AN OVERVIEW OF THE SYSTEMATICS AND BIOGEOGRAPHY OF THE FLATFISHES

Until about 25 years ago, classification of the flatfishes was based o n the Regan-Norman model. Beginning with the work of Amaoka in 1969, t he order started to be analysed in finer detail, and in the 1980s many questions arose concerning flatfish phylogeny as expressed in the Reg an-Norman model. Two of the major questions were whether the order is monophyletic and which groups within the order are: monophyletic. Rece nt research has clarified many of these questions. Chapleau recently r edefined the order based on shared derived characters, thus supporting the hypothesis of monophyly. The most recent classifications based on phylogenetic studies have split several of the traditionally recogniz ed families. Some flatfish groups were shown to be monophyletic once c ertain species were excluded. As phylogenetic studies and work on the alpha-level taxonomy continue, we are: beginning to see some very inte resting biogeographic patterns. Some of these distribution patterns we re not previously obvious due to polyphyly of some of the flatfish gro ups. There is still much work to be done on the systematics and biogeo graphy of flatfishes. Some of the more important questions that remain to be addressed in future studies are the following. (1) What is the sister group of the order? (2) What is the sister group of the Souther n Ocean Achiropsettidae? (3) What an the relationships of the remainin g groups in the polyphyletic Pleuronectidae? (4) What ale the relation ships of certain genera that are excluded from recently redefined fami lies? (5) What are the intergeneric relationships within monophyletic groups such as the Bothidae, Achiridae and Soleidae? A great deal of w ork at the alpha-taxonomic level with flatfishes is still needed. Espe cially in tropical areas, new species and great range extensions are r outinely discovered. There is also a need for more ontogenetic studies of flatfishes.