Huvadhoo Atoll is a little-known and generally uncontaminated atoll of the southern Maldives, although the human pressure is increasing. This study represents the first attempt to characterize the meiofaunal and nematode assemblages of its lagoon both from a taxonomic and functional point of view. The nematode assemblage was made up of a total of 131 genera in 33 families. Desmodoridae, Chromadoridae and Xyalidae represented the richest and most abundant families, followed in terms of abundance by Selachinematidae and Comesomatidae. The nematode richness was overall higher than that reported in the previous studies carried out in the Central part of the archipelago. The diversity patterns revealed higher values than those reported for the back-reefs platforms, so confirming the positive influence of the water depth on the biodiversity of the nematode assemblage. The statistical analysis highlighted a significant taxonomic difference of the assemblages between the stations characterized by fine and medium-coarse sands, respectively, in line with the auto-ecological preferences of the taxa detected. The use of some nematode descriptors for assessing the ecological quality status (EQS) of the lagoon has revealed a slight disturbance in the station close to Viligili, one of the most urbanized islands. However, the summarization of all the descriptors used allows the highlighting of the good EQS of the Huvadhoo lagoon. Thus, the results of this study may be taken as the starting point for the future monitoring of the potential and real impact of the anthropogenic activity on the area over time.

Two nematode species living in association with chemoautotrophic prokaryotes were found in two deep-sea canyon/channel systems, the Whittard Canyon and Gollum Channels, north-east Atlantic. Parabostrichus bathyalis gen. nov. sp. nov. (Desmodorida: Desmodoridae: Stilbonematinae) relates to Eubostrichus Greeff 1869 but differs in having well-developed paired dorso-caudal apophyses of the gubernaculum, small pre- and postcloacal latero-ventral papillae with short apical setae, elongate tail with slender posterior portion, and the absence of thorn-like setae (porids) in males. Body of P. bathyalis is loosely covered with elongate cells of prokaryote ectosymbionts. Astomonema southwardorum Austen et al. 1993, originally found at a methane seep pockmark in the North Sea, constitutes a significant portion of nematode communities in certain areas of the deep-sea canyon/channel systems. Taxonomic difficulties within Astomonematinae are discussed in light of the character state of paired male gonads discovered in A. southwardorum. Canyon populations of A. southwardorum are characterized by frequent loss of part of the hind body and wound healing posterior to the vulva in females. Both species tend to occur in deeper subsurface layers of the bottom sediment. Abundance of the nematode species associated with aggregations of ectosymbiotic (Parabostrichus) and endosymbiotic (Astomonema) chemoautotrophic bacteria may indicate reduced conditions at sites in these deep-sea canyons/channels and suggests a potentially substantial ecological role for chemolitotrophic fauna there.