Rhachotropis riina Corbari, Frutos & Sorbe, 2024

Rhachotropis riina Corbari, Frutos & Sorbe View in CoL sp. nov.

( Figs. 10 View Fig , 11 View Fig , 12, 13, 14, 15, 16, 23 and 24)

L S I D: u r n: l s i d: z o o b a n k. org:act: 27DE4F21-EB15-4225-8CC0-D7597342D8F7.

Type material. Holotype: Brooding female, empty marsupium, 27.5 mm BL (MNHN-IU-2017-524), Solomon Islands, N Savo Island , SALOMON 1 cruise, Stn CP 1754, 09° 00′ S, 159° 49′ E, 1169–1203 m, 26/09/2001. GoogleMaps

Paratypes: Brooding female, with 2 intra-marsupial individuals, 24.2 mm BL (MNHN-IU-2017-525); brooding female, empty marsupium, 12.2 mm anterior part of the body until pleonite 1 (MNHN-IU-2017-526); brooding female, empty marsupium 23.4 mm BL (MNHN-IU-2017-527), Solomon Islands, NW Choiseul Island , SALOMON 2 cruise, Stn CP 2230, 06° 28′ S, 156° 24′ E, 837–945 m, 29/10/2004 GoogleMaps . Brooding female, empty marsupium 24.4 mm BL (MNHN- IU-2017-528) Solomon Islands, NW Choiseul, SALOMON 2 cruise Stn CP 2231, 06° 25′ S, 156° 21′ E, 1083–1100 m, 29/10/2004 GoogleMaps . Brooding female, empty marsupium 23.2 mm BL (MNHN-IU-2017-522), Solomon Islands, SW Santa Isabel Island, SALOMON 2 cruise, Stn CP 2197, 08° 24′ S, 159° 23′ E, 897–1057 m, 24/10/2004 GoogleMaps . Brooding female, empty marsupium 27.7 mm BL (MNHN-IU-2017-523), Solomon Archipelago, NW Malaita Island, SALOMON 1 cruise, Stn CP 1781, 8° 31′ S, 60° 38′ E, 1036–1138 m, 29/09/2001 GoogleMaps .

Other material examined: Brooding female, empty marsupium, 24.1 mm BL (MNHN-IU-2021-6589), Vanuatu, SW Anatom Island , MUSORSTOM 8 cruise, Stn CP 956, 20° 33.4′ S, 169° 35.9′ E, 1175–1210 m, 20/09/1994; brooding female, empty marsupium, 25.1 mm GoogleMaps

1 https://expeditions.mnhn.fr/campaign/biopapua/event/CP3747? area=1

BL (MNHN-IU-2021-6639), Vanuatu, SE Santo, MUSORSTOM 8 cruise, Stn CP 1129, 16° 00.7′ S, 166° 39.4′ E, 1014–1050 m, 10/10/1994 GoogleMaps .

Type locality. Solomon Archipelago, SW Pacific Ocean, West Pacific province.

Etymology. The name refers to Riina, the great warrior woman of the Solomon Islands. Noun in apposition.

Description. Holotype brooding female (MNHN-IU-2017-524), paratype brooding female (MNHN-IU-2017-525)

Body ( Fig. 11 View Fig ): Rostrum short (30% length of antenna 1 peduncle article 1), very curved ( Fig. 10 View Fig ); eyes present,

bulging laterally, without distinct ommatidia, non-pigmented (specimens preserved in ethanol). Pereonites 1 − 7 ( Fig. 11b View Fig ) smooth. Pleonite 1 bearing short mediodorsal pointed process and elongated dorsolateral pointed processes; pleonite 2 bearing mediodorsal pointed process and elongated dorsolateral pointed processes; pleonite 3 bearing three shorter processes, a bigger one in mediodorsal position and two small ones in dorsolateral position, all elongated processes ending a keel extending along the dorsal surface of the corresponding somite ( Fig. 11a View Fig ). Epimeral plates 1 ‒ 2 with a median tooth on posterior margin, epimeral plate 3 with 2 median teeth on posterior margin, the upper one smaller. Urosomites 1 − 3 without process.

Antenna 1 ( Figs. 11 View Fig and 12): Shorter than half body length and slightly shorter than antenna 2, if not broken. Peduncle article 1 with two acute dorso-distal process; article 2 subequal to article 1, more than 2.6 times as long as article 3, ornamented with subdistal plumose setae; article 3 bearing a distal tiny 1-articulate accessory flagellum with two short simple setae. Main flagellum 14 − articulate, all articles longer than wide, the 12th and 13th ones with one distal aesthetasc.

Antenna 2 (Fig. 12): Shorter than half body length. Peduncle articles 4 and 5 subequal in length; ventral margin of article 4 with one longitudinal row of setae, plumose on proximal part; apex of article 5 with a row of setae on dorsal margin and one distal plumose seta. Flagellum at least 21-articulate, each article longer than wide, with two subdistal short setae.

Upper lip (Fig. 13): Entire, circular, triangular apex with blunt tip and subapical crown of short setules.

Mandibles (Fig. 13): Mandibles asymmetrical. Incisor process asymmetrical and well-developed on both mandibles; apex bifid on right one, partly dentate on left one. Laciniae mobilis asymmetrical, left one more massive than right one and dentate at apex. Left and right setal row with 7 cuspidate setae. Molar process cylindrical, with large triturative apex delineated by a ring of stout blades. Mandibular palp triarticulate; article 1 short; article 2 longer than article 3 with long slender setae on half distal part; article 3 tapering distally, ending with few long setae.

Lower lip (Fig. 13): Outer lobes separated by broad gap, distally rounded and setose. Inner lobes not visible. Mandibular projections broken, apparently poorly developed.

Maxilla 1 (Fig. 13): Inner plate with two subapical plumose setae and numerous setules on distal part. Outer plate with 7 bifid/multifid cuspidate setae and 2 simple cuspidate setae. Palp 2-articulate, proximal article shorter than distal one, bearing one distal long seta; distal article with long and very long setae on distal two-third.

Maxilla 2 (Fig. 13): Inner plate and outer plate subequal in length, inner one slightly wider than outer one. Both plates fringed with numerous slender simple setae and setules in their distal part. Inner margin of inner plate with two subapical plumose setae and numerous setules.

Maxilliped (Fig. 12): Inner plate shorter than outer plate, with 5 cuspidate stout setae irregularly shaped and implanted at apex, 1 submarginal stout seta near inner margin on anterior face. Outer plate not reaching half of palp article 2, with a submarginal row of stout setae near inner margin and marginal setae at apex. Palp 4-articulate, long and setose; article 1 with 2 subdistal plumose setae near outer margin; article 2 longest, with submarginal row of simple setae near inner margin and 1 subdistal simple seta on outer margin; article 3 widened subdistally, with a transverse row of simple setae on anterior face and marginal/submarginal simple setae at apex; article 4 shorter than article 3, slightly curved.

Gnathopods ( Fig. 14 View Fig ). Gnathopod 1: slightly smaller than gnathopod 2, similar in shape, both strongly subchelate. Coxa small, acute and produced anteriorly, over-reaching the

d

nov. holotype, brooding female (MNHN-IU-2017-524). c Rhachotropis afekan sp. nov. holotype, brooding female (MNHN- IU-2015-708). d Rhachotropis kergueleni type serie, brooding female (NHM1889515:97). Scale bars: 1 mm

anterior margin of pereonite 1. Basis weakly arched, anterior margins with 4 stout setae, distal part with 8 long setae and 2 long setae at postero-distal corner. Ischium with 2 long setae and merus with 10 long setae at postero-distal corner. Carpus strongly produced, carpal process with 3 distal stout setae. Propodus large and oval, 1.9× as long as broad with 3 anterodistal long setae. Palmar margin with 2 rows of setae, one plumose, other long ones ending by one stout seta. Proximal part of the propodus with 4 stout setae (one broken) where the tip of dactylus is folded. Subdistal palmar margin with 2 long simple setae. The dactylus is narrow and curved with one long seta on proximal part. Gnathopod 2: Coxa subquadrate, posterior margin slightly concave. Basis with 6 (one broken) anterodistal long setae and fringed of short setae on anterior and distal margins. Merus with 8 long setae at postero-distal corner. Carpus strongly produced, carpal process long over-reaching the proximal part of palmar margin, bearing 1 distal stout seta and 1 subdistal rows of stout setae. The propodus exhibits the same shape and proportion as Gn1. Palmar margin with 2 rows of setae, one plumose, other long ones ending by one stout seta. Subdistal palmar margin with 3 long simple setae. Proximal part of the propodus with 2 stout setae where the tip of dactylus is folded. Dactylus is narrow and curved with one long seta on proximal part.

Pereopods (Fig. 15). Pereopod 3: narrow and elongate, shorter than pereopods 5 ‒ 7. Coxa subquadrate, posterior margin slightly concave. Basis recto-linear. Dactylus long and slightly curved, 1.2× propodus length. Pereopod 4: Similar to P3. Coxa subquadrate, slightly produced anteriorly, hind margin slightly excavated. Basis rectolinear with 4 short stout setae on proximal part of anterior margin. Dactylus long and slightly curved, 0.89× propodus length. Pereopod 5: Longer than P3 ‒ 4. Coxa distally bilobed. Basis slightly expanded posteriorly, with pointed median process on posterior margin. Cuspidate setae along posterior margin of merus and anterior margin of propodus. Propodus long, 3× basis length. Dactylus long and curved, 0.5× propodus length. Pereopod 6: Longer than P5. Coxa bilobed, posterior lobe bigger than anterior one. Basis slightly expanded posteriorly, with bluntly median process on posterior margin. Cuspidate setae along posterior margin of merus as well as on anterior margin of propodus. Dactylus long and slightly curved, 0.6× propodus length. Pereopod 7: Longer than P3 ‒ P6. Coxa unilobate, distally convex, with acute process at postero-distal corner. Basis expanded posteriorly, with acute median process on posterior margin (holotype) or larger process ( Fig. 24 View Fig ; see “Discussion”). Merus with cuspidate setae on anterior and posterior margins, ending in a spiniform process at postero-distal tip. Carpus and propodus with cuspidate setae on anterior and posterior margins. Dactylus long and linear, 0.4× propodus length.

Uropods ( Fig. 16 View Fig ). Uropod 1: Peduncle longer than unequal rami, fringed with a few stout setae along inner margin. Outer ramus 0.92× inner ramus length, smooth. Inner ramus fringed with a few cuspidate setae along inner margin. Uropod 2: peduncle shorter than unequal rami, with 3 cuspidate setae on distomedial margin, and one at distomedial corner. Outer ramus 0.90× inner ramus length, with a row of cuspidate setae on outer margin. Inner ramus fringed with a few cuspidate setae along inner margin. Uropod 3: peduncle shorter than lanceolate rami, with cuspidate setae along inner margin. Outer ramus 0.92× inner ramus length, with one cuspidate seta on outer margin. Inner margin smooth.

Telson ( Fig. 16 View Fig ): Elongated (length/width ratio: 3.33), slightly tapering towards apex, cleft 8.6% of its length, with dehiscent acute lobes.

Molecular identification. COI sequences were obtained for the following specimens (inventory numbers (GenBank accession numbers), see Supplementary Table 1): MNHN-IU-2017-523 (PP495384), MNHN-IU-2017-524 (PP495383), MNHN-IU-2017-525 (PP495382), MNHN- IU-2017 -526 (PP 495381), MNHN-IU-2017- 527 (PP495380). Following the definition given by Pleijel et al. (2008), the holotype (MNHN-IU-2017-524) is designed as the hologenophore.

Biological considerations. Male unknown, all nine specimens were brooding females with empty marsupium at the exception of the specimen MNHN-IU-2017-525, which was keeping 2 individuals in the brood pouch. Intra-marsupial pre-juveniles: BL = 3.8 mm. Eyes no bulging. Dorsal spiniform processes of pleonites 1–3 not yet developed, but a medial dorsal tooth visible on posterior margin. Gnathopods and pereopods fully segmented. Spiniform process on posterior margin of P5–7 basis already visible. Telson cleft and dehiscent.

Distribution. Southwestern Pacific, Solomon, and Vanuatu islands, depth range 837 ‒ 1210 m.

Remarks. R. riina sp. nov. belongs to the Rhachotropis group with long dorsal spiniform processes on pleonites 1 ‒ 3 (see remarks on R. sido sp. nov.), with a combination of morphological affinities shared either with R. sido sp. nov. and/or R. oweni : the presence of eyes, bulging laterally, median process at postero-distal corner of basis P5 ‒ 7, the presence of two subapical plumose setae on inner margin of inner plate of Mx2 (only in R. sido sp. nov.), pleonite 2 bearing mediodorsal pointed process and long dorsolateral pointed processes (only in R. oweni ). R. riina sp. nov. differs from both species by the strong curvature of its rostrum, A1 with two dorsal teeth on distal peduncle article 1, smooth pereonites 1 ‒ 7, by the absence of dorsal prominent protuberances near posterior margin of the head and epimeral plate 3 with 2 median teeth on posterior margin, the upper one smaller. The genetic divergences (uncorrected p-distance) between R. riina sp. nov. and R. oweni (NIWA-82905, see Fig. 23) ranged from 15.8 to 16% and from 17 to 17.2% with R. cf. palporum (MG521132, see Fig. 23).

Ecological data. R. riina sp. nov. was collected at seven stations by trawling on muddy bottoms. Available information after on-board pictures (SALOMON2 cruise only) 2 and log book notes also noticed the occurrence of abundant sunken wood and “long-stick” forams in the samples from the Salomon Islands, whereas some pumice stones were collected in the Vanuatu area. Megabenthic communities were represented by octocorals ( Chrysogorgiidae , Acanella , and Parantiphates), Flabellum - type scleractinian, hexactinellid sponges, turrid gastropods, scaphopods, and decapods (galatheids, chirostylids, polychelids, and crangonids, oplophorids, and pandalids).