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Underwater Photographer's Critter Corner- Phyllodesmium Rudmani
 March 4, 2009 @ 02:00 AM (EST)

By Jeff De Guzman

Underwater Photograph of Phyllodesmium rudmani
Canon 400d, Canon 100mm Macro USM, Woody Diopter, 2x Inon Z240s, Sea & Sea Housing. F-stop: f/22, Shutter Speed: 1/200 sec, ISO Speed Rating: 100

Phyllodesmium rudmani is a very unique nudibranch that mimics Xenia coral. The only way you can tell if it is a nudibranch is that it has rhinopores. Technically, it is distinguished by the cerata having long cylindrical stalks with a swollen region on top. That distended region has about 8, white, longitudinal ridges separated by deep, brown or brownish purple grooves. Thus each ceras mimics a polyp of the soft coral Xenia (the specific host food of this species) with its tentacles closed together.

Here are five tips on how to photograph Nudibranchs.

1. In general Nudibranchs are very small ( 1mm to 4 inches) - closeup filters and wet diopters are a must to help fill the frame with the subject.

Examples of quality closeup filters that will produce minimal chromatic aberrations

Underwater photography diopters



Underwater photography diopters

*some of these are no longer in production, but may sometimes be found at used photographic dealers or online classifieds and auctions.

Popular Wet Diopters currently on the market


  • Subsee Adapter from ReefNet - a +10 wet diopter, giving over 2:1 magnification with 100/105mm lenses.

  • Woody Diopter - 25% magnification

  • Macro Mate - provdes a 2:1 ratio on a Canon 100mm or Nikon 105 mm lens

2. Avoid shooting Nudibranchs from the top down, a head on shot is more dramatic and esthetically more pleasing.

3. Employ the the diagonal lines, try to position the gills on the top left of the frame and rhinophores on the bottom right. Sometimes, this not be possible due to the position of the Nudibranch - a quick "Flip Horizontal Canvas" in Photoshop should do the trick.

4. Reading and immersing yourself in identification/behavior books will broaden your knowledge of what is out there to see and photograph. Books provide hints on how to find critters based what they eat and where they live.

5. Glide very slowly over the sand or reef, keeping your eyes peeled for any movement. Periodically stop and hold very still, when you exhale observe any sudden movements on the reef or sand.


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