Latitudinal shift of the associated hosts inSagamiscintilla thalassemicola(Galeommatoidea: Galeommatidae), a rare ectosymbiotic bivalve that lives on the proboscis of echiuran worms

Abstract

AbstractSagamiscintilla thalassemicola(Bivalvia: Galeommatoidea: Galeommatidae) is a rare ectocommensal bivalve that lives on the proboscis of echiuran worms,Anelassorhynchusspp. (Annelida: Thalassematidae: Thalassematinae: Thalassematini), and has been known only from the temperate zones of Japan. In this study, we foundS. thalassemicolaon the proboscis of the large echiuranOchetostomasp. (Thalassematidae: Thalassematinae: Thalassematini) on intertidal flats of three islands of the Ryukyu Archipelago, southern Japan. These are the first records ofS. thalassemicolaon non-Anelassorhynchushosts and also from the subtropical regions. Additionally, we also collectedS. thalassemicolafrom an intertidal flat of Kushimoto, Wakayama, Kii Peninsula, Japan, which is an update of the easternmost record of this species. The genetic differences in the mitochondrial cytochromecoxidase subunit I and nuclear internal transcribed spacer 2 genes amongS. thalassemicola, including those withOchetostomasp. from the subtropical region and withAnelassorhynchusspp. from the temperate region, can be considered within the intraspecific variation. These suggest thatS. thalassemicolauses different echiuran hosts in the temperate and subtropical regions, respectively.