ABSTRACT
I. INTRODUCTION Enchytraeidae (potworms) are a globally distributed family of small terrestrial and aquatic worms from the phylum Annelida, class Oligochaeta. Their size and generally whitish appearance distinguish them from their larger relatives, the earthworms (Chapter 6). Most species are between 2 and 20 mm long, although some species may reach up to 50 mm. With a body diameter of 0.05 to 1.5 mm enchytraeids belong to the soil mesofauna. Figure 1 shows the internal organi zation of enchytraeid worms. About 600 species of enchytraeids have been described, but this number is expanding steadily. This is a corollary partly to the relative late start of enchytraeid taxonomy, partly to the lack of sufficiently clear taxonomic criteria. Thus, much of the ecological research on potworms has been conducted on the family level. Like all oligochaetes, enchytraeids are hermaphroditic and most species reproduce sexually, although parthenogenetically (e.g., several species from the genera Lumbricillus and Enchytraeus) as well as asexually (e.g., Enchytraeus fragmentosus, Buchholzia appendiculata, and Cognettia sphagnetorum) reproducing species are also known. Combinations
of reproductive strategies may also occur. Terrestrial enchytraeids occur in almost all soil types, in divergent abundances, although their abundances may be charac teristic for specific habitats. Average abundances range from several hundreds per square meter (m~2) ( in dry sclerophyll forests) to approximately 150,000 m“2 (in temperature and subalpine forests and moors) (Didden, 1993), but peak abundances may be much higher. Their populations exhibit clear seasonal dynamics, with maxima in late spring and autumn and minima in summer and winter in temperate zones, but in other climatic zones there may occur only one maximum and minimum (O’Connor, 1967; Dash, 1990). Table 1 lists some characteristic abundances reported from arable land, grassland and forest. Table 2 mentions some of the 50-100 species that are common in Middle European agricultural soils.
