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

Abstract This paper presents the first teratological records for Peruvian waters of Chiton cumingsii Frembly, 1827 and Chiton granosus Frembly, 1827, both species very common in the Southeast Pacific. We found five abnormal individuals in C. cumingsii, and two in C. granosus, including the first recorded splitting abnormalities for these species. An individual of C. cumingsii with a new insertion plate in the tail valve was also observed. We observed that splitting abnormalities in Polyplacophora can be classified as perfect or imperfect, depending on whether the splitted valves are clearly recognized as individual fragments or not. Coalescence between the splitted valves seems to be a common phenomenon, and this coalescence can be homogeneous or heterogeneous. As both species show a combination of hypomerism, coalescence and splitting, we suggest that they are probably interrelated and represent an attempt of the developmental mechanisms of chitons to overcome a valve malformation.