Abstract This chapter introduces the Oligochaeta annelids, here treated as a paraphyletic stem group of the class Clitellata separated from the Hirudinea, Acanthobdellida, and Branchiobdellida. It starts by considering the group in a phylogenetic and taxonomic framework, as well as in terms of geographical distribution and diversity. It then deals with the general biology of these worms in describing their anatomy, physiology, reproduction and life history. Ecological and behavioral aspects of Oligochaeta are next addressed through topics related to habitat distribution and limitations due to physiological constraints, feeding behavior, predators and parasites, competition, impact on the environment, and their use as organic pollution indicators. By the end of the chapter, the scientific study of the Oligochaeta is addressed via practical aspects such as collecting, culturing, and specimen preparation for identification.
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The Latest Danian Event (LDE) has been recognized on the southern Tethyan margin (Egypt; Tunisia), and in the Atlantic (Zumaia, Spain) and Pacific Oceans (ODP Site 1209). Based on a supraregional carbon isotope excursion, and a negative shift in oxygen isotopes in the Pacific it has been suggested that the LDE is an early Paleogene transient warming event. So far the environmental effects of the LDE have been observed in few sections and details on its impact and duration are scarce. We present a quantitative study of benthic foraminiferal assemblages retrieved from five sections along a depth transect on the Paleocene southern Tethyan shelf (Nile Basin, Egypt) to assess paleoenvironmental change during the LDE. The lithologic sequences and foraminiferal assemblages indicate that the onset of the LDE is related to widespread shelf dysoxia. The organic-rich laminated marls of lower LDE bed I contain levels devoid of benthic foraminifera. During the later stage of the LDE (dark-gray shales of bed II) the shelf is repopulated by a Neoeponides duwi benthic assemblage, occurring in all sections, initiating a gradual restoration of normal-marine shelf environments. Q-mode and R-mode correspondence analysis assist in the interpretation of the N. duwi assemblage, which is related to disturbed conditions at the sea floor following oxygen depletion and increased organic loading. The sharp lithologic boundary at the base of the LDE suggests that the event coincides with a rapid transgression following a sea-level fall, with an estimated amplitude of ~ 50 m or less. Comparison with the Dan-C2 and ELPE/MPBE, two proposed transient warming episodes preceding and postdating the LDE, shows that the three Paleocene events have several characteristics in common. However, the duration of the LDE (~ 200 kyr) exceeds the estimated duration of the other events, and a sea-level cycle is only reported from the LDE.
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