INTRODUCTION

Benthic foraminifers play a central role in deep-sea paleoceanographical research because of their geographic ubiquity, their abundance in Cretaceous to Recent deep-sea sediments, and because of their utility as indicators of environmental conditions both at and below the sediment-water interface. Additionally, stable isotopes and geochemical tracers obtained from the foraminiferal tests provide environmental information that is of major significance in studies of global climatic change. Nevertheless, the taxonomy of benthic foraminifers remains extremely unwieldy. The standard of published illustrations and descriptions of type specimens in major museum collections, which serve as the basis of benthic foraminiferal taxonomy, varies enormously in both quality and accessibility. This is mainly due to the fact that taxonomic terminology is not standardized, and that descriptions and illustrations are dispersed in a wide range of publications that have strong historical or regional connotation. Because of these factors, taxonomic work with benthic foraminifers all too often represents a cumbersome task, that prohibits real evaluation and data synthesis, as well as severely compromising the use of benthic foraminifers for paleoceanographical research.

Line drawings have been used to illustrate benthic foraminiferal morphology since the late eighteenth century. While some of these illustrations are true works of art, most benthic foraminiferal line drawings are simplistic and often neglect to include important taxonomic characters. Light micrographs are, in principle, superior to line drawings in the sense that they provide a more accurate record of the morphology. This type of illustration also has the advantage of closely resembling what is actually seen in the microscope. However, there are inherent limits on the resolving power of the microscope due to the wavelength of light. At the relatively high magnifications required to resolve many of the structural elements of the benthic foraminiferal test, the focal plane is often much narrower than the size of the structures being examined. This means that the entire structure cannot be brought into focus simultaneously. Taxonomists compensate for this by adjusting the microscope's focus so that they are able to scan the structure and construct a composite image in their mind. Nevertheless, even at relatively low magnifications, light micrographs of benthic foraminifers appear blurred and out of focus.

The development of the Scanning Electron Microscope (SEM) in the late 1950s held the promise of solving the focal plane depth problem for micropaleontological imaging. Even at the highest conceivable magnifications employed for benthic foraminiferal taxonomic study, SEM photomicrographs usually exhibit adequate focal depths, and have become the standard mode of micropaleontological illustration. However, as the SEM collects electrons emitted from a thin metallic film deposited on the surface of the benthic foraminiferal test, it is unable to image any of the taxonomically important characters (e.g., suture patterns, chamber numbers) that lie below the test surface.

First attempts to overcome this problem were made in the 1980s with the development of a technique that used a Scanning Light Microscope (Scott et al., 2000). This allowed a composite photograph of the specimen to be taken as it moved through a lighted focal plane with a bandwidth of 50-100 microns. However, this system has several limitations: 1) smaller specimens may be of smaller width than the light bandwidth; 2) the magnification of the system is limited (i.e., to x 40 for the system used by Scott et al., 2000); 3) the horizontal narrow band lighting may fail to illuminate some parts of the test, resulting in an unequally lighted illustration with markedly darker areas; and 4) the images obtained still have to be digitized.

Over the past several years, researchers at The Natural History Museum, London have been investigating and developing techniques that employ digital images to overcome the limitations of light micrographs. These digital imaging techniques involve taking a number of images per specimen. This image set constitutes a series of `slices' taken sequentially at different focal plane depths such that all aspects of the specimens' morphology are captured within an in-focus slice for the set in aggregate. A composite image is then built up by combining the areas in each image slice that are in focus. The resulting composite image is a true-colour image of specimen viewed in transmitted and/or reflected light with full focus throughout the field of view. These images, while not completely replacing other methods of illustrating foraminifers, are the most realistic and representative view of what the micropalaeontologist actually 'sees' through the microscope tube. They are particularly useful when illustrating previously un-illustrated or poorly illustrated type specimens, and the technique has the added benefit of not altering the original specimen.

We have compiled a digital database of deep-water benthic foraminifers which comprises sets of fully focused, composite images and standardized, taxonomic descriptions that consolidate previous taxonomic efforts by individuals and research groups. The use of consistent morphological descriptors (Appendix 1) also provides a structured and searchable framework, that facilitates comparison between species and identification. We present here a selection of records from the database, and document 36 benthic foraminiferal taxa including ten holotypes, four paratypes, three syntypes and one lectotype. We illustrate whenever possible type specimens, mainly deposited in collections of the Smithsonian Institute; The Natural History Museum, London (Challenger foraminifera), and Krakow University, for which only drawings or black and white illustrations are available. We additionally illustrate well-preserved material, mainly topotypic, from deep-sea cores, commercial wells, and land sections. For selected species, SEM micrographs are given for comparison.

We have focused on agglutinated taxa to highlight morphologic features such as wall texture, grain and cement composition, test colour and opacity, chamber arrangement, shape of sutures, and inner structure including early ontogenic stages, as these represent important taxonomic criteria that are not otherwise detectable in SEM illustrations. We have additionally focused on some calcareous groups that are of stratigraphical and/or paleoecological significance for ODP/IODP studies, but had a particularly confused taxonomic history including the genera Stilostomella, Planulina, and Cibicidoides, in the hope that the new illustrations and descriptions might contribute to the clarification of their taxonomy.

Digital Imaging Equipment Used At The Natural History Museum, London

The specimens were imaged using either a Kontron Electronic ProgRes 3012 camera scanner, attached to a Leica Diaplan Microscope or an Allen Compact Video Microscope. Using an image manipulation application (e.g., Adobe Photoshop) a fully in focus composite image was produced. By applying further standard digital processing techniques (e.g., sharpening, colour and level balance, brightness/contrast and the addition of a uniform background colour), the final image was completed.

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