Leptonemella species (Desmodoridae, Stilbonematinae), benthic marine nematodes with ectosymbiotic bacteria, from littoral sand of the North Sea island of Sylt: taxonomy and ecological aspects

Abstract

Leptonemella species represent a dominant element of the nematode fauna in sulfidic, deep sediment layers on the sandy shore of Sylt. Based on collections sampled here in 1991-1999, a taxonomic treatise is presented on the three co-existing species, Leptonemella aphanothecae Gerlach, 1950, the closely related L. vicina sp. nov., and L. gorgo Gerlach, 1950. The high incidence of pseudohermaphrodites in the material, mostly functional females with a male copulatory apparatus, is remarkable. The highest population densities of Leptonemella spp. (up to 73 individuals/10 ml sand) were found near polychaete burrows. Because of the great spatial and temporal variations in the oxygen/sulfide regime of these microhabitats, and because of the strong adhesive capabilities of Leptonemella spp., which can anchor themselves firmly to sand grains using caudal glands, we propose that a hemisessile life strategy is employed by these nematodes to fulfill the metabolic needs of their sulfide-oxidizing ectosymbionts.

The distribution of meiofauna on back-reef sandy platforms in the Maldives (Indian Ocean)

“…2005). Curiously, high abundances of Stilbonematinae have been frequently reported in subtropical and tropical sediments, and especially coralline sands (Gerlach 1963a,b; Boucher 1997; Riemann et al. 2003; Raes et al.…”

“…2007). The great abundance of these species in carbonate sediments may be related to the presence of large grains in generally sheltered habitats, a condition which represents an unusual combination of wide interstitial spaces and sulfide conditions with an associated rich thiobios (Riemann et al. 2003; Giere 2009).…”

“…Of the Desmodoridae genera identified, (Hentschel et al 1999;Ott et al 2005). Curiously, high abundances of Stilbonematinae have been frequently reported in subtropical and tropical sediments, and especially coralline sands (Gerlach 1963a,b;Boucher 1997;Riemann et al 2003;Raes et al 2007). The great abundance of these species in carbonate sediments may be related to the presence of large grains in generally sheltered habitats, a condition which represents an unusual combination of wide interstitial spaces and sulfide conditions with an associated rich thiobios (Riemann et al 2003;Giere 2009).…”

Symbiosis of epi- and endocuticular bacteria with Helicoradomenia spp. (Mollusca, Aplacophora, Solenogastres) from deep-sea hydrothermal vents

“…For a number of ectosymbioses including Zoothamnium niveum (Bauer-Nebelsick et al 1996), Rimicaris exoculata (Polz et al 1998) and several species of Stilbonematinae (Ott & Novak 1989, Riemann et al 2003 it is known that the symbionts are a source of nutrition for their hosts. However, species of Helicoradomenia have a functional digestive tract and are able to ingest small prey; thus, they are considered to be scavengers (Scheltema 2000, Todt 2004).…”

Taxonomic and functional biodiversity variations of meiobenthic and nematode assemblages across an extreme environment: a study case in a Blue Hole cave

“…The species of this sub-family usually appear with a multi-or single-layered coat made of ectosymbiotic bacteria, which cover the body cuticle, while some other species have filamentous ectocommensals covering their entire body surface, giving the animal a bushy appearance. Stilbonematinae species live in sheltered intertidal and subtidal marine, sulphide-rich sediments, where they aggregate around the Redox Potential Discontinuity (RPD) layer depth (Riemann et al 2003;Ott et al 2005;Raes et al 2007;Semprucci et al 2010b;Vanreusel et al 2010b). Eubostrichus, even if detected also in the shallow subtidal habitats of this archipelago (Semprucci et al 2010b, was one of the most abundant or exclusive genera of the Blue Hole seabed.…”