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How are spiny turbots different from most other flatfishes?

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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*).

Spiny turbots (family Psettodidae) are considered the least-specialized and most primitive members of the order Pleuronectiformes. Unlike most other flatfishes, which are characterized by the absence of spines in their fins, spiny turbots possess spines in their dorsal, anal, and pelvic fins.1

Additionally, they differ from the majority of flatfishes in the following ways:
* Dorsal fin placement: Their dorsal fin does not extend onto the head, whereas in other flatfishes (suborder Pleuronectoidei), it typically extends forward onto the head.1
* Jaw structure: They possess a well-developed supplemental bone on the maxillary (upper jaw), a feature generally absent in other flatfishes.1
* Vertebral count: They have a lower number of vertebrae (24–25) compared to most other flatfishes, which generally have 27 or more.1

While most flatfishes are strictly defined by their asymmetry, spiny turbots retain these more primitive, generalized characteristics while still exhibiting the order's defining trait of having both eyes on one side of the head.21