Cambrian helcionelloids (univalved molluscs) from the Korean Peninsula: systematic revision and biostratigraphy

Abstract Helcionelloids from the Korean Peninsula are revised based on a re-examination of type specimens and new material collected from the Cambrian Mungyeong Group of South Korea. The fauna comprises Coreospira rugosa, Hampilina goniospira, Dorispira pacifica, cf. Igorella coreanica, and Helcionelloid indet. Coreospira and Hampilina are distinguished from other helcionelloids by their angular junction between dorsal and lateral surfaces, and from each other by the presence or absence of a rounded ridge along the junction, respectively. The Korean helcionelloids range stratigraphically from the base of Maochuangian to the lower Hsuchuangian using the chronostratigraphical scheme from North China; this correlates with upper Stage 4 to the lower Wuliuan Stage. Unusual septal features, such as complex suture lines in Hampilina and a central circular structure in the simple convex septa of Coreospira, occur in the apical region of the Korean helcionelloids, and could have implications for univalved molluscan evolution. Yeongju Oh [yjoh@kopri.re.kr ], Department of Earth and Environmental Sciences, Chungbuk National University, Cheongju, Chungbuk 28644, Republic of Korea; Dong-Chan Lee [dclee@chungbuk.ac.kr ], Department of Earth Science Education, Chungbuk National University, Cheongju, Chungbuk 28644, Republic of Korea; Dong-Jin Lee [lichenaria@daum.net ], College of Earth Sciences, Jilin University, Changchun 130061, China; Jeong-Gu Lee [leejg0310@korea.kr ] Gwacheon National Science Museum, Gwacheon 13817, Republic of Korea