4.1 | Pleuronectoidei taxonomy Flatfish taxonomy has long overlooked the family‐level diversity present in Pleuronectoidei. The earliest flatfish classification simply placed all fifteen known species into a single genus, Pleuronectes, within the order Thoracici without any family divisions present (Linnaeus, 1758). Later, Pleuronectidae of Cuvier contained five subfamilies, the Cynoglossinae, Hippoglossinae, Platessinae, Pleuronectinae and Soleinae (Cuvier, 1817). Additional complexity with flatfish taxonomy was advanced with the concept of flatfishes as a suborder, the Heterosamata, and two families— the Pleuronectidae and Soleidae (Jordan & Evermann, 1896). Subsequently, Regan (1910) proposed two suborders of the Psettodoidea with the single family of Psettodidae and the Pleuronectoidea with two divisions (Pleuronectiformes and Soleiformes). The Pleuronectiformes of Regan (1910) had two families, the Bothidae and Pleuronectidae, and a Soleiformes with two families, the Soleidae and Cynoglossidae. Since then, the largest divisions within the suborder Pleuronectoidei have followed a division between pleuronectids and their relatives (superfamily Pleuronectoidea; Nelson (2006)) and soleids and their relatives (superfamily Soleoidea; Nelson (2006)) such as Norman (1934) proposing three families for the flatfish lineage, Psettodidae, Bothidae and Pleuronectidae. From the two divisions with Pleuronectoidei, the distinction of Citharidae became evident in further investigations. Hubbs (1945) defined a Citharidae (Citharinae + Brachypleurinae) closely related to Scophthalmidae, and these being most closely related to all other Pleuronectoidea indicating another major division within the flatfish lineage and a concept that has been reflected in subsequent classifications (Chapleau, 1993; Hensley & Ahlstrom, 1984). The citharids composed of the genera Brachypleura, Citharoides, Citharus, Lepidoblepharon, and Paracitharus were demonstrated by Hoshino (2001) to be monophyletic—contradicting Chapleau (1993) who indicated they were paraphyletic—and the earliest‐branching lineage of Pleuronectoidei. The current taxonomy of the Pleuronectoidei may be characterized by three superfamilies: Citharoidea, Pleuronectoidea and Soleoidea (Chanet et al., 2004; Hoshino, 2001; Nelson, 2006). In this study, we find support for these three superfamilies.

Published as part of Campbell, Matthew A., Chen, Wei-Jen, Chanet, Bruno, Chen, Jhen-Nien & Lee, Mao-Ying, 2019, Origins and relationships of the Pleuronectoidei: Molecular and morphological analysis of living and fossil taxa, pp. 640-656 in Zoologica Scripta 48 (5) on page 648, DOI: 10.1111/zsc.12372, http://zenodo.org/record/15787530