Samuel Yong Jie Diong, Rene S. L. Ong, Samantha J. W. Tong, Tashfia Raquib, Yin Cheong Aden Ip, Danwei Huang & Jia Jin Marc Chang

Abstract. The taxonomy of polyclads has been a subject of contention due to the inconsistent emphases on different morphological traits. While past molecular phylogenetic analyses have illuminated relationships amongst suborders and several families, uncertainties persist at the lower taxonomic levels. This study analysed 270 sequences of 28S rRNA from 135 species to gain insights into many of these relationships, particularly at lower taxonomic levels. The results recovered the monophyly of the suborders Acotylea and Cotylea, and of the cotylean families Pseudocerotidae and Prosthiostomidae. However, the family Euryleptidae and the genera Pseudobiceros, Nymphozoon, and Thysanozoon were shown to be non-monophyletic. Euryleptidae was split into two distinct clades while Pseudobiceros, Nymphozoon, and Thysanozoon have other genera nested within. The analysis recovered a clade with Thysanozoon and Acanthozoon that was sister to the clade containing Pseudobiceros, Phrikoceros and
Nymphozoon. The synonymies of Tytthosoceros and Phrikoceros, Pseudobiceros hymanae, and Pseudobiceros splendidus, as well as Pseudoceros duplicinctus and Pseudoceros prudhoei were rejected; our results supported their distinction and so they remain separate. New Tytthosoceros combinations were established from the phylogeny. The diagnosis of Pseudoceros prudhoei was also emended. Importantly, the study generated 26 novel cotylean sequences, further enriching our understanding of this diverse order.

Key words. Polycladida, phylogeny, Pseudocerotidae, Euryleptidae, Prosthiostomidae, Cotylea

Read article here: RBZ-2025-0025