Cycloachelous, WARD, 1942

Koch, Milan, Spiridonov, Vassily A. & Ďuriš, Zdeněk, 2023, Revision of the generic system for the swimming crab subfamily Portuninae (Decapoda: Brachyura: Portunidae) based on molecular and morphological analyses, Zoological Journal of the Linnean Society 197, pp. 127-175 : 151-153

CYCLOACHELOUS WARD, 1942

( FIGS 4F, 10, 11)

= Cycloachelous Ward, 1942 (type species Lupea granulatus H. Milne Edwards, 1834 , by original designation; gender masculine).

Included species: Nine. Cycloachelous elongatus (A. Milne-Edwards, 1861)

= Achelous elongatus A. Milne-Edwards, 1861 Cycloachelous euglyphus (Laurie, 1906) comb. nov.

= Neptunus (Amphitrite) euglyphus Laurie, 1906 Cycloachelous granulatus (H. Milne Edwards, 1834) = Lupea granulatus granulatus H.Milne Edwards,1834

= Amphitrite speciosa Dana, 1852

Cycloachelous levigatus Koch, 2021

Cycloachelous octodentatus (Gordon, 1938)

= Neptunus (Achelous) octodentatus Gordon, 1938 Cycloachelous orbicularis (Richters, 1880)

= Achelous orbicularis Richters, 1880

Cycloachelous orbitosinus (Rathbun, 1911)

= Portunus (Achelous) orbitosinus Rathbun, 1911 Cycloachelous suborbicularis (Stephenson, 1975)

= Portunus suborbicularis Stephenson, 1975 Cycloachelous unispinosus ( Miers, 1884)

= Achelous granulatus unispinosus Miers, 1884

Diagnosis: Carapace ( Fig. 10A) quasi-hexagonal or almost circular in shape, usually <1.5 times broader than long, flattened, with granular ridges and/or patches or entirely covered with granules. Regions moderately developed. Orbit ellipsoidal, with two shallow fissures on supraorbital margin. Infraorbital margin visible in dorsal view, with pronounced notch; outer infraorbital lobe appressed to ventral side of outer supraorbital lobe (= first anterolateral tooth). Frontal margin ( Fig. 10B) consisting of four low lobes. Nine well-developed anterolateral teeth: first to eighth subequal; ninth somewhat longer than others or of similar size. Posterolateral junction of carapace rounded. Sutures on thoracic sternum distinct ( Fig. 10C); suture between thoracic sternites 6 and 7 nearly complete in males and interrupted in females; thoracic sternites usually smooth. Anterolateral angle of maxilliped 3 merus strongly produced laterally or auriculate. Chelipeds relatively slender; merus with three or four spines on anterior margin and two distal spines on posterior margin; carpus with single spine on anterior margin of outer face. Chelae ( Fig. 10D) usually of nearly equal size and homoiodontic, without proximal molariform tooth on cutting edge of dactylus; palm with two carinae and single spine on upper face (excluding spine at articulation with carpus) and three carinae on outer face. Dactyli of pereiopods 2–4 cultriform, costate, weakly setose on ventral margin. Merus of pereiopod 5 distinctly longer than broad, without spine on posterior margin. Male pleon ( Fig. 10C) quasi-triangular or with lateral margin of sixth pleomere markedly convex. Lateral margins of pleomere 3 straight or slightly concave; terminal part of posterior thoracic episternite fills interspace between anterior margin of pleomere 3 and thoracic sternite 8. Pleonal terga 3–5 fused, without remaining sutures; keels usually absent. Gonopod 1 ( Fig. 10E) short and stout, distally hooked, or moderately slender, curved. Female vulva ( Fig. 4F) a narrow, oblique fissure, relatively distant from margins.

Systematic position: In our three-marker phylogenetic reconstruction ( Fig. 1), Cycloachelous forms a sister group to Monomia and Eodemus , with unsupported internal relationships. Cycloachelous , together with Cavoportunus (see above), shares with these genera some morphological apomorphies, such as the female vulva in the form of a narrow slit, and (mostly) two distal spines on the posterior margin of the cheliped merus. However, Cycloachelous spp. are distinct in overall appearance from other genera of the former Portunus (s.l.) owing to their carapace shape and symmetrical chelipeds.

Remarks: Cycloachelous granulatus has been considered to comprise two subspecies: the nominotypic one and Cycloachelous granulatus unispinosus , originally Achelous granulatus var. unispinosus Miers, 1884 . The latter subspecies was described based upon a single type specimen from Prince of Wales Channel, Queensland, Australia ( Miers, 1884: 230, pl. 23B). Later, Miers (1886: 180) considered it as a separate species, Neptunus (Achelous) unispinosus . Miers (1884: 230) suggested it could be distinguished from Cycloachelous granulatus ‘in wanting the submedian spine of the posterior margin of the arm of the chelipedes’, meaning by a single spine on the posterior margin of the cheliped merus, vs. two spines (a generic character of Cycloachelous ). In the subsequent description, he added an important character of the frontal teeth or lobes: ‘the median teeth smaller, but not less prominent than submedian teeth’ ( Miers, 1886: 180). However, in Cycloachelous granulatus the median frontal teeth are distinctly less prominent than submedians (laterals in the present terminology). This indicates that Miers’ variety unispinosus is indeed a separate species, probably not even belonging to Cycloachelous . We (M.K. and Z.Ď.) examined the holotype specimen of Achelous granulatus var. unispinosus Miers, 1886 (NHM 82.7); the distinctions mentioned by Miers (above) were confirmed. In addition, the male pleons also differ in both the crabs, in that the penultimate somite is shorter, but wider anteriorly in Cycloachelous granulatus (vs. longer, but narrower distally) and the telson is respectively larger (vs. smaller).

The morphology of P. (Monomia) euglyphus (as listed by Ng et al., 2008) shows some characters typical for Cycloachelous , the most significant being the unique shape of the male gonopods, which are similar to those of the type species, Cycloachelous granulatus (compare: Serène, 1969: fig. 6; Nguyen & Ng, 2010: fig. 5D). The present analysis confirms the inclusion of Neptunus (Amphitrite) euglyphus Laurie, 1906 in Cycloachelous .