Susceptibility of preparasitic stages of Chordodes nobilii (Gordiida, Nematomorpha) to the fungicide carbendazim.

We evaluated the effect of carbendazim on non-target organisms using the parasite Chordodes nobilii as a test organism. The Gordiida act as a link between freshwater and terrestrial ecosystems; and C. nobilii, a neotropical representative species of this group, has been shown to be sensitive to other contaminants even at environmentally acceptable concentrations. The taxa susceptible to carbendazim, however, may not be adequately represented among the standard aquatic test species used in ecotoxicological risk assessment. Moreover, the autochthonous organisms in this area that could be used as bioindicators still need to be found. The aim of the present work was therefore to assess the susceptibility of the preparasitic stages of C. nobilii to noxious effects by carbendazim. The assay protocol consisted in 96- and 48-h acute exposures of early embryonic stages and larvae, respectively, to concentrations ranging from 10 to 360 µg/l. Embryonic development was not inhibited by carbendazim at any of the evaluated concentrations, but the infectivity of larvae emerging from the exposed eggs was significantly diminished. Larval survival rate was also affected at the lowest concentration assayed. Values of the mean inhibition concentration (IC50) were 7 and 11 µg/l for embryos and larvae, respectively. Compared to other freshwater organisms, C. nobilii can be considered a species moderately to highly susceptible to carbendazim. As the expected environmental concentrations of carbendazim range from 6.25 to 41.3 µg/l, C. nobilii could well be a species in danger when exposed to this fungicide.

Sexual size dimorphism, sex ratio and the relationship between seasonality and water quality in four species of Gordiida (Nematomorpha) from Catamarca, Argentina.

A total of 687 adult nematomorphs of four species of Gordiida: Chordodes brasiliensis (393 specimens), Noteochorododes cymatium (47 specimens), N. talensis (162 specimens) and Pseudochordodes dugesi (85 specimens) were collected during a period of 1 year from El Simbolar stream, Argentina. Free-living worms were abundant during autumn and spring, but their number decreased during winter and summer. Males were shorter and significantly more abundant than females. The presence of N. cymatium, N. talensis and P. dugesi was correlated with water temperature and these species were most abundant in winter and spring. The presence of C. brasiliensis was correlated with flow rate and pH; this species was more abundant in autumn and winter. These four species are sympatric.

Scanning electron microscopy and intraspecific variation of Chordodes festae Camerano, 1897 and C. peraccae (Camerano, 1894) (Nematomorpha: Gordioidea).

The nematomorph species Chordodes festae Camerano, 1897 and C. peraccae (Camerano, 1894) are redescribed by using scanning electron microscopy (SEM). C. festae has a cuticle with four different areolar types, the crown areoles being the most noticeable with long spiniform processes. The terminal end in the male specimen has two short lobe-like structures and a ventral groove. C. peraccae has three areolar types in which, as in C. festae, some areoles form groups surrounding the crown areoles. Intraspecific variations were found in body length and body colour in both species and, in C. peraccae, also in the cuticle.

Description of Gordionus porosus n. sP. and redescription of Gordionus ondulatus (Nematomorpha, parachordodinae) with scanning electron microscopy.

Two hairworms from Argentina, Gordionus porosus n. sp. and Gordionus ondulatus (Nematomorpha, Gordioidea), are described and illustrated. The cuticle of both species shows only 1 areolar type. Areoles of G. porosus are polygonal and surrounded by minute bristles and the interareolar groove is wide and with large pores. Gordionus ondulatus is characterized by rectangular or irregular areoles from which margins cuticular elongations project as finger-like structures, giving an undulated appearance. Comparing these species to the remaining American species of Gordionus, G. porosus is close to Gordionus violaceus by virtue of the large number of small bristles surrounding the areoles and can be distinguished by the shape of these bristles and by the arrangement and shape of the areoles. Gordionus ondulatus differs from the other species of the genus by its undulating margins. Giordinus lineatus and Giordinus violaceus have been reported in North America, Giordinus platycephalus in North and Central America, Giordinus capitosulcatus in Central America, and Giordinus prismaticus, G. ondulatus, and G. porosus only in South America.