Monomia, GISTEL, 1848

MONOMIA GISTEL, 1848 View in CoL

( FIGS 3D, 4G, 14)

= Portunus (Amphitrite) De Haan, 1833 {type species Portunus gladiator Fabricius, 1798 , subsequent designation by Miers (1886); name pre-occupied by Amphitrite Müller, 1771 [ Polychaeta]; gender feminine.

= Portunus (Monomia) Gistel, 1848 (replacement name for Amphitrite De Haan, 1833 ; gender feminine).

Included species: Ten.

Monomia argentata (A. Milne-Edwards, 1861) View in CoL

= Amphitrite argentata White, 1847 View in CoL (nomen nudum)

= Neptunus argentatus A. Milne-Edwards, 1861 View in CoL Monomia australiensis ( Stephenson & Cook, 1973) View in CoL

= Portunus australiensis Stephenson & Cook, 1973 View in CoL Monomia curvipenis (Stephenson, 1961) View in CoL

= Portunus curvipenis Stephenson, 1961 View in CoL

Monomia gladiator (Fabricius, 1798)

= Portunus gladiator Fabricius, 1798

= Cancer menestho Herbst, 1803

Monomia glareosa ( Alcock, 1899) View in CoL

= Neptunus (Amphitrite) argentatus Alcock, 1899 View in CoL Monomia haani (Stimpson, 1858) View in CoL

= Amphitrite haanii Stimpson, 1858 View in CoL

= Portunus pseudoargentata Stephenson, 1961 Monomia lucida Koch & ĎuriŠ, 2018 View in CoL

Monomia petrea ( Alcock, 1899) View in CoL

= Neptunus (Amphitrite) petrea Alcock, 1899 Monomia rubromarginata (Lanchester, 1900)

= Achelous rubro-marginatus Lanchester, 1900 View in CoL Monomia samoensis Ward, 1939 View in CoL

Diagnosis: Carapace ( Fig. 14A) quasi-hexagonal; ~1.6–1.8 times as broad as long; margins setose, dorsal surface tomentose, with well-defined granulate regions. Front ( Fig. 14B) with four subtriangular blunt teeth, submedian teeth usually distinctly lower than lateral ones, all teeth projecting slightly beyond tip of inner orbital lobe; median epistomial apophysis well developed, reaching distinctly beyond front. Orbit relatively large, ellipsoidal, with upper margin granulate and two well-developed fissures, in middle and near base of first anterolateral tooth; lower orbital margin with large lateral notch, one or two strong obtuse mesial teeth, and outer infraorbital lobe appressed to ventral side of outer supraorbital lobe (= first anterolateral tooth). Anterolateral margin of carapace convex, slightly longer than posterolateral margin, armed by nine teeth: eight anterior ones subequal, small, acute and projecting forwards; ninth tooth distinctly larger, lateral. Posterolateral angle of carapace broadly rounded. Sutures on thoracic sternum well developed ( Fig. 14C). Merus of third maxilliped with anterolateral lobe subtriangular. Chelipeds moderately stout; merus with four or five spines on anterior border and two (rarely one) spine on posterior border; carpus with spine on outer face, which may be reduced; upper surface of palm with two granular crests, inner one strong, ending by spine distally; outer surface with two granular crests ending at level of finger joint, lower arched, creating outer ventral, sharply produced margin. Chelae ( Fig. 14D) slightly unequal, weakly heterodontic, with molariform tooth on cutting edge of dactylus (this molariform tooth may be reduced in large specimens). Dactyli of pereiopods 2–4 styliform, densely setose on ventral margin. Merus of pereiopod 5 a little longer than broad, without spine on posterior margin. Male pleon ‘T’-shaped ( Figs 3D, 14C). Pleomeres 2 and 3 forming transverse laminar crests; lateral margins of pleomere 3 usually distinctly concave; apex of posterior thoracic episternite fills interspace between anterior margin of pleomere 3 and thoracic sternite 8. Pleomeres 3–5 fused, but a groove remains at place of suture between pleomeres 3 and 4; usually keels and crests present on these pleomere terga. Pleomere 6 as long as broad or longer, sometimes with a small median spine directing backwards on distal part; with telson narrowly triangular. First male gonopods ( Fig. 14E) long, bent; gonopods in pair overlapping each other by bent regions, with distal parts directed anterolaterally, or subparallel and touching only medially. Female vulva ( Fig. 4G) slit-shaped, located at anteromesial margin of sternite, often covered with cuticular cup.

Systematic position: The genus is morphologically similar to the newly established genus Allomonomia (see discussion under that genus). They share the following morphological features: rounded posterolateral angles of the carapace, third maxilliped merus with a triangular anterodistal projection and the chelae with two teeth on the upper surface of the palm. Monomia differs from Allomonomia by the front having four low and subequal teeth, with the submedians lower than the laterals, projecting slightly beyond the tip of the inner supraorbital angle, the median epistomial spine reaching distinctly beyond the front, predominantly two posterodistal spines on the cheliped merus and by the first male gonopods in a pair usually overlapping each other along their bent parts.

The three-marker phylogenetic analysis ( Fig. 1) shows Monomia as most closely related to Cycloachelous and Eodemus (see above), together forming a basal well-supported clade. As already discussed, these three genera are similar in the presence of granular patches on the dorsal regions of the carapace, four frontal teeth with the submedian pair smaller, a produced anterolateral lobe of the third maxilliped merus, two posterodistal spines on the cheliped merus (rarely single in Monomia spp. ), the ‘T’-shaped male pleon, concave lateral margins of the third male pleomere, and the first gonopods relatively long, usually bent, distally slender, and a slit-shaped female vulva. They differ, as discussed above for Eodemus , in mostly larger body sizes in Monomia , usually longer posterior lateral tooth and acutely produced posterolateral angle of the carapace in Eodemus (latter rounded in Monomia ) and the medially produced epistome in Monomia . The first male gonopods overlap each other along their bent parts in the majority of Monomia spp. (except for some Australian spp. with subparallel, not overlapping, distal parts of the gonopods), whereas they only touch at their bent parts in Eodemus .

Cycloachelous shares with the aforementioned taxa some apparent morphological apomorphies, such as a slit-shaped female vulva and (generally) two distal spines on the posterior margin of the cheliped merus. However, Cycloachelous spp. are distinct in their general appearance from other genera owing to their circular carapace shape, stout gonopods with unique shapes and symmetrical chelipeds (see Remarks for the respective genera).

Remarks: Monomia now contains ten species. Previously, 14 species were included in Monomia (see Ng et al., 2008; Koch et al., 2015b; Koch & ĎuriŠ, 2018). Four species are herein removed and transferred to different genera: two species, P. (M.) lecromi and M. calla , are placed in the new genus Allomonomia ; P. (M.) euglyphus is transferred to Cycloachelous ; and P. (M.) ponticus is transferred to Lupocycloporus .

There has been substantial confusion regarding the nomenclature of the type species of the genus Monomia , Portunus gladiator Fabricius, 1798 . It has been considered as a secondary homonym of Cancer gladiator Fabricius, 1793 , a junior subjective synonym of P. sanguinolentus ( Stephenson & Cook, 1973; Chertoprud et al., 2012). Stephenson & Cook (1973) then suggested Amphitrite haani Stimpson, 1858 as the next available synonym of P. gladiator . However, there is current agreement that this suggestion of homonymy is based on a misinterpretation of the International Code of Zoological Nomenclature ( Ng et al., 2008; Spiridonov et al., 2014; Windsor et al., 2019). Furthermore, both morphological and molecular genetic evidence ( Windsor et al., 2019) clearly indicate that M. gladiator and M. haani are distinct species and that M. pseudoargentata (Stephenson, 1961) is a junior subjective synonym of M. haani .

The morphological examination of the Australian species, M. curvipenis (one male, AM P.80096) and M. rubromarginata (1 female, MV J45390 View Materials ; four males, MV J45533 View Materials ) showed some characteristics such as the small median spine directed backwards on the distal part of the sixth male pleomere and a different shape of the first gonopods compared with the rest of the species. The generic affiliation of these species needs to be confirmed by further molecular analyses .

Size: These are medium to large portunid crabs, with the maximum size (CL × CW) ranging from 22.0 mm × 38.0 mm ( M. argentata ; Yang et al., 2012) to 61.0 mm × 111.6 mm ( M. haani , this study; ZIN RAN male).

Ecological notes: This group comprises predominantly lower subtidal crabs occurring to depths not exceeding 100 m, with soft, mainly sandy bottoms ( Sakai, 1939, 1976; Crosnier, 1962; Dai & Yang, 1991; Apel & Spiridonov, 1998; Chertoprud et al., 2012), but M. argentata seems to be a deepwater species known from depths down to 400–402 m (four males, MNHN-IU-2018-4942).

Geographical range: Indo-West Pacific: from the Red Sea and south-eastern Africa to Japan, the Philippines, Australia, New Caledonia and Samoa ( Sakai, 1939, 1976; Stephenson, 1972a, b; Apel & Spiridonov, 1998; Poupin, 2010); there is a questionable record of M. argentata from the Hawaiian Islands ( Castro, 2011).