A new freshwater crab of the family Hymenosomatidae MacLeay, 1838 (Crustacea, Decapoda, Brachyura) and an updated review of the hymenosomatid fauna of New Caledonia

A new genus and species, Richerius marqueti gen. et sp. nov., of a crab of the family Hymenosomatidae MacLeay, 1838 are described from the inland waters of New Caledonia based on several specimens collected in two streams at altitudes of 180 m and 500 m, respectively. Richerius marqueti gen. et sp. nov. was compared to the other freshwater species known in New Caledonia, Odiomaris pilosus (A. Milne-Edwards, 1873), and to species of Amarinus Lucas, 1980, a genus comprising many freshwater species in New Zealand, Australia, Indonesia, the Philippines, and Papua New Guinea, but never recorded in New Caledonia. The barcode fragment of the COI mitochondrial gene was sequenced for seven specimens of R. marqueti gen. et sp. nov., and all sequences were deposited in GenBank. A brief and updated review of the New Caledonian marine and freshwater hymenosmatid fauna is provided.


Introduction
Over the last five years, two French expeditions (Hydrobio expeditions), as part of "Our Planet reviewed", a major exploration program of the natural world that the Muséum national d'histoire naturelle (MNHN) has been leading since 2006, managed to collect a number of specimens belonging to the family Hymenosomatidae MacLeay, 1838 from New Caledonia. They were caught in inland freshwaters in the North and South Provinces. To this material were added hymenosomatids obtained separately by some colleagues during previous biodiversity discovery expeditions led by the MNHN.
A hymenosomatid crab from two streams at altitudes of 180 m and 500 m, respectively, could not be assigned to the well known New Caledonian endemic freshwater species Odiomaris pilosus (A. Milne-Edwards, 1873) and appeared new to science. A new genus and a new species, Richerius marqueti gen. et sp. nov., are described within the subfamily Odiomarinae Guinot, 2011, and compared to O. pilosus and to the second species of the genus, O. estuarius Davie & richer de Forges, 1996, exclusively brackish. The characters that differentiate Richerius gen. nov. from Amarinus Lucas, 1980, a genus known from the fresh and brackish waters of New zealand, Australia, Indonesia, the Philippines, and Papua New Guinea, but never from New Caledonia, required a thorough examination. As the genus Amarinus appears to be paraphyletic, including a variable arrangement of the antennule and antenna, we have therefore limited our comparison to the type species, A. lacustris (Chilton, 1882), also freshwater.

Material and methods
Institutional abbreviations MNHN = Muséum national d'histoire naturelle, Paris, France rMNH = Nationaal Natuurhistorisch Museum (currently Naturalis Biodiversity Center, NBC), Leiden, the Netherlands zrC = zoological reference Collection of the Lee Kong Chian Natural History Museum (ex Raffles Museum of Biodiversity Research), National University of Singapore, Singapore

DNA sequences
In order to ease future studies, we sequenced the barcode fragment of the COI mitochondrial gene (Folmer et al. 1994) for seven specimens of the new species Richerius marqueti gen. et sp. nov. (Table 1). DNA was extracted from pereiopods using the semi-automatic Eppendorf ep-Motion 5075 robot. Fragments of the mitochondrial COI (~ 600 bp) were amplified using the standard Folmer primers (LCO1490: 5'-GGTCAACAAATCATAAAGATATTGG-3'; HCO2198: 5'-TAAACTTCAGGGTGACCAAAAAATCA-3') (Folmer et al. 1994). DNA amplifications were performed in 20 µl PCr reactions, containing approximately 3 ng of template DNA, 2.5 mM MgCl 2 , 0.26 mM of each nucleotide, 0.3 µM of each primer, 5% DMSO, 1 ng of BSA and 1.5 units of QBIOTAQ polymerase (MPBiomedicals). Amplification products were generated by an initial denaturation step of 4 min at 94°C followed by 35 cycles of denaturation at 94°C for 30 s, annealing at 48°C for 40 s, extension at 72°C for 60 s and a final extension step at 72°C for 7 min.
PCr products were sequenced using the same primers and in both directions to ensure the accuracy of base calls. Chromatograms were edited using Geneious ver. 8 software (http://www.geneious.com/ Kearse et al. 2012). All sequences were deposited in GenBank (Table 1).

Type species
Richerius marqueti sp. nov. by present designation.

Diagnosis
Carapace circular to oval, width only slightly exceeding length; dorsal carapace surface not strongly outlined by grooves; only gastrocardiac and thoracic grooves well defined, not reaching antero-and posterolateral margins; carapace rim continuous across behind rostrum. rostrum broadly rounded, spade-shaped, slightly deflexed but not ending in narrow triangular tip extending between antennules. Proepistome represented by ventral expansion of rostrum (and not rostrum itself). Antennules obliquely folded along hollowed ventral parts of rostrum, entirely hidden dorsally. Antennae well separated from antennules, at least at their bases; urinary article at level of moderately developed epistome. Proepistome represented by ventral expansion of rostrum (and not rostrum itself). Lower orbital margin with one Male chelipeds much stouter than walking legs; propodus inflated, covered with long soft setae partially extending on fingers; merus and carpus with stiff, regularly spaced setae; fingers not gaping. Female chelipeds narrow, propodus only slighly inflated, devoid of long setae; fingers very elongate and with finely denticulate cutting edges completely joined. Pereiopods in both sexes rather long, with margins bearing stiff, regularly spaced setae.

Etymology
The genus name is in honour of Bertrand richer de Forges for his lifetime commitment to carcinology, especially of New Caledonia, for having always been an excellent and untiring researcher, and for his friendship.

Etymology
The species name is in honour of Gérard Marquet, who made extensive collections of freshwater crustaceans for more than 30 years in the Indo-Pacific islands and in particular in New Caledonia where he collected the new species here described, for his friendship and his constant enthusiasm in the field as well as in the laboratory.

Description
Carapace (Figs 1A, 5B) approximately circular to oval, slightly broader than long; dorsal carapace surface slightly concave, not strongly outlined by grooves, only with well defined gastrocardiac and thoracic grooves, approaching but not reaching antero-and posterolateral margins, respectively; no row of setae along lateral margins, except for some regularly mid-spaced setae in males; carapace angles not well marked. Anterolateral margin entire, without crenulations, lobes or teeth. Branchiostegite only weakly visible dorsally.
Male chelipeds much stouter than walking legs, particularly in large males (Fig. 4); merus and carpus with stiff, regularly spaced setae; propodus very inflated, covered with long soft setae partially extending on fingers; fingers with finely denticulate cutting edges, not gaping. Female chelipeds narrow, propodus moderately inflated, devoid of long setae; fingers proportionally rather long, with with finely denticulate cutting edges completely joined. walking legs proportionally rather long, with margins bearing stiff, regularly spaced, scattered setae; dactyli slender but not distinctly longer than respective propodi, smoothly curved, setose, without teeth, ending in pointed tip.    Thoracic sternum of male ( Fig. 2A) with sternites 4-8 considerably enlarged, with suture 4/5 to 7/8 laterally confined. Sternites 1 and 2 not separated by suture but their demarcation visible on lateral margins; sternite 2 separated from sternite 3 by complete suture; sternite 3 as narrow pentagonal band; suture 3/4 tiny, only lateral, just at level of extension of sternite 4. No longitudinal line. Paired branchiosternal canal apertures located posterolaterally on sternite 8, concealed by pleon (Fig. 3A).

Colour
In life (Fig. 5B-D), the colour is overall brown, mottled with yellowish dots.

Distribution
Richerius marqueti gen. et sp. nov. is exclusively known from freshwaters in small flowing streams where it lives among the aquatic vegetation (Fig. 5A). It is found at an altitude of up 500 m, therefore further from the sea than Odiomaris pilosus (that is usually encountered in the lower course of rivers). By comparison, Amarinus lacustris (Chilton, 1882) has been reported from New zealand freshwaters from Lord Howe Island at altitudes between 61-92 m (Etheridge 1889) and even about 800-900 m (Chilton 1915;Holthuis 1968); A. angelicus Holthuis, 1968, from the central mountain range of Papua New Guinea, was collected in pure freshwater of a watercress swamp at an altitude of 1600 m (Holthuis 1968(Holthuis , 1982.

Remarks
The subfamily Odiomarinae was erected by Guinot (2011a) to receive two genera of the family Hymenosomatidae characterised by the presence on the male pleon of intercalated platelets, either articulated and moveable (Guinot 2011a: fig. 2) or relatively less well-demarcated: Odiomaris Ng & richer de Forges, 1996, endemic to New Caledonia, and Amarinu (at least pro parte), mostly from fresh and estuarine waters of the Indo-West Pacific region. Richerius gen. nov. shows several plesiomorphic characters that include the male and female pleons without fused somites (except for pleotelson), thus consisting of six elements (namely the maximum of somites existing in Hymenosomatidae), the prominent, partially demarcated intercalated platelets, the thoracic sternum with the anterior sternites forming a small produced plate, the vulvae not anteriorly displaced, the G1 only gently curved and simple. Richerius gen. nov. can be assigned to the Odiomarinae.
Odiomaris is known from two species: the type species Elamena pilosa A. Milne-Edwards, 1873, referred to as Halicarcinus white, 1846 by Holthuis (1968), as Amarinus by Lucas (1980) then as Odiomaris by Ng & richer de Forges (1996), mainly freshwater but also euryhaline; and O. estuarius Davie & richer de Forges, 1996, exclusively brackish. An important difference between these two species is the rostrum: it is lowered ventrally as a triangular, V-shaped projection in O. pilosus so as to be positioned between the antennules (Fig. 7A) fig. 6c-d), whereas it is spatulate and does not extend to form a ventral projection between the antennules in O. estuarius (Fig. 8A-B) (Davie & richer de Forges 1996: fig. 1a-b).
Richerius gen. nov. shares with Odiomaris the same arrangement of the cephalic appendices. But its rostrum is spatulate without folding down ventrally (Figs 1, 4, 5D), instead of being lowered ventrally as a V-shaped projection located between the antennules as in Odiomaris pilosus (Fig. 7A). In Richerius gen. nov. (Fig. 1B), the proepistome is represented by a ventral expansion of the rostrum; therefore, the antennules are located along the proepistome, whereas in Odiomaris pilosus the antennules are obliquely folded in a fossa hollowed all along with the lateral parts of the V-shaped rostrum and the eye. Richerius marqueti gen. et sp. nov. actually has a rostrum and proepistome more similar to those of O. estuarius (Fig. 8) (Davie & Richer de Forges 1996: fig. 1) than to those of O. pilosus. In fact, the genus-level differences between Richerius gen. nov. and Odiomaris remain unclear. Actually, O. estuarius seems morphologically closer to Richerius gen. nov. than to O. pilosus, at least in some characteristics. A possible transfer of O. estuarius to Richerius gen. nov. has been considered but needs to be decided later, especially when the status of Odiomaris aff. pilosus is resolved (see below, 'remarks on Odiomaris aff. pilosus from the Iouanga river and two other streams').
Along the lower orbital margin there are two salient knobs in both species of Odiomaris, both prominent in dorsal view in O. pilosus (A. Milne-Edwards 1873: pl. 18, fig. 6a; Ng & Richer de Forges 1996: fig. 6a, d, not figured in fig. 6c; Guinot & Richer de Forges 1997: figs 1a, c, 2c), but shorter and not dorsally visible in O. estuarius (Davie & Richer de Forges 1996: fig. 1a; not figured in fig. 1b). In contrast, there is only one, smaller knob in Richerius gen. nov. (Fig. 1B). The cheliped palm of R. marqueti gen. et sp. nov. is covered with long, flexible setae ( Fig. 5C-D), instead of numerous spinules (or stiff setae) in O. pilosus (Fig. 6) fig. 6f), and sparse, short setae in O. estuarius (Fig. 8). In fact, the whole body (including the margins of the rostrum) and legs of O. pilosus are covered with spiniform, stiff setae that give a bristle appearance (Ng & richer de Forges 1996: figs 5a-b, 6a, d; fig. 1a) Fig. 2A). The intercalated platelets, which are completely demarcated and moveable in O. pilosus (Guinot 2011a: fig. 2), are only partially delineated in R. marqueti gen. et sp. nov., and not detached in O. estuarius. The female pleon is rather similar in Richerius gen. nov. and Odiomaris, with five somites plus pleotelson. The G1 of Richerius gen. nov. (Fig. 2D) is curved at the base, otherwise with little curvature, with a terminal portion bearing fine setae and ending in one lobe without corneous process, whereas the G1 of Odiomaris is characterised by two distinct distal processes, a longer corneous process and a shorter lobular elongation of the stem (Fig. 7B The main differences to distinguish the two genera Odiomaris and Amarinus stated by Davie & richer de Forges (1996: 259) were: 1) in Odiomaris, the G1 (see Fig. 7B) more slender, with two distinct distal processes, a longer corneous process and a shorter lobular elongation of the stem than in Amarinus; 2) in Odiomaris, the elongated triangular telson of the male pleon is significantly longer than wide at base, whereas in Amarinus the telson is more or less rounded and short, being much wider than long.
The genus Amarinus Lucas, 1980 (type species by original designation: Elamena lacustris Chilton, 1882) is known from more than ten species. They all inhabit low salinity environments, from brackish habitats to pure freshwater waters permanently (streams, lakes, swamps), and have a large distribution (New zealand, Australia, Indonesia, the Philippines, Papua New Guinea). Cases where Amarinus has been reported from New Caledonia, as in Chuang & Ng (1994: 87, 90, table 1, under A. pilosus) and erroneously as in Guinot (2011a: 23), are attributable to the fact that the species pilosus was previously associated with the genus Amarinus (see Lucas 1980) until Ng & richer de Forges (1996 made it the type species of their new genus Odiomaris. So far, no species of Amarinus has actually been reported in New Caledonia. Suspecting that our new species might belong to the genus Amarinus, we therefore carefully compared Richerius gen. nov. to Amarinus, and in particular to its type species, A. lacustris, another freshwater hymenosomatid. Richerius marqueti gen. et sp. nov. can be distinguished from Amarinus lacustris by: the wide male pleon, with prominent marks corresponding to intercalated platelets ( Fig. 2A)  In providing a key of the Southeast Asian hymenosomatids, Ng & Chuang (1996: 3-5, 6-12) have shown the presence of several groups of species within Amarinus, suggesting that the genus could be paraphyletic. Today, another problem arises, especially regarding the antennular morphology. Melrose (1975: 84, 87, figs 41-42, as Halicarcinus lacustris), who has thoroughly studied the type species A. lacustris, confined to lakes and non-tidal rivers of New Zealand and southeastern Australia, states that the antennules are "small, not visible dorsally when folded". Her figure 41d actually seems to show a folded antennule, only with the broad basal article and the second cylindrical article, without the short, supposedly folded flagellum being seen [the frontal view of fig. 41e in Melrose (1975) shows a complete, unfolded antennule]. Our examination of Amarinus lacustris, on the other hand, reveals that both antennules and antennae are inserted very closely together at their bases and remain parallel, with both flagella visible dorsally, as represented by Lucas (1980: fig. 1d) for a generalised hymenosomatid or by Melrose (1975: fig. 43c) for Halicarinus tongi Melrose, 1975. In fact, if it is possible for the antennule of A. lacustris to fold itself down [but not obliquely along the rostrum as in Odiomaris (Fig. 7A), see A. Milne-Edwards 1873: pl. 18, fig. 6a], this does not correspond to the resting position. In the seven specimens of A. lacustris examined, the antennule and antenna are very closely inserted and remain parallel, both being stretched forward; the unfolded flagellum is visible dorsally in all individuals. In any event, the disposition of the antennule and antenna differs from that Odiomaris (Fig. 7A: O. pilosus) (Ng & Richer de Forges 1996: fig. 6c-d: O. pilosus).
A picture of the cephalic region in ventral view of Amarinus angelicus (Holthuis 1968: 114, fig. 2b) shows an antennule "entirely hidden below the rostrum", obliquely folded, which does not seem to correspond to the condition of A. lacustris. This character deserves to be reviewed for all species of Amarinus, and the allocation of Amarinus (including the type species and other included species) to the Odiomarinae needs further investigation. In the new species described here, Richerius marqueti gen. et sp. nov. (Fig. 1B), the antennule and antenna are separated at least at their insertion site, and only the antennal flagellum is visible dorsally; thus it shares an arrangement substantially similar to that of Odiomaris.
It was the study of spermatozoa carried out first in the two species of Odiomaris, O. pilosus and O. estuarius, by richer de Forges et al. (1997) and later in Elamena vesca by Jamieson & Tudge (2000) that showed the very particular nature of the hymenosomatid sperm within the Brachyura. Indeed, they are distinguished by at least nine major characteristics from those of all the other Brachyura taxa studied, particularly the groups with which they have been associated, the Majoidea Samouelle, 1819 and the Thoracotremata Guinot, 1977. The 'hymenosomatid-type of spermatozoon' is unique within Brachyura (Tudge et al. 2014). The highly developed projection of the acrosome from the nucleus in hymenosomatid spermatozoon recalls the totally emergent acrosome of Podotremata Guinot, 1977 and may represent the plesiomorphic condition in the Eubrachyura Saint Laurent, 1980 (Guinot 2011a(Guinot , 2011b.

Remarks on Odiomaris aff. pilosus from the Iouanga River and two other streams
A lot of specimens obtained belatedly in the course of our research poses a problem: collected in the Iouanga River on 17 November 2016 (see Fig. 10) (MNHN-IU-2018-2999 and previously identified to Odiomaris pilosus, they split into two species: four males are certainly O. pilosus, but about twenty individuals of various sizes (a few males and a larger number of females) do not correspond either to this species or to Richerius marqueti gen. et sp. nov.; nor is it identifiable with Odiomaris estuarius. The same unidentified species was found in another stream of the North Province and is believed to inhabit another stream in the South Province (Fig. 10) (manuscript in progress).

The hymenosomatid fauna of New Caledonia
The checklist of brachyuran crabs from New Caledonia (the area considered included the Loyalty Islands, Chesterfield and Bellona Plateau and Lord Howe seamounts, Matthew & Hunter Islands as well as the Norfolk ridge seamounts) established by Ng & richer de Forges (2007) included 558 species. New Caledonia (Fig. 10), a very old, isolated Darwinian island dating to 37 Ma (Grandcolas et al. 2008), does not host any of the exclusively freshwater crabs that undergo direct development and belong to various primarily freshwater families (Yeo et al. 2008). But crabs found in freshwater include also numerous euryhaline species or secondary freshwater species from primarily marine brachyuran stock, such as Australocarcinus kanaka Davie & Guinot, 1996(Chasmocarcinidae Serène, 1964, Trogloplacinae Guinot, 1986) recorded up to 400 m above sea level in various New Caledonian freshwater habitats (Davie & Guinot 1996). This is also the case of some species of the family Hymenosomatidae that, with 119 species in 19 genera (updated from Ng et al. 2008: 108;Davie et al. 2015b) distributed worldwide (also throughout the southern hemisphere, also circumpolar in the subantarctic region), is found in a wide variety of environments: from the open ocean: 244 m depth from Taupo Seamount, Tasman Sea, for Micas lucasi (richer de Forges, 1993) (richer de Forges 1993, as Halicarcinus lucasi); about 500 m depth for Halicarcinus tongi Melrose, 1975(Melrose 1975; estuarine and brackish waters (Lucas & Davie 1982); inland freshwaters (e.g., Lucas 1980;Lucas & Davie 1982;McLay 1988;Ng & Chuang 1996); swamps at an altitude of 1600 m (Holthuis 1968); pools of arid zones (Kemp 1917;Ali et al. 1995;; caves (Ng 1991;Naruse et al. 2008b); it may be also symbiotic with echinoderms (Lucas 1980;Poore 2004). Hymenosomatids are probably the most ecologically diverse group of crabs, indicative of successful morphological adaptations (Guinot 2011a). Freshwater taxa are present everywhere (including the Philippines, India, Sulawesi, New Guinea, New Caledonia, Australia and New zealand).
Hymenosomatids have no more than three stages zoeae in marine species and display unique characters, including the absence of a megalopa stage in the larval development of all its members, as well as occurrence in marine, brackish and freshwater habitats (rice 1980, 1981a, 1981b, 1983Fukuda 1981;rabalais & Gore 1985;Krishnan & Kannupandi 1988;Dornelas et al. 2003;Guinot 2011aGuinot , 2011b. Some estuarine species and all freshwater species have a direct development (Lucas 1971;Chuang & Ng 1994;wear & Fielder 1985): for example, Amarinus lacustris is known to carry ca 35 eggs (Lucas 1980: 202, table 4); the cave-dwelling Sulaplax ensifer Naruse, Ng & Guinot, 2008 possesses the largest eggs (mean 1.19 mm, n = 10) and the smallest clutch size (17 eggs) known for any hymenosomatid crab (Naruse et al. 2008b). The troglobitic Cancrocaeca xenomorpha Ng, 1991, from Sulawesi and confined to freshwater and most common on pieces of driftwood brought into the caves by rivers, can only have a direct development (Ng 1991;Chuang & Ng 1994;Naruse et al. 2008a). A female of Neorhynchoplax bovis (Barnard, 1946), an estuarine species, contained 13 juveniles under the pleon (Barnard 1950: 72, as

Rhynchoplax bovis).
In lower Mesopotamia, Iraq, Elamenopsis kempi is adapted to live among branches of a water plant in a habitat of oligohaline brackish water with a salinity of 1.3-2.7‰ and a temperature range of 12-35°C (Chuang & Ng 1994;Ali et al. 1995Ali et al. , 2000. Considering the habits and habitat of the New Caledonian freshwater species Odiomaris pilosus and Richerius marqueti gen. et sp. nov., which live even further from the sea and are found above sea level and even at relatively high altitude, it is likely that both have direct development. A few large eggs of about 1.0 mm in diameter and forming a small clutch are present under the female pleon of R. marqueti gen. et sp. nov. (Fig. 3A).
The present revision of the taxonomy of all the species of Hymenosomatidae known so far from New Caledonia provides interesting results. Until 1996, all species in New Caledonia had been known for more than 140 years, each described by A. Milne-Edwards (1873). And, with the exception of Elamenopsis lineata A. Milne-Edwards, 1873 that has remained unchanged over these years, all were assigned to new genera by Davie & richer de Forges (1996), Ng & richer de Forges (1996), Poore et al. (2016) and .
The hymenosomatid fauna of New Caledonia comprises secondary freshwater, brackish and marine species. To date, only one species, Odiomaris pilosus, has been known from shallow fresh waters of the Island, from the estuary inland for several kilometres, in rivers with rapid currents. Richerius marqueti gen. et sp. nov. is a more inland species found in two streams at 180 m and 500 m of altitude. A third species, here tentatively named Odiomaris aff. pilosus, also inhabits streams but close to the sea and is euryhaline (manuscript in progress).
It should be noted our revision is preliminary, as recent expeditions (KOUMAC 2018(KOUMAC , 2019, aimed at updating the marine biodiversity inventory of New Caledonia, show the existence of more taxa to be studied.
The currently known genera and species are as follows.

Odiomaris aff. pilosus
See above, 'remarks on Odiomaris aff. pilosus from the Iouanga river and two other streams'.
Several species of Neorhynchoplax are regarded as true freshwater species: N. dentata Ng, 1995 (Sarawak, Malaysia), N. inermis Takeda & Miyake, 1971 (Palau Islands), N. introversa (Kemp, 1917) (Kiangsu, China), N. kempi (Chopra & Das, 1930) (Basra, Iraq), N. prima Ng & Chuang, 1996 (Pulau Bintan, Indonesia), N. frontalis (Lucas & Davie, 1982) (NE Queensland, Australia), N. hirtirostris (Lucas & Davie, 1982) (NE Queensland, Australia), N. nasalis (Kemp, 1917) Shen 1932;Chuang & Ng 1994;Ng et al. 1999Ng et al. , 2008Ng et al. , 2011Naruse et al. 2008b;Hsueh 2018). Others species are from brackish waters or are marine intertidal and marine subtidal. Davie & richer de Forges, 1996 Fig. 9 Neorhynchoplax euryrostris Davie & Richer de Forges, 1996: 260, figs 2b, d, 3. Belongs to the group of species of Neorhynchoplax in which the lateral carapace margin is armed with a distinct recurved spiniform tooth just above the first ambulatory leg (P2); a characteristic shared with Richerius marqueti gen. et sp. nov. is the long setae that cover the outer surface of the stout palm and the fingers of the chelipeds, especially in males (Fig. 9). It is estuarine to tidal freshwater. The species was  until now only known from the type material collected on the western coast of New Caledonia (Dumbea, Le Cap) where it inhabits crevices in rotting logs at the edge of the water at low tide; and under stones in freshwater (Davie & Richer de Forges 1996: 261). Thanks to the Hydrobio Expedition, "Our Planet reviewed", it was found in the Iouanga river and in a stream tributary of the Negropo river, at 4 m a.s.l., where it cohabits with Odiomaris aff. pilosus. These newly collected specimens were all found in a similar habitat, among aquatic vegetation in the lower part of the river under the marine influence, with a variable salinity ranging from freshwater to brackish water depending on the tide. Elamenopsis lineata, based on one specimen collected at Dotio, New Caledonia (and whose holotype is not a male as reported by A. Milne-Edwards in 1873 but a female as noted by Lucas in 1980) and redescribed by Ng & Chuang (1996: 40, figs 15-16), was not collected by the Hydrobio Expedition. The species is known from Queensland (Australia) and Sulawesi (Indonesia) (Ng & Chuang 1996). It is an
The genus Elamena, which, with 24 species, is one of the most species-rich in the family Hymenosomatidae, can be separated into two groups (Lucas 1980). Elamena vesca is included in the group with a truncated rostrum and a polygonal carapace (rahayu & Nugroho 2019). Ng & richer de Forges, 1996 Elamene  (1858) from Japan. According to Kemp (1917), these similar specific names are due to coincidence. The two species are in fact different, and a new name, E. vesca, was created by Ng & richer de Forges (1996) using fresh specimens from New Caledonia as holotype and paratypes. The species is cryptic, intertidal on rocky shores, in shallow waters (about 0.5 m).

Discussion
The new hymenosomatid Richerius marqueti gen. et sp. nov., found in two streams at altitudes of 180 m and 500 m in the inland waters of New Caledonia, is distinguished from the long-established taxon Odiomaris pilosus (with which it had been confused in the collections), which is also freshwater (but usually encountered in the lower course of rivers of New Caledonia) and euryhaline. Richerius gen. nov. differs from Amarinus, and in particular from its type species A. lacustris, reported from New zealand freshwaters at altitudes of 61-92 m and even about 800-900 m a.s.l. Amarinus, which comprises many freshwater species of New zealand, Australia, Indonesia, the Philippines and Papua New Guinea, is for the moment not known from New Caledonia. Another species (Odiomaris aff. pilosus) previously identified as Odiomaris pilosus, collected close to the sea in the Iouanga river and in other streams of the North Province and South Province, does not correspond to this species or to Richerius marqueti gen. et sp. nov. either; nor is it identifiable with the brackish representative of the genus, Odiomaris estuarius. DNA sequences of all these species that are in preparation hopefully will provide satisfactory answers to outstanding questions.
The carcinological fauna of New Caledonia, which does not host any of the exclusively primarily freshwater families, includes secondary freshwater species from primarily marine hymenosomatid stock, euryhaline species and strictly marine species. Our updated review lists seven genera: Richerius gen. nov., exclusively freshwater; Odiomaris, endemic, with a freshwater and euryhaline species, O. pilosus, and one brackish species, O. estuarius; Neorhynchoplax, with N. euryrostris, estuarine to tidal freshwater; Lucascinus, with L. keijibabai, from intertidal reef and perhaps endemic to New Caledonia; Micas, endemic, with two species: M. falcipes, from shallow reef, and M. minutus, from the intertidal zone or fringing reef; Elamenopsis, with E. lineata, an estuarine species, found in sandy mud, and in mangrove area; and Elamena, with E. vesca, cryptic, intertidal, in shallow waters. Other newly collected marine species, in study, will soon increase our knowledge of New Caledonian hymenosomatid fauna. programme, implemented by the Muséum national d'histoire naturelle (MNHN; Pascale Joannot, Head of expeditions programme) in partnership with the Conservatoire d'Espaces naturels (CEN), with funding from the Gouvernement de la Nouvelle-Calédonie, Province Sud, Province Nord, Office des Postes et Télécommunications (OPT), Maison de la Nouvelle-Calédonie, and the Ministère des Outre-mer (French Ministry for the Overseas). The expeditions operated under permits issued by the Province Sud (under APA_NCPS_2017_028) and Province Nord, and the organizers thank, respectively, Emmanuel Couture and Isabelle Jurquet (Province Sud) and Jean-Jérôme Cassan and Yannick Monlouis (Province Nord) for their help in issuing these permits. For logistics before, during and after the field work, we thank Sébastien Faninoz and Alice Leblond. Following research expeditions to the Forgotten Coast (in 2016), the landlocked Katalupatik massif in the North Province (in 2017), inland water systems in the Main Island (since 2016), and the Koumac lagoons and reefs (in September 2016), Our Planet reviewed teams returned in 2019-2020 to continue the exploratory operations in New Caledonia.