External morphology and habitat preferences of Ephippiochthonius tetrachelatus and E. kewi (Pseudoscorpiones: Chthoniidae)

Abstract

All available Danish Ephippiochthonius Beier, 1930 material was examined in this study to investigate if some specimens conform to E. kewiGabbutt, 1966, a species previously not reported from Denmark. Specimens were sorted into four groups by number of microsetae (0–3) present along the posterior border of the cephalothorax. The distribution of each group was mapped and related to recorded habitat, chaetotaxy of genital opercula, number of preocular microsetae and colouration of the cephalothorax. It was possible to assign most specimens of the four groups to two taxa conforming to E. kewi and E. tetrachelatus (Preyssler, 1790), thus both species are members of the Danish fauna. The grey-brown and strictly coastal E. kewi inhabits sheltered coasts throughout Denmark, while the yellow-brown E. tetrachelatus shows a distinct south-eastern distribution and is found at both inland and coastal sites. Chaetotaxy of the genital opercula did not differ between females of the two species, but for males it was found that E. tetrachelatus has a statistically significant higher proportion of specimens with 11 rather than 10 setae on the anterior genital operculum compared to E. kewi. The most frequent configuration of preocular microsetae in both species is two on each side, but E. kewi has significantly fewer (average a lower mean of microsetae) compared to E. tetrachelatus. The variation in chaetotaxy of the cephalothorax is limited in each species in those regions where species distributions do not overlap. But in regions with overlapping distributions, like south-eastern Denmark, some populations exhibited a higher variability in chaetotaxy which could be due to local hybridisation events. These assumed hybrids are grey-brown as E. kewi, but possess the habitat preferences of E. tetrachelatus which may explain why they are not strictly coastal, but usually found near the coast. Ephippiochthonius tetrachelatus is frequently introduced from abroad, resulting in establishment of at least temporary populations in garden centres and botanical gardens. A limited number of Ephippiochthonius specimens from Sweden were also examined and it appears that both species are present in this material as well.