First records of pseudocerotid flatworms (Platyhelminthes: Polycladida: Cotylea) from Singapore: A taxonomic report with remarks on colour variation

A detailed taxonomic report of 16 species of polyclad flatworms found in Singapore during the Comprehensive Marine Biodiversity Survey is presented. Representatives of the genera Nymphozoon, Phrikoceros, Pseudobiceros, Pseudoceros, and Tytthosoceros are described using high quality photographs, extended descriptions with information on colour variation, together with a compilation of geographic distribution based on the known records. All species belong to the family Pseudocerotidae and all represent new records for Singapore except Pseudobiceros bedfordi, P. hancockanus, and Pseudoceros indicus. Identifications were based mainly on external morphological characters, with particular emphasis on their living colours and patterns. The genus Nymphozoon is re-described, and a new combination Nymphozoon orsaki nov. comb. is established as it is shown that the monotypic genus Maiazoon is a junior synonym of Nymphozoon. Emended diagnoses for Pseudobiceros damawan, P. hancockanus, and Pseudoceros laingensis are also included. Pseudoceros caeruleocinctus is reinstated as a valid species and is recognised as a senior synonym of Pseudoceros sapphirinus, while Pseudobiceros uniarborensis is identified as a junior synonym of Pseudobiceros hancockanus. This study shows that polyclads are significantly diverse in Singapore, and also highlights the need for further studies using both morphological and molecular data to confirm their identities.