Summary1. As many species of marine benthic invertebrates have a limited capacity for movement as adults, dispersal mode is often considered as a determinant of geographical ranges, genetic structure and evolutionary history. Species that reproduce without a larval stage can only disperse by floating or rafting. It is proposed that the colonization processes associated with such direct developing species result in spatial distributions that show relatively greater fine scale patchiness than the distributions of species with a larval dispersal stage. This hypothesis was tested by collecting molluscs at different spatial scales in the Isle of Man. 2. Spatial distribution patterns supported the predictions based on dispersal mode. Estimated variance components for species with larval dispersal suggested that the majority of the spatial variation was associated with variation between shores. In comparison, there was relatively more variability within shores for abundance counts of species with direct development. 3. Multivariate analyses reflected the univariate results. An assemblage of direct developers provided a better discrimination between sites (100 m separation) but the group of species with larval dispersal gave a clearer separation of shores (separated by several km). 4. The fine scale spatial structure of direct developing species was reflected in higher average species diversity within quadrats. Species richness also reflected dispersal mode, with a higher fraction of the regional species pool present for direct developers in comparison to species with larval dispersal. This may reflect the improved local persistence of taxa that avoid the larval dispersal stage.

The earthworms of arable and pasture fields from 100 randomly chosen arable farms were identified and counted and their relationship with soil factors examined. Thirteen species of earthworm were recorded including Lumbricus friendi from Scotland for the first time. The most prevalent and numerous species were Aporrectodea longa, Aporrectodea caliginosa and Lumbricus terrestris. All earthworm species had cosmopolitan distributions apart from Aporrectodea nocturna and Lumbricus festivus which were confined to southerdcentral Scotland. Four soil characteristics (% moisture, % sand, % organic matter and pH) shared no relationship with species recorded but tillage may have had a detrimental effect on species composition and size of population. It is suggested that the magnitudes of the earthworm populations found, particularly in permanent pasture, were important in maintaining soil structure and fertility, and the spread of the New Zealand flatworm (Artioposthia triangulata), an obligate predator of earthworms, could have a considerable impact on agricultural productivity and wildlife in Scotland. This paper reports the results of an investigation into the distribution of earthworms occurring in Scotland and aims to define their prevalence and intensity in agricultural soil and to study the factors potentially influencing their populations. Materials and MethodsA stratified random sample of 100 arable farms from throughout Scotland was generated from the 1990 census returns to the Scottish Office Agriculture and Fisheries Department. These farms were visited between July 1991 and June 1992 and wherever possible earthworms were counted from one arable and one permanent pasture field. However, only 56 farms had both field types and, of the remainder, 38 farms had permanent pasture fields only and six farms arable fields only. In a randomly selected area of each field, five 0.5 m square metal quadrats were sunk 5-10 cm into the ground at 10 m intervals in a polygonal array. If present, vegetation was cut to ground level and removed prior to two applications of 4.5 litres of 0.5% formaldehyde solution (Raw, 1959). Hand sorting is time consuming but considered the most efficient way of detecting and quantifying most earthworm species while the use of formalin is known to work well for deep-burrowing species. An initial comparison of these two techniques (unpublished data) indicated that the use of formalin gave results which showed similar extraction efficiencies for both arable and pasture fields the respective values being 30. I % and 29.1 %. There were differences in the efficiency with which different species were extracted using the formalin extraction procedure, e.g. for Aporrectodea caliginosa and Fig. I , Distribution of 10 lan squares containing farms which were sampled, 0 are those in which A.nocfurnu, and L. festivus, 0 were present. Annual rainfall; below 100 mm, no shading; between 100-150 mm. dark shading; above 200 mrn, intermediate shading.

An inventory of polychaete species is presented from the north-east coast of Tunisia with an historic review of the previous literature from Tunisian coasts. Altogether 40 families, 146 genera, and 238 species are currently known from the area, of which 86 taxa, 4 families (Chrysopetalidae, Pilargidae, Protodrilidae and Saccocirridae) and 40 genera (Saccocirrus, Protodrilus, Parathelepus, Thelepus, Petta, Isolda, Brada, Tharyx, Paraprionospio, Jasmineira, Hypsicomus, Euchone, Pseudobranchiomma, Laonome, Galathowenia, Lugia, Pseudomystides, Protomystides, Pirakia, Mysta, Eurysyllis, Parapionosyllis, Streptosyllis, Paraehlersia, Sigambra, Ancistrosyllis, Kefersteinia, Chrysopetalum, Bhawania, Fimbriosthenelais, Subadyte, Panthalis, Dorvillea, Scalibregma, Paradoneis, Cirrophorus, Metasychis, Websterinereis, Euniphysa and Mastobranchus) are new additions to the polychaete fauna of Tunisia. The list, which provides a synthesis of the regional taxonomic work, including coastal areas from Sidi Daoud to the area of Menzel Hurr (Cap Bon Peninsula, Western Mediterranean Sea), can serve as a baseline for future studies.

Many species of Cirratulidae have been recorded from the Mediterranean Sea since the descriptions and figures of the Naples fauna in one of the first comprehensive studies of polychaetes by delle Chiaje, 1823-30. This original publication included only multi-tentaculate cirratulids and what we would now identify as Cirriformia and Cirratulus. Since delle Chiaje's publication, 25 bi-tentaculate taxa have been recorded from the Mediterranean. During recent sampling programmes Chaetozone carpenteri McIntosh, 1911, a bi-tentaculate cirratulid, has been recorded from several Mediterranean sites and is redescribed. All records of C. setosa will need to be re-examined as they may have been misidentified.

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