Respiratory stratagems, mechanisms, and morphology of the ‘lung’ of a tropical swamp worm, Alma emini Mich. (Oligochaeta: Glossoscolecidae): a transmission and scanning electron microscope study, with field and laboratory observations
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The swamp worm Alma emini subsists in the highly productive waterlogged swamps around the East African Lake Victoria. The soil consists of putrefying plant matter from which gases like methane, carbon dioxide, and hydrogen sulphide are formed and profusely discharged. The interstitial spaces in the soil are generally anoxic and the soil is highly reducing. To survive in such an inimical habitat, Alma has evolved a remarkably unique respiratory strategy. The posterodorsal part of the body, which is well supplied with blood, is regularly converted into a ‘lung’ across which gases are exchanged at the surface or under water. Air and/or water may be entrapped in the ‘lung’ and carried for use (as a source of oxygen and/or a depository of carbon dioxide) during the ensuing underground sojourn. By evolving a unique respiratory potential, Alma emini has been able to flourish in a highly dynamic and virtually anoxic habitat while essentially having a capacity for aerobic biochemistry. Putative indications of cellular adaptations against hydrogen sulphide toxicity were observed, especially in the cells that line the ‘lung’. A. emini presents a good example of nature's tenacious and innovative designs for surviving in severe environments.