Colloniidae

Kaim, Andrzej, Jenkins, Robert G., Tanabe, Kazushige & Kiel, Steffen, 2014, Mollusks from late Mesozoic seep deposits, chiefly in California, Zootaxa 3861 (5), pp. 401-440 : 406

Family Colloniidae ? Cossmann in Cossmann & Peyrot, 1917

Remarks. The new genus Hikidea described below is only hesitantly placed among the Colloniidae here. This classification is based on the overall similarity of the adult shell with colloniids such as Homalopoma Carpenter, 1864 and the even more similar Cantrainea Jeffreys 1883 . Problematic with this classification is that typical colloniids appear to lack a nacreous layer in their shell ( Knight et al. 1960; Schröder 1995), while at least one species assigned here to Hikidea ( H. yasukawaensis ) has a nacreous layer (Kaim et al. 2009). Recent molecular phylogenetic studies place colloniids among the phasianellids ( Williams & Ozawa 2006; Williams et al. 2008), a group that also lacks nacre ( Hedegaard, 1997). However, the genus Cantrainea , which is most similar to Hikidea amongst the colloniids, has neither been included in molecular phylogenetic studies yet, nor is the presence or absence of a nacreous layer known. The same applies to the presumed colloniid genus Phanerolepida Dall, 1907 , for which we describe a new species below, because both Eocene and Cretaceous species have a nacreous shell ( Hickman 1972).