Madangella, Frolová & Ďuriš, 2018

Frolová, Pavlína & Ďuriš, Zdeněk, 2018, Madangella altirostris, a new genus and species of palaemonid shrimps (Crustacea: Decapoda: Palaemonidae) from Papua New Guinea, Zootaxa 4438 (2), pp. 327-338 : 329-330

Madangella gen. n.

Diagnosis. Small, slender shrimp, body subcylindrical, smooth. Carapace with epigastric spine, with antennal and hepatic teeth, without supraorbital teeth. Rostrum compressed, short and deep, leaf-like, reaching distal end of basal antennular segment, dorsal and ventral margins convex, dorsally dentate, with subapical ventral tooth, apex acutely produced. Fourth thoracic sternite with finger-like median process. Eyes large, depressed, cornea slightly broader than stalk, latter short, stout; accessory pigment spot undeveloped. Antennule with stylocerite acutely produced distolaterally, statocyst large, rounded; distolateral margin convex, distal margin with small lateral tooth and rounded lobe medially; with ventromedial tooth; intermediate and distal peduncular segments elongate; outer flagellum biramous, fused part slender, long. Antennal basicerite with small lateral tooth, scaphocerite far overreaching antennular peduncle, elongate, with distolateral tooth subequal to convex distal margin of lamella; carpocerite short. Mandible with well-developed incisor and molar processes. Maxillula with normal palp and endites. Basal endite of maxilla bilobed, palp elongate, scaphognathite ovoid. Maxillipeds normal, with welldeveloped exopods; endites on first maxilliped separated by distinct incision, palp setose, caridean lobe small, epipod broadly triangular; second maxilliped with epipod elongate, without podobranch; third maxilliped with merus laterally denticulate, ischium feebly separated, basis distinct, coxa with lateral lobe, arthrobranchs absent. First pereiopods slender, fingers simple, longer than palm, carpus longer than both chela and merus, coxa unarmed. Second pereiopods feeble, symmetrical, slender, similar to first pereiopods, overreaching latter by chela and distal carpus; fingers simple, longer than palm, carpus almost twice as long as chela or merus. Ambulatory legs long and slender, dactylus very slender, simple, slightly curved, with acute unguis; propodus slender, almost twice as long as dactylus, with only small distoventral spines. Pleonites unarmed, pleurae 1–5 rounded; sixth pleonal segment compressed, elongate and twice as long as fifth segment. Telson elongate, with 2 pairs of minute dorsolateral denticles; posterior margin convex, with 3 pairs of cuspidate spines, lateral spines minute, intermediate longest. Uropodal protopod unarmed, rami elliptically elongate, overreaching telson; endopod shorter and narrower distally; exopod with minute distolateral tooth and longer movable spine medially, diaeresis indistinct.

Etymology. The generic name is derived from Madang Province, Papua New Guinea, in which the type locality is situated; gender feminine.

Type species. Madangella altirostris sp. n., by monotypy and present designation.

Included species. Monotypic.

Systematic position. The new genus belongs to the group of predominantly free-living palaemonid genera of the ‘ Cuapetes – Palaemonella clade’. All of its currently known 10 genera possess a slender finger-like median process on the third thoracic sternite. Madangella gen. n., can be easily separated from all those genera, by the presence of a uniquely short and deep leaf-like rostrum, but also by the short second pereiopods, not markedly longer than the first pereiopods, with small chelae and long carpi. The absence of the mandibular palp distinguishes the new genus from the genera Exoclimenella , Eupontonia , Palaemonella , and Vir , and, thus, affiliates the new genus to the group of remaining genera, i.e. Anapontonia , Cuapetes , Harpilius , Ischnopontonia , Periclimenella , and Philarius (e.g., Bruce 1995, 2004; Okuno 2009). Within the latter, only the genera Periclimenella , Cuapetes , and Harpilius share the presence of antennal and hepatic teeth with the new genus. All these genera are characterized by well-developed large second pereiopods with strong chelae, while in the new genus the second pereiopods are feebly developed, only moderately larger, but very similar to the first pereiopods.

Based on the present molecular analysis ( Fig. 5 ), Madangella gen. n. is basally separated from the scleractinian coral symbiotic genera Anapontonia , Ischnopontonia , Harpilius , and Philarius . As already stated, the new genus differs from those genera by slender and feebly developed second pereiopods with small chelae, and by extremely slender simple ambulatory dactyli, while the other genera are characterized by comparatively large second pereiopods with strong chelae, and by stout hooked ambulatory dactyli.

The representatives of the genera Harpilius and Philarius possess a moderately slender, distally tapering rostrum, dentate both dorsally and ventrally, and strongly hooked ambulatory dactyli surrounded by a dense tuft of distal propodal setae, while the new genus has a short and deep leaf-like rostrum, which, aside from the convex series of dorsal teeth, only harbours a single subdistal ventral tooth, and simple slender ambulatory dactyli and feeble propodal setation. Philarius also lacks a hepatic tooth on the carapace, while the latter is well developed in Madangella gen. n. The highly specialized symbiotic shrimps of the genera Ischnopontonia and Anapontonia have strongly compressed bodies, numerous postorbital dorsal teeth on the carapace (vs. a single epigastric tooth in the new genus), stout second pereiopods chelae, which are subapically articulated with a distally swollen carpus (vs. slender, terminally articulated segments on chelipeds), a reduced median sternal process (vs. well developed), and strong lateral teeth on the uropodal exopods (vs. uropods without special features), but also lack antennal and hepatic teeth on the carapace (vs. well-developed ones).

Madangella gen. n. is thus morphologically different and phylogenetically isolated from the coral associated genera of the CP clade. The combination of the rostral shape, the similarity of the first and second pereiopods, and the extremely long and slender ambulatory dactyli in Madangella gen. n. are unique among the members of this clade.

Figures

FIGURE 5. Phylogenetic position of Madangella altirostris gen. et sp. n. resolved by Bayesian inference based on the combined dataset of two genes (16S, H3). RAxML bootstrap supports are expressed as percentages. The asterisk (*) indicates different topology of RAxML tree.