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Which flatfish suborder is considered the least specialized?

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Body plan and sexual dimorphism in the common sole (Solea solea) and dusky flounder (Syacium papillosum). — pleuronectiform Body plan and sexual dimorphism in the common sole (*Solea solea*) and dusky flounder (*Syacium papillosum*).

The suborder Psettodoidei is considered the least specialized, or most primitive, group of flatfish.1

Unlike the more derived suborder Pleuronectoidei, members of the Psettodoidei retain several ancestral characteristics, including the presence of spines in their dorsal, anal, and pelvic fins. Additionally, their dorsal fins do not extend onto the head, and they possess a well-developed supplemental bone on the maxillary. These fish, which include the spiny turbots, can have their eyes on either the right or left side of the head.1