Existence of Precoxa in the Thoracic Appendages of Decapod Crustaceans and its Functions

Abstract

The protopodal development of the decapod appendages is examined by the paraffin sections of the larval and postlarval stages in Metapenaeus ensis (DE HAAN) and Chiromantes haematocheir (DE HAAN). The appendage consists of a three-segmented protopod (basis, coxa and precoxa). The existence of precoxa is significant as follows : 1) The body wall of the branchial chamber is originally fused with the precoxae of the thoracic appendages. 2) The arthro- and pleurobranchiae arise from the precoxal portion. 3) The fused precoxal region of the thorax is well-developed in the decapodid stage, and forms the basis for walking. This precoxal enlargement of the Brachyura is a typical example within decapoda.