Example of Organism of phylum nematoda not having protonephridia for excretion.
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Aquatic invertebrates primarily excrete their nitrogenous waste in the form of ammonia, a highly toxic waste product of amino acid catabolism. However, very little is known about the mechanism and for that fact the tissues that are actually responsible for ammonia excretion in freshwater and soil-dwelling invertebrates. This chapter provides an overview of the current literature examining the ammonia excretion mechanisms in three phyla: Nematoda, Platyhelminthes, and Annelida. The introduction will briefly cover the challenges faced by freshwater and soil-dwelling invertebrates in terms of their ionoregulatory capabilities in addition to a general overview of nitrogenous waste excretion in aquatic invertebrates. Subsequently, nitrogenous waste excretion in the nematodes, annelids, and platyhelminthes will be discussed with an emphasis placed on the potential tissues involved in ammonia excretion, e.g., the nephridial system, epidermis, hypodermis, intestine, and the nematode-specific excretory system. This chapter will also provide an extensive review of the cutaneous ammonia excretion mechanism in two freshwater representatives of the phyla Annelida and Platyhelminthes, the ribbon leech (Nephelopsis obscura) and planarian (Schmidtea mediterranea). Additionally, the mechanisms of hypodermal ammonia excretion in the soil nematode (Caenorhabditis elegans) will be discussed in comparison with the mechanisms seen in N. obscura and S. mediterranea. Here a focus will be placed on the role of Na+/K+-ATPase, Na+/H+ exchangers (NHEs), H+-ATPase, Rhesus (Rh) proteins, and vesicular transport. With increasing studies on freshwater and soil-dwelling invertebrates, common mechanisms to that seen in more widely studied vertebrates are becoming more and more evident
In many marine nematodes, one or two unicellular 'renette glands' excrete salt through a pore on the underside of the animal, close to the pharynx. In most other nematodes, these specialized cells have been replaced by an organ consisting of two parallel ducts connected by a single transverse duct.