Xiphonectes aculeatus Koch & Ďuriš 2019, sp. nov.
Creators: name: Koch, Milan
name: Ďuriš, Zdeněk
Publisher: name: Zenodo
Year: 2019
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Portunidae
Xiphonectes
Xiphonectes aculeatus

description: Xiphonectes aculeatus sp. nov.
(Figs 1–3, 4C, D)
Type material. Holotype: 1 female, CW 19.5 mm, MNHN-IU-2010-3218 (COI sequence GenBank MK330852), Atimo Vatae Expedition, 9 Jun. 2010, stn TA46, 24° 59.1' S, 47° 05.6' E, Pointe Evatra, Anse Itapera, south of Madagascar, depth 2–12 m.
Description of holotype. Carapace (Figs 1A, 3A, 4D) anterior margin approximately triangular; posterior margin reduced, narrow, subrectangular; CL/CW ratio 0.54; frontal margin (including inner orbital angle) 0.23 CW, fronto-orbital width 0.46 CW. Front with 4 distinct obtuse triangular teeth; median pair distinctly smaller than lateral, with short, broadly V-shaped median notch; lateral frontal teeth separated from median ones, with asymmetric U-shaped notch approximately twice depth of median notch, outer margins slightly sinuate. Inner orbital tooth reduced but forming distinct obtuse angle extending anteriorly beyond first anterolateral tooth; notch undeveloped, indicated as short suture. Supraorbital margin with well-developed medial notch and one indistinct lateral notch. Infraorbital margin granular with a distinct V-shaped lateral notch and a prominent obtuse medial tooth approximately level with the frontal teeth in dorsal view. Anterolateral margin slightly convex, with 6 teeth; anterior 5 teeth projecting forward, first tooth bluntly rounded and smaller; second to fifth teeth subequal in size and gradually sharper posteriorly; sixth tooth (epibranchial) projecting laterally, spiniform, strong, about three times longer than preceding one, posterior margin straight, 2.5 times longer than anterior margin. Posterior part of carapace distinctly narrower than anterior one, posterolateral margin of carapace oblique, short, about half length of anterolateral margin; posterolateral angle forming laterally and upward-directed subacute tooth-like process; posterior margin slightly convex.
Dorsal surface of carapace sparsely tomentose, with elevated but feebly demarcated regions bounded by patches of fine granules, and with 11 prominent knob-like tubercles, each in centre of main regions. Mesogastric region narrow, slightly elevated; metagastric regions well elevated, with large knob-like tubercle in centre; protogastric regions rounded, elevated, and with similar large tubercle in centres; mesobranchial regions each subdivided into 2 elevated areas, with central tubercles more obscured; anterolateral regions with two feeble elevations situated near 2 nd and 3 rd anterolateral teeth, respectively, anterior one larger; cardiac and median postcardiac regions each with distinct conical elevation; lateral postcardiac regions indistinct, obsolete; posterolateral regions elongated, elevated, without prominent tubercles.
Epistome (Fig. 2A) narrow, with median triangular lobe formed by pair of appressed teeth, and with pair of deep notches on margins of efferent branchial channels more laterally; median epistomial tooth undeveloped. Narrow median septum fused anteriorly to front, continuing posteriorly and laterally into transverse posterior laminar walls of antennular cavities, and separated from epistome by deep narrow furrow comprising tubules of antennal glands laterally; laminar walls fused laterally to immovable basal antennal segment forming inner wall of orbit; basal antennal segment projecting with elongate process into orbit.
Female thoracic sternites (Figs 2B, 3C) finely granulate, sternites 3 and 4 fused, with distinct sulcus laterally only; sternite 4 with shallow median groove; sternites 5–8 well defined, with broad median pleonal cavity; sternal sulci 4/5–6/7 with deep submedian incisions. Vulvae (Fig. 3C) large, located on sixth sternite laterally on walls of sterno-pleonal cavity, margins transversely subcircular, tear-like, with anterior margin straight, well defined, laterally rounded with sharp margin, medially leading into shallow groove running anteromedially towards midline of sterno-pleonal cavity. Transverse fissure on bottom of vulva leading into gonopore, latter hidden under lateral margin of vulva.
Female pleon (Fig. 3B) with somites 3–5 each bearing distinct transverse crest on outer surface. Pleomere 6 broadly rounded, almost semicircular, with anterior margin concave to accommodate base of telson, about 0.4 of proximal width of segment; telson small and broadly triangular with convex base, height/base ratio about 0.75.
Third maxilliped (Fig. 1B) finely granular on ischium, merus, and exopodal peduncle, with margins densely setose. Palp with dactylus and propodus tapering distally, carpus with large rounded transverse crest on outer side forming flattened, slightly concave, broad frontal field. Merus subtrapezoidal, lateral margin produced distally into subquadrate projection, latter bent outwards forming swollen distolateral crest with broad longitudinal furrow narrowing proximally, and demarcated medially by strong oblique crest; ischium about 1.4 times merus length, 1.8 times as long as wide, with shallow longitudinal sulcus. Exopod relatively stout, about half of ischium width, with subdistal triangular projection on inner medial border; flagellum longer than merus width.
Right cheliped lost in holotype. Left cheliped (Figs 1A, 1C, 3A) moderately stout. Merus with 3 spines on anterior border, and one relatively small spine distally on posterior border. Carpus with 2 indistinct carinae on dorsal surface, and 1 sharp, very long dorsomedial, obliquely anteriorly erected spine far overreaching middle of dorsal margin of palm; flattened ventral margin forming outer angular projection visible from dorsal view. Upper surface of palm with 2 longitudinal crests, inner one distinct, ending distally into strong, compressed, obliquely anteriad erected spine reaching distal dorsal end of palm, outer crest defined only by row of granules and ending with small distal spine and distinct spiniform proximal tooth proximally over articulation with carpus. Outer surface with 2 granular crests ending on level of finger joint; inner surface of palm flattened, with 1 indistinct longitudinal keel. Fingers straight, tapering, 0.5 of maximum chela length, distinctly carinate; movable finger with distinct bilobed molariform tooth proximally on cutting edge; fingers otherwise with some bi- or trilobed serial conical teeth separated by series of small simple teeth.
Ambulatory pereopods 2–4 relatively short, glabrous, dactyli and propodi compressed, both latter with row of dense setae along ventral margin, additional setal row dorsomedially on dactyli. Fifth pereopod (= swimming leg) with merus finely serrate on posterodistal margin, posterodistal angle acutely projecting, spiniform. Dactylus oval, broadly rounded distally.
Colouration. The holotype has been preserved in ethanol for more than 6 years, but displays a dark broad Vshaped pattern (Fig. 3A, 4B) beginning just behind each orbit and extending posteriorly to meet on the cardiac region. Small dark ornamentations also appear on the mesobranchial regions, and the tips of the last anterolateral teeth bear traces of reddish orange colour.
Etymology. The species name is derived from Latin word aculeus (sharp pointed process, thorn) to emphasise the spiniform projection on the meri of the swimming legs.
Remarks. Xiphonectes A. Milne-Edwards, 1873, is comprised of 29 species (Ng et al. 2008; Spiridonov 2016). However, limited molecular phylogenetic analyses (e.g., Evans 2018) and significant intrageneric morphological variability suggest this genus may not be monophyletic. Nevertheless, the general morphology of X. aculeatus sp. nov. supports its placement in Xiphonectes, but it can be easily distinguished from most congeners by an elongate spine on the inner dorsal margin of the cheliped carpus, six anterolateral teeth on the carapace, and the shape of its third maxilliped carpus and merus. These morphological characteristics are also found in X. latibrachium (Rathbun, 1906) and X. paralatibrachium (Crosnier, 2002). However, X. aculeatus sp. nov. can be distinguished from these congeners by the following traits: (1) the anterolateral carapace teeth are subequal in size (Figs 1A, 3A, 4D), versus gradually decreasing posteriorly (Figs 4B, F); (2) the last anterolateral tooth is straight and directed laterally (Figs 1A, 2A, 3D), versus arched and directed forward (Figs 4B, F); (3) the posterolateral angles of the carapace are sharp, distinct, upward and laterally directed (Figs 1A, 3A, 4D), versus feebly upturned, not produced laterally (Figs 4B, F); (4) the frontal teeth are unequal (Figs 1A, 3A, 4D), versus subequal in size (Figs 4B, F); and (5) meri of the fifth ambulatory legs are with distinct spurlike posterodistal angle (Figs 3A, 4C), versus with obtuse anterodistal angle (Figs 4A, E; Crosnier 2002: figs 6A, 7A–D).
The present record of X. aculeatus sp. nov. in the western Indian Ocean is notably remote from the related Pacific congeners, with X. latibrachium putatively restricted to Hawaii and X. paralatibrachium to French Polynesia (Rathbun 1906; Crosnier 2002). Xiphonectes aculeatus sp. nov., together with these related congeners, are quite rare in collections even when sampling efforts have been significant. The collection of Madagascan portunid crabs from the Atimo Vatae Expedition were also extensive, but included just a single specimen of X. aculeatus sp. nov. For X. paralatibrachium, only the three type specimens (MNHN) have been reported, and only the holotype specimen is known for X. latibrachium (USNM). Crosnier (1984) mentioned an additional specimen of X. latibrachium from the Seychelles REVES II Expedition (not examined here), but examination of his figures (Crosnier 1984: figs 2C–F) suggest that the specimen may represent a separate, undescribed species. Crosnier’s specimen is morphologically most similar to X. latibrachium, but displays clear differences in the shape of its carapace, including the frontal margin, and in the meri of its swimming legs.
Morphologically, X. aculeatus sp. nov., X. latibrachium, and X. paralatibrachium appear to constitute a distinct Xiphonectes lineage or species complex. Unfortunately, given the rarity, poor condition, and age of vouchered material for these species, molecular phylogenetic analysis of the group was not possible. Nevertheless, we successfully generated a COI DNA barcode sequence from the holotype of X. aculeatus sp. nov. This data may prove critical for future analyses of this lineage and Xiphonectes more generally.
Distribution. Known only from the type locality, off southern Madagascar, the western Indian Ocean.
GenBank accession number. COI: MK330852.
description: Published as part of Koch, Milan & Ďuriš, Zdeněk, 2019, Xiphonectes aculeatus sp. nov., a new swimming crab (Crustacea: Decapoda: Portunidae) from Madagascar, pp. 455-462 in Zootaxa 4551 (4) on pages 456-462, DOI: 10.11646/zootaxa.4551.4.5, http://zenodo.org/record/2623091