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An examination of the thoracic endophrag- mal system in trichodactylid freshwater crabs revealed several derived features that appear restricted to this family. Trichodactylids have a highly reduced sella turcica with a rim-like overall configuration; as a consequence of sella turcica reduction the median septum is dorsoven- trally diminished and exposed along its length. In addi- tion, interosternite 7/8 is medially erased with the rem- nants restricted to the lateral regions of the sternum. The configurations of the sella turcica and interosternite 7/8 in trichodactylids underscore the monophyly of this family. The Dilocarcininae is characterized by having interoster- nites 5/6 through 7/8 restricted to the lateral sectors of the sternum, the lateral remnants of interosternite 4/5 form- ing prominent, rib-like ridges oriented diagonally to the longitudinal axis of the crab, and the median septum forming with interosternite 4/5 a Y-shaped pattern. These autapomorphies of the endophragmal system separate the trichodactylids from all other eubrachyurans and empha- size the morphological distinctness of the group. A de- scription of the trichodactylid endophragmal junction plate is also provided. J. Morphol. 256:23-28, 2003. © 2003 Wiley-Liss, Inc. |
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