Pleuronectoidea

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, Zoologica Scripta 48 (5), pp. 640-656 : 649

4.3 | Pleuronectoidea

Pleuronectoidea is identified to contain the families Scophthalmidae , Pleuronectidae , Paralichthyidae and Bothidae . Scophthalmidae is the earliest‐branching lineage of the Pleuronectoidea and sister to the remainder of this clade with high support (Figures 1 and 2). This placement receives support from several studies (Betancur‐R., Li, et al., 2013; Campbell et al., 2013; Harrington et al., 2016; Near et al., 2012), but is not widely supported across multilocus and mitochondrial DNA‐based studies. Alternative placements of Scophthalmidae closely related to Rhombosoleidae and Achiropsettidae are found in other data sets, not exclusively those based on mitochondrial genomes (Betancur‐R., Broughton, et al., 2013; Campbell, Chen, et al., 2014; Shi et al., 2018). Some morphological classifications have indicated that Scophthalmidae is closely related to Citharidae , for example ( Chapleau, 1993; Hubbs, 1945); however, the most recent studies provide additional evidence that Scophthalmidae is a lineage within Pleuronectoidea ( Chanet et al., 2004; Hoshino, 2001).

Early flatfish classification schemes placed all species in Pleuronectidae and it continued to contain many fishes of uncertain affinity. More recent efforts have advanced the understanding of composition and inter‐relationships within this family ( Cooper & Chapleau, 1998a; Vinnikov, Thomson, & Munroe, 2018). The placement of Pleuronectidae as the sister lineage to one lineage of the polyphyletic Paralichthyidae ( Paralichthyidae I) and Bothidae to another ( Paralichthyidae II ) in this study was demonstrated in early molecular phylogenetic studies and has continued to be apparent with larger samplings of lineages and characters, for example ( Berendzen & Dimmick, 2002; Campbell, López, et al., 2014; Harrington et al., 2016). Non‐monophyly of paralichthyids is well known from both anatomical and molecular studies (Azevedo, Oliveira, Pardo, Martínez, & Foresti, 2008; Berendzen & Dimmick, 2002; Chanet et al., 2004; Chapleau, 1993; Khidir, Chapleau, & Renaud, 2005; Pardo et al., 2005). The affinities of some paralichthyids with pleuronectids and some with bothids have long been indicated by classifications, with all or some of these fishes being considered most closely related to one or both of these other families, for example (Hensley, Amaoka, Hensley, Moser, & Sumida, 1984; Hubbs, 1945; Norman, 1934). We identify a clade including Paralichthys and relatives ( Paralichthys , Pseudorhombus , Xystreurys )— Paralichthyidae I in this study—as sister to the Pleuronectidae . Paralichthyidae II is composed of Cyclopsetta , Etropus and Citharichthys in this study and is sister to the Bothidae (Figures 1 and 2).

A polyphyletic Paralichthyidae may be resolved through the creation of two families, Paralichthyidae and Cyclopsettidae . Previously, Hensley and Ahlstrom (1984) indicated a Cyclopsetta group and a Pseudorhombus group. Based on our analyses and others, Paralichthyidae presumably contains 10 genera including the Pseudorhombus group: Ancylopsetta , Cephalopsetta , Gastropsetta , Hippoglossina , Lioglossina , Paralichthys , Pseudorhombus , Tarphops, Verecundum and Xystreurys ( Chapleau, 1993). Cyclopsettidae contains at least four genera, Cyclopsetta , Etropus and Citharichthys , which were examined in this study, and Syacium . Syacium , while not examined here, based on previous anatomical and molecular work should be considered a member of Cyclopsettidae ( Chapleau, 1993; Hensley & Ahlstrom, 1984; Pardo et al., 2005). Within the Cyclopsettidae , the monophyly of genera requires further evaluation, for example ( Azevedo et al., 2008; Betancur‐R., Broughton, et al., 2013; Betancur‐R., Li, et al., 2013). Morphological support for a sister relationship between Cyclopsettidae and Bothidae , as shown in this study, is present as both clades have vertebral apophyses and lack a first neural spine ( Hensley & Ahlstrom, 1984).

We included two fossils in our total evidence analysis that belong in the Pleuronectoidea (Figure 2). The relationships of Eobothus mimimus † have long been uncertain, and the mostresolved placement of Eobothus mimimus † to date has been as a member of the Pleuronectoidea . Eobothus minimus † had previously been indicated to be a bothid species ( Berg, 1940, 1941; Blot, 1980; Norman, 1934; Patterson, 1993b), a scophthalmid species ( Chabanaud, 1936, 1940, 1949) and later a crown pleuronectoid ( Chanet, 1997). Eobothus minimus † may not be considered a member of an extant family, as it shares derived characteristics with Bothidae , Pleuronectidae , Paralichthyidae (I & II), Scophthalmidae and Brachypleura ( Chanet, 1999). Chanet (1999) considered Eobothus minimus † to be incertae sedis within a “bothoid” lineage of Brachypleura , Scophthalmidae , Paralichthyidae (I & II), Bothidae and Pleuronectidae . Here, we refine the placement so that Eobothus mimimus † forms part of a three‐branch polytomy ( Eobothus mimimus †, ( Pleuronectidae , Paralichthyidae I), ( Bothidae , Paralichthyidae II )). Eobothus mimimus † is more closely related to Bothidae , Paralichthyidae (I & II) and Pleuronectidae than Scophthalmidae or Brachypleura . The results of our total evidence analysis indicate that E. minimus † is most likely a member of an extinct family‐level lineage within Pleuronectoidea . Oligobothus pristinus † has previously been clearly placed in the Bothidae and we recover that relationship ( Baciu & Chanet, 2002).