Lernaea species are crustacean, copepod parasites that can infect and cause disease and mortality in many types of freshwater fishes, especially wildcaught and pond-raised species (both cultured and natural populations). L. cyprinacea (commonly known as Anchor worm), a parasitic cyclopoid copepod, is found worldwide; mostly in cyprinids. Several species (~110 species) of lernaeids (Lernaea and Lernaea-like parasites) have been described and L. cyprinacea, is one of the more common among them (1). The economic importance of lernaeids has increased in several parts of the world as the cause of one of numerous diseases among most farmed fish species; especially fingerlings, leading to death even with only a small number of infested lernaeids (2-4). Death of fish and/or associated damage is relative to the rate of parasitic infestation (5). Infestations occur more commonly in stagnant or slow-moving water bodies. L. cyprinacea, exhibits little host specificity and has been reported previously from a variety of freshwater fishes, frogs, frog tadpoles, and adult and larval salamanders. Although infestations are common in cyprinids, including koi, goldfish, and other related carp, numerous other freshwater species are susceptible (6-8). Lernaea species have nine stages in their life cycle, including three free-living naupliar stages, five copepodid stages and one adult stage. During development, the different stages live on and off the fish. After mating, the male copepod dies and the female bores into fish tissue, eventually using a large anchor anterior end "head" to permanently embed into the skin and muscle of the fish (9,10). This direct life cycle can take from 18 to 25 days to complete and only a fish (or an amphibian) is necessary for Lernaea spp. to develop from egg to mature adult. Common sites of Lernaea infestation include the skin, fins, gills, and oral cavity. Large numbers of lernaeids in their copepodid stages can kill small fish by damaging their gills and interfering with their breathing. Fish can survive with Lernaea infestation, but chronic conditions frequently result in poor growth and debilitation; the fish become more susceptible to secondary infection by bacteria and fungus which ultimately kills them (11-14) .

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Background: The structure of cordons is a principal characteristic in the identification of acuariid nematodes. The cordons of Desportesius invaginatus are formed of consecutive structurally elaborated plates of variable size and topography. Energy dispersive X-ray microanalysis (EDXMA) is an analytical technique that has been used to evaluate the element composition and crystalline nature of the body surface of cestodes, nematodes and acanthocephalans. It has been also used to measure the concentration of minor elements [sulphur (S), phosphorus (P), calcium (Ca) and potassium (K)] and trace elements (Fe, Zn). Objective: The present study was undertaken to investigate the concentration and distribution pattern of some chemical elements, namely: S, Ca and P in the cuticular elaborations of the cordon plates of D. invaginatus using dispersive X-ray spectrometry, aiming to supplement information regarding the composition and function of these structures. Results: Energy dispersive X-ray microanalysis revealed variations in the concentration of Ca, S and P in different regions of the cuticular ridges (tip, middle and base) of the three regions (anterior, middle, posterior) of the cordons of D. invaginatus. In the anterior region of the cordon, P was the highest in concentration followed by Ca then S; in the middle region, S exhibited highest concentration followed by P then Ca; while in the posterior region, S showed the highest concentration followed by Ca and P. The study revealed a specific pattern for the distribution and concentration of each element in relation to the region in the cuticular ridges of the cordons. Highest concentration of Ca and S was presented in the posterior region, where Ca decreased significantly towards the middle region to reach the lowest levels, then significantly increased again towards the anterior region; while S reached its lowest concentration in the anterior region, where P recorded its highest concentration. Conclusion: The concentration and distribution pattern of S, Ca, and P could be related to the anchorage function of the ridges. The high concentration of S in the base gives flexibility to these structures and facilitates the piercing action of the host tissue; while the accumulation of both Ca and P at the tip could result from the polymerization of both elements to give the rigidity and hardness that secure the position of the parasite in the host's tissue and prevent its detachment.