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INTRODUCTION About 300 species of horsehair worms (Nematomorpha) are known, about a third of them from Europe (Schmidt-Rhaesa 1997). The sampling within Europe is nevertheless far from being homogeneous and from some countries no or only a few records are known. This applies to Estonia as well as to the other Baltic states. There is only one brief report of some specimens determined as Gordius aquaticus Linnaeus, 1758 from Lake Vortsjarv (as lake Wirzjerw) by Muhlen & Schneider (1920). We report here several records, including the description of three new species of Nematomorpha from Estonia. It can be expected that the species reported here do not represent the entire diversity of species in the region. As only very fragmentary data are known from neighbouring countries, no estimates on the absolute number can be given here. Adult horsehair worms can be found in fresh water (with the exception of 5 species living in the sea), where they copulate and deposit eggs. From the eggs small larvae (around 100 [micro]m) hatch, which infect hosts. The exact life cycle is still unclear (Hanelt et al. 2005), but there is indication for a host change from aquatic to terrestrial hosts. The major development takes place within hosts such as carabid beetles, crickets, or others. Adult worms have been shown to manipulate their hosts, making them enter water so that the nematomorph can emerge (Thomas et al. 2002). Important for the determination of Nematomorpha species are cuticular characters such as the structure of the body cuticle or cuticular structures in the male posterior end. Representatives of genera such as Gordionus, for example, have spines and bristles in characteristic distribution patterns on the ventral side of the male posterior end (see e.g. Fig. 1C). In contrast, representatives of the genus Gordius are comparably poor in cuticular structures. Characteristic of the genus Gordius is a semicircular cuticular fold, the postcloacal crescent (see e.g. Fig. 2A), but bristles are much finer and fewer compared to Gordionus. Some of such bristles as well as the fine structure of the superficially smooth body cuticle might have been overlooked in earlier investigations that did not use scanning electron microscopy. Both genera, Gordius and Gordionus, are comparably species-rich, with about 60 and 46 described species, respectively. Both are distributed almost worldwide, but Europe appears to host most species, including abundant ones such as Gordius aquaticus Linnaeus, 1758 and Gordionus violaceus (Baird, 1853). MATERIALS AND METHODS Specimens reported here were collected in different locations in Estonia between 1971 and 2009 (in addition one record from Russia). Investigation of the specimens by scanning electron microscopy (SEM) took place in the Zoological Museum of the University Hamburg, Germany. Specimens were preserved in ethanol. Pieces of the cuticle and/or the posterior end were prepared for SEM. Pieces were dehydrated in an increasing ethanol series, critically point dried, and coated with gold in a sputter coater. Observation took place using a LEO SEM 1524 under 10 kV. Digital images were taken. Specimens are deposited in the Zoological Museum Hamburg (ZMH), in the Zoological Museum of the University of Tartu (TUZ), and in the personal collection of Andreas Schmidt-Rhaesa. In total, 39 specimens were investigated, 4 of which could not be determined. Four species could be determined to species level, three of these are new to science. RESULTS AND DISCUSSION A total of 39 specimens were investigated. Four specimens could not be determined because they were damaged and are omitted from this report. The remaining 35 specimens belong to four species, three of which are new to science. Seven specimens belong to the genus Gordius, but could not be determined to species level. Gordionus violaceus (Baird, 1853) Figure 1 Distribution: Himmiste, Saaremaa, found halfway emerging from a Pterostichus niger (Schaller, 1783) (Carabidae) which was caught on a yellow plate (1[female], collected by M. …

Records of horsehair worms (Nematomorpha) in Estonia, with description of three new species from the genusGordiusL.