New fossil mussels (Bivalvia: Mytilidae) from Miocene hydrocarbon seep deposits, North Island, New Zealand, with general remarks on vent and seep mussels Author Saether, Kristian P. Author Little, Crispin T. S. Author Campbell, Kathleen A. Author Marshall, Bruce A. Author Collins, Mike Author Alfaro, Andrea C. text Zootaxa 2010 2577 1 45 journal article 10.5281/zenodo.197498 688ce0fc-f816-4dbb-aa80-7978d2e6a37d 1175-5326 197498 Genus Gigantidas Cosel and B. Marshall , 2003 Gigantidas Cosel and B. Marshall , 2003 : 37 . Type species (by original designation): Gigantidas gladius Cosel and B. Marshall , 2003 . Discussion. Of the groups of vent and seep mussels that have been established, Gigantidas has the most distinctive features, including shell elongation and shape, as well as in the attachment of the anterior byssal retractor directly behind the anterior adductor in front of the umbones, rather than in the posterior of the umbonal cavity ( Cosel and Janssen 2008 ).