Some Oligocene chitons (Mollusca: Polyplacophora) from Germany and France

New records of teratology in Chiton cumingsii and Chiton granosus (Mollusca: Polyplacophora) from the Peruvian coast

“…Head valve, valve IV and tail valve were removed from these specimens. In addition to the typical cases of teratology (Dell'Angelo & Schwabe, 2010), we also searched for other abnormalities in the valves or girdle.…”

“…Teratology is the science that studies permanent structural or functional abnormalities that arise during the embryonic development (Clegg, 1971) in relation to internal factors (genetics), external factors (environment) or a combination of both (Calado & Dos Anjos Pires, 2018). Although members of Polyplacophora (Mollusca) normally have eight dorsal valves, abnormal specimens with an unusual number of valves have been extensively reported in many regions around the world (Taki, 1932;Dell'Angelo & Schwabe, 2010;Torres et al, 2018;Guillén & Urteaga, 2019). Dell'Angelo & Schwabe (2010) provided an overview of teratological cases in chitons, establishing four typical categories: (1) hypomerism, the complete absence of one or more valves; (2) hypermerism, the presence of additional valves; (3) coalescence, the union of adjacent valves; and (4) splitting, the division of one valve into two valves.…”

“…Although members of Polyplacophora (Mollusca) normally have eight dorsal valves, abnormal specimens with an unusual number of valves have been extensively reported in many regions around the world (Taki, 1932;Dell'Angelo & Schwabe, 2010;Torres et al, 2018;Guillén & Urteaga, 2019). Dell'Angelo & Schwabe (2010) provided an overview of teratological cases in chitons, establishing four typical categories: (1) hypomerism, the complete absence of one or more valves; (2) hypermerism, the presence of additional valves; (3) coalescence, the union of adjacent valves; and (4) splitting, the division of one valve into two valves. However, Avila-Poveda et al (2019) have proposed a more complex classification of teratology cases in chitons by considering the degree of coalescence between the valves, and the number of slits and slit-rays of each valve.…”

“…Even though Chiton cumingsii Frembly, 1827 and Chiton granosus Frembly, 1827 are among the most abundant species of Polyplacophora along the Peruvian Marine Province (Ibáñez et al, 2019), all recorded teratological cases for both species come from Chile, including hypomerism and coalescence in C. granosus (Peña, 1977;Peña & Castro, 1982;Torres et al, 2018) as well as hypomerism and abnormal valves in C. cumingsii (Schwabe, 2001). Therefore, the objective of this study is to present new records of teratology in C. cumingsii and C. granosus from the Peruvian coast and to compare the usefulness of Dell'Angelo & Schwabe (2010) and Avila-Poveda et al (2019) classifications to better describe teratological cases in Polyplacophora.…”

Paleocene genus Incisiochiton Van Belle, 1985 (Mollusca: Polyplacophora) with the description of a new species from Ukraine

“…It should be noted here that in 1985 Van Belle described a new genus, Incisiochiton Van Belle, 1985, taking C. baylei as the type species. In 1999, Bielokrys (Bielokrys 1999) added three more extinct species to this family from the Upper Eocene deposits on the left bank of the Dnieper River in the vicinity of the city of Dnepropetrovsk: Schizochiton parcus Bielokrys, 1999, S. carinatus Bielokrys, 1999and S. hirtus Bielokrys, 1999. Dell'Angelo et al (2018 added one more fossil chiton, S. tasteti, from Gaas (Lagouarde), France, Aquitaine Basin, Oligocene (Rupelian).…”