Serge Gofas

Seasonality in a taxocoenosis of molluscs from soft bottoms in the Bay of Cádiz (southern Spain)

The macrofauna of molluscs associated with soft bottoms in the Bay of Cadiz (southern Spain) was studied monthly from February 1994 to January 1996. The number of species (63) is high for a soft bottom and is related to environmental characteristics (growth of macrophytes) and the biogeographical setting of the studied area. Corbula gibba (∼90%) was the dominant species in this taxocoenosis together with the gastropod Nassarius pygmaeus and the bivalves Pandora inaequivalvis , Parvicardium exiguum and Macoma melo . The most frequent species during the two years was also the bivalve Corbula gibba (100%) followed by the gastropods Nassarius pygmaeus , Tricolia tenuis , Rissoa membranacea and the bivalve Macoma melo . Total abundance of the taxocoenosis in both years reached higher values in spring. The dynamics of the ecological indices such as diversity or evenness, and the species richness showed a similar pattern in both years, with low values of diversity and evenness together with high species richness in spring and summer months and the reverse in autumn and winter. The qualitative correspondence analysis of monthly samples shows an ordination related to seasonality in both studied years, however the values of Jaccards coefficient do not indicate significant boundaries among the monthly samples. The quantitative correspondence analysis shows an ordination and grouping of samples related to the biology of species, particularly with the recruitment of C. gibba , the dominant species. The existence of similar trends in the structure of the taxocoenoses over both years, and the seasonality highlighted by the qualitative correspondence analysis, seems to indicate a certain stability of the ecosystem.

A new species of Monoplacophora, redescription of the genera Veleropilina and Rokopella, and new information on three species of the class

Vema levinae Warén, sp. n. is described from a submarine volcano off western Mexico. The type species of Rokopella and Veleropilina are redescribed, the usage of the names is discussed and Rokopella and Veleropilina are recognized as valid genera in Neopilinidae. Rokopella euglypta(Dautzenberg & Fischer, 1897) is redescribed from shells and a single live specimen taken from seamounts south of the Azores, from a depth of 1200–1600 m. Tectura reticulata Seguenza, 1876 (Gastropoda, ‘Acmaeidae’, southern Italy, Upper Pliocene/Lower Pleistocene) is considered to have been based on the monoplacophoran species previously known as Neopilina zografi from the Mediterranean, and is classified in the genus Veleropilina. Veleropilina zografi (Dautzenberg & Fischer, 1896) is redescribed based on shells from several seamounts south of the Azores. It is considered distinct from Rokopella euglypta and classified in the genus Veleropilina. An undescribed species of Veleropilina from a seamount off southern Baja California is reported, figured and discussed but not formally described.

Genetic variation, systematics and distribution of the venerid clam Chamelea gallina

Two morphotypes of the venerid bivalve Chamelea gallina (L.), viz. C. gallina s.s. and C. striatula , were electrophoretically compared at seven polymorphic enzyme loci. In three populations from the Ria Formosa (southern Portugal), both morphotypes occurred sympatrically. Analyses of genotype frequencies in these mixed populations revealed departures from Hardy-Weinberg expectations at nearly all loci. These deviations were mainly attributable to a Wahlund effect, caused by mixing the two morphotypes. Neis mean unbiased genetic distance between the two forms was D =1·138, while the mean genetic distances between populations within morphotypes were D=0·083 in C. gallina s.s. and D =0·229 in C. striatula . It is therefore concluded that C. gallina and C. striatula are reproductively isolated (biological) species, the geographical distribution of which is outlined.

Molluscan assemblages in littoral soft bottoms of the Alboran Sea (Western Mediterranean Sea)

Abstract The structure of the molluscan assemblages inhabiting the subtidal bottoms off the west coast of Malaga province (southern Spain) and their relation to sediment characteristics were analysed with both univariate and multivariate parameters. Five significantly different molluscan assemblages were identified and assigned to ‘sables fins bien calibrés’ (SFBC, well sorted fine sands); ‘détritique côtier’ (DC, coastal bioclastic sands); ‘détritique envasé’ (DE, muddy bioclastic sands); and ‘coralligène’ (CO, coralligenous) biocoenoses of Pérès and Picard classification. A total of 234 molluscan species were identified, with gastropods as the dominant group (135 species). An increase of diversity and evenness with depth has been observed, with the highest values for both indexes on a rocky outcrop, and the lowest in the shallower fine sand assemblage dominated by few species. The different molluscan assemblages inhabiting these sublittoral bottoms were conditioned by depth, percentage of gravel and percentage of clay. A large proportion of tropical West African species is found in the area, some of them reaching their distributional limit towards the Mediterranean Sea. The southern Iberian coasts, in the confluence of Atlantic and Mediterranean waters and between Africa and Europe, are therefore highlighted as one of the areas with highest molluscan species richness in Europe, and require a conservation policy in order to preserve this unique European biodiversity heritage.

Rissoidae (Mollusca: Gastropoda) from northeast Atlantic seamounts

The gastropod family Rissoidae is revised at the species level for the Lusitanian seamounts, situated between Portugal and Madeira, and the Meteor group of seamounts, situated south of the Azores in the northeast Atlantic Ocean. Based on material obtained by dredging and trawling, 48 species are reported, of which 30 are described as new. There is very little overlap between the assemblages found on both groups of seamounts, with only two shared species. On the Lusitanian seamounts, 24 species were collected. Seven species (six with planktotrophic development) are shared with the mainland shelf or slope and are represented in low numbers. Eleven species are endemic to this seamount group as a whole and of these, three account for 75% of individuals. Of the species not shared with the mainland, only one is found on the four seamounts, eight (three new) are found on two or three seamounts and/or neighbouring islands, and six (all new) are endemic to a single seamount. On the Meteor group, 26 species were found, of which five are shared with the Azores and 20 (all new) are endemic to the seamount group as a whole. Most species are found on only two or three seamounts, whereas nine species are endemic to only one of the seamounts, and of these five are concentrated on Atlantis seamount. Eight endemic species of the Meteor group included in Porosalvania n. gen. have very different shapes and occupy discrete bathymetric intervals, but are best interpreted as a local radiation originating from a relatively old colonization of this seamount group. The endemic species, and among them the successful ones, all have a paucispiral protoconch denoting non‐planktotrophic development. As in the Macaronesian archipelagos, the Rissoidae are the most species‐rich molluscan family on the northeast Atlantic seamounts.

Description of four new species of Neolepton Monterosato, 1875 (Mollusca: Bivalvia: Neoleptonidae), with comments on the genus and on its affinity with the Veneracea

Abstract The type species of Neolepton Monterosato, 1875, Lepton sulcatulum Jeffreys, 1859, is redescribed using SEM of shells, critical-point dried soft parts, and semi-thin sections. Four new species (N. guanche from the Canary Is., N. cancellatum from the Azores, N. benguelensis from Angola, N. caledonicum from New Caledonia) are described; for the latter species is presented data on living animals and anatomy. Notolepton Finlay, 1927 and Neodavisia Chavan in Moore, 1969 are confirmed as synonyms of Neolepton, and the shells of their type species are figured. Kellya atlantica Smith, 1890 (with Rochefortia milda Bartsch, 1915 as a new synonym) from St Helena and South Africa, and Halodakra subtrigona (Carpenter, 1857) from California, are newly assigned to Neolepton. Notolepton atlanticum Soot-Ryen, 1960 from Tristan da Cunha is renamed Neolepton sootryeni n. nov. The hinges of postlarval Veneridae, Gouldia minima (Montagu, 1803) and Chamelen striatula (da Costa, 1778) were found to share essential trai...

New records of upper shore Mollusca for the Tunisian coast: newcomers or overlooked?

Mouna Antit, Serge Gofas and Atf Azzouna Marine Biodiversity Records / Volume 1 / January 2008 / e99 DOI: 10.1017/S1755267207000206, Published online: 02 March 2009 Link to this article: http://journals.cambridge.org/abstract_S1755267207000206 How to cite this article: Mouna Antit, Serge Gofas and Atf Azzouna (2008). New records of upper shore Mollusca for the Tunisian coast: newcomers or overlooked?. Marine Biodiversity Records, 1, e99 doi:10.1017/S1755267207000206 Request Permissions : Click here

A species rich molluscan assemblage in a coralligenous bottom of the Alboran sea (south-western Mediterranean): intra-annual changes and ecological considerations

The composition and structure of a molluscan assemblage inhabiting an outcrop with a coralligenous community was studied in southern Spain. A total of 117 molluscan species were identified, with gastropods as the dominant group. Calyptraea chinensis was the dominant species and the family Conidae presented the highest number of species. The Shannon ― Wiener diversity index and the Evenness showed non-significant changes between cold and warm months, displaying high values (∼4 bits and ∼0.8 bits respectively). Some of the dominant and/or frequent species are strictly associated with coralligenous-building organisms, such as Neosimnia spelta with gorgonians. Regarding trophic guilds, carnivores are the dominant group, followed by filter feeders due to the high abundance of C. chinensis. Regarding biogeographical distributions, most of these species (<95%) are widely distributed in European waters, the number of strictly Mediterranean species being very low. The Alboran Sea represents the distributional limit towards the Mediterranean for some species found in this bottom, such as the Atlantic Bela powisiana. Rocky-coralligenous bottoms are scarce in the western Alboran Sea but support a high species richness molluscan assemblage, displaying higher diversity values than the surrounding soft bottoms and increasing the biodiversity at local scale. This high biodiversity is partly explained by the coexistence of different taxa with contrasting biogeographical affinities promoted by the geographical location of the area. Due to this, conservation efforts should be required to protect this stretch of coastline where one of the most biodiverse invertebrate assemblages along the European coasts can be found.

A gastropod from the tropical Atlantic becomes an established alien in the Mediterranean

We report the occurrence of an established population of the gastropod Mitrella psilla (Duclos, 1846), native on west African coasts of Mauritania, Senegal and Angola, on the shore of La Goulette, Bay of Tunis. The molluscan species of tropical West African affinity hitherto ascertained in the Mediterranean are not aliens, but have a native range which encompasses at least part of the Alboran Sea since historical times. Mitrella psilla appears therefore as the first instance of a mollusc with a tropical Atlantic origin being added to the Mediterranean fauna. The species was found near an important commercial harbour and is presumed to have been introduced by shipping.

The systematics of Pyrenean and Cantabrian Cochlostoma (Gastropoda, Cyclophoroidea) revisited

The systematics of Pyrenean and Cantabrian species of the terrestrial prosobranch genus Cochlostoma Jan, 1830 is readdressed using morphology of shell and soft parts, anatomy and allozyme electrophoresis. Ten biological species are recognized: C. obscurum (Draparnaud, 1805), C. crassilabrum (Dupuy, 1849), C. partioti (Moquin-Tandon, 1848), C. martorelli (Bourguignat, 1880), C. gigas Gofas and Backeljau, 1994, C. nouleti (Dupuy, 1851), C. hidalgoi (Crosse, 1864), C. bicostulatum Gofas, 1989, C. oscitans Gofas, 1989 and C. asturicum (Raven, 1990); forty other available species-group names are synonymized accordingly. The populations are very isolated one from another in the southern Pyrenees, with a high incidence of fixed alleles. Cochlostoma gigas is given species status but may be interpreted as a peripheral isolate from C. martorelli. The amount of divergence found between populations of C. martorelli is high, and the intrapopulation polymorphism is very low, a setting which is very prone to further breakup. In the Cantabrian range, C. asturicum has hardly diverged from C. hidalgoi, but fixed or nearly fixed alleles for three enzymatic loci are evidence for reproductive isolation in fully sympatric populations. Cochlostoma asturicum is nevertheless genetically closer to the local C. hidalgoi than the latter is to distant conspecific populations. This points to a sympatric speciation for C. asturicum. It is suggested that the montane habitat of several species is the consequence of an adaptation developed when a colder climate forced the species into coastal refuges. The onset of temperate climate could then result in a disruptive selection, with alternate pathways of a retreat to higher altitude, or colonisation of newly available space in the lowlands; this process is considered as a possible explanation for the lowland/montane divergence between C. obscurum and C. crassilabrum.