Molecular characterization of free-living nematodes from Kermadec Trench (Nematoda: Aegialoalaimidae, Xyalidae) with description of emAegialoalaimus/em emtereticauda/em n. sp.

The Kermadec Trench is the world's fifth deepest trench and extends from approximately 26 to 36°S near the northeastern tip of New Zealand's North Island. Here, we describe a new species of Aegialoalaimus, a nematode genus with unusual buccal cavity and pharynx morphology, from a site at 9540 metres water depth in Kermadec Trench, and provide the first SSU and D2-D3 of LSU sequences for Aegialoalaimus, Manganonema, Metasphaerolaimus constrictus and Daptonema amphorum. Aegialoalaimus tereticauda n. sp. is characterised by body length 755-864 µm, cephalic sensilla papilliform ( 1 µm long), excretory pore located slightly anterior to posterior bulb in males and slightly anterior to nerve ring in females, arcuate spicules 18-22 µm long, gubernaculum present, precloacal supplements absent, and cylindrical tail 58-64 µm long with rounded tip. Relationships between Aegialoalaimus and Chromadorean orders could not be elucidated based on our SSU analysis; no link could be found with the Plectida, where the Aegialoalaimidae is currently placed, or with the Isolamiida or Cylindrolaimus (Areaolaimida), which share a similar and unusual buccal and pharynx morphology. Our SSU phylogenetic analysis confirms the placement of Manganonema within the Xyalidae, although relationships with other xyalid genera remain unclear. The Sphaerolaimidae formed a clade together with the Monhysteridae, which contradicts the current classification where the Sphaerolaimidae and Xyalidae are classified together into the superfamily Sphaerolaimoidea and the Monhysteridae into the Monhysteroidea. Although limited research has been conducted on the nematode diversity in Kermadec Trench to date, the available data show that half of all invertebrate species known from the trench are nematodes, which highlights the importance of conducting further taxonomic research on this group in hadal environments.

emEubostrichopsis/em emjohnpearsei/em n. gen., n. sp., the first stilbonematid nematode (Nematoda, Desmodoridae) from the US West Coast.

A new genus of the marine Stilbonematinae (Nematoda, Desmodoridae) is described from the Pacific coast of the United States of America. The worms inhabit the sulfidic sediment among the roots of the surfgrass Phyllospadix sp. in the rocky intertidal. The ectosymbiotic coat is of a new type for Stilbonematinae. It consists of rod-shaped bacteria pointed at both poles densely attached with one pole to the host cuticle. This is the first report of this symbiotic nematode subfamily from the US West Coast.

Flatworm mucus as the base of a food web.

BACKGROUND: By altering their habitats, engineering species can improve their own fitness. However, the effect of this strategy on the fitness of coexisting species or on the structure of the respective food web is poorly understood. In this study, bacteria and bacterivorous nematodes with short (Caenorhabditis elegans) and long (Plectus acuminatus) life cycles were exposed to the mucus secreted by the freshwater flatworm Polycelis tenuis. The growth, reproduction, and feeding preferences of the nematodes in the presence/absence of the mucus were then determined. In addition, confocal laser scanning microscopy (CLSM) was used to examine the structural footprint of the mucus and the mucus colonization dynamics of bacteria and protozoans. RESULTS: Mucus exposure resulted in a greater reproductive output in P. acuminatus than in C. elegans. In a cafeteria experiment, both nematode species were attracted by bacteria-rich patches and were not deterred by mucus. CLSM showed that the flatworms spread a layer of polysaccharide-rich mucus ca. 15 µm thick from their tails. Subsequent colonization of the mucus by bacteria and protozoans resulted in an architecture that progressively resembled a complex biofilm. The presence of protozoans reduced nematode reproduction, presumably due to competition for their bacterial food supply. CONCLUSION: Animal secretions such as mucus may have broader, community-level consequences and contribute to fueling microbial food webs.