DYNOMENIDAE Ortmann, 1892

Guinot, Danièle & Quenette, Gwenaël, 2005, The spermatheca in podotreme crabs (Crustacea, Decapoda, Brachyura, Podotremata) and its phylogenetic implications, Zoosystema 27 (2), pp. 267-342 : 282

Family DYNOMENIDAE Ortmann, 1892

The family Dynomenidae , reviewed by McLay (1999) and with recent new records ( McLay 2001b), is worldwide in distribution but consists of only five genera and less than 20 described species, which are often associated with corals. The Dynomenidae are probably known from the Jurassic ( Glaessner 1969), but Müller (1984: 64) wrote that Dynomene Guérin-Méneville, 1832 remained unrecognized in fossil form “because of the similarity of its carapace to some Xanthids”.

We agree with Beschin et al. (2004: 113): the Eocene Kromtitis tetratuberculatus Beschin, Busulini, De Angeli & Tessier, 2002 (p. 12, fig. 7, pl. 2, figs 2, 3), originally referred to the family Dromiidae , shows close relationship with the living Paradynomene Sakai, 1963 .

The dynomenid thoracic sternum is relatively broad, with all the sutures laterally located. The sternum clearly widens in some members of the family ( Guinot & Bouchard 1998). In males the sternoabdominal depression is not deeply hollowed (except for Acanthodromia ), always with a well developed central flat surface, a great part of sternites 1-6 being fused in a single wide plate. Sternites 7 (narrow) and 8 do not markedly slope backwards, even in females (except for Acanthodromia ). Sutures 4/5, 5/6 and 6/7 are faint, being completely lateral and concealed inside the sterno-coxal depressions. Female sutures 7/8 are short but marked, and generally lie close to the margins of the P3 coxae. The broad, flexible male abdomen is not closely held on the sternum, retains vestigial pleopods on segments 3-5 and may be involved in the locomotion (A. Milne-Edwards 1879: 4; McLay 1999: 456). In males the sternal plate is covered by a long abdomen that occupies its whole length ( Acanthodromia A. Milne-Edwards, 1880 ), or the abdomen is shorter and leaves the anterior sternites uncovered (all other dynomenid genera). The sternum is either entirely covered laterally ( Acanthodromia , Metadynomene McLay, 1999 , Paradynomene ) or partly visible on each external side ( Dynomene , Hirsutodynomene McLay, 1999 ). The latter condition is considered the advanced one ( Guinot & Bouchard 1998). Due to the shortness of sutures 7/8 the spermathecal apertures lie just below or slightly behind the female gonopores on the P3 coxae. They are ovate, small but deep, and always end apart, either beneath a curved over-hanging lip ( Acanthodromia ) or behind low tubercles ( Hirsutodynomene , Dynomene ) ( McLay 1999: 455). Junctions occur by fusion in the dynomenid axial skeleton, as in the Dromiidae , and the intertagmal phragma skirts the last endosternite to join the median mass from below. The skeletal system shows two distinct patterns in the two genera that were examined. In Dynomene pilumnoides Alcock, 1900 the transverse bridge is shorter and thicker ( Fig. 4D ) than in Metadynomene tanensis (Yokoya, 1933) ( Fig. 4B ), which corroborates the more advanced condition of Dynomene . A third pattern is represented by Paradynomene ( Secretan 1998: figs 7, 8), in which the skeletal parts seem more layered, and the median fusion is longitudinally extended on a longer part.

Figures

FIG. 4. — A, B, Metadynomene tanensis (Yokoya, 1933), female 20.5 × 21.9 mm, New Caledonia (MNHN-B 26576); C, D, Dynomene pilumnoides Alcock, 1900, female 12.4 × 14.5 mm, Madagascar (MNHN-B 6913); A, C, thoracic sternum; B, D, axial skeleton, with connections by fusion. Abbreviations: a, spermathecal aperture at extremity of sternal suture 7/8; br, transverse bridge; cx3, P3 coxae; g, female gonopore; i.p., intertagmal phragma; 1-3, sternites 1-3; 4-8, sternites 4-8; 7/8, thoracic sternal suture 7/8. Scale bars: 5 mm.