Eodemus, Koch & Spiridonov & Ďuriš, 2023

EODEMUS View in CoL GEN. NOV.

( FIGS 4H, 12)

Z o o b a n k r e g i s t r a t i o n: u r n: l s i d: z o o b a n k. org:act: 0676E050-17EF-4030-8605-BB6D580EC7D7

Type species: Portunus pseudohastatoides Yang & Tang, 2006 , by present designation.

Included species: Six.

Eodemus arabicus (Nobili, 1905) comb. nov. = Neptunus (Hellenus) arabicus (Nobili, 1905) = Portunus acerbiterminalis Stephenson & Rees, 1967

Eodemus hastatoides (Fabricius, 1798) comb. nov. = Portunus hastatoides Fabricius, 1798 = Portunus hastatoides Weber, 1795 (nomen nudum)

E o d e mu s p s e u d o h a s t a t o i d e s (Yang & Tang, 2006) comb. nov. = Portunus pseudohastatoides Yang & Tang, 2006

Eodemus subtilis ( Nguyen & Ng, 2021) View in CoL comb. nov. = Xiphonectes subtilis Nguyen & Ng, 2021 View in CoL

Eodemus unidens (Laurie, 1906) View in CoL comb. nov. = Neptunus (Hellenus) unidens Laurie, 1906 View in CoL = Portunus dayawanensis H.-L. Chen, 1986 View in CoL = Portunus trilobatus Stephenson, 1972 View in CoL = Neptunus (Hellenus) tweediei Shen, 1937 View in CoL

Eodemus vassilyi ( Nguyen & Ng, 2021) View in CoL comb. nov. = Xiphonectes vassilyi Nguyen & Ng, 2021 View in CoL

Diagnosis: Cephalothorax and chelipeds with fine, hair-like marginal setae. Carapace ( Fig. 12A) hexagonal, more than two times as broad as long (including lateral teeth); dorsal surface tomentose, regions feebly defined by patches of fine granules. Front ( Fig. 12B) with three or four lobes slightly projecting beyond tip of inner orbital lobe; median tooth or pair distinctly smaller than laterals. Orbit relatively large, approaching circular; inner supraorbital lobe rounded; supraorbital margin with two narrow fissures with appressed walls; infraorbital margin with broad, ‘Y’-shaped lateral notch. Anterolateral margin with nine sharp teeth: first to eighth teeth subequal in size; eighth tooth arising anteriorly from base of ninth tooth; ninth tooth large, directed laterally. Posterolateral junction of carapace produced to distally upturned spiniform tooth. Sutures of thoracic sternum well expressed ( Fig. 12C); thoracic sternites usually smooth or sparsely granular. Merus of third maxilliped anterolaterally produced to elongate projection. Chelipeds relatively robust; merus with four spines on anterior and two spines distally on posterior border; carpus with usual outer spine. Chelae ( Fig. 12D) slightly unequal, heterodontic; in larger chela, molariform tooth present proximally at cutting edge of dactylus; fingers densely setose distomedially. Dactyli of pereiopods 2–4 cultriform, costate, setose on ventral margin. Merus of pereiopod 5 distinctly longer than broad, without spine on posterior margin. Male pleon ‘T’-shaped ( Fig. 12C), with sixth pleomere elongate, narrow. Lateral margins of pleomere 3 markedly concave; pleomere terga 3–5 fused, without remaining sutures. First gonopod ( Fig. 12E) relatively long, arched, tapering distally; pair of first gonopods not overlapping, only touching each other in median body plane, with distal parts directed anteriorly. Female vulva ( Fig. 4H) in form of a narrow slit located close to mesial margin of sternite.

Etymology: Derived from Latin eodem, ‘to the same place’, alluding to the similar outer appearance of included species; gender masculine.

Systematic position: The species of the portunine Eodemus and of the newly established genera Incultus and Trionectes , plus the lupocycline Alionectes , were previously affiliated in the genus (or subgenus) Xiphonectes (as listed by Ng et al., 2008; Spiridonov et al., 2014). These genera are similar in their overall appearance, with a more or less strongly depressed carapace, usually with a long pair of lateral teeth and elevated patches of granules on the dorsum, and with produced or subacute posterolateral angles.

Their morphological distinction, together with Xiphonectes in its present reduced extent (below), is discussed under those genera. Eodemus can be distinguished easily by the more distinct ‘T’-shape of the male pleon, concave lateral margins of the third male pleomere and the distinctly laterally produced anterolateral lobe of the third maxilliped merus.

Based on our three-marker analysis, Eodemus is closely related to the species of Monomia (s.s., below) and Cycloachelous . Those genera share, among other features, the overall shape of the carapace, with granular patches on regions of the dorsum, and four frontal teeth, with the submedian pair smaller (in some Eodemus spp. , the submedians are fused to a single tooth; see also Wong et al., 2010). Other potential synapomorphies are the produced anterolateral lobe of the third maxilliped merus, two posterodistal spines on the cheliped merus, the ‘T’-shaped male pleon, concave lateral margins of the third pleomere (at least in most Monomia ) and a slit-shaped female vulva located close to the mesial margin of the sternite. The first gonopods are relatively long, usually bent and distally slender in Eodemus and Monomia (s.s.), whereas they are stout or moderately slender and curved in Cycloachelous .

All examined specimens of Eodemus are relatively small (CW usually ≤ 41 mm), whereas the species of Monomia are represented by distinctly larger specimens (see below). The posterior lateral tooth of the carapace is of variable length in both genera, but generally longer in Eodemus . The posterolateral junction of the carapace is produced to a distally upturned spine in the new genus, whereas it is greatly rounded in Monomia spp. In the latter, the epistome is medially produced to a long median spine distinctly overreaching the front, whereas such a structure is not recognizable from the dorsal view in Eodemus spp. The first male gonopods, despite the generally similar shape in both genera, touch in the median body plane along their bent parts in Eodemus spp. , but in the majority of Monomia spp. they overlap each other (except for some Australian species with subparallel, not overlapping, distal parts of the gonopods).

Remarks: For Monomia argentata , the iridescence of the cuticle had been incorporated as a typical character to its specific name by White (1847; as Amphitrite argentata ; a nomen nudum). The name was subsequently also accepted by A. Milne-Edwards (1861; as Neptunus argentatus ). This remarkable phenomenon of iridescence was also observed by us in E.pseudohastatoides (see Koch et al., 2015a), which also contributes to the hypothetical relationship of Eodemus and Monomia indicated by the molecular analysis ( Fig. 1).

Among all other species of the genus, E. arabicus (types examined, MNHN B5926, B5927) can be distinguished by the posterolateral junction of the carapace not as upturned as in the former two species. Neptunus (Hellenus) tweediei , P. trilobatus and P. dayawanensis have recently been synonymized with Xiphonectes unidens (now E. unidens ) by Nguyen & Ng (2021). Two new Xiphonectes species described in the latter study, X. subtilis and X. vassilyi , as formerly belonging to the X.hastatoides species complex ( Nguyen & Ng, 2021), are now also affiliated in Eodemus .

Size: Maximum reported size ranges from CW 25 mm [ E. unidens , in Stephenson & Rees, 1967a (as Portunus tweediei )] to 19.4 mm × 41.0 mm [ E. hastatoides , in Apel & Spiridonov, 1998 (as Portunus hastatoides )].

Ecological notes: Some species appear to be mostly shallow-water living species, such as E. arabicus recorded in the intertidal to the upper subtidal zone down to 55 m (Red Sea, ZMMU Ma 3295) or E. hastatoides with a depth range from 7 to 100 m ( Stephenson & Rees, 1967a; Stephenson, 1972a, b; Moosa, 1981a; Apel & Spiridonov, 1998; Yang et al., 2012; Nguyen & Ng, 2021).

Geographical range: Indo-West Pacific: from the Red Sea and the western Indian Ocean to Japan, the Philippines, Indonesia, Australia, the Chesterfield Islands and New Caledonia ( Crosnier, 1962; Stephenson, 1972a, b; Moosa, 1996; Apel & Spiridonov, 1998; Neumann & Spiridonov, 1999; Poupin, 2010).