Leptarma, Shahdadi & Fratini & Schubart, 2020

LEPTARMA View in CoL GEN. NOV.

lsid: zoobank.org:act: E4B034FF-1F44-434D-AC67- 70CDE0D2E078

Type species: Leptarma leptosoma ( Hilgendorf, 1869) comb. nov. = Sesarma leptosoma Hilgendorf, 1869 , present designation.

Diagnosis: Small crabs (usually cw <20 mm; largest specimen examined here with cw = 20.8 mm; Table 1). Carapace almost squarish (slightly broader than long; the ratio cw/cl ranges from 1.06 to 1.21 in examined material). Carapace regions well defined: front moderately deflexed, with median concavity; four postfrontal lobes; median groove extending to gastric region ( Figs 8H–N, 11C); gastric region well defined ( Fig. 11C). Eyestalk shorter than wide in dorsal view; cornea wider than eyestalk ( Figs 8H–N, 9A). Male chelipeds robust, palm with one or two (usually two) oblique (more longitudinal) pectinated crests on the upper surface ( Fig. 5F, G), which consist of tall chitinous teeth, each flanked by large tubercle on the inner side and a line of coarse granules on the outer side, which creates a ridge, dividing the upper surface of the palm into two separate parts (outer and inner; Fig. 6D–F); chelar dactylus dorsally with a row of tubercles; proximal tubercles at middle of dactylar dorsal face; a virtual line of dactylar tubercles proximally would be directed towards the outer tubercle of the distal pectinated crest ( Fig. 7B). Ambulatory legs dorsoventrally flattened, proportionally long (P4/ cw ranges from 1.81 to 2.2; Figs 9B, 11C). Pleon of male triangular; somite 3 widest and somite 6 longest. Female vulvae on the anterior part of sternite 6.

Etymology: The name Leptarma is composed of the Greek λεπτός, leptos, thin, referring to the name of the type species epithet leptosoma , derived from λεπτόσωμα, thin body, which in turn refers to the slim walking legs of the comprised representatives, and the suffix - arma, derived from the last part of the genus Sesarma (in turn derived from the Greek σαιρω, the act of gaping; Say, 1817). The genus is gender neuter.

Remarks: This new genus includes 17 species as listed in Table 4, which were previously assigned to the genus Parasesarma (see Ng et al., 2008; Shahdadi & Schubart, 2017; Li et al., 2018, 2019).

Our morphological comparisons and genetic results revealed that two species with neighbouring distribution ranges, viz. Leptarma moluccense ( De Man, 1892) comb. nov. and Leptarma paucitorum ( Rahayu & Ng, 2009) comb. nov. ( Indonesia: Flores Island and Sulawesi, respectively; for type localities, see Table 4), have a close relationship (see Fig. 1, ML tree). The description and comparison of L. paucitorum by Rahayu & Ng (2009) did not include L. moluccense . Here, we suggest targeted morphological and genetic comparisons in order to evaluate the validity of L. paucitorum .

Leptarma lenzii ( De Man, 1895) View in CoL comb. nov. was originally described from Aceh ( Indonesia: Sumatra; De Man, 1895) and was later recorded from the Cocos (Keeling) Islands ( Tweedie, 1950). In the redescription of P. sigillatum View in CoL from the Cocos (Keeling) Islands, Ng et al. (2016) noted that specimens of a taxon allied to L. lenzii View in CoL were also obtained. Shahdadi et al. (2019c) confirmed the identity of material from the Cocos (Keeling) Islands after morphological and genetic comparisons. Recently, Li et al. (2019) recorded this species from Taiwan and confirmed the identity using morphology and COX 1 as the genetic marker. However, Shahdadi et al. (2019c) doubted the identities of what has been reported as ‘ Parasesarma lenzii View in CoL ’ from Fiji ( De Man, 1889: 434), the Moluccas ( De Man, 1902: 536) and the Flores Sea ( Tesch, 1918: 114). The material of Crosnier (1965; one male and one female) from Madagascar and the specimen of Poupin et al. (2012; one male) from Europa Island, which were reported as ‘ Parasesarma lenzii View in CoL ’, were also examined for the present study (see Table 1: material examined of P. gazi View in CoL ). As a result of DNA degradation, PCR amplifications failed for the specimens of Crosnier (1965). Both G1 of the male specimen from Madagascar were also missing. However, the specimens resemble L. gazi (Cannicci, Innocenti, & Fratini, 2017) View in CoL comb. nov. in other features, as previously assigned by Cannicci et al. (2017) according to the drawings given by Crosnier (1965). The specimen from Europa Island differs from both L. gazi View in CoL and L. lenzii View in CoL and from other species of Leptarma View in CoL and will therefore be described as a new species. The ZRC specimens from Singapore that were identified as ‘ P. lenzii View in CoL ’ were also examined. According to their horseshoe-like chelar dactylar tubercles, they are identified as P. melissa View in CoL (e.g. ZRC 2000.1955; see Table 1).

Leptarma kui ( Li, Rahayu & Ng, 2018) View in CoL comb. nov. was described from Taiwan and is here reported from Cebu ( Philippines). We have examined two male specimens, one from Cebu and one from Taiwan ( Table 1), and both match the diagnostic characters described by Li et al. (2018). There is only one mutation in the barcode region of COX 1 between the sequences from Cebu and the holotype of L. kui View in CoL (for the GenBank accession numbers, see Table 2).

After morphological re-examinations and genetic comparisons of the types and extra material of P. cognatum View in CoL and Leptarma liho ( Koller, Liu & Schubart, 2010) View in CoL comb.nov., Shih et al. (2019) identified P.cognatum View in CoL as a junior synonym of L. liho View in CoL , which is now known from Japan (Okinawa, Miyako and Ishigaki), Taiwan (Hualien, Taitung and Pingtung), the Philippines (Cebu) and Indonesia (Sulawesi). Leptarma liho View in CoL also resembles Leptarma jamelense ( Rathbun, 1914) View in CoL comb. nov. from Luzon ( Philippines) in its general and G1 morphology. Koller et al. (2010) did not include L. jamelense View in CoL for comparison in their description of L. liho View in CoL as a new species. In the present study, the DNA amplification from L. jamelense View in CoL was unsuccessful owing to DNA degradation. A targeted sampling from the type locality of L. jamelense View in CoL ( Philippines: Luzon: Batangas) and genetic comparisons should clarify this uncertainty.

The present generic assignment of Leptarma aurifrons (Li, Shih & Ng, 2019) comb. nov. is based on its position in the mitochondrial phylogenetic tree ( Fig. 2; see also Li et al., 2019: fig. 13). In our mitochondrial tree ( Fig. 2), L. aurifrons is nested in the Leptarma clade, clustering with L. moluccense , L. paucitorum and L. liho . This is confirmed by the presence of proximal tubercles positioned on the mid-dorsal face of the chelar dactylus (see Li et al., 2019: fig. 4C), which is one of the diagnostic characters of Leptarma .