Allomonomia, Koch & Spiridonov & Ďuriš, 2023

ALLOMONOMIA View in CoL GEN. NOV.

( FIG. 8)

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: 98CEC882-F852-4A87-88C6-99AB5FDC0C51

Type species: Portunus lecromi Moosa, 1996 , by present designation.

Included species: Two. Allomonomia calla (Koch, Nguyen & ĎuriŠ,

2015) comb. nov.

= Monomia calla Koch, Nguyen View in CoL & ĎuriŠ, 2015 Allomonomia lecromi ( Moosa, 1996) View in CoL comb. nov.

= Portunus lecromi Moosa, 1996 View in CoL

Diagnosis: Carapace ( Fig. 8A) subhexagonal, with anterior outline semicircular; width (without lateral teeth) ~1.3 × length; dorsal surface with well-defined granulate regions. Front ( Fig. 5B) with four sharp triangular teeth, submedian teeth narrower than lateral teeth, all distinctly projecting beyond tip of inner supraorbital lobe. Epistome apophysis well developed and may be visible between median frontal lobes. Orbit relatively large, ellipsoidal, with supraorbital margin granulate, with two well-developed fissures in middle and on base of first anterolateral tooth; infraorbital margin strongly granulated, with narrow, deep lateral notch, with tooth-like elevation mesially and on ventral side of first anterolateral tooth. Anterolateral margin convex, longer than posterolateral margin, armed by nine teeth: eight anterior ones subequal, small, acutely forward projecting; ninth tooth distinctly larger, lateral. Posterolateral angle of carapace rounded. Sutures of thoracic sternum well expressed ( Fig. 8C); thoracic sternites partly granular. Merus of third maxilliped with anterolateral lobe subrectangular. Chelipeds moderately stout; merus with four spines on anterior and one spine distally on posterior border; carpus with usual sharp spine on outer face. Upper surface of palm with two granular crests, inner one ending by spine distally; outer surface with two granular crests ending on level of finger joint. Chelae ( Fig. 8D) nearly symmetrical but heterodontic; flattened molariform tooth present proximally at cutting edge of dactylus of one of the chelae. Dactyli of pereiopods 2–4 cultriform, costate, setose on ventral margin. Merus of pereiopod 5 a little longer than broad, without spine on posterior margin. Male pleon ( Fig. 8C) ‘T’-shaped. Posterior pleonal margin forming a pair of subparallel transverse laminar crests on both second and third pleomeres. Lateral margins of pleomere 3 straight, terminal part of posterior thoracic episternites narrow, fits in interspace between anterior margin of pleomere 3 and thoracic sternite 8. Pleomeres 3–5 fused, without sutures, but with elevated submarginal ridge posteriorly on fourth pleomere; telson narrowly triangular. First male ( Fig. 8E) gonopod moderately robust; distal half slender, held subparallel to each other; tip with wide opening. Female vulva remains undescribed.

Etymology: Derived from the generic name Monomia [from Greek, meaning ‘only one’], to which the new genus is generally similar, and the prefix allo- (Greek άλλο, other), alluding to the superficial morphological similarity but different systematic position of the new genus to the former; gender feminine.

Systematic position: The two known species of Allomonomia were members of the subgenus/genus Monomia in earlier concepts ( Ng et al., 2008; Koch et al., 2015b). They share some general morphological characters (i.e. the carapace with a rounded posterolateral angle, the third meri of the maxillipeds with a triangular anterodistal projection, and the chelae with two teeth on the upper surface of the palm). Allomonomia differs from Monomia by the semicircular shape of the carapace (vs. more widened, semi-elliptic or hexagonal), the front with four subequal triangular teeth projecting distinctly beyond the inner supraorbital angle (vs. low and subequal ones with submedians lower than laterals, projecting slightly beyond the tip of the inner supraorbital angle), an indistinct median epistomial spine (vs. reaching distinctly beyond front), only one posterodistal spine on the cheliped merus (vs. predominantly two spines) and by the first male gonopods lying in a subparallel position, with broadened apical openings (vs. gonopods generally overlapping each other by bent region medially, with narrow terminal opening).

In the present 16S molecular analysis ( Fig. 2), both species of Allomonomia are in a sister position to Incultus , whereas the three-marker analysis ( Fig. 1) revealed paraphyly of Allomonomia , with the latter genus positioned as sister to Allomonomia calla . However, morphological characters provide proper support to an independent generic status of both genera. Both of them are very similar in the bent shape of the first male gonopods, which are lying in a pair with subparallel distal parts in Allomonomia ( Fig. 8E) but overlapping each other by the bent regions in Incultus ( Fig. 13E). Both these genera are also characterized by the presence of only a single posterodistal tooth on the cheliped merus. Together with this, Allomonomia species are different in the general appearance of the body from the species of Incultus , with a distinctly convex dorsal carapace with a semicircular anterior outline and rounded posterolateral angles (vs. hexagonal, deeply depressed, with elevated, swollen regions and with posterolateral angles acutely produced).

The sister clade to the Allomonomia – Incultus clade in the present three-marker analysis ( Fig. 1) is a branch composed of Xiphonectes and Trionectes (see below). The Allomonomia spp. were previously included in Monomia , whereas the species now included in Incultus and Trionectes were all previously included in the genus/subgenus Xiphonectes (as listed by Ng et al., 2008; Spiridonov et al., 2014). All species of the large, combined clade have the first male gonopod consisting of a robust basal part and bent distal part. The species of the Xiphonectes – Trionectes clade have the distal part short and hooked ( Figs 16E, 17E), whereas species belonging to the Allomonomia – Incultus genera have the distal part of the first gonopod distinctly more sharply bent, more slender and longer ( Figs 8E, 13E). Trionectes is also easily distinguished by having three frontal teeth on the carapace.

Size: Although few specimens have been available for measurements, Allomonomia spp. appear to be medium-sized portunids, ranging from 20 mm × 30 mm in Allomonomia lecromi ( Moosa, 1996) to a maximum CW of 38.4 mm in Allomonomia calla ( Koch et al., 2015b) .

Ecological notes: The two known species of the genus have been collected from relatively deep waters: Allomonomia lecromi at 120–150 m from the Chesterfield Islands ( Moosa, 1996), Allomonomia calla at 106–111 m and from a tangle net deeper than 50 m, from the Philippines ( Koch et al., 2015b).

Geographical range: Indo-West Pacific: known from Madagascar, the Philippines and New Caledonia.