Development and Organization of the Posterior Field of Ctenoid Scales in the Platycephalidae

The development and organization of four morphologically distinct structures comprising the posterior field of ctenoid scales in the Platycephalidae are described from scanning electron micrographs. The posterior margins of ctenoid scales are formed by two rows of cteni. Cteni of each row alternate with each other and at the ends of each row of cteni subcteni occur. Growth of the scale at the posterior margin proceeds by the addition of new cteni behind the more anterior cteni and subcteni. The formation of a new row of cteni leads to the degeneration of the spines of the more anterior cteni and subcteni, leaving ctenial bases and subctenial bases. The subctenial bases form the border of the posterior field with the circuli. The number of ctenial bases varies with the age of the fish and the size of the structures increases with the addition of each new row; neither number nor size are reliable taxonomic characters. The morphology of ctenial bases varies in different platycephalid species, and appears to have potential value as a taxonomic character.