Xiphonectes, A. MILNE EDWARDS, 1873

XIPHONECTES A. MILNE EDWARDS, 1873 View in CoL

( FIG. 17)

= Xiphonectes A. Milne-Edwards, 1873 View in CoL [type species Amphitrite vigilans Dana, 1852 View in CoL , subsequent designation by Rathbun (1930); gender masculine].

Included species: Fourteen.

Xiphonectes aculeatus Koch & ĎuriŠ, 2019 Xiphonectes bidens (Laurie, 1906)

= Neptunus (Hellenus) bidens Laurie, 1906 Xiphonectes gracillimus (Stimpson, 1858)

= Amphitrite gracillimus Stimpson, 1858 Xiphonectes guinotae (Stephenson & Rees, 1961)

= Portunus guinotae Stephenson & Rees, 1961 Xiphonectes hainanensis (H.-L. Chen, 1986)

= Portunus hainanensis H.-L. Chen, 1986 View in CoL Xiphonectes iranjae ( Crosnier, 1962) View in CoL

= Portunus iranjae Crosnier, 1962 View in CoL

Xiphonectes latibrachium (Rathbun, 1906) View in CoL

= Parathranites latibrachium Rathbun, 1906 Xiphonectes leptocheles A. Milne-Edwards, 1873 View in CoL Xiphonectes longispinosus ( Dana, 1852) View in CoL

= Amphitrite longispinosus Dana, 1852

= Amphitrite vigilans Dana, 1852 View in CoL

= Xiphonectes vigilans var. obtusidentatus Miers, 1884 View in CoL

Xiphonectes macrophthalmus (Rathbun, 1906) View in CoL

= Portunus (Xiphonectes) macrophthalmus Rathbun, 1906

Xiphonectes paralatibrachium ( Crosnier, 2002) View in CoL

= Portunus paralatibrachium Crosnier, 2002 View in CoL

Xiphonectes stephensoni (Moosa, 1981) View in CoL

= Portunus stephensoni Moosa, 1981

= Portunus emarginatus Stephenson & Campbell, 1959 View in CoL [pre-occupied name, primary junior homonym of P. emarginatus Leach, 1814 View in CoL , = synonym of Macropipus arcuatus (Leach, 1814) View in CoL ]

Xiphonectes tenuicaudatus (Stephenson, 1961) View in CoL

= Portunus tenuicaudatus Stephenson, 1961

Xiphonectes tuerkayi Spiridonov, 2016 View in CoL

= Portunus longispinosus View in CoL forma longimera Spiridonov, 1994 (nomen nudum)

Diagnosis: Carapace ( Fig. 17A) broadly hexagonal, about twice as broad as long when lateral spines are included, width (without lateral teeth) ~1.5 × length; dorsal surface variously granulate, with regions moderately demarcated, with patches of granules, sometimes in some species projecting to centre, forming elevated tubercles. Front ( Fig. 17B) with four triangular or rounded lobes; submedian lobes distinctly smaller than laterals, sometimes fused, projecting beyond tip of inner supraorbital lobe. Orbit nearly circular, with inner supraorbital lobe small, angulate, often merged to inner supraorbital margin, latter with two short fissures; infraorbital margin clearly visible in dorsal view, with narrow lateral notch. Anterolateral margin with six to nine spiniform teeth; particular teeth may have a tendency to reduction; teeth of anterior series (except last tooth) short, irregular in size, last tooth distinctly larger, lateral. Posterolateral junction of carapace angular, pointed, often distinctly upturned, sharp. Thoracic sternites partly granular, with sutures ( Fig. 17C) well demarcated. Merus of third maxilliped elongate, distally produced to rounded lobe, rarely angulate. Chelipeds usually relatively slender; with merus bearing three to five spines on anterior border and one spine or obtuse lobe distally on posterior border; carpus with a sharp spine on outer face; upper surface of palm with two (rarely one) distal teeth. Chelae ( Fig. 17D) slightly inaequal, heterodontic, with a moderate molariform tooth at cutting edge of dactylus in larger chela. Dactyli of pereiopods 2–4 cultriform, costate, with short, hairy emargination on ventral margin. Merus of pereiopod 5 a little longer than broad. Male pleon quasi-triangular ( Fig. 17C). Pleomeres 2 and 3 with low transverse smooth crests, that on pleomere 2 higher; lateral margins of pleomere 3 convex or acuminated; terminal part of posterior thoracic episternite fills interspace between anterior margin of pleomere 3 and thoracic sternite 8. Pleomeres 3–5 fused without apparent sutures, but feeble keels may be present. Pleomere 6 with lateral margins sinuate, constricted subdistally, rarely elongate, simple. First male gonopod ( Fig. 17E) in most cases elongate, curved, tapering distally to slender tip; pair of first gonopods lying obliquely directed inwards but not touching medially, apices curved anterolaterally. Female vulva relatively large, located in medial part of proximal portion of sternite, drop-shaped or ovoid, with long axis subparallel or oblique to anterior margin of sternite.

Systematic position: Xiphonectes (as listed by Ng et al., 2008; Spiridonov et al., 2014) is subdivided here, based on the present molecular analyses, into five genera, of which four (i.e. Eodemus , Incultus , Trionectes and the lupocycline Alionectes ] are newly established. The four new genera are nested inside three unrelated clades, and two of them occupy sister positions with other currently known or new portuniine genera. All these taxa are similar by their overall appearance, with a more or less strongly depressed carapace, usually with a pair of long lateral teeth, elevated patches of granules on the dorsum, and produced or subacute posterolateral angles.

Of the above new taxa, Trionectes is sister positioned in the present molecular analysis to the newly restricted Xiphonectes , whereas Incultus is more basal. Xiphonectes differs from these by: (1) feebly demarcated dorsal regions of the carapace (vs. distinctly elevated in Incultus ); (2) predominantly sharply triangular anterolateral teeth on the carapace (vs. lobate in Incultus ); (3) frequent cases of reductions in the number of anterolateral teeth (vs. a full set of nine teeth in Incultus and Trionectes ); (4) the front with four distinct triangular or rounded teeth, with submedian ones smaller (vs. four shallow subequal teeth in Incultus and three subequal triangular or blunt teeth in Trionectes ); (5) the infraorbital margin with a narrow lateral notch (vs. a broad lateral notch in Incultus and deep, ‘V’-shaped notch in Trionectes ); (6) the male pleon with the sixth somite distinctly constricted subdistally (vs. elongately trapezoid in Incultus and Trionectes ); (7) the chelipeds comparatively slender in Xiphonectes (vs. stout in the other two), with fingers subequal to the palm length (vs. distinctly shorter in Incultus ); (8) the first male gonopods slender, smoothly out-curved distally, not meeting medially in Xiphonectes (vs. short and stout in Trionectes , but relatively long, bent in midlength, with the pair of gonopods overlapping each other medially in Incultus ); and (9) by the female vulva being located relatively distant from the sternite margins, vs. located at the mesial margin or posteromesial in Incultus .

Xiphonectes is distinguishable from Alionectes by the presence of a dorsally incised orbital margin, which is entire in Alionectes , by a single posterodistal spine on the cheliped merus (vs. two spines in Alionectes ) and by a smooth laminar crest on the second pleonal somite of males, whereas the margin is serrated in the latter genus.

Eodemus is distinguishable easily from Xiphonectes by the ‘T’-shaped male pleon (vs. subtriangular) and by the distinctly laterally produced anterolateral lobe of the third maxilliped merus (vs. distally produced, rounded or angular, not distolaterally produced) and by a slit-like female vulva.

Remarks: Since Xiphonectes was raised to full generic status by Spiridonov et al. (2014), it has become one of the most species-rich portunid genera, containing, according to Ng et al. (2008), 28 species, with X. longispinosus composed of four subspecies. Ng et al. (2008) include X. longispinosus longimerus Spiridonov, 1994 , which they consider to be an available name for the species. This name was originally introduced as Portunus longispinosus forma longimera by one of us ( Spiridonov, 1994). When introducing this name, Spiridonov (1994: fig. 5) used an infrasubspecific rank with the status of ‘forma’, intentionally making this name unavailable ( ICZN, 1999: Articles 10.2 and 15.2); the reason for this was to introduce the forms of X. longispinosus as a preliminary step towards the revision of this species complex. Recently, this species was described by Spiridonov (2016) as X. tuerkayi Spiridonov, 2016 .

The list by Ng et al. (2008) does not include X. leptocheles . This species was described and illustrated by A. Milne-Edwards (1873: 159, pl. 4, fig. 1), but was synonymized, without particular discussion, with X. longispinosus by Stephenson & Campbell (1959). Later, this name disappeared even from major portunid accounts (i.e. Stephenson, 1972a, b; Sakai, 1939, 1976; Crosnier, 2002), but was listed in Xiphonectes (s.l.) in the studies by Spiridonov (2016) and Nguyen & Ng (2021) as a synonym of X. longispinosus . The photograph of the type specimen of X. longispinosus from HMCZ was previously kindly sent by A. Baldinger to one of us for another study ( Spiridonov, 2016: fig. 1). Its current re-examination and comparison with the description and illustration of X. leptocheles confirms a separate status of the latter species.

As a result of the present revision, only 14 species currently remain in Xiphonectes , with the four former X. longispinosus subspecies all elevated to species level. The remaining species are herein transferred to the newly established Eodemus (six species), Incultus (three species), Trionectes (eight species) and to the new lupocycline Alionectes (two species). Two species that were not included in our molecular analysis, X. latibrachium and X. paralatibrachium , show some morphological differences; they have the median frontal teeth projecting beyond the lateral ones, indistinct supraorbital notches and more robust chelipeds. Their inclusion in Xiphonectes should be confirmed by future genetic analyses.

During the examination of the MNHN material in Paris, additional morphotypes of the X. longispinosus complex, with some potentially new species, were recognized by one of us (M.K.). A further revision of this group may therefore be necessary.

Size: Small crabs; maximum reported size ranges from CL × CW: 8.8 mm × 17.0 mm in X. guinotae ( Apel & Spiridonov, 1998) to 14.0 mm × 30.3 mm in X. iranjae ( Yang et al., 2012) .

Ecological notes: The genus includes both upper subtidal species (e.g. X. guinotae , X. iranjae and X. longispinosus ; see Apel & Spiridonov, 1998; Spiridonov, 1999, 2016) and lower subtidal species (e.g. X. tuerkayi from the western Indian Ocean; Spiridonov, 2016) occurring mostly on sandy substrates.

Geographical range: Indo-West Pacific: from the Red Sea and the western Indian Ocean to Japan, Australia, the Hawaiian Islands and French Polynesia ( Stephenson, 1972a, b; Poupin, 2010; Castro, 2011).