(2004) recorded 35 taxa in newly created intertidal mussel beds that resulted in more shore crabs Carcinus maenas, amphipods Melita palmata, and oligochaete worms Tubificoides benedeni, but fewer of the polychaetes Pygospio elegans and Notomastus latericeus, and the eumalacostracan
In the present investigation, I used the anti-engrailed antibody mAb 4D9 (Patel et al., 1989) to analyze the segmentation of the embryonic pleon of a eumalacostracan, the Australian freshwater crayfish Cherax destructor.
This result confirms some of the suggestions of Manton (1928a, b), and since there is good evidence that the tail fans of all eumalacostracan groups are homologous (Hessler, 1983; Wagele, 1994), the findings presented here might also be valid for eumalacostracans in general.
Therefore, the "seventh pleonic segment" of lophogastrids is apparently the result of a secondary nonsegmental(?) subdivision of the terminal eumalacostracan segment, as was suggested earlier by Claus (1888).
On the basis of anatomical and paleontological data, Siewing (1956, 1963) argued that the uropods might be the appendages of the seventh pleomere and that the sixth (penultimate) pleomere has been lost in most eumalacostracans. Based on her embryological studies in mysidaceans, Manton (1928a, b), in contrast, suggested that the uropods belong to the sixth pleomere and that the original seventh is fused to the sixth pleomere.
Adult eumalacostracans possess only six pleonic ganglia (see Hanstrom, 1928), and this is also true for leptostracans with a seventh pleomere (Claus, 1888; Manton, 1928a).
It demarcates the posterior border of an additional (seventh) pleonic segment that is missing in adult crayfish and other eumalacostracans but is present in adult Leptostraca.