What do forams and diatoms have in common

There are several features of a phytoplankton cell that can identify it as a diatom or dinoflagellate. Details about site history, funding, and sources of information and images can be found here. Diatoms are commonly between microns in diameter or length, although sometimes they can be up to 2 millimeters long. The cell may be solitary or colonial attached by mucous filaments or by bands into long chains.

Diatoms may occur in such large numbers and be well preserved enough to form sediments composed almost entirely of diatom frustules diatomites , these deposits are of economic benefit being used in filters, paints, toothpaste, and many other applications.

This site concentrates on marine diatoms since information on feshwater diatoms is already available at the Environmental Change Research Centre at University College London as well as many other web-sites. Please see the links page for more links to diatom resources available on the web. Diatoms have been studied since the late eighteenth century, however the first real advances in the field came in the early nineteenth century when diatoms were popular with microscopists utilising the emerging improvements in microscope resolution.

Several European workers produced hand illustrated monographs on diatoms in the late nineteenth century. In the early twentieth century fossil diatoms were first studied and, most famously, Hustedt produced a taxonomic and ecological study of diatoms which remains a key reference today.

Perhaps the most complete treatment of diatoms is that of Round et al. First recorded occurrences of diatoms are from the Jurassic, however, these are uncertain and the earliest recorded well preserved diatoms are centric forms from the Aptian-Albian stages of the Cretaceous.

Since these are quite diverse assemblages it is assumed diatoms have an earlier evolutionary history, perhaps lacking a relatively robust silica frustule. As with coccoliths, the earliest forms in the fossil record may reflect a biomineralisation event rather than an evolutionary appearance. The earliest araphid lacking a raphe pennate diatoms appear in the Late Cretaceous, and raphid pennates in the Middle Eocene. In a similar manner to Radiolaria, it has been noticed that there has been a gradual progression towards less heavily silicified frustules, probably as a result of increasing competition for a limited resource silica.

Diatoms are divided into two Orders. The Centrales now called the Biddulphiales which have valve striae arranged basically in relation to a point, an annulus or a central areola and tend to appear radially symmetrical, and the Pennales now called Bacillariales which have valve striae arranged in relation to a line and tend to appear bilaterally symmetrical. The valve face of the diatom frustule is ornamented with pores areolae , processes, spines, hyaline areas and other distinguishing features.

It is these skeletal features which are used to classify and describe diatoms, which is an advantage in terms of palaeontology since the same features are used to define extant species as extinct ones. These tiny fossils include whole skeletons or parts thereof so small that they cannot be seen by the naked eye and thus a microscope of some kind is required to see them.

They include representatives from most phylogenetic groups—animals, plants, protists, algae, and various microbes Fig. Bacteria and algal eukaryotes go back even farther, some to the origin of life itself at nearly 4 billion years. Single-celled protists with skeletons, like foraminifera, radiolaria, diatoms, coccoliths, tintinnids, silicoflagellates, and others, are abundant in both marine and nonmarine Phanerozoic rocks.

Microfossils are not commonly collected by avocational paleontologists, although in the past, people with microscopes, like doctors or their spouses, collected diatoms micro-algae with siliceous skeletons and arranged them on glass slides into pictures formed by their unique shapes and patterns.

These were traded among the advocates. Foraminifera forams were rarely collected by amateurs, even though they are easily retrieved from marine rocks exposed in most places in the world and have been around since the latest Precambrian. Forams also are perhaps the best known microfossils because they have been intensely studied scientifically in geology since the late s for biostratigraphic and paleoenvironmental interpretations, particularly in the oil industry, and more recently in modern ecology and biology, including phylogenetics.

Forams Fig. They have occupied every marine habitat from the very deepest oceans to the shallowest pelagic and near-shore. Infaunal forms are probably detritivores and commonly have elongate tests to facilitate movement through the substrate.

Benthic and planktonic foraminifera which inhabit the photic zone often live symbiotically with photosynthesising algae such as dinoflagellates, diiatoms and chlorophytes.

It is thought the large benthic, discoidal and fusiform foraminifera attain their large size in part because of such associations. Foraminifera are preyed upon by many different organisms including worms, crustacea, gastropods, echinoderms, and fish. It should be remembered that the biocoenosis life assemblage will be distorted by selective destruction by predators. Of the approximately living species of foraminifera the life cycles of only 20 or so are known.

There are a great variety of reproductive, growth and feeding strategies, however the alternation of sexual and asexual generations is common throughout the group and this feature differentiates the foraminifera from other members of the Granuloreticulosea. An asexually produced haploid generation commonly form a large proloculus initial chamber and are therefore termed megalospheric.

Sexually produced diploid generations tend to produce a smaller proloculus and are therefore termed microspheric. Importantly in terms of the fossil record, many foraminiferal tests are either partially dissolved or partially disintegrate during the reproductive process.

The planktonic foraminifera Hastigerina pelagica reproduces by gametogenesis at depth, the spines, septa and apertural region are resorbed leaving a tell-tale test. Globigerinoides sacculifer produces a sac-like final chamber and additional calcification of later chambers before dissolution of spines occurs, this again produces a distinctive test, which once gametogenesis is complete sinks to the sea bed.

WARNING: Please remember all preparation techniques require the use of hazardous materials and equipment and should only be carried out in properly equiped laboratories, wearing the correct safety clothing and under the supervision of qualified staff.

Foraminifera range in size from several millimeters to a few tens of microns and are preserved in a variety of rock types. The preparation techniques used depend on the rock type and the "predicted" type of foraminifera one expects to find. Very hard rocks such as many limestones are best thin sectioned as in normal petrological studies, except instead of grinding to a set thickness commonly 30 microns the sample is ground very carefully by hand until the optimum thickness is obtained for each individual sample.

This is a skilled job and requires expensive equipment but provides excellent results and is particularly used in the study of larger benthic foraminifera from reef type settings. Planktic and smaller benthic foraminifera are prepared by crushing the sample into roughly five millimeter fragments. The length of time the sample is left to simmer depends on the rock type involved and if peroxide is used the sample should not be left immersed in the solution for more than about half an hour.

Next, the material is washed through a 63 micron sieve untill the liquid coming through the sieve is clean i. The sample can then be dried and sieved into fractions generally microns, microns, microns and greater than microns using a "nest" of dry sieves. Care must be taken to clean all sieves and materials used between the preparation of each sample to prevent contamination. Thin sections are veiwed using transmitted-light petrological type microscopes.