Radiolarian in Rheinberg Illumination

The radiolarian exoskeleton (test) presented above was captured utilizing a Nikon Optiphot microscope operating in Rheinberg illumination mode with an achromatic condenser and 20x fluorite objective. The Rheinberg filter pack consisted of a dark blue central filter surrounded by yellow and red annular filters positioned at 90-degree intervals. Successive optical serial sections of the specimen were recorded on a Nikon DXM 1200 camera system attached to the microscope, and merged together with an image-editing software package (Adobe Photoshop). By adding optical sections and removing out-of-focus blur, a more detailed image of the skeleton can be obtained. The specialized Rheinberg illumination technique, a form of optical staining, enhances the apparent three-dimensional effect of the photomicrograph and increases contrast in the specimen image, revealing details of the thoracic pores.

The specimen, most likely a member of the Carpocanistrum genus (family Carpocaniidae : order Nassellaria), is characterized by a head region (referred to as the cephalis) that is similar in structure to the ovate body (thorax) with longitudinally aligned pores. As with other radiolarians, the pores provide openings for extension of the pseudopods employed in prey capture and limited locomotion. Note in the photomicrograph that the head region is positioned at the top of the thorax, and there is an internal collar ring containing four pores that serves to separate the two regions. Depending on the position of the mouth, the thorax of these radiolarians is highly variable in shape, ranging from nearly cylindrical (when the mouth is open) to almost spherical (when the mouth is closed). Members of this marine planktonic group are found in the southern two-thirds of the Gulf of California, but can often be located further north where they are sometimes carried by ocean currents.

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