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3 Posts tagged with the mollusca tag
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The great majority of the more than 400 families of snails are found only in the sea, while about 5% of them are exclusively freshwater. Very few snail groups are common in both environments and just three marine families have rare freshwater members.

 

One of these is the Littorinidae (periwinkles), familiar from rocky shores. In the nineteenth century three freshwater periwinkle species (genus Cremnoconchus) were discovered in the mountainous Western Ghats of India, living in fast-flowing streams at altitudes between 300 and 1400 m. These have not been studied for over 100 years.

 

Cremnoconchus.JPGFigure from the original description of Cremnoconchus (images 1-7) Image courtesy of Biodiversity Heritage Library. http://www.biodiversitylibrary.org

 

In a collaboration with scientists from the NHM's partner organisation the Ashoka Trust for Research in Ecology and the Environment (ATREE), Bangalore, David Reid revisited the type localities of the three known species to collect new specimens. (The type locality is the place in which the reference specimen was found that was originally used to describe and name the species.) These were studied to find out more about the snails and allowed the relationships between the species to be investigagted in more detail and revised.  There are distinctive differences between the species particularly in terms of their radula (the rasping tongue of snails), their reproductive systems and the calcified operculum (the disc that fits into the shell opening when the snail retreats into the shell, providing additional protection from predators and desiccation).

 

In addition, an unknown radiation of six new Cremnoconchus species was discovered in the central Western Ghats, 500 km south of the previously known range where David and his collaborators looked at the known species.

 

Cremnoconchus is interesting in evolutionary terms: the current evidence suggests that its closest living relatives are marine snails found only in New Zealand and Australia, suggesting that the ancestral population was split by the breakup of the ancient continent Gondwana during the Cretaceous, between 145 and 65 million years ago.  However, more evidence and DNA studies would be needed to confirm this hypothesis.


Each of the six new species was restricted to a single stream system on the steep western escarpment of the Deccan Plateau, with limited overlap in distribution in two places.  This suggests that populations of ancestral species were isolated by waterfalls or other features allowing evolutionary divergence over time The habitat of these snails is fragile, being very limited in scale and threatened by tourism, road construction and domestic pollution: all the species are judged to be endangered.

 

Reid, D.G., Aravind, N.A. & Madhyastha, N.A. (2013) A unique radiation of marine littorinid snails in the freshwater streams of the Western Ghats of India: the genus Cremnoconchus W.T. Blanford, 1869 (Gastropoda: Littorinidae). Zoological  Journal of the Linnean Society. 167: 93-135.
DOI: 10.1111/j.1096-3642.2012.00875.x

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Tropical periwinkles

Posted by John Jackson Nov 29, 2011

David Reid (Zoology) has published the fourth and final monograph of the worldwide tropical periwinkle genus Echinolittorina which concludes a taxonomic review of all 60 species of this littoral gastropod mollusc.

 

This completes a 20-year project, which has required  collection of anatomical and molecular samples from across the globe,  study of all major museum collections and a 3-year NERC-funded molecular  programme (by PDRA Suzanne Williams, now also a Researcher in Zoology).  The recognized species diversity has been increased by about 50% and 14  new species have been described.

species-bahav-banner_85379_1.jpg

 

A scanning electron micrograph of a portion (3 tooth rows from a lotal length of 5 mm) of the long radula ribbon of Echinolittorina placida.

 

 

As a result the group is now among the most comprehensively known of all marine invertebrates, with taxonomy, morphology, development, distribution and molecular phylogeny all described in detail. It has become a model system for the study of the evolution of tropical marine invertebrates in shallow water, and has been used, for example, to demonstrate the prevalence of allopatric speciation (speciation following geographical separation of populations), the Miocene origin of many extant species, the influence of tectonic activity on diversification, and evolution of mating signals by reinforcement.

 

More information on an example of the group, Echinolittorina placida, is found on the NHM species of the day pages.


Reid, D.G. (2011) The genus Echinolittorina Habe, 1956 (Gastropoda: Littorinidae) in the eastern Atlantic Ocean and Mediterranean Sea. Zootaxa 2974 1–65

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The discovery of hydrothermal vents in the late 1970s triggered an  enormous biological interest in chemoautotrophic organisms dependant on  previously unknown symbioses with sulphide and methane oxidising  bacteria. Molluscs, particularly bivalves, are the most diverse and  widespread group of chemosymbiotic animals ranging from the intertidal  to hadal depths. Thirteen international speakers will review the  biology, diversity, evolution,host-symbiont interactions and habitats of  these molluscs.

 

The Malacological Society of London and Department of Zoology, The Natural History Museum, are organising a meeting 7 - 8 April 2011 Chemosymbiotic molluscs and their environments: from intertidal to hydrothermal vents at The Natural History Museum, Cromwell Road, London SW7 5BD

 

1000-1800h, 7 April 2011, Flett Theatre
1000-1300h, 8 April 2011, Sir Neil Chalmers Seminar Room

 

No registration fee but for catering purposes PLEASE LET US KNOW IN ADVANCE if you will be attending.

 

Organisers and contact: John Taylor and Emily Glover  j.taylor@nhm.ac.uk

 

 

Speakers and titles

 

  • Sarah Samadi (Systématique, Adaptation et Evolution, Université Pierre et Marie Curie, Paris) ‘Mytilids associated with sunken wood shed new light on the evolution of Bathymodiolinae’
  • Sebastien Duperron (Systématique, Adaptation et Evolution, Université Pierre & Marie Curie, Paris) ‘Connectivity and flexibility of mussel symbioses: how to cope with fragmented and variable habitats?’
  • Nicole Dubilier (Max Planck Institute of Marine Microbiology, Bremen) ‘The unrecognized diversity of bacterial symbionts in chemosymbiotic molluscs’
  • Clara Rodrigues (Universidade de Aveiro, Portugal) ‘Chemosymbiotic bivalves from mud volcanoes in the Gulf of Cadiz: an overview’
  • Graham Oliver (National Museum of Wales, Cardiff) ‘Thyasiridae: the known and the unknown: setting priorities for future research’
  • Heiko Sahling (Geosciences, University of Bremen) ‘The geological and geochemical environment of vesicomyid clams’
  • Elena Krylova (Institute of Oceanology, Moscow) ‘Vesicomyidae (Bivalvia): current systematics and distribution’
  • Steffen Kiel (Geobiology, University of Göttingen) ‘The fossil history of chemosymbiotic bivalves’
  • John Taylor and Emily Glover (Zoology, NHM London) ‘Ancient chemosymbioses – contrasting diversification histories of Lucinidae and Solemyidae’
  • Olivier Gros (Université des Antilles et de la Guyane, Guadeloupe) ‘Codakia orbicularis gill-endosymbiont produces quorum-sensing signals of the AHLclass: putative impact on the bacterial population control in lucinids’
  • Caroline Verna (Max Planck Institute of Marine Microbiology, Bremen) ‘Lucinid symbiont diversity: influence of host selection, geography, habitat and depth’
  • Jenna Judge (Integrative Biology, University of California Berkeley) ‘Testing diversification processes in chemosymbiotic gastropods: a phylogenetic approach’
  • Adrian Glover (Zoology, NHM London) 'Chemosynthetic ecosystems of the Antarctic: a test of dispersal'
  • Paul Dando Marine Biological Association, Plymouth "Fjord thyasirid populations and sediment geochemistry"
  • Matthijs van der Geest (Royal Netherlands Institute for Sea Research) "Ecological importance of chemoautotrophic lucinid bivalves in the Banc d'Arguin (Mauritania) intertidal ecosystem"
  • Karina van der Heijden (Max Planck Institute of Marine Microbiology, Bremen) ‘Biogeography of Mid-Atlantic Ridge hydrothermal vent mussels and associated bacterial symbionts’
  • Graham Oliver & John Taylor 'First confirmation of bacterial symbiosis in Nucinellidae'
  • John Hartley (Hartley Anderson Ltd, Aberdeen) ’Chemosynthetic bivalve responses to oil contamination around North Sea wells and platforms’