Incultus, Koch & Spiridonov & Ďuriš, 2023

INCULTUS View in CoL GEN. NOV.

( FIGS 3A, 4E, 13)

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: 2B1B6DEC-6146-4A5B-A77B-4340C140CDF5

Type species: Neptunus tuberculosus A. Milne-Edwards, 1861 , by present designation.

Included species: Three.

Incultus alcocki (Nobili, 1905) comb. nov.

= Neptunus (Hellenus) alcocki Nobili, 1906 Incultus brockii (De Man, 1887) comb. nov.

= Neptunus brockii De Man, 1888

Incultus tuberculosus (A. Milne-Edwards, 1861) View in CoL comb. nov.

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

Diagnosis: Carapace ( Fig. 13A) flattened, broadly hexagonal,> 1.5 times as long as broad (including lateral teeth). Dorsal surface granulated; regions conspicuously elevated, with pair of closely set cardiac elevations most prominent; distinct wide depressions present behind orbits. Front ( Fig. 13B) with three or four subequal low or obsolete lobes distinctly projecting beyond inner supraorbital lobe. Orbit relatively large, ellipsoidal, with inner supraorbital lobe rounded; upper border of orbit with two short fissures. Infraorbital margin granulated, with broad lateral notch. Anterolateral margin with nine blunt or lobiform teeth; ninth distinctly larger, lateral. Posterolateral angles of carapace produced, distinctly upturned over posterior margin. Sutures ( Fig. 13C) and grooves of thoracic sternum poorly to moderately distinct; thoracic sternites partly granular. Antennal flagellum long, more than twice orbital width. Merus of third maxilliped elongate, anterolaterally produced to rounded lobe. Chelipeds stout; merus with three or four spines on anterior border, one distal spine on posterior border, followed more basally with distinct, obliquely elevated sulcus forming small tuberculate lobe and continuing as transverse groove or crossing distal merus. Carpus with short spine on outer face. Chelae ( Fig. 13D) moderately unequal, heterodontic, with flattened molariform tooth located proximally at cutting edge of dactylus; palm unarmed or with small spine distally over dactylar articulation, two distinct longitudinal crests on outer surfact and two on upper surfaces of palm; fingers distinctly shorter than palm. 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 ( Fig. 13C) quasi-triangular; crests on second and third pleomeres low. Lateral margins of third pleomere straight; apex of thoracic episternite 7 fills in interspace between anterior margin of pleomere 3 and episternite 8; third to fifth somites fused, without remaining sutures, crests or keels on them may be present; last pleomere elongate. First male gonopod ( Fig. 13E) stout or moderately slender distally, arched or almost rectangularly bent; tip rounded, with moderately wide subterminal opening; gonopods in pair overlapping each other by bent regions (not obvious in I. alcocki possessing relatively short gonopods). Female vulva ( Fig. 4E) elliptic, located at mesial or posteromesial margin of sternite.

Etymology: The genus name is derived from the Latin adjective ‘ incultus ’, meaning rough, unkempt, but is here treated as a masculine noun in apposition. It alludes to the somewhat untidy external appearance of the known species; gender masculine.

Systematic position: All three included species were listed in the subgenus Xiphonectes by Ng et al. (2008), but later accepted at generic level following Spiridonov et al. (2014). The included species are similar to Xiphonectes (as restricted in this study) and to Eodemus , Trionectes and the lupocycline Alionectes , in general appearance of the body. The carapace in all these genera is flattened, with a similarly long posterior tooth of the anterolateral series and with an angulate junction of the posterolateral and posterior margins.

Incultus bears a morphologically close relationship to Xiphonectes and Trionectes . It differs from these genera by: (1) distinctly elevated dorsal regions on the carapace (vs. feebly demarcated in both); (2) lobate anterolateral teeth on the carapace (vs. predominantly sharply triangular in both); (3) the front with three or four low and often indistinct subequal teeth (vs. four distinct triangular or rounded teeth, with submedian ones smaller in Xiphonectes , and three subequal triangular or blunt teeth, with the median one more slender in Trionectes ); (4) the infraorbital margin with a broad lateral notch (vs. narrow in Xiphonectes and deep, ‘V’-shaped in Trionectes ); (5) the male pleon with second and third somites each bearing a low transverse crest (vs. second high, laminar and third shallow; the latter might also be high in some Xiphonectes spp. ); (6) the male pleon with the sixth somite elongately trapezoid (vs. similar in Trionectes , but distinctly constricted subdistally in Xiphonectes ); (7) the stout chelipeds (vs. comparatively slender in Xiphonectes ), with fingers distinctly shorter than the palm (vs. subequal in both other genera); and (8) the first male gonopod with a rounded tip, being relatively long, almost rectangularly bent at the midlength at least in I. brockii and I. tuberculosus ; the pair of gonopods overlap each other by the bent regions (vs. gonopods slender, smoothly out-curved distally, not meeting medially in Xiphonectes ; similar but shorter and stouter in Trionectes ).

Eodemus is distinguishable from Incultus by deep orbits, with two incisions with fully appressed walls, and with the inferior margin bearing a broad ‘Y’-shaped lateral notch. The cheliped merus bears two spines distally on the posterior border. The male pleon is almost ‘T’-shaped, with the sixth somite elongate, narrow (vs. pleon subtriangular in Incultus , with the sixth pleomere trapezoid). The first gonopods are relatively long, arched, distally slender; the pair of first gonopods are touching in the median body plane at the bent parts.

Based on the present molecular analyses, Incultus is closely related to Allomonomia . Species of both taxa have the first male gonopods bent in a similar way; those lie in a pair overlapping each other by their bent regions in Incultus gen. nov., while being subparallel with distal parts in Allomonomia . Both genera are also characterized by the presence of only a single posterodistal tooth on the cheliped merus. Additionally, Incultus is different from Allomonomia in having a hexagonal and deeply depressed carapace with elevated swollen regions and the posterolateral angles acutely produced; whereas in Allomonomia , the carapace is distinctly convex dorsally, with a semicircular anterior outline and with rounded postrolateral angles.

In addition to the general shape of the body mentioned above, Alionectes differs from Incultus mainly by large circular orbits without dorsal fissures (vs. with small, ‘Y’-shaped fissures in Incultus ) and by a distinct posterodistal tooth on the merus of the swimming legs. The cheliped merus bears two spines distally on the posterior border (vs. a single distal spine and an oblique keel more proximally). The male pleon has the second and third somites with subequally low crests, marginally serrated on the second pleomere. The first male gonopods are relatively short and robust proximally, tapering distally to the out-curved tip; the pair of first gonopods lies obliquely inwards, touching at their subdistal parts.

Remarks: Neptunus (Hellenus) alcocki Nobili, 1905 (= Portunus alcocki ; see: Stephenson, 1972a, b; Neumann & Spiridonov, 1999) has until recently been included in the subgenus Portunus (Xiphonectes) . It is known from the holotype male and a single female from the Gulf of Aden ( Neumann & Spiridonov, 1999); it has also been recorded in the Red Sea [ Laurie, 1915; and present material, SMF (V.A.S.)]. The species was not included in the present molecular analyses. Based on the holotype, illustrated by Guinot (1957: figs 3, 4, 9, 10) and examined by us (M.K. and Z.Ď.), the species possesses three low frontal lobes, a character typical for Trionectes or some species of Eodemus and Xiphonectes . However, it shows a closer morphological affinity to Incultus rather than to other portunine genera. Its median frontal tooth is evidently derived from the fusion of two small submedian teeth and it has low lateral frontal teeth, similar to I. brockii , with four obsolescent teeth forming a shallowly undulating margin (in I. tuberculosus , the two submedians are distinct but small). In contrast, in the other three genera the frontal teeth are triangular. The stout arched first male gonopods are also distinct from those of Trionectes , which distally are strongly bent and slender, with a minute terminal opening, whereas in I. alcocki they only feebly taper distally to a moderately wide opening (see Guinot, 1957: figs 8–10). Furthermore, I. alocki shares with other Incultus spp. the unique morphology of the rounded female vulva located at the mesial or posteromesial margin of the sternite (compare Neumann & Spiridonov, 1999: fig. 2C; Apel & Spiridonov, 1998: fig. 117d) and is herein thus transferred to Incultus .

Size: Small to medium-sized species; maximal recorded size range from 7.8 mm × 16.3 mm in I. alcocki ( Neumann & Spiridonov, 1999) to 20.5 mm × 35.0 mm in I. brockii ( Yang et al., 2012) and 29.0 mm × 49.0 mm in I. tuberculosus ( Stephenson & Rees, 1967a) .

Ecological notes: The included species show different depth ranges, with I. brockii being an intertidal to upper subtidal species (Spiridonov, 1999), whereas I. tuberculosus occurs on various substrates from the upper subtidal to continental slope, ranging from 7–9 to 580 m in depth ( Stephenson, 1972a, b; Apel & Spiridonov, 1998; Yang et al., 2012). Incultus alcocki appears to be an upper subtidal species occurring mostly on sand ( Laurie, 1915; Neumann & Spiridonov, 1999; present material, SMF).

Geographical range: Indo-West Pacific: I. tuberculosus has the broadest range, from the Red Sea and East Africa to the Hawaiian Islands ( Stephenson, 1972a, b; Apel & Spiridonov, 1998); I. brockii is restricted to the eastern Indian Ocean and the western Pacific; and I. alcocki is currently known only from the Red Sea and the Gulf of Aden (see above).