Morphology and Ecological Characteristics of Paracyclops Novenarius Reid, 1987: A Cyclopoid Copepod Inhabiting a Highly Contaminated Aquifer in Central-North of Mexico

Abstract This work reports the freshwater copepod Paracyclops novenarius, in a water body with high arsenic concentrations. Morphologic analysis, abundances, body size of the copepod and physical and chemical variables of the water (including arsenic concentrations) were evaluated in two different climatic seasons (rainy and dry). Morphological analysis showed that the high arsenic concentrations do not affect the morphology of P. novenarius, including all its development and adult instars. The highest abundances of this species were found in the dry season for all development stages, with values ​​of 1.51 and 1.50, 4.46, 0.21 ind/L-1, for nauplii, copepodites, females, and males, respectively. However, these values are lower than other aquatic systems of the region and the world, without polluting agents. The highest arsenic concentration was found in the dry season (58 mg/L-1) and the lowest during the rainy (54.5 mg/L-1). The body size of the analyzed organisms was larger in rainy compared to dry, with an average of 637.2 ± 42 µm for females and 650 ± 37 µm for males. A Mann-Whitney U test showed significant differences in lengths by season and by arsenic concentration (U = 1284.5, U = 1284.5; p < 0.05). The results of this study could provide information for environmental impact assessments on aquatic systems.