Polybius Leach, 1820

García-Raso, J. Enrique, D'Udekem D'Acoz, Cédric, Moukrim, Abdellatif, Schubart, Christoph D. & Cuesta, Jose A., 2024, A new cryptic species of Polybiidae (Crustacea: Decapoda: Portunoidea) from the East Atlantic, with considerations on the genus Polybius, European Journal of Taxonomy 930 (1), pp. 277-313 : 286

Genus Polybius Leach, 1820 [in Leach, 1815 –1875]

Modified diagnosis

Carapace circular or suboval, slightly or clearly broader than long, often convex longitudinally; generally with well-defined regions; smooth, or ornamented with transverse ridges or granules; naked or with short hairiness. Frontal margin tri-lobulated or tridentate. Anterolateral margins with five teeth, including external orbital, somewhat flattened, more or less equal or decreasing in size, from third to fifth, with pointed or rounded apices; the first four teeth are directed forwards, the last one may be directed laterally or anterolaterally. Marked posterolateral reentrants. Orbits with two fissures on upper orbital margin, ventral outer orbital margin with a broad to narrow longitudinal incision. With a gap between the ventral internal orbital margin and the second antenal peduncle segment that is in contact with the lower-lateral margin of the frontal region. Chelipeds generally shorter than pereiopods; merus without distal ventral tooth, carpus of cheliped with large spine on inner angle. Propodus of pereiopod 2 to 4 each with a ventral ridge. Dactylus of pereiopod 5 compressed, paddle-like or broadly lanceolate.

Remarks

Within this genus, and according to our data and the previous information provided by Schubart & Reuschel (2009), Spiridonov et al. (2014), Plagge et al. (2016) and Evans (2018), the following species should be included: Polybius henslowii , Liocarcinus holsatus , L. marmoreus , L. vernalis , P. dioscurus sp. nov. (which constitute a group of species morphologically and molecularly very closely related, Figs 1–2 , this study), L. bolivari (Zariquiey Álvarez, 1948) , L. depurator and L. zariquieyi ( Gordon, 1968) . The species L. maculatus and L. pusillus must be confirmed by DNA genetic analysis. As it is further separated, we suggest that L. navigator should be transferred to a different genus as mentioned above. In addition, the species and genera Liocarcinus corrugatus , Liocarcinus strigilis , Necora Holthuis, 1987 , Macropipus Prestandrea, 1833 and Bathynectes Stimpson, 1871 are morphologically and genetically more different (see first references of this paragraph) and their position-statuses need to be analysed and justified in more detail (Schubart pers. comm. to other co-authors before his death).

Furthermore, Ng et al. (2008) and WoRMS Editorial Board (2023) also included Liocarcinus subcorrugatus (A. Milne-Edwards, 1861) and Liocarcinus rondeletii ( Risso, 1816) within Liocarcinus , for which there is no genetic information. The former is apparently endemic of the Red Sea ( Spiridonov et al. 2013), but its status is doubtful ( d’Udekem d’Acoz 1999; Noël 2016). The latter, which is similar to L. navigator , is separated by Risso (1816: 26) from its congeners by the presence of only four anterolateral teeth on the margins of the carapace “bords latéraux à quatre dents” (also in Risso 1826–1827: 2), while all the species in this genus have five (e.g., Manning & Holthuis 1981: 83, diagnosis here). However, in the related P. navigator the fourth is smallest, sometimes almost obsolete ( Ingle 1980) and Risso’s descriptions are known to be sometimes inaccurate ( Holthuis 1977). Palmer (1927), Miranda y Rivera (1933) treated it as a synonym of Liocarcinus arcuatus (= L. navigator ). However, Zariquiey Álvarez (1968: 369), due to the morphological differences he observed between the Atlantic and Mediterranean populations, considered that the Mediterranean specimens belonged to a different subspecies ( L. arcuatus rondeletii ). Ng et al. (2008) and WoRMS Editorial Board (2023) accept Liocarcinus rondeletii as a valid species, but we are not aware of recent genetic or morphological studies to support this new status. The validity of this taxon cannot be accepted without in-depth studies (as in for L. subcorrugatus ), as it is known that within some species of this genus, e.g., P. vernalis , there is considerable morphological variability between populations (see below).

Figures

Fig. 1. Neighbor-Joning (NJ) phylogenetic tree based on mitochondrial 16S rRNA sequences of species of Polybius Leach, 1820 and Liocarcinus Stimpson, 1871, using 2000 Bootstrap replicates. Number on nodes represent NJ Bootstrap values, only values>70 are included. Carcinus aestuarii Nardo, 1847 and C. maenas (Linnaeus, 1758) are used as outgroup. GenBank accession codes are indicated for each species, except those with codes XX## which sequences are listed in Supp. file 1.

Fig. 2. Maximum likelihood (ML) phylogenetic tree based on mitochondrial cytochrome c oxidase subunit I sequences of species of Polybius Leach, 1820 and Liocarcinus Stimpson, 1871, using 2000 Bootstrap replicates. Number on nodes represent ML Bootstrap values, only values>70 are included. Carcinus aestuarii Nardo, 1847 and C. maenas (Linnaeus, 1758) are used as outgroup. GenBank accession codes are indicated for each species, except those with codes XX## which sequences are listed in Supp. file 1.