Is the Brachyura Podotremata a Monophyletic Group? 429

Figure 13. Gill structures. The plesiomorphic trichobranchiate gills of a freshwater crayfish (A) and of two species of dromiaceans, a homolodromiid (Dicranodromia karubar) (B) and a dynomenid (Dynomene pilum-noides) (C), the latter with a kind of intermediate gill type between trichobranchiate and phyllobranchiate gills (cross-section). (D) The heart-shaped special type of phyllobranchiate gills that evolved within Dromiacea (Hypoconcha arcuata). (E-G): Phyllobranchiate gills of the homoloid Dagnaudus petterdi (E), the raninoid Lyreidus tridentatus (F), and the eubrachyuran Hemigrapsus crenulatus (G). and Galathea are examples of convergent evolution towards phyllobranchiate gills in anomalans). Interestingly enough, dromiaceans show patterns of transition between trichobranchiate and phyllo-branchiate gills (see Bouvier 1896) (Figs. 13B-D). The latter occur, in particular, in the Dromiidae. These are differently shaped from the phyllobranchiate gills of the remainder of the crabs (Ho-moloidea, Cyclodorippoidea, Eubrachyura) (Figs. 13E-G) and are a clear case of convergence. 3.2.4 Synapomorphies ofEubrachyura-Cyclodorippoidea-Raninoidea-Homoloidea and Dromiacea = apomorphies of Brachyura (character set 9) The endopod of the 1st maxilliped is characteristically shaped with a rectangular bend to form the bottom of a tunnel for the breathing current (Fig. 14). The endopods of the 1st maxilliped in other reptants are flat. The carapace is locked posteriorly by projections of the epimeral walls of the segments of pere-opods 4 and 5 (Fig. 11). Corresponding structures were not found in outgroup species, not even in the very crab-like Petrolisthes (Fig. 11 A). The arthrophragms of the last thoracic segment are elongated, incompletely fused medially, and forming two anterior wings (primitive "sella turcica " with hole) (see Fig. 9). The outgroups show short and separated arthrophragms of the last thoracic segment. There are a number of other morphological characters indicating the monophyly of the Brachyur