A total of 106 genera of nematodes was recorded, among which 19 were recorded in the closed lagoons, 71 in the intermittently open/closed, and 68 in the open lagoons (Table 1). Most of the nematode genera recorded in open lagoons (70.5%) were those typically found in brackish or marine waters. This proportion was reduced in ICOLLs (49%) with an increasing number of brackish/freshwater or freshwater genera. In closed lagoons, freshwater or brackish/freshwater genera accounted for 95% of the collected fauna. Only 5 genera occurred in all the three types of lagoons, namely Anonchus (Aphanolaimidae), Anoplostoma (Anoplostomatidae), Desmodora (Desmodoridae), Dichromadora and Hypodontolaimus (Chromadoridae). The percentage of exclusive genera (those found exclusively in only one type of lagoon) decreased with increasing connectivity: 13 genera occurred exclusively in the closed lagoons (65%), 26 in the intermittently open/closed (35%) and 21 in open lagoons (30%; Table 1). Trischistoma (Trypilidae), Semitobrilus (Trobilidae) and Ironus (Ironidae) were the most abundant genera in closed lagoons, accounting for 55% of the nematodes collected. At the intermittently open/closed and open, the genera Microlaimus (Microlaimidae), Spirinia and Desmodora (Desmodoridae) were the most abundant genera in both types of lagoons (Table 1).