Achelous, DE HAAN, 1833

ACHELOUS DE HAAN, 1833 View in CoL

( FIGS 4D, 5)

= Portunus (Achelous) De Haan, 1833 (type species Portunus spinimanus Latreille, 1819 , by monotypy; gender masculine).

= Portunus (Hellenus) A. Milne Edwards, 1874 (type species Achelous spinicarpus Stimpson, 1871 View in CoL , subsequent designation by Rathbun, 1930; gender masculine).

= Lupella Rathbun, 1897 View in CoL (type species Cancer forceps Fabricius, 1793 , by monotypy; gender feminine).

Included species: Twenty-eight.

Achelous acuminatus Stimpson, 1871 View in CoL

Achelous affinis Faxon, 1893 View in CoL

Achelous anceps (de Saussure, 1858) View in CoL comb. nov.

= Lupea anceps de Saussure, 1858

= Lupea duchassagni Desbonne in Desbonne & Schramm, 1867

= Neptunus sulcatus A. Milne-Edwards, 1879 Achelous angustus (Rathbun, 1898)

= Portunus (Achelous) angustus Rathbun, 1898 View in CoL Achelous asper (A. Milne-Edwards, 1861) View in CoL

= Neptunus asper A. Milne-Edwards, 1861 View in CoL

= Achelous transversus Stimpson, 1871 View in CoL

= Amphitrite paucispinis Lockington, 1877 View in CoL

Achelous binoculus (Holthuis, 1969)

= Portunus binoculus Holthuis, 1969

Achelous brevimanus Faxon, 1895

Achelous depressifrons (Stimson, 1859)

= Amphitrite depressifrons Stimpson, 1859

= Portunus (Achelous) bahamensis Rathbun, 1930 View in CoL Achelous floridanus ( Rathbun, 1930) View in CoL

= Portunus (Achelous) floridanus Rathbun, 1930 View in CoL Achelous forceps (Fabricius, 1793) View in CoL comb. nov.

= Cancer forceps Fabricius, 1793

= Lupa leachii De Haan, 1833

Achelous gibbesii (Stimpson, 1859)

= Lupa gibbesii Stimpson, 1859

Achelous guaymasensis ( Garth & Stephenson, 1966) View in CoL

= Portunus guaymasensis Garth & Stephenson, 1966 View in CoL Achelous hastatus (Linnaeus, 1767) View in CoL comb. nov.

= Cancer hastatus Linnaeus, 1767

= Cancer ponticus Herbst, 1790

= Portunus dufourii Latreille, 1819

= Eriphia prismaticus Risso, 1827

= Neptunus hastatus var. rubromaculatus Steinitz, 1932

Achelous inaequalis (Miers, 1881) comb. nov.

= Neptunus (Amphitrite) inaequalis Miers, 1881

Achelous iridescens (Rathbun, 1894) = Neptunu s (Hellenus) iridescens Rathbun, 1894

Achelous isolamargaritensis (Türkay, 1968) = Portunus (Achelous) floridanus isolamargaritensis Türkay, 1968

Achelous minimus (Rathbun, 1898) View in CoL = Portunus (Achelous) minimus Rathbun, 1898 View in CoL = Portunus (Achelous) pichilinquei Rathbun, 1930 View in CoL

Achelus ordwayi Stimpson, 1860 = Neptunus cruentatus A. Milne-Edwards, 1861 View in CoL = Portunus aurimanus Gundlach & Torralbas, 1900 View in CoL

Achelous panamensis Stimpson, 1871 View in CoL

Achelous rufiremus ( Holthuis, 1959) View in CoL = Portunus rufiremus Holthuis, 1959 View in CoL

Achelous sebae (H. Milne Edwards, 1834) View in CoL = Lupea sebae H. Milne Edwards, 1834 View in CoL = Lupa biocellata Gundlach & Torralbas, 1900 View in CoL

Achelous spinicarpus Stimpson, 1871 View in CoL

Achelous spinimanus (Latreille, 1819) View in CoL = Portunus spinimanus Latreille, 1819 View in CoL = Lupa banksii Leach, 1816 View in CoL = Achelous spinimanus smithii Verrill, 1908 View in CoL = Portunus vossi Lemaitre, 1991 View in CoL

Achelous stanfordi (Rathbun, 1902) View in CoL = Portunu s (Achelous) stanfordi Rathbun, 1902 View in CoL

Achelous tuberculatus Stimpson, 1860 View in CoL

Achelous tumidulus Stimpson, 1871 View in CoL

Achelous ventralis (A. Milne-Edwards, 1879) View in CoL comb. nov. = Neptunus ventralis A. Milne-Edwards, 1879 View in CoL

Achelous xantusii Stimpson, 1860 View in CoL

Diagnosis: Carapace ( Fig. 5A) approaching hexagonal shape,> 1.5 times as broad as long; dorsal surface finely granulate, with regions moderately demarcated, often with ridges or patches of granules in centre of regions; urogastric depression distinctly posterior to halflength of carapace. Front ( Fig. 5B) with four triangular or rounded lobes. Orbit ellipsoidal; supraorbital margin with relatively deep median and reduced lateral fissures. Inner supraorbital lobe often truncate or subdivided into two teeth or lobes. Infraorbital margin with broad notch. Anterolateral margin with nine spiniform teeth: anterior eight ones subequal in size; last tooth lateral, large, in most cases two or more times longer than other teeth. Posterolateral junction of carapace usually rounded. Sutures ( Fig. 5C) on thoracic sternum well developed; thoracic sternites partly granular. Chelipeds with merus bearing three to five spines on anterior border, unarmed or with one spine distally on posterior border; carpus with single spine on outer face and spine on inner face that can be extremely long; upper surface of palm with two or three teeth including usual tooth near articulation with carpus; chelae ( Fig. 5D) costate, moderately unequal and heterodontic; in larger chela, molariform tooth present proximally on cutting edge of dactylus. Dactyli of pereiopods 2–4 ensiform or cultriform, rarely lanceolate, usually markedly costate; setose on ventral margin. Merus of pereiopod 5 distinctly longer than broad, posterodistal spine present but may be obsolete. Male pleon ( Fig. 5C) narrowly triangular; crest on third pleomere moderately laminar; lateral margins of third pleomere straight or convex; terminal part of posterior thoracic episternite fills interspace between anterior margin of pleomere 3 and thoracic sternite 8; third to fifth terga fused but unclear sutures may remain, combined part usually with keels, subequal to sixth pleomere; sixth pleomere with lateral margins straight or sinuous, convergent distally. Telson elongately triangular. First male ( Fig. 5E) gonopod of moderate length, arched or sinuous; basal part robust, lying obliquely inwards; distal part moderately slender, curved anterolaterally and tapering distally to slender tip; pair of first gonopods not touching medially in pleonal cavity. Female vulva ( Fig. 4D) elongately drop-like, with long axis usually almost parallel to anterior margin of sternite.

Systematic position: The clade of four Achelous species analysed in the present three-marker study ( Fig. 1; as Achelous or Portunus ) is in a sister position to the thalamitine genus Charybdis . Their combined clade is nested within the basal polytomy of the four clades [i.e. together with the clade of the lupocycline Lupocycloporus and the new genus Alionectes , the clade of the portunine Portunus (s.s.) and Callinectes ] and with the joint clade of all remaining IWP genera previously included in Portunus (s.l.). The true phylogenetic relationship of those four clades thus remains unresolved at present, and the subfamily composition of the family Portunidae remains provisional owing to the paraphyly or polyphyly of the subfamily Portuninae itself.

In none of the recent molecular phylogenetic reconstructions ( Spiridonov et al., 2014; Evans, 2018; Mantelatto et al., 2018; present study) is Achelous shown as related to Portunus , the nominotypic genus of subfamily Portuninae . Achelous and Lupella (see discussion on the latter genus below) are distinguished by a peculiar set of morphological characters, with some apparent plesiomorphies (e.g. sutures still visible on fused male pleomeres 3–5) and apomorphies (e.g. a tendency for a long inner spine on the cheliped carpus). For these reasons, Spiridonov (2020) has recently separated these two genera into a new subfamily Achelouinae . This was also regarded as a step towards purifying the concept of Portuninae , which remains most probably paraphyletic, even with Achelous excluded.

In the present 16S analysis ( Fig. 2), all Achelous species form a well-supported clade of mixed Atlantic and eastern Pacific representatives together with Lupella forceps and some Atlantic ‘ Portunus ’ species. This is consistent with the phylogenetic results in the studies of Evans (2018) and Mantelatto et al. (2007, 2009, 2018). The systematic position of those Lupella or ‘ Portunus ’ taxa, however, remained unresolved in these papers.

Lupella forceps View in CoL was considered to be a portunine crab with distinctively slender and long chelipeds in adult males ( Rathbun, 1930; Taissoun, 1973), but otherwise not principally differing from Achelous View in CoL (e.g. Rathbun, 1930; Monod, 1956; Garth & Stephenson, 1966) in either carapacial morphology or the shape of the male pleon and the first gonopods. The chelipeds of Lupella forceps View in CoL bear uniquely long and slender (‘filiform’, see Rathbun, 1930: 133) fingers, about three times longer than the short palm in adult males, whereas in females those fingers are filiform too, but distinctly shorter, only slightly longer than the palm ( Taissoun, 1973). Some Achelous species also possess chelae with fingers subequal to the palm length (e.g. Achelous tuberculatus View in CoL , Achelous spinimanus View in CoL and Achelous xantusii View in CoL ). The remarkable chelae of Lupella forceps View in CoL are therefore best regarded as a species-specific apomorphy. Besides that character, Lupella View in CoL does not differ materially from Achelous View in CoL . The male first gonopods are short, basally stout and distally bent, slender and tapering; similar in shape to those of Achelous spinicarpus View in CoL or Achelous inaequalis View in CoL , for example, whereas the gonopods might be more slender, sinuate and with the apex recurved in some other Achelous species (e.g. Achelous gibbesii View in CoL , Achelous hastatus View in CoL or Achelous spinimanus View in CoL ; see Monod, 1956; Taissoun, 1973). The male pleon is elongately triangular in Lupella forceps View in CoL , with a feebly convex, distally tapering sixth segment, whereas in Achelous View in CoL it is generally shorter, with convex sides of the sixth segment; the pleon of Achelous anceps View in CoL is, however, similar to that of Lupella View in CoL (see Rathbun, 1930; Taissoun, 1973). The general outline of the carapace is variable in Achelous View in CoL , from subhexagonal, with long lateral teeth, to semicircular, with those teeth not noticeably larger than the preceding teeth ( Rathbun, 1930). As is evident from published photographs and figures of the dorsal structures of a fairly flattened carapace ( Monod, 1956; Rathbun, 1930; Taissoun 1973), the epibranchial ridge surrounding the somewhat swollen metagastric region is most prominent and is highly arched in most Achelous species; but in Lupella forceps View in CoL the ridge is straight and slightly oblique.

In the present single-marker molecular analysis, Lupella forceps View in CoL is nested in a clade with five species of Portunus View in CoL [as listed by Mantellato et al. (2007, 2018)], all affiliated into Achelous View in CoL ( Achelous anceps View in CoL , Achelous floridanus View in CoL , Achelous hastatus View in CoL , Achelous inaequalis View in CoL and Achelous ventralis View in CoL ) in this study. These five species do not differ morphologically from the remaining Achelous species and are, to a similar extent, variable in carapace shape (hexagonal or semicircular), chelipeds or the male pleon. The male first gonopods in this group also are of both types (see Monod, 1956: figs 227–231) discussed above. Based on the morphological arguments (above) and the present molecular support, we propose here to transfer Lupella forceps View in CoL to Achelous View in CoL , with placement of the generic name Lupella View in CoL into the synonymy of the genus. Nevertheless, the taxonomic position of Lupella View in CoL and closer taxa might be tested in the future by means of wider molecular analyses.

A series of species up to now considered to be ‘ Portunus ’ or ‘ Portunus (Portunus) ’ [as listed by Mantelatto et al. (2018) or Evans (2018), respectively], and here transferred to Achelous (see below), are superficially similar to the genus Portunus (s.s.) in having a relatively broad carapace and a single tooth on the posterior border of the cheliped merus. Portunus (s.s.) differs from Achelous by the triangular pleon with a rounded telson apex ( Fig. 15C) vs. with a sharp telson apex ( Fig. 5C) and by the male gonopods, which are straight and threadlike ( Fig. 15E) vs. distinctly shorter, arched ( Fig. 5E).

Most Achelous spp. also have a distinct tooth on the posterior margin of the merus of the last pereiopods ( Fig. 5A). Although reduced in some Achelous species, this character is shared by this genus and the taxa of the lupocycline clade in the present analyses consisting of Alionectes and Lupocycloporus ( Figs 6A, 7A; see below).

Remarks: The current composition of Achelous consists of species distributed in the Atlantic and the eastern Pacific. Among them, some species from the previous nominotypic subgenus Portunus (as listed by Ng et al., 2008) are also present. The support for separating most of them into a taxon distinct from the mostly IWP Portunus (Portunus) has already been highlighted by the molecular results of Mantelatto et al. (2007, 2009, 2018); the separate biogeographical affiliations also sustain such subdivision.

Mantelatto et al. (2009) elevated six species from the subgenus Achelous to generic level. Three others were transferred there from the subgenus Portunus , and one from the genus Cronius Stimpson, 1860 . Mantelatto et al. (2009) suggested the position of a group of four Atlantic Portunus species (i.e. Achelous anceps , Achelous floridanus , Achelous hastatus and Achelous ventralis ) to be unclear owing to their basal separation from the main assemblage of species of their genus. In a subsequent study, Mantelatto et al. (2018) revealed an isolated position for Portunus anceps , whereas in the former study it was placed among the other Achelous species mentioned above in this paragraph. This is also the case for our 16S analysis ( Fig. 2), where these four species form an isolated but basally well-supported clade together with two other Atlantic species, Achelous inaequalis and Achelous forceps (= previously Lupella forceps ). In the recent systematic account of the Brazilian portunids, Rodrigues et al. (2017) retained Achelous anceps , Achelous floridanus and Achelous ventralis in the genus Portunus based on a morphological distinction between Achelous and Portunus originally proposed by Verrill (1908): dactyli of pereiopods 2–4 ensiform or cultriform, markedly costate vs. relatively broad, lanceolate, leaf-like or cultriform, indistinctly costate. Given that there is no substantial morphological distinction between these three species and Achelous hastatus from the genus Achelous , we regard them as being congeneric.

Four species of Portunus (Portunus) or Portunus (Achelous) [as listed by Ng et al., 2008; i.e. P. (P.) acuminatus , P. (P.) affinis , (P.) P. xantusii and P. (A.) floridanus ] were originally affiliated with the genus Achelous (see: Stimpson, 1860, 1871; Faxon, 1893; Rathbun, 1930). Given that they agree with the main diagnostic characters of the genus, Mantelatto et al. (2018) resurrected their original generic name for the first three of these. Recently, Marco-Herrero et al. (2021) have also listed the remaining species, P. (A.) floridanus , under the generic name Achelous but left Achelous gibbesii under Portunus , despite its new affiliation already provided by Mantelatto et al. (2009).

A further Portunus species, the eastern Pacific Achelous minimus , has never before been included in Achelous , but was regarded as a subspecies of Portunus xantusii by Garth & Stephenson (1966), which was originally in Achelous (see Stimpson, 1860; above). It is transferred here to Achelous based on the morphology of its male pleon and gonopods (see Garth & Stephenson, 1966).

Size: Mostly medium-size portunids; maximum recorded size(CL × CW) ranges from 13.8mm × 32.4mm in Achelous tuberculatus to 65.0 mm × 110.0 mm in Achelous spinimanus ( Verrill, 1908; Rathbun, 1930; Garth & Stephenson, 1966; Williams, 1984).

Ecological notes: Achelous spp. generally occur from the upper subtidal zone to a depth of 200 m, with most species having a relatively broad depth range [ Verrill, 1908; Rathbun, 1930; Garth & Stephenson, 1966; Williams, 1984; de Melo, 1996; Rodrigues et al., 2017; i.e. from 0 to 500– 550 m in Achelous spinicarpus and Achelous spinimanus (see Holthuis, 1959; de Melo, 1996) or even to 640 m in Achelous floridanus (see Williams, 1984)]. They are not usually reported from estuaries, except for Achelous inaequalis in West Africa ( Manning & Holthuis, 1981). These crabs prefer mostly soft, often mixed substrates and sometimes hard bottoms with algae or seagrass (in the upper subtidal zone) or sessile macrofauna ( Garth & Stephenson, 1966; de Melo, 1996). Several species were found swimming in the water column or on flotsam (i.e. Sargasso seaweed; Verrill, 1908; Rathbun, 1930; Garth & Stephenson, 1966; Jerde, 1967), which implies an important role of swimming in their ecology.

Geographical range: Tropical and subtropical West and East Atlantic, Mediterranean and Tropical East

142 M. KOCH ET AL.

Pacific ( Rathbun, 1930; Garth & Stephenson, 1966; Manning & Holthuis, 1981; d’Udekem d’Acoz, 1999).

SUBFAMILY LUPOCYCLINAE PAULSON, 1875 View in CoL