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ZOOTAXA

ISSN 1175-5326 (print edition)

ISSN 1175-5334 (online edition)Copyright © 2013 Magnolia Press

Zootaxa 3734 (3): 331–344

www.mapress.com/zootaxa/Article

http://dx.doi.org/10.11646/zootaxa.3734.3.3

http://zoobank.org/urn:lsid:zoobank.org:pub:6D25E1F3-B596-4BAA-938C-27157B67F42E

A re-appraisal of the systematic status of selected genera in Palaemoninae

(Crustacea: Decapoda: Palaemonidae)

SAMMY DE GRAVE1 & CHRISTOPHER W. ASHELBY2

1Oxford University Museum of Natural History, Parks Road, Oxford, OX1 3PW, United Kingdom.

E-mail: sammy.degrave@oum.ox.ac.uk2APEM Ltd., Diamond Centre, Works Road, Letchworth Garden City, SG6 1LW, United Kingdom. E-mail:c.ashelby@apemltd.co.uk

Abstract

Recent phylogenetic work (Ashelby et al., 2012) has demonstrated the need for a fresh appraisal of the systematic status

of some Palaemoninae genera. In the present contribution the accumulated morphological as well as molecular evidence

is reviewed. The genera Palaemonetes, Exopalaemon and Coutierella are demonstrated to be junior synonyms of Palae-

mon, which now contains 83 species. As a result of this systematic re-arrangement, two replacement names are needed.

Palaemon kwantung nom. nov. now replaces Exopalaemon guangdongensis Guo, Wang & Zhang, 2005, nec Palaemon

guangdongensis Liu, Liang & Yan, 1990. Palaemon mundusnovus nom. nov. is the replacement name for Palaemonetes

intermedius Holthuis, 1949, nec Palaemon intermedius (Stimpson, 1860).

Key words: Decapoda, Palaemonidae, Palaemon, Palaemonetes, Coutierella, Exopalaemon, systematics

Introduction

In recent years, considerable strides have been taken in deriving a stable and usable classification for caridean shrimps, with De Grave et al. (2009) setting out a framework at family and generic level integrated with, and comparable to, the other groups in Decapoda. This was followed by the global checklist of species in De Grave & Fransen (2011) perhaps generating the impression of a fully resolved taxonomy and systematic arrangement. However, in tandem with these compilations and perhaps partly due to their holistic overview, recent years have seen a renewed interest in resolving long standing systematic controversies, as well as attempts to place the classification of caridean shrimps on a more natural footing, following Darwinian principles. Much of this research has focussed on higher systematic levels, such as resolving the position of the enigmatic family Procarididae (see Bracken et al. 2010) and the continued usage of superfamilies (see Li et al. 2011). However, due to the growing usage of genetic analysis in biology in general, and systematics in particular, much focus has also been devoted to resolving more basic taxonomic and systematic questions, such as delineation of species and genera. Due to the species-rich nature and world-wide distribution of Palaemonidae, it is no surprise that this family has been scrutinised in recent years in this regard. Although many questions remain unanswered, especially in relation to the existence of the two subfamilies, Palaemoninae and Pontoniinae, or indeed the phylogenetic relationships amongst pontoniine genera and species, significant progress has been made in the last decade or so regarding the systematics of the subfamily Palaemoninae.

Pereira (1997) performed one of the first cladistic analysis of its kind on Palaemoninae, based on a matrix of 81 characters and 172 species. His results demonstrated considerable paraphyly at various levels, including the potential inclusion of several Palaemoninae genera (Brachycarpus, Leander, Leandrites) in Pontoniinae. At a lower taxonomic level, paraphyly was demonstrated in three of the major Palaemoninae genera, Palaemon, Palaemonetes and Macrobrachium. Following this, Murphy & Austin (2003) carried out a phylogenetic study using partial 16S sequences on Australian species of the subfamily, and found that Macrobrachium intermedium

(Stimpson, 1860), Palaemon serenus Heller, 1862 and Palaemonetes australis Dakin, 1915 are so closely related,

Accepted by S. Ahyong: 16 Oct. 2013; published: 6 Nov. 2013 331

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that their observed genetic differences would be suggestive of all three species being congeneric. Although Walker & Poore (2003) subsequently transferred the species commonly known as M. intermedium to Palaemon (as P.

intermedius), the suggestion that the Australian species of Palaemon and Palaemonetes could be congeneric was not followed through. Quite recently, a comprehensive phylogeny for the subfamily was performed by Ashelby et

al. (2012) using both 16S and Histone 3, which discovered significant paraphyly of Palaemon and Palaemonetes, instead recovering geographically delineated clades resulting in independent, regional invasions of the freshwater realm. As is traditional in such studies, no taxonomic decisions were taken and any systematic re-arrangement was left for future, morphologically supported work. Shortly afterwards, two further molecular studies appeared (Cuesta et al. 2012; Botello & Alvarez, 2013), which, although much more limited in geographical scope, nevertheless added a few important pieces to the puzzle.

The purpose of the present contribution is thus to morphologically assess the paraphyletic genera recovered by Ashelby et al. (2012) and their potential support from other studies and to establish a formal systematic framework for selected Palaemoninae genera in line with these conclusions.

Comments on the genus Palaemonetes Heller, 1869

The genus Palaemonetes is separated from Palaemon solely by the absence of the mandibular palp (e.g. Holthuis 1950a, 1993; Walker & Poore 2003), which Kemp (1925) already remarked on “the genus, being based on a single negative character, might well be imagined to possess small claim to a monophyletic origin and it is indeed possible that some of the species have been separately evolved from different forms of Leander [= Palaemon]”. In general, the genus has been long recognised on that basis, particularly in Europe, where a clear habitat separation of forms assigned to Palaemon or Palaemonetes is present, Palaemonetes species being freshwater or brackish as opposed to marine. On a more worldwide basis, species have not always been assigned to their respective genera on the basis of the palp. For instance, Carvacho (1979) assigned his new species, karukera, to Palaemonetes, even though the species clearly exhibits a reduced mandibular palp. The variability in both the presence/absence of the mandibular palp in this group has long been discussed and commented on. Gurney (1939) described Palaemonetes

pacificus from Saipan, assigning it to that genus as the mandibular palp was absent. A re-examination of the type specimen (Gurney, 1940) showed that whilst it was indeed lacking on one side, the other side harboured a three-segmented palp, making Palaemonetes pacificus a synonym of Leander gardineri Borradaile, 1901, itself a synonym of the widely distributed Palaemon debilis Dana, 1852. Later, Chace (1972) examined around 100 specimens of Palaemon debilis from several locations (both freshwater and marine) around Hawai’i, which revealed that no specimens harboured a palp and led him to remark the species should be assigned to Palaemonetes. However, he refrained from such action as further study from material from Palau as well as the Tuamotu Archipelago revealed a great variability in both the number of segments, as well as the presence of the palp in that species (Chace 1972). Slightly earlier, Fujino & Miyake (1968) had already drawn attention to the considerable variability of the number of palp segments in seven species of Japanese Palaemon, although they did not report any specimens without a palp. Bray (1976) reported that at least some specimens of Palaemonetes

australis Dakin, 1915, at every location examined in Western Australia, harboured a mandibular palp and further quotes an unpublished thesis in which 20% of individuals had a palp. To name but a few further studies, Tirmizi & Kazmi (1984) reported considerable variation in the number of segments in Palaemon pacificus (Stimpson, 1960), with similar variation reported for Palaemon maculatus (Thallwitz, 1892) by Ashelby & De Grave (2009), including a specimen which had no palp on the left mandible, but with a three segmented palp on the right mandible.

Despite this rather large body of evidence that the presence/absence of the mandibular palp is not a stable character, both genera have been maintained in recent literature, largely due to convenience perhaps of the diffuse, but clear general habitat separation of both genera, with Palaemonetes being noted for a low salinity through to fully freshwater preference (see Strenth 1976) and Palaemon being largely fully marine species. However, as noted by Holthuis in Strenth (1976) a thorough revision of both genera is needed, the start of which is to resolve the discussion about their separate status as genera.

Pereira (1997) carried out a morphological, cladistic analysis of 81 characters in 172 species in the subfamily Palaemoninae, including 27 species of Palaemonetes and 17 Palaemon. Although the mandibular palp was

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included as a character (with character states absent, 2 jointed, 3 jointed, 3 jointed + broad), his study did not reveal the character to be informative in separating taxa assigned to either genus. Instead, a major clade emerged containing all included species of Palaemon and Palaemonetes, separated into geographically delineated sub-clades. This result mirrors the genetic analysis in Ashelby et al. (2012) which also recovered geographically delineated clades, comprising of species currently assigned to Palaemon and Palaemonetes alike. As the morphological and genetic analyses are congruent in this respect, it is overwhelmingly clear that the presence/absence of the mandibular palp cannot be used as the sole character separating both genera. No other morphological characters are known to separate both genera, and the results of both analyses strongly support the synonymy of Palaemonetes Heller, 1869 with Palaemon Weber, 1795. Aside from the genetic and morphological evidence, larval development studies conducted by Knowlton & Vargo (2004) compared the development of three coastal Palaemonetes species in the USA with three species of Palaemon. This study concluded that the differences within genera are more pronounced than between genera and suggested a close evolutionary relationship, close to being congeneric. The genus Palaemonetes is therefore formally synonymised herein and all its constituent species transferred to Palaemon (see below).

Comments on the genus Exopalaemon Holthuis, 1950a

Holthuis (1950a) erected the subgenus Exopalaemon in Palaemon, with Palaemon styliferus H. Milne Edwards, 1840 as the type species, to include those species with an elongated, slender rostrum, bearing an elevated basal crest on the dorsal margin. In contrast to the subgenus Nematopalaemon, which Holthuis (1950a) considered closely related, members of Exopalaemon harbour a branchiostegal groove and have non-elongated dactyli on the ambulatory pereiopods. Although Holthuis (1980) informally used Exopalaemon at generic level, it was formally recognised as a genus by Chace & Bruce (1993). Since then, the genus has received universal recognition in taxonomic literature and comprises 10 species (see De Grave & Fransen 2011), all of which have an Asian distribution, primarily brackish to freshwater.

In the analysis of Ashelby et al. (2012), four members of this genus were included, which consistently are embedded in a clade, comprised of Asian Palaemon species, within the over-arching Palaemon sensu lato clade. This is supported by the morphological, cladistic analysis of Pereira (1997) which included E. orientis only. In that study, the species is embedded in a clade, primarily comprised of members of Palaemon (as then recognised). Both genetic and morphological data are thus congruent, that this group of crested species does not form a generic level clade. Indeed, Kemp (1917) already pointed out that this group of species grades into “...more normally constituted elements of the genus...”, specifically such species as the long rostral Palaemon concinnus form.

The genus is thus herein formally considered to be a synonym of Palaemon and its constituent species are re-assigned to that genus. It is interesting to note that another group of crested taxa, the genus Exhippolysmata

(Hippolytidae) in genetic analysis (e.g. Baeza 2010; Fielder et al. 2010) also embeds itself in a wider clade (Lysmata in this case) composed of taxa with shorter, non-crested rostra. A re-appraisal of Exhippolysmata thus also appears warranted.

Comments on the genus Coutierella Sollaud, 1914

Sollaud (1914) erected the genus Coutierella with the following diagnosis: anterior border of the carapace provided with an antennal and branchiostegal tooth; mandible without palp; posterior border of the lacinia of the maxilla straight and furnished with plumose setae; basial endite of first maxilliped with prominent lobe on dorsal surface, provided with numerous plumose setae, distinctly separated from coxal endite. A single species, C. tonkinensis

Sollaud, 1914 was included based on a series of specimens obtained from the Red River delta in Vietnam, considered to be a true freshwater species with abbreviated larval development (Sollaud 1914). The species was said to be commercially fished and used as one of the principal species in Vietnamese shrimp paste, mắm tôm (Sollaud 1914) (also see Holthuis 1980).

Although Sollaud (1914) considered the mouthparts to be of generic significance, this was disputed by Kemp

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(1925) who considered the mouthparts to be “...interesting...” but not being of generic importance. Kemp (1925) did however draw attention to the apex of the telson of the species being “...concave and armed with 6 pairs of spines…” Although he did consider that “… if the description is a correct account of the structure of the normal telson, there is perhaps some reason for regarding the species as generically or subgenerically distinct from Palaemonetes...”. He nevertheless included tonkinensis in the key to the genus Palaemonetes (Kemp 1925: 316), thus establishing the synonymy of Coutierella with Palaemonetes.

In contrast, Bruce (1989) considered the genus to be valid, although closely related to Palaemonetes, sharing with it a very similar form of rostrum, inferior orbital angle, and the presence of both antennal and branchiostegal spines, as well as a branchiostegal groove. Bruce (1989) stated that Coutierella differs from Palaemonetes in lacking a well-developed pleurobranch on the fourth thoracic somite, the second pereiopods being very feebly developed and distinctly subspatulate and three or more pairs of spines being present on the posterior margin of the telson. Bruce (1989) also discussed a suite of modifications to the mouthparts (maxillula, maxilla, first maxilliped), expanding on the information presented in Sollaud (1914) and which he considered to be a specialized feature not present in any other palaemonid shrimps.

In the genetic analysis of Ashelby et al. (2012) Coutierella tonkinensis forms a weakly supported clade with Palaemon paucidens, but deeply embedded within a well-supported monophyletic clade, comprising the majority of species currently assigned to Palaemon, as well as the included representatives of Palaemonetes and Exopalaemon. Following the above argued synonymy of Palaemonetes and Exopalaemon with Palaemon, the genus Coutierella is thus also herein relegated to the synonymy of Palaemon, supporting Kemp’s (1925) assertion that the unique mouthparts of the species do not warrant generic status. This is further supported by the morphological cladistic analysis of Pereira (1997), which recovered the taxon embedded in a clade, chiefly comprising of species then assigned to Palaemonetes. The unusual ornamentation of the posterior margin of the telson, as well as the subspatulate, feebly developed second pereiopods are considered diagnostic for the species.

De Grave & Fransen (2011) list two valid subspecies for C. tonkinensis: C. tonkinensis tonkinensis Sollaud, 1914 and C. tonkinensis guangdongensis (Liu, Liang & Yan, 1990). The latter subspecies was described as Palaemonetes tonkinensis guangdongensis by Liu et al. (1990) based on material, collected from freshwater from samples ranging from Fujian Province to the estuary of the Zhujiang River, Guangdong province, P.R. China, with Guangzhou on the Zhujiang River as the type locality. Li et al. (2004) also consider some of this material to be more estuarine in habitat, although the exact salinity range for the taxon remains unclear. Liu et al. (1990) state that the new subspecies differs from the nominotypical one in its rostral formula being 0–1 + 5–7/2–3 (versus 1–2 + 7–9/1–2 in C. tonkinensis tonkinensis), the distal telson margin being “mostly slightly concave, some are convex or pointed, very rarely deep-concave” (versus “mostly deeply concave, some are truncate” in C. tonkinensis

tonkinensis) and harbouring 1–3 pairs of plumose setae between the distal spines (vs. without plumose setae in C.

tonkinensis tonkinensis). Although Li et al. (2004) highlighted considerable morphological variability in their material from Hainan Island and entertained the possibility that the two taxa, as described, present extreme forms of variation of the same taxon, they left both subspecies as valid until more, morphologically intermediate, material could be examined.

This morphological variation is herein interpreted afresh, based on the descriptions and illustration in Sollaud (1914), Bruce (1989), Liu et al. (1990), Li et al. (2004), as well as newly studied material in the collections of the Oxford University Museum of Natural History (OUMNH.ZC.2003-07-001, traditional shrimp pond, Mai Po Nature Reserve, Hong Kong, leg. KM Wong, 01.06.2002; OUMNH.ZC.2011-02-022, Tonkin, Vietnam, 1913, coll. Sollaud, don MNHN).

Sollaud (1914) gives the rostral formula of the syntypic series from the Red River Delta as 1 + 6–7/1–2; Bruce (1989) states his material from Hong Kong to be 1 + 4–6/1–3; Liu et al. (1990) give 1–2 + 7–9/1–2 for material from Guangxi Province, whilst Li et al. (2004) provide 1 + 5–7/1–3 for material from Hainan Island. The rostral variation from at least some of these populations is higher, as OUMNH.ZC.2011-02-022 from Tonkin has 1 + 6-9/1–3 (contemporary with the syntypic series), whilst OUMNH.ZC.2003-07-001 has 1 + 4–5/1–3 (sampled 15 years after the sample reported upon in Bruce 1989). Liu et al. (1990) state that the rostral formula of their C. tonkinensis

guangdongensis is 0–1 + 5–7/ 2–3. As, however, the total variation in the nominotypical subspecies is 1–2 + 4–9/1–3, it is clear that this cannot be a distinguishing feature. Considerable rostral variation also being very common in several species of Palaemon (see De Grave 1999a, 1999b). The second character mentioned by Liu et al. (1990) to distinguish both subspecies, hinges on a subtle variation of the distal telson margin, being mostly slightly

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concave versus mostly deeply concave. The illustrations in Bruce (1989) of both Vietnamese and Hong Kong material, as well as the observed variation in the related Palaemon varians (see De Grave 1999a) amply demonstrate this to be of no taxonomic significance.

Although Li et al. (2004) imply that the description in Liu et al. (1990) differentiates both subspecies on the basis of the number of distal telson setae (as “spines”), this is incorrect. Liu et al. (1990) instead used the presence of plumose setae as the character differentiating both taxa, being absent in the nominotypical subspecies, and with 1–3 pairs in C. tonkinensis guangdongensis. Sollaud (1914) does not indicate whether plumose setae are present in the syntypic series or not. In the illustration by Bruce (1989: fig. 6C) of the distal telson margin of a single syntype, no plumose setae can be discerned (in contrast to the statement to that affect in Li et al. 2004). In the contemporary material from the type locality herein examined (OUMNH.ZC.2011-02-022), one specimen has a single plumose seta, in the other six specimens no plumose setae are present. In the material from Hong Kong discussed by Bruce (1989) three pairs of plumose setae are present, whilst in the herein examined sample from the same location (OUMNH.ZC.2003-07-001) 1–4 pairs are present in all specimens, both thus corresponding to C. tonkinensis

guangdongensis. In contrast, in the material from Hainan Island (Li et al. 2004) and Liu et al. (1990)’s material from Guangxi, no plumose setae are present, corresponding to the nominotypical subspecies. At our request, C. Fransen (NCB-Naturalis) examined the 16 syntypes of C. tonkinensis tonkinensis deposited in Leiden (RMNH D 6529). Although the majority of the syntypes lack plumose setae, several specimens harboured 1–3 plumose setae. It is, therefore, clear that neither the presence versus absence nor indeed the number of plumose setae on the distal margin of the telson can be used to differentiate both subspecies. As none of the three characters listed by Liu et al.

(1990) appear to have any taxonomic value, both subspecies are herein considered to be the same taxon.

Comments on the genus Palaemon Weber, 1795

With the transfer of species previously included in Coutierella, Exopalaemon and Palaemonetes, the genus Palaemon now contains 83 species. Not surprisingly, a larger morphological disparity is also now present in the genus, ranging from the absence and presence of the mandibular palp to the presence or absence of a basal crest on the rostrum, and including the presence of supernumerary setae on the telson margin, a character previously assumed to be of higher systematic relevance. A new generic definition is thus clearly needed.

Holthuis (1950a) provided an exhaustive definition of the genus, which was condensed into a more succinct diagnosis by Walker & Poore (2003), taking into account the variation of the position of the hepatic/branchiostegal tooth in Australian members of the genus. A revised generic diagnosis is offered below.

Diagnosis. Rostrum well developed, toothed dorsally and ventrally, without or with an elevated basal crest; upper margin bearing single row of setae between dorsal teeth. Carapace smooth, bearing distinct branchiostegal tooth and groove; branchiostegal tooth usually situated on carapace edge but may be set back in a hepatic position; branchiostegal groove variable, usually running straight back from carapace edge in a shallow arc. Antennal tooth generally strong, on anterior margin of carapace some distance below rounded lower orbital angle. Mandibular palp present or absent, if present normally comprised of 2 or 3 articles. Anterior margin of antennular peduncle rounded, anterolateral spine small. First pleopod of male without or with rudimentary appendix interna on endopod. Propodus of fifth pereiopod with several transverse rows of setae on distal part of the posterior margin. Telson usually with 2 slender median setae on posterior margin (variable number in P. tonkinensis). Pleuron of fifth abdominal somite usually ending in small sharp point.

In the analysis of Ashelby et al. (2012) two further clades of species currently assigned to Palaemon are placed outside of the main Palaemon clade, closer to Macrobrachium than Palaemon sensu stricto. One clade comprised Palaemon gracilis and Palaemon pandaliformis which form part of a morphologically homogeneous group of three species living in reduced salinity and freshwater in Central and northern South America. The other clade was comprised of the widespread Indo-Pacific species, Palaemon concinnus.

The Central and northern South American group (P. gracilis, P. pandaliformis, P. hancocki) can be characterised by a long, slender, upturned rostrum, with dorsal teeth primarily restricted to the basal part. A detailed study of their morphology at present reveals no other features which would unite these species and distinguish them from all other members of the genus Palaemon at a generic level. Further, a similar rostral form is known to occur in other taxa, for instance Palaemon debilis (see Chace 1972) which is recovered inside the main

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Palaemon clade by Ashelby et al. (2012). No support for a placement of this group outside of Palaemon is found in the cladistic study of Pereira (1997) who recovered them inside his main Palaemon clade, as a sister lineage to Exopalaemon orientis, Nematopalaemon schmitti and Leptocarpus potamiscus, only one of which has a somewhat similar rostral form. Interestingly, a closer evolutionary relationship of this group to Leptocarpus is also supported by Ashelby et al. (2012), but as this has a shorter rostrum, basing a new genus on the sole character uniting this group seems futile.

No support was found by Pereira (1997) for the placement of P. concinnus outside Palaemon, with P.

concinnus clustering with a miscellaneous, non-geographically delineated assemblage of species, inside the Palaemon clade in his analysis. Palaemon concinnus does have a unique characteristic within the genus, namely the presence of a rudimentary appendix on the endopod of the first pleopod of males (see Holthuis 1950a; Li et al.

2007). It shares this characteristic with four genera in the subfamily, Brachycarpus, Leander, Leandrites

and Urocaridella. However, each of these genera is also characterised to at least some degree by a suite of other distinguishing features. The presence of a reduced appendix on the first pleopod in itself does not seem sufficient to warrant generic separation of P. concinnus and a reassessment of its position must consider other stable morphological characters.

Although maintaining these two putative clades in Palaemon, as currently defined, may still result in a paraphyletic genus, the lack of defining characters for these two groups currently does not provide an alternative. Nevertheless, the branch support recovered by Ashelby et al. (2012) for the positions of these outlier “Palaemon” clades was statistically equivocal, so phylogenetic placement with the main Palaemon clade cannot be excluded. A fully resolved, satisfactory solution to the discrepancy provided between the molecular and morphological data for these two groups must await a comprehensive, cladistic analysis.

A revised list of currently accepted synonyms of Palaemon, as well as an updated list of species currently included in the genus is given below.

Palaemon Weber, 1795

= Palaemon Weber, 1795 (type species Palaemon adspersus Rathke, 1837)= Palaemon Fabricius, 1798 (type species Cancer Squilla Linnaeus, 1758)= Palaemonetes Heller, 1869 (type species Palaemon Varians Leach, 1813 [in Leach, 1813-1814]) syn. nov.

= Palaemonopsis Stimpson, 1871 (type species Palaemonopsis carolinus Stimpson, 1871) = Allocaris Sollaud, 1911 (type species Allocaris sinensis Sollaud, 1911)= Coutierella Sollaud, 1914 (type species Coutierella tonkinensis Sollaud, 1914) syn. nov.

= Alaocaris Holthuis, 1949 (type species Palaemonetes antrorum Benedict, 1896)= Exopalaemon Holthuis, 1950a (type species Palaemon styliferus H. Milne Edwards, 1840) syn. nov.

= Palaeander Holthuis, 1950a (type species Palaemon elegans Rathke, 1837)

List of currently included, valid species in Palaemon Weber, 1795

For each species their geographical distribution is indicated, as well as habitat preferences, if known. Full synonymies and citations to the original descriptions can be found in De Grave & Fransen (2011).

Palaemon adspersus Rathke, 1837 [north-western Europe, Mediterranean, Black Sea; introduced to Caspian Sea and Aral Sea; marine and high salinity estuaries]

Palaemon affinis H. Milne Edwards, 1837 [in H. Milne Edwards, 1834-1840] [New Zealand; marine]Palaemon africanus (Balss, 1916) comb. nov. (herein transferred from Palaemonetes, see nomenclatorial

comments below) [Nigeria]Palaemon annandalei (Kemp, 1917) (herein transferred from Exopalaemon) [northern China; estuaries and

freshwater]Palaemon antennarius H. Milne Edwards, 1837 [in H. Milne Edwards, 1834-1840] (herein transferred from

Palaemonetes) [northern Mediterranean from Italy to Turkey; freshwater]Palaemon antrorum (Benedict, 1896) comb. nov. (herein transferred from Palaemonetes) [Texas; subterranean]Palaemon argentinus (Nobili, 1901) comb. nov. (herein transferred from Palaemonetes) [southern Brazil to

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Argentina; freshwater to brackish water]Palaemon atrinubes (Bray, 1976) comb. nov. (herein transferred from Palaemonetes) [Queensland, Western

Australia, New Caledonia; estuarine]Palaemon australis (Dakin, 1915) comb. nov. (herein transferred from Palaemonetes, see nomenclatorial

comments below) [Western Australia, ?Northern Territory; estuarine to freshwater]Palaemon camranhi (Nguyên, 1997) comb. nov. (herein transferred from Palaemonetes) [Vietnam; brackish

water]Palaemon capensis (De Man in Weber, 1897) [South Africa; freshwater]Palaemon carteri (Gordon, 1935) comb. nov. (herein transferred from Palaemonetes) [Venezuela, Guyana,

Suriname and French Guiana; freshwater]Palaemon carinicauda Holthuis, 1950a (herein transferred from Exopalaemon) [northern China; estuaries]Palaemon concinnus Dana, 1852 [Indo-west Pacific, widespread; marine, brackish and freshwater]Palaemon cummingi (Chace, 1954) comb. nov. (herein transferred from Palaemonetes) [Florida; subterranean]Palaemon curvirostris Nguyên, 1992 [Vietnam; mangroves.]Palaemon debilis Dana, 1852 [Indo-west Pacific, widespread; marine, brackish and freshwater]Palaemon dolospinus Walker & Poore, 2003 [Tasmania and south-eastern Australia; marine]Palaemon elegans Rathke, 1837 [north-western Europe, Mediterranean, Black Sea, ?Red Sea; introduced to

Caspian Sea, Baltic Sea, Aral Sea and Iraq; marine and high salinity estuaries]Palaemon floridanus Chace, 1942 [Florida; marine]Palaemon gladiator Holthuis, 1950b [Clipperton Island, Galapagos Islands; marine]Palaemon gracilis (Smith, 1871) [Nicaragua to Panama; freshwater]Palaemon gravieri (Yu, 1930) [northern China to Korea; marine]Palaemon guangdongensis Liu, Liang & Yan, 1990 [southern China; marine]Palaemon hainanensis (Liang, 2000) comb. nov. (herein transferred from Exopalaemon,) [southern China]Palaemon hancocki Holthuis, 1950b [Colombia to Ecuador; freshwater.]Palaemon hiltoni (Schmitt, 1921) comb. nov. (herein transferred from Palaemonetes) [California to northern

Mexico; estuarine]Palaemon hobbsi (Strenth, 1994) comb. nov. (herein transferred from Palaemonetes) [Mexico; freshwater]Palaemon intermedius (Stimpson, 1860) [western, eastern and southern Australia, Tasmania; marine and high

salinity estuaries]Palaemon ivonicus (Holthuis, 1950b) comb. nov. (herein transferred from Palaemonetes) [Brazil, Colombia,

Bolivia, Paraguay, Peru, Venezuela; freshwater]Palaemon kadiakensis (Rathbun, 1902) comb. nov. (herein transferred from Palaemonetes) [central USA to

northern Mexico; fresh to brackish waters]Palaemon karukera (Carvacho, 1979) comb. nov. (herein transferred from Palaemonetes) [Guadeloupe;

mangroves]Palaemon khori De Grave & Al-Maslamani, 2006 [Qatar; mangroves]Palaemon kwangtung nom. nov. (replacement name for Exopalaemon guangdongensis Guo, Wang & Zhang,

2005, nec Palaemon guangdongensis Liu, Liang & Yan, 1990; see nomenclatorial comments below) [southern China; estuarine]

Palaemon lindsayi (Villalobos Figueroa & H.H.Jr. Hobbs, 1974) comb. nov. (herein transferred from Palaemonetes) [Mexico; freshwater]

Palaemon litoreus (McCulloch, 1909) [New South Wales, South Australia; marine]Palaemon longirostris H. Milne Edwards, 1837 [in H. Milne Edwards, 1834-1840] [north-western Europe to

southern Spain, Morocco, Algeria, ?Mediterranean, ?Black Sea; low salinity estuaries.]Palaemon macrodactylus Rathbun, 1902 [Japan, Korea, China; introduced to western and eastern USA, Australia,

Argentina, Atlantic coasts of Europe and the Black Sea, Mediterranean (larvae only) (see Ashelby et al., 2013); medium salinity estuaries]

Palaemon maculatus (Thallwitz, 1892) [Senegal to southern Angola; brackish water, occasionally marine]Palaemon mani (Sollaud, 1914) (herein transferred from Exopalaemon) [Vietnam; freshwater]Palaemon mercedae (Pereira, 1986) comb. nov. (herein transferred from Palaemonetes) [Brazil, Colombia,

Venezuela; freshwater]

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Palaemon mesogenitor (Sollaud, 1912) comb. nov. (herein transferred from Palaemonetes) [Tunisia, Algeria; freshwater]

Palaemon mesopotamicus (Pesta, 1913) comb. nov. (herein transferred from Palaemonetes) [Syria, Turkey; freshwater]

Palaemon mexicanus (Strenth, 1976) comb. nov. (herein transferred from Palaemonetes, see nomenclatorial comments below) [Mexico; freshwater]

Palaemon miyadii (Kubo, 1938) [north-eastern China; freshwater.]Palaemon modestus (Heller, 1862) (herein transferred from Exopalaemon) [southern China to Siberia, Taiwan;

introduced to northern USA and Kazakhstan (see De Grave & Mann, 2012); freshwater]Palaemon mundusnovus nom. nov. (replacement name for Palaemonetes intermedius Holthuis, 1949; see

nomenclatorial comments below) [Massachusetts to Texas, Yucatán to Quintana Roo; brackish and low salinity estuaries]

Palaemon northropi (Rankin, 1898) [Bermuda to Uruguay, Caribbean; marine]Palaemon octaviae (Chace, 1972) comb. nov. (herein transferred from Palaemonetes) [Guadeloupe, Quintana

Roo; marine]Palaemon ogasawaraensis Kato & Takeda, 1981 [Ogasawara Islands; estuaries]Palaemon orientis Holthuis, 1950a (herein transferred from Exopalaemon) [Japan, Korea, south-eastern China,

Taiwan; marine and brackish water]Palaemon ortmanni Rathbun, 1902 [Japan, China, Taiwan; marine.]Palaemon pacificus (Stimpson, 1860) [Indo-west Pacific, widespread; marine]Palaemon paivai Fausto Filho, 1967 [north-eastern Brazil; marine]Palaemon paludosus (Gibbes, 1850) (herein transferred from Palaemonetes) [New Jersey to eastern Texas;

introduced to southern California and northern Mexico; freshwater]Palaemon pandaliformis (Stimpson, 1871) [Guatemala to south-eastern Brazil, Caribbean; freshwater]Palaemon paucidens De Haan, 1844 [in De Haan, 1833-1850] [Siberia to southern China, Japan; brackish and

freshwater, ?marine]Palaemon peringueyi (Stebbing, 1915) [South Africa to southern Namibia; marine and high salinity estuaries]Palaemon peruanus Holthuis, 1950b [northern Peru; brackish]Palaemon powelli Ashelby & De Grave, 2009 [Nigeria; low salinity mangroves]Palaemon pugio (Holthuis, 1949) comb. nov. (herein transferred from Palaemonetes) [northern Massachusetts to

Yucatán; brackish to freshwater]Palaemon ritteri Holmes, 1895 [California to Peru, Galapagos Islands, ?Brazil; marine]Palaemon schmitti (Holthuis, 1950b) comb. nov. (herein transferred from Palaemonetes, see nomenclatorial notes

below) [Panama to Mexico; marine]Palaemon semmelinkii (De Man, 1881) [India, Thailand, Myanmar, Philippines, Singapore, Vietnam, Northern

Territory; marine]Palaemon serenus Heller, 1862 [Queensland to Victoria, Tasmania; marine]Palaemon serratus (Pennant, 1777) [north-western Europe to Azores, Mediterranean, Black Sea; marine and high

salinity estuaries]Palaemon serrifer (Stimpson, 1860) [Myanmar, India, Indonesia, southern China to Siberia, Taiwan, Japan,

Northern Territory; marine]Palaemon sewelli (Kemp, 1925) [India, Thailand, China, Vietnam. Brackish waters]Palaemon sinensis (Sollaud, 1911) comb. nov. (herein transferred from Palaemonetes, see nomenclatorial notes

below) [Siberia to Vietnam, Myanmar; freshwater]Palaemon styliferus H. Milne Edwards, 1840 [in H. Milne Edwards, 1834-1840] herein transferred from

Exopalaemon) [Pakistan, India, Thailand, Indonesia; brackish water and marine, ?freshwater]Palaemon suttkusi (Smalley, 1964) comb. nov. (herein transferred from Palaemonetes) [Mexico; freshwater]Palaemon tenuidactylus Liu, Liang & Yan, 1990 [northern China to Korea; brackish]Palaemon texanus (Strenth, 1976) comb. nov. (herein transferred from Palaemonetes) [Texas; freshwater]Palaemon tonkinensis (Sollaud, 1914) comb. nov. (herein transferred from Coutierella) [southern China, Hong

Kong, Vietnam; freshwater to brackish]= Palaemonetes tonkinensis guangdongensis Liu, Liang & Yan, 1990 syn nov.

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Palaemon turcorum (Holthuis, 1961) comb. nov. (herein transferred from Palaemonetes) [Turkey; freshwater]Palaemon varians Leach, 1813 [in Leach, 1813-1814] (herein transferred from Palaemonetes) [northern Europe to

Morocco, Mediterranean; brackish]Palaemon vicinus Ashelby, 2009 [Cape Verde to Cameroon; marine]Palaemon vietnamicus (Nguyên, 1992) comb. nov. (herein transferred from Exopalaemon) [Vietnam; marine to

brackish water]Palaemon vulgaris Say, 1818 (herein transferred from Palaemonetes) [eastern and south-eastern coasts of USA;

marine and brackish]Palaemon xinjiangensis (Liang, 2000) comb. nov. (herein transferred from Exopalaemon) [north-western China]Palaemon xiphias Risso, 1816 [Mediterranean, Canary Islands; marine]Palaemon yamashitai Fujino & Miyake, 1970 [northern China; marine]Palaemon zariquieyi (Sollaud, 1938) comb. nov. (herein transferred from Palaemonetes) [Spain; brackish to

freshwater]

Comments on replacement (and other) names

The species name Palaemon africanus (Balss, 1916), herein transferred from Palaemonetes to Palaemon has a senior secondary homonym, Palaemon africanus Kingsley, 1883. Since Thallwitz (1892) the latter name has been considered to be a synonym of Palaemon macrobrachion Herklots 1851, currently a valid species in Macrobrachium, namely M. macrobrachion (see De Grave & Fransen 2011). Following Art. 59.2 (ICZN 1999), the junior secondary homonym does not require a replacement name, as both taxa are no longer considered congeneric.

Palaemonetes australis Dakin, 1915, herein transferred to Palaemon, has a senior secondary homonym, Palaemon australis Guérin-Méneville, 1838 [in Guérin-Méneville, 1829–1838], currently considered a valid species of Macrobrachium, namely M. australe (see De Grave & Fransen 2011). Following Art. 59.2 (ICZN 1999), the junior secondary homonym does not require a replacement name, as both taxa are no longer considered congeneric.

Following the transfer herein of Exopalaemon guangdongensis Guo, Wang & Zhang, 2005, to Palaemon, the name becomes a junior homonym of Palaemon guangdongensis Liu, Liang & Yan, 1990. As the junior synonym has no further available synonyms, following Art. 60.3 (ICZN 1999), a replacement name, Palaemon kwangtung

nom. nov. is herein proposed for this species. The name is derived from an English translation (Kwangtung) for Guangdong Province (P.R. China), from which the name of the junior homonym was originally derived (see Guo et

al. 2005), and is used as a noun in apposition.Following the transfer herein of Palaemonetes intermedius Holthuis, 1949 to Palaemon, the name becomes a

junior homonym of Palaemon intermedius (Stimpson, 1860). As the junior synonym has no further available synonyms, following Art. 60.3 (ICZN 1999), a replacement name, Palaemon mundusnovus nom. nov. is herein proposed for this taxon, used as a noun in apposition. The name alludes to the New World occurrence (Atlantic coasts of the USA from Massachusetts to Texas, Mexico from Yucatán to Quintana Roo) of the taxon, as opposed to the Australian occurrence of the senior name.

Palaemonetes mexicanus Strenth, 1976, herein transferred to Palaemon, has a senior secondary homonym, Palaemon mexicanus de Saussure, 1857. Since Holthuis (1952) the latter name has been considered to be a synonym of Palaemon acanthurus Wiegmann, 1836, currently a valid species in Macrobrachium, namely M.

acanthurus (see De Grave & Fransen 2011). Following Art. 59.2 (ICZN 1999), the junior secondary homonym does not require a replacement name, as both taxa are no longer considered congeneric.

Holthuis (1950b) briefly described Palaemon schmitti and Palaemonetes schmitti in the same preliminary contribution, with fuller, illustrated descriptions of both taxa appearing in his monumental work on the palaemonid fauna of the Americas (Holthuis 1952). In a further contribution (Holthuis 1950a) the subgenus Nematopalaemon

was erected, in which Palaemon schmitti was included. The subgenus was informally used at genus level in Holthuis (1980), but formally recognised as a genus by Chace & Bruce (1993). Since then, the genus has received universal recognition in taxonomic literature and remains as a separate clade in the analysis of Ashelby et al.

(2012). The current transfer of Palaemonetes schmitti Holthuis, 1950b into Palaemon makes both names secondary homonyms. As both taxa are no longer considered to be congeneric, no replacement name is required (Art. 59.2, ICZN 1999).

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Allocaris sinensis Sollaud, 1911 has up to now been placed in the genus Palaemonetes as a valid species, but is herein transferred to Palaemon. As a result, the name becomes a junior secondary homonym of Palaemon sinensis

Heller, 1862. The latter name has long been considered to be a junior synonym of Macrobrachium nipponense De Haan, 1849 [in De Haan, 1833–1850] (see De Grave & Fransen 2011). Following Art. 59.2 (ICZN 1999), the junior secondary homonym does thus not require a replacement name, as both taxa are no longer considered congeneric.

Comments on the subgenus Palaeander Holthuis, 1950a

Holthuis (1950a) erected three additional subgenera, aside from the nominotypical one in Palaemon, namely Exopalaemon, Nematopalaemon and Palaeander, with Palaemon (Palaeander) elegans Rathke, 1837 as the type species. In contrast to the other two subgenera, Palaeander was never elevated to genus level, but continues to be in occasional usage. Holthuis (1950a) separated the subgenus from the nomino-typical one on the basis of a two-jointed mandibular palp versus three-jointed in Palaemon (Palaemon). Asides from the variability in the number of segments of the mandibular palp discussed above, the phylogenetic analyses of Ashelby et al. (2012) and Cuesta et

al. (2012) do not support this to be a monophyletic taxon.

Comments on Palaemonopsis Stimpson, 1871 and Allocaris Sollaud, 1911

Palaemonopsis was mentioned in Stimpson (1871) under his introduction to the genus Palaemonetes, with the comment that: “…The genus [Palaemonetes] was described by me in manuscript about twelve years ago under the name Palaeomonopsis, but this name has never before been published, and I believe it to be identical with Palaemonetes of Heller…”. Stimpson (1871) did not further discuss the name and goes on to list Palaemonetes

vulgaris, Palaemonetes carolinus Stimpson, 1871 and Palaemonetes exilipes Stimpson, 1871; the latter long since regarded as a junior synonym of Palaemonetes paludosus (Gibbes, 1850). Holthuis (1955) lists the genus under the synonymy of Palaemonetes and selected a type species by subsequent designation, namely Palaemonopsis

carolinus Stimpson, 1871, which he also considered to be a junior synonym of Palaemon vulgaris Say, 1818; up to now included in Palaemonetes. This generic level synonymy is upheld by the results in Ashelby et al. (2102), who recover P. vulgaris deeply embedded within their Palaemon sensu lato clade.

Allocaris was erected as a new genus by Sollaud (1911), with Allocaris sinensis Sollaud, 1911 as its type species, by monotypy. The genus was considered distinct from Palaemonetes on the basis of the wide separation of the coxal and basal segments of the first maxilliped, as well as the more numerous apical telson setae. Pesta (1913) discusses the invalidity of these differences and placed Allocaris into the synonymy of Palaemonetes, treating Sollaud’s (1911) species as Palaemonetes varians var. loci sinensis. Although Kemp (1918) agreed with the generic synonymy, he disagreed with Pesta’s view to consider A. sinensis as a local race, affording full species status to Palaemonetes sinensis (Sollaud, 1911). Since then, this generic level synonymy has been accepted (see Bruce 1994) and is upheld by the results in Ashelby et al. (2102), who recover P. sinensis deeply embedded within their Palaemon sensu lato clade.

Comments on Alaocaris Holthuis, 1949 and Calathaemon Bruce & Short, 1993

Holthuis (1949) erected Alaocaris as a subgenus in Palaemonetes, for the Texan cave dwelling species, Palaemonetes antrorum Benedict, 1896. Strenth (1976) however, considered three out of the four distinguishing features of the subgenus to be regressive characters linked to the subterranean environment of P. antrorum, with the remaining character, the absence of a movable spine on the exopod of the uropod, showing considerable variation across the genus, even amongst North American epigean species of the genus. Logically, he therefore synonymised both subgenera, an action generally followed since then in all major compilations.

Bruce & Short (1993) erected the genus Calathaemon for the aberrant subterranean species Palaemonetes

holthuisi Strenth, 1976; which was subsequently placed in the family Kakaducarididae by Bruce (1993), although with some reservation. As discussed below, following Short et al. (2013), Calathaemon is herein transferred to

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Palaemoninae, which potentially raises a further taxonomic issue. Short et al. (2013) drew attention to the fact that despite the unique mouthpart morphology of C. holthuisi, this species, morphologically at least, most closely resembles the sympatric P. antrorum, which could either be due to convergent evolution or a phylogenetic link between both species. Should these taxa indeed form a distinct clade separate from Palaemon sensu lato (as herein defined), then the generic name Alaocaris Holthuis, 1949 would take priority over Calathaemon Bruce & Short, 1993. Alternatively, both species may belong to Palaemon sensu lato, with their morphologies being unique adaptations to their subterranean environment, as indeed was the view of Strenth (1976). Currently, this cannot be resolved, as neither species could be included in the phylogeny of Ashelby et al. (2012) and further fresh material suitable for genetic analysis has not been forthcoming. For now, the genus Calathaemon is thus treated as valid and monotypic, primarily supported by its unique mouthpart morphology, whilst P. antrorum is herein transferred to Palaemon.

Current composition of the subfamily Palaemoninae Rafinesque, 1815

De Grave & Fransen (2011) list 21 genera in the subfamily Palaemoninae, with the above changes reducing this number to 18. However, Short et al. (2013) reappraised the systematic status of the related family Kakaducarididae Bruce, 1993, which they synonymised with Palaemonidae on the basis of a combined molecular-morphological dataset. Furthermore the monotypic genus Kakaducaris Bruce, 1993 was synonymised with Leptopalaemon Bruce & Short, 1993. As a direct result of that study, two genera were thus transferred to Palaemonidae, viz. Leptopalaemon and the monotypic Texan cave dwelling genus Calathaemon Bruce & Short, 1993. Short et al.

(2013) discuss the fact that neither genus easily fits the current diagnosis of the subfamily Palaemoninae, namely two pairs of spines (spiniform setae) on the posterior margin of the telson, two arthrobranchs above the third maxilliped and usually a podobranch above the second maxilliped (see Davie 2002). Although they do not formally include either genus in Palaemoninae, they highlight that both genera appear more closely related to those that clearly belong in that subfamily as currently defined. Pending a revision of the systematic status of both subfamilies, Leptopalaemon and Calathaemon are herein formally included in the subfamily Palaemoninae.

The current composition of the subfamily Palaemoninae is thus as follows: Arachnochium Wowor & Ng, 2010 (2 species); Brachycarpus Spence Bate, 1888 (3); Calathaemon Bruce & Short (1); Creaseria Holthuis, 1950a (1); Cryphiops Dana, 1852 (6); Leander Desmarest, 1849 (5); Leandrites Holthuis, 1950a (4); Leptocarpus Holthuis, 1950a (3); Leptopalaemon Bruce & Short, 1993 (5); Macrobrachium Spence Bate, 1868 (246 - incl subspecies); Nematopalaemon Holthuis, 1950a (5); Neopalaemon Hobbs, 1973 (1); Palaemon Weber, 1795 (83); Pseudopalaemon Sollaud, 1911 (7); Rhopalaemon Ashelby & De Grave (1); Tenuipedium Wowor & Ng, 2010 (1); Troglindicus Sankolli & Shenoy, 1979 (1); Troglocubanus Holthuis, 1949 (5); Troglomexicanus Villalobos, Alvarez & Iliffe, 1999 (3) and Urocaridella Borradaille, 1915 (4).

By necessity, the present contribution focuses on the genus Palaemon and its allied genera. A further, important, systematic issue at genus level remains in the subfamily, notably the status of the South and Central American freshwater genus Cryphiops Dana, 1852. This genus currently comprises two subgenera, Cryphiops and Bithynops Holthuis, 1973, with the nominotypical subgenus being monotypic and Bithynops comprised of five species (De Grave & Fransen 2011). Pileggi & Mantellato (2010) on the basis of a 16S phylogeny recover the two included members of this genus embedded within Macrobrachium. Although this may ultimately prove to be correct and both genera will need to be synonymised, no congruence currently exists between morphological and phylogenetic work. Pereira (1997) in his cladistic analysis does recover the three included species, C. caementarius

(Molina, 1782), C. luscus (Holthuis, 1973) and C. brasiliensis (Gomes Corrêa, 1973) as part of a larger clade of Macrobrachium species. At the same time, however, some members of Macrobrachium are excluded from his clade and cluster with distantly related genera, such as Pseudopalaemon Sollaud, 1911 or Creaseria Holthuis, 1950a. In contrast, the analysis of Pileggi & Mantellato (2010) recovers Macrobrachium as a monophyletic clade, if the genus Cryphiops is included. This discrepancy will need to be resolved by additional morphological or extra genes before the systematic status of Cryphiops can be resolved. Macrobrachium is not only one of the most species-rich caridean genera, but of considerable economic importance and much cited throughout the scientific literature. Therefore, in this case extra caution is advised, as Cryphiops Dana, 1852 would be the senior name and could take precedence over Macrobrachium Spence Bate, 1868.

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The only morphological difference between Macrobrachium and Cryphiops, as currently defined is the presence versus absence of a hepatic spine on the carapace, not only a character of major importance in the delineation of Palaemoninae genera but also of considerable usage in any generic-level key (see Holthuis 1993), although Short (2004) discusses some variability in Macrobrachium. As discussed above, Palaemon as herein constituted is potentially paraphyletic and in time, one or more other genera may need to be constructed for those species falling outside the main Palaemon clade in Ashelby et al. (2012). Finally, it is noted that another two genera in Palaemoninae, Leander Desmarest, 1849 and Leandrites Holthuis, 1950a, are also only separated from each other by the presence versus absence of the mandibular palp. Although Pereira’s (1997) analysis hints at a particularly close relationship of both genera, at present no genetic study has included members of both genera. As such, no conclusion can be reached regarding their true systematic status. It is thus clear that all systematic issues at generic level within Palaemoninae are not yet fully resolved and a further re-appraisal of morphological characters at generic-level, combined with further genetic work needs to be undertaken before a stable classification is derived.

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