Comparison of iron,manganese, and phosphorus retention in freshwater littoral sediment with growth of Littorella uniflora and benthic microalgae

Sediment columns from an oligotrophic lake were percolatedwith artificial porewater in two 46-day experiments toexamine the effects of Littorella uniflora and benthicmicroalgae on retention of phosphorus (P) by either iron(Fe) or manganese (Mn). Cumulative retention of P, Fe, andMn was 2–5 times higher in sediment with L. uniflora thanin sediment with microalgae, because of higher P uptake andmore efficient Fe and Mn oxidation by L. uniflora than bymicroalgae. Thus 34% and 21%of added P was retained in L. uniflora inhabited sediments asmetal-oxide bound P compared to 11% and2% in microalgae inhabited sediments, inexperiments supplied with Fe and Mn, respectively. Theatomic ratio of Fe/P precipitation was about 1 and forMn/P precipitation it was about 5. These ratios indicateprecipitation of Fe(III)-phosphate (strengite) and metastableMn(IV)-compounds containing phosphate and hydroxide ions invariable amounts. In addition to metal-oxide P precipitation,increased P retention in the vegetated sediment was also causedby the presence of humic acid compounds, which accountedfor about 26% of total retained P.     

A new cavernicolous, semiaquatic species of Serradium (Diplopoda, Polydesmidae) and its terrestrial, sympatric congener. With notes on the genus Serradium

Serradium semiaquaticum sp. n. is described from several North Italian caves. The new species is very similar to, and probably the closest relative of S. hirsutipes Verhoeff, 1941, which lives in the same caves as S. semiaquaticum but has a wider distribution. Serradium hirsutipes is redescribed and newly recorded from several caves. Serradium semiaquaticum is remarkable by its semiaquatic habits and correspondingly modified spiracles and mouthparts, whereas S. hirsutipes is normal in these respects. The genus Serradium is reviewed, and a key to the known species is given. Serradium as currently defined may not be a monophyletic group. Serradium semiaquaticum and S. hirsutipes show strong gonopodal similarity (synapomorphy?) with species of Polydesmus, subgenus Acanthotarsius.     

Review of Ptycholaimellus Cobb (Nematoda, Chromadoridae), with descriptions of three species

Nematodes of the genus Ptycholaimellus Cobb, 1920 are unique in possessing a collar by which the head is separated from the body. The collar is raised from a groove at the border between the neck and the remainder of the body. The contents of the ventral gland cell are emptied in the groove in at least 9 out of 14 species. It is suggested that the amphids are located in the groove. Fourteen species are considered to belong to Ptycholaimellus . Two Ptycholaimellus species are described as new to science, that is, P. jacobi sp.n. and P. vincxae sp.n.; P. ponticus (Fihpjev, 1922) is redescribed. Ptycholaimellus ponticus sensu Stekhoven (1950) and Boucher (1972) from the Mediterranean off France differs from the other Ptycholaimellus species by its subcuticular ornamentation and shape of spicules, hence these specimens are regarded as belonging to a new species: Ptycholaimellus boucheri sp.n. Chromadorissa inaequibulba Aminova & Galtsova, 1978 is transferred to Ptycholai- mellus as P. inaequibulbus. Ptycholaimellus ponticus from Europe and P pandispiculatus (Hopper, 1961) from the east coast of North America are assumed to have colonized brackish waters independently.