A faunistic survey of the Belgian marine molluscs: a first progress report

A first step towards the compilation of a critical faunistic inventory of the Belgian marine mollusks, was the publication of a preliminary nomenclatural list in 1986. This list mentioned 136 species which until then bad been recorded alive in Belgium. Yet, such records do not necessarily mean that the species involved actually belong to our fauna. Hence, the next thing to do, was to start a more profound survey of the Belgian marine malacofauna in order to determine which species form well-established populations along our coast. This is a long term study relying upon 1) recent explorations and collecting efforts, 2) revision of the collections of the K.B.I.N. and other institutions, 3) a detailed survey of the literature and 4) field data provided by several malacologists and naturalists (e.g. members of the "Strandwerkgroep"). As a result of this work, at least 11 additional species were recorded alive along our coast, viz. Littorina mariae, L. neglecta, Caecum glabrum, Retusa obtusa, Aeolidia papillosa, Musculus discors, Ensis americanus, Tellina pygmaeus, Abra nitida, Barnea parva and Thracia papyracea. For several other species, detailed information on their distribution in Belgium is now also available (e.g. for the Littorinidae). All our distributional data will be incorporated in the "5ea Area Atlas" edited by D.R. SEAWARD (the Belgian marine fauna pertains to the sea areas 513 and 553). The final purpose of this faunistic survey will be the publication of a "Fauna of the Belgian marine molluscs", in addition to a series of specialised papers on more restricted topics

Small ribosomal-subunit RNA and the phylogeny of Mollusca

We determined the complete sequence of the small ribosomal subunit RNA of the pulmonate snail Onchidella celtica. This sequence and the one recently determined for the chiton Acanthopleura japonica were added to an alignment of 25 18S rRNA sequences of Metazoa, including three other Mollusca. The data set was used to assess certain aspects of molluscan phylogeny by distance matrix and character state methods. The trees obtained were tested for effects of random and systematic errors. The results of our analyses support: (a) molluscan monophyly; (b) gastropod monophyly; (c) bivalve monophyly; (d) a sister group relationship of Gastropoda and Polyplacophora. The position of the phylum among other Metazoa remains uncertain due to a lack of representatives of many invertebrate phyla in our data set. Most of our results are congruent with existing hypotheses

Spatio-temporal genetic structure and gene flow between two distinct shell morphs of the planktonic developing periwinkle <i>Littorina striata</i> (Mollusca : Prosobranchia)

The planktonic developing periwinkle Littorina striata produces both nodulose and smooth shells, which were originally regarded as 2 separate species. Although both morphs occur microsympatrically, their distribution is not random. Nodulose shells predominate at wave-sheltered sites, whereas smooth shells are more common at wave-exposed sites. The degree of genetic similarity between the 2 shell types and their microgeographic spatio-temporal genetic structuring were investigated using allozyme electrophoresis. This indicated that: (1) both morphs share a common gene pool, (2) gene flow between populations is high and of comparable magnitude to gene flow between both morphs, (3) the population genetic structure of L. striata remains stable over a sampling period of 3 yr, and (4) genetic and morphological distances between populations are not correlated. These results thus confirm the conspecific status of the 2 shell types and suggest that shell variability and spatial patterning in L. striata persist in the presence of intense gene flow

Faunistic and anatomical data on the Antarctic Opisthobranchia (Mollusca, Gastropoda) in the collections of the Royal Belgian Institute of Natural Sciences

Five opisthobranch species were collected during the Belgian and Belgian-Dutch Antarctica expeditions to the Riiser-Larsen Sea, the Princess Ragnhild Coast ("Mission Iris") (1960-1967) and Admiralty Bay (King George Island) (1987-1991). These species include Philine alata Thiele, 1912, Bathyberthella antarctica Willan & Bertsch, 1987, Notaeolidia gigas Eliot, 1905, Aegires (Anaegires) albus Thiele, 1912 and Austrodoris kerguelenensis Bergh, 1884. This material is deposited in the Royal Belgian Institute of Natural Sciences. The present contribution provides anatomical and faunistic data on this collection and extends the distributional range of several species

Mitochondrial DNA variation and cryptic speciation within the free-living marine nematode <i>Pellioditis marina</i>

An inverse correlation between dispersal ability and genetic differentiation among populations of a species is frequently observed in the marine environment. We investigated the population genetic structure of the free-living marine nematode Pellioditis marina. A total of 426 bp of the mitochondrial cytochrome oxidase subunit 1 (COI) gene were surveyed on a geographical scale of approximately 100 km during spring 2003. Nematodes were collected from 2 coastal locations in Belgium, and from 2 estuaries and a saltwater lake (Lake Grevelingen) in The Netherlands. Molecular variation was assessed with the single-strand conformation polymorphism (SSCP) method. In total, 32 different haplotypes were observed, and sequence divergence among 452 individuals ranged from 0.2 to 10.6%. We discovered 4 distinct mitochondrial lineages, with low divergences within the lineages (0.2 to 1.6%) and high divergences between the lineages (5.1 to 10.6%). The nuclear ribosomal ITS (internal transcribed spacer) region showed concordant phylogenetic patterns, suggesting that nematode species diversity may be considerably underestimated. Analysis of molecular variance (AMOVA) indicated a strong genetic differentiation among populations. The Lake Grevelingen population was clearly differentiated from all other populations, but genetic structuring was also significant within the Westerschelde and was correlated with gradients in salinity and pollution. The observed population genetic structure is in accordance with the limited active dispersal capacity of P. marina, but is at variance with its significant potential for passive dispersal. We therefore suggest that autecological characteristics, including short generation time, high colonization potential and local adaptation, may be at the basis of this nematode’s population genetic structure