the coverslip was gently pressed down onto the hydra using a mounted needle until the hydra was lightly squashed. This will discharge many nematocysts, some of which will detach. In fact quite a large number were available for examination in detached state, so it was just a case of looking around for a good one to photograph. The vaseline helps slow down water evaporation and also stabilises the preparation so that the coverslip is not dragged around by the immersion oil/glycerin as the mechanical stage is adjusted.

Charlie, I was interested in the different appearance between your DIC images and mine. I always seem to get a creamy, almost embossed in white clay effect, rather than the clarity you achieve. It looks to me as though the Leitz DIC is the source of the difference, rather than anything photographic. Have you any experience with Leitz DIC optics?

Charles Krebs · Post by **Charles Krebs** » Thu Feb 22, 2007 10:00 am

Graham... no I don't, just Olympus. I too get the "embossed in clay" look then dealing with subjects that are transparent or "clear" with no real color of their own (such as your first picture above). With subjects that are more opaque and have good color it is quite different. (An example of both cases in the same shot would be this one).

The objective/prism combination I have for my 100X is not exactly right. Sometimes I like the look it gives, other times it seems too subtle and not really much different from oblique bright-field.

I now take about 95% of the DIC in the raw file format instead of jpg. While I can work an out-of-camera jpg to look pretty close if I try, I seems easier to get a result I like using raw.