Metadynomeninae

Guinot, Danièle, 2008, A re-evaluation of the Dynomenidae Ortmann, 1892 (Crustacea, Decapoda, Brachyura, Podotremata), with the recognition of four subfamilies, Zootaxa 1850, pp. 1-26 : 10-11

Metadynomeninae n. subfam.

( Figures 1 C, 3A, B, 4F, 5I –L)

Type genus. Metadynomene McLay, 1999 (type species by original designation: Dynomene devaney i Takeda, 1977).

Diagnosis. Carapace as wide as long, or only slightly wider than long, subcircular, rather thick; dorsal surface convex, densely covered by short tomentum giving surface uneven undulating appearance with transverse troughs. Cervical groove well defined, complete (sulcus, however, interrupted between rounded gastric pits), crossing whole carapace, forming notch with lateral carapace margin; branchial groove absent medially, but well developed laterally, parallel to cervical groove, prolonging onto ventral side; branchiocardiac groove well marked. Anterolateral margin long, beginning at postorbital angle, well defined, notched or armed with few teeth. Posterior margin concave. Frontal margin broadly triangular, V-shaped, continuous above orbit; proepistome wide, moderately long, may be short; supraorbital margin oblique, smooth, not notched, not ornamented; infraorbital margin not toothed or notched, projecting, shelf-like, clearly visible from dorsal view. Orbits deep, long, oblique, clearly exposed dorsally; eyestalks well protected. Antenna with urinal article long, relatively narrow, suboval transversely, beaked medially; second article with exopod firmly fixed. Anterior border of endostome not markedly raised. Mxp3 not strongly operculiform; basis separated from ischium by incomplete suture. Branchiostegite may be decalcified. Thoracic sternum tilted posteriorly, rather wide, filled laterally by male abdomen when folded; episternites 5, 6 not visible dorsally, except for small external extensions inserted between P2–P3 and P3–P4 coxae. Sternites 1, 2 fused into pentagonal, narrow shield, which may be slightly pointed; sternite 3 as short band, of same width as sternite 4 in anterior portion, delimited posteriorly by deep depression ( Figure 3 A); most portions of sternites 4–8 fused into single wide plate; limit between sternites 4, 5 marked by transverse convex setiferous line (more salient, serrated in males); limit between sternites 5–6 indicated by membranous, translucent band across sternum. Sterno-coxal depressions very deep. Female sutures 7/ 8 in shallow groove, below prominent ridge; spermathecal aperture slightly posterior to level of female gonopore on P3 coxa, small but clearly visible. Sterno-abdominal depression slightly excavated, either shallow or with more oblique external sides. Male abdomen with all somites free, not entirely filling sterno-abdominal depression when folded, wide, in contact with P3–P5 coxae, leaving exposed thoracic sternites 1–3, major portion of sternite 4, and very small lateral portions of episternites 5 and 6; first somite dorsally visible, extended laterally, much wider than narrow somite 2. Male abdominal somites 3–5 with biramous (two equal rami) vestigial pleopods. Pl1 vestigial in females. Uropods not sexually dimorphic, being very large in both sexes, immobile; in males and females, uropod filling entire length of abdominal somite 6, excluding it from reaching lateral margin of abdomen. Abdominal holding by coxal structures in males, one developed on P2 coxa close to the uropod margin or base of telson, a smaller one on P3 coxa; these coxal structures only restrict lateral movements of abdomen in males, are absent in females. Chelipeds unequal (at least in males), stouter than P2–P4; with a small gap between fingers, prehensile borders of fingers touching for most of their length, dactylus barely curved. P2–P4 without spines, weakly ornamented with granules; dactyli with 2–4 spines on inferior margin. P5 sexually dimorphic, reduced; basis-ischium free, not fused to merus; dactylus rudimentary. P5 c oxa modified in males, extended to enclose penis. Gonopod 1 stout, forming semi-rolled tube, with apical plate. G2 needle-like, row of curved spines on anterior surface.

Remarks. The subfamily is monotypic. Metadynomene , which contains only three extant species, forms a remarkably homogeneous group ( Table 1). That the Metadynomeninae n. subfam. and the Sphaerodromiinae (see McLay & Crosnier 1991) appear related is due to a number of comparable plesiomorphic features, as has already been noted by McLay (1991: 465, table 1), who illustrated the similarities between M. devaneyi and the species of Sphaerodromia (see also discussion and key in Guinot & Tavares 2003).

Figures

FIGURE 1. Representative species of the four subfamilies of Dynomenidae, overall view. A, Acanthodromiinae n. subfam.: Acanthodromia margarita (Alcock, 1899), Balicasag Island, Panglao, Bohol, Visayas, Philippines (ZRC) (see McLay & Ng 2005: 18); B, Paradynomeninae n. subfam.: Paradynomene tuberculata Sakai, 1963, Balicasag Island, Panglao, Bohol, Visayas, Philippines (ZRC) (see McLay & Ng 2004: 4); C, Metadynomeninae n. subfam.: Metadynomene tanensis (Yokoya, 1933) with its undulating tomentum, Balicasag Island, Panglao, Bohol, Visayas, Philippines (ZRC) (see McLay & Ng 2005: 25); D, Dynomeninae Ortmann, 1892: Hirsutodynomene vespertilio McLay & Ng, 2005, Balicasag Island, Panglao, Bohol, Visayas, Philippines (ZRC) (see McLay & Ng 2005: 21). E, Paradynomene tuberculata Sakai, 1963, New Caledonia, frontal view showing the characteristic “ face ” (ZRC). (All photographs courtesy of P. K. L. Ng).

FIGURE 3. Metadynomeninae n. subfam. (A, B) and Dynomeninae Ortmann (C, D), views of thoracic sternum and abdomen (A, C, D) and ventral surface of abdomen (B). A, Metadynomene tanensis (Yokoya, 1933), male 12, 5 x 13, 5 mm, New Caledonia, SMIB 2 (MNHN-B 25583): abdominal holding by P 2 coxa; B, Metadynomene crosnieri McLay, 1999, holotype, male, 23.2 x 22.7 mm, western Indian Ocean, îles Glorieuses, Benthedi Exp. (MNHN-B 22510): biramous vestigial pleopods 3 – 5; detail at right; C, Dynomene hispida (Latreille, in Milbert 1812), male 6.9 x 8.8 mm, New Caledonia (MNHN-B 22091): abdominal holding mechanism by sternal structure; D, Hirsutodynomene spinosa (Rathbun, 1911), male, 14.3 x 16.4 mm, western Indian Ocean, îles Glorieuses (MNHN-B 6899): abdominal holding mechanism by sternal structure (see Bouchard 2000: fig. 24 A). a 3 – a 6, abdominal somites 3 – 6; cx 1 – cx 4, coxae of P 1 – P 4; e 4 – e 6, episternites 4 – 6; pl 3 – pl 5, vestigial pleopods on abdominal somites 3 – 5; pr, coxal projection; s, shield; t, telson; u, uropod; 4, sternite 4. Scale bars: 1 mm.