Orchomenella rinamontiae sp. nov., 2024

Giulianini, Piero G, De Broyer, Claude, Hendrycks, Ed A, Greco, Samuele, D’Agostino, Elisa, Donato, Sandro, Giglio, Anita, Gerdol, Marco, Pallavicini, Alberto & Manfrin, Chiara, 2024, A new Antarctic species of Orchomenella G. O. Sars, 1890 (Amphipoda: Lysianassoidea: Tryphosidae): is phase-contrast micro-tomography a mature technique for digital holotypes?, Zoological Journal of the Linnean Society 201 (3), pp. 1-17 : 4-10

Orchomenella rinamontiae sp. nov.

( Figs 1–11 ; Supporting Information, Video S1)

Ŋe line drawings ( Figs 8 , 10 , 11 ) refer to the female holotype specimen, whereas the SR-PhC micro-CT and SEM images ( Figs 1–7 , 9 ) refer to the male paratypes. Ŋe figures are cited in the description of the holotype, because the structures are very similar.

Etymology

Named in recognition of Cesarina (Rina) Monti (born 16 August 1871 in Arcisate, died 25 January 1937 in Pavia), an Italian zoologist who, in 1907, became the first woman to hold a chair at the University of Sassari in the Kingdom of Italy.

Material examined

Holotype: SOUTHERN OCEAN, female (mature, 24.4 mm), figured, appendages on 16 slides; Mario Zucchelli Antarctic Station in Terra Nova Bay , Ross Sea, 74°39.924 S, 164°11.584 E; 11 November 2017; depth 3 m; Erica Carlig/Simonepietro Canese (CNR, Genova/Stazione Zoologica Anton Dohrn, Napoli); RBINS INV. 159071.

Allotype: SOUTHERN OCEAN, one male (19.3 mm, appendages on two slides); same collection data as for holotype; RBINS INV. 159072.

Paratypes: SOUTHERN OCEAN: two females (16.0–18.6 mm), one male (19.6 mm); same collection data as for holotype; CMNC 2024-0521.

Ŋree females (13.6–23.4 mm); same collection data as for holotype; RBINS INV. 159073. One female (20.4 mm), one male (17.0 mm); same collection data as for holotype; TNHM C-1214 and C-1215.

Diagnosis

Lateral cephalic lobe: Subovate, very broad. Epimeron 3: Subrectangular, with posterodistal angle quadrate. Urosomite 1: With a weak, broadly rounded low carina. Antenna 1: Peduncular article 1 without anterodistal lobe, subcylindrical, length about twice the width. Peduncular articles 2 and 3 not telescoped. Epistome: Convex, not protruding in front of upper lip. Mandible: Molar subcolumnar, with large, suboval, triturative surface. Maxilliped: Outer plate reaching about half palp article 2, with two strong apical spines. Gnathopod 1: Coxa 1 subrectangular, subequal to coxa 2. Carpus short, with narrow posterior lobe not guarding propodus. Propodus subrectangular, length 1.6 × width, subchelate. Gnathopod 2: Propodus subchelate, suboval. Pereopod 5: Coxa 5 with well-developed posterior lobe. Pereopod 7: Basis subrectangular, with evenly convex hind margin. Uropod 3: Rami with numerous plumose setae on inner margins. Inner ramus reaching 70% of the length of outer ramus, far from reaching base of article 2. Outer ramus second article very short (0.14 × length of the first article). Telson: Short, length 1.1 × width, lobes broadly rounded with wide cless, cless 0.5 × length.

Description: holotype

Mature ♀, 24.4 mm, RBINS INV. 159071.

Body integument ( Fig. 1 ): Body segments, coxae, and basis of pereopods 5–7 covered in prominent pits.

Pereonites 1–7 and pleonites 1 and 2 ( Fig. 1 ): Without dorsodistal hump.

Pleonite 3 ( Fig. 1 ): Pleon smooth, without projections.

Coxa 1 and 2 ( Fig. 1 ): Distinctly longer (1.4×) than the depth of corresponding pereonites (in lateral view).

Coxa 3 and 4 ( Fig. 1 ): Distinctly longer (1.5×) than the depth of corresponding pereonites.

Epimeron 3 (Fig. 1): Subrectangular, with posterodistal angle quadrate; posterior margin very weakly convex.

Urosomite 1 ( Fig. 1 ): With a weak, broadly rounded, low carina.

Head ( Fig. 1 ): Dorsal length subequal to pereonite 1.

Lateral cephalic lobe ( Fig. 1 ): Subovate, very broad.

Eye: Ommatidian, subovate, black in fixed specimens; large, ~60% of the head depth.

Antenna 1 ( Figs 1–3 ): Peduncular article 1 without anterodistal lobe, subcylindrical, with ventral margin concave, length about twice width. Peduncular articles 2 and 3 weakly telescoped, measuring 25%and 21%, respectively, of article 1 length.Flagellum 24-articulate, lacking calceoli (in female); first article of flagellum callynophorate, very short, about as long as the following 2.5 articles, with double row of medial aesthetascs. Accessory flagellum 6-articulate, article 1 ~80% of the length of remaining articles.

Antenna 2: Slightly longer (~1.3×) than antenna 1. Gland cone rounded. Peduncular article 5 slightly shorter than peduncular article 4, both articles lined with anteromedial brush setae. Flagellum 29-articulate, lacking calceoli.

Epistome: Level with upper lip, convex, weakly concave upward.

Upper lip: With a midventral asymmetrical, angular projection.

Mandible ( Fig 5 ): Incisor nearly straight, weakly widened. Less lacinia mobilis strongly curved, with one (visible) apical tooth. Accessory spine row with three strong spines, followed proximally by fine setae on the medial side of the molar. Molar subcolumnar, with relatively large suboval triturative surface. Hairy process aưached proximal to molar. Palp article 2, 1.60 × length of article 3, with 14 A2 setae. Palp article 3 with 23 D3 setae and 3 E3 setae.

Lower lip: Without inner lobes.

Maxilla 1 ( Figs 4 , 6 ): Inner plate apically rounded, with two apical plumose setae. Outer plate with 11 spine-teeth in 7/4 arrangement. Palp article 2 not weakly expanded, with six contiguous long apical spines.

Maxilla 2 ( Figs 4 , 6 ): Inner plate slightly shorter (85%) than the distinctly wider outer plate. Ŋe distal end of the inner plate slightly surpassing the proximal end of the setal row of the outer plate.

Maxilliped ( Figs 4 , 7 , 8 ): Inner plate reaching about distal margin of palp article 1; distal margin with three nearly contiguous apical embedded spines, without mediodistal extension. Outer plate reaching about half length of palp article 2, with two strong apical spines; medial margin weakly scalloped with 15 embedded, conical spines. Palp dactyl with more than eight mediodistal setae.

Gnathopod 1 ( Fig. 9 ): Coxa 1 very weakly widened distally, nearly subrectangular, subequal to coxa 2; anterior margin very weakly concave; posterior margin almost straight. Basis slightly narrower (0.80×) than propodus, with ~20 long, thin setae on anterior margin. Ischium slightly longer (1.26×) than merus. Carpus short, ~25% of the propodus length, with narrow posterior lobe not guarding propodus. Propodus subchelate, subrectangular, not narrowing distally, length ~1.6 × width, hind and anterior margins very weakly convex; palm oblique, microserrate. Dactylus fiưing the palmar corner, marked by two outer and one inner spine.

Gnathopod 2 ( Figs 9 , 10 ): Carpus distally dilated (largest width ~1.35 × propodus width). Propodus subchelate, suboval, anterodistal margin broadly expanded and slightly protruding, length ~1.7 × width, posterior margin straight; palm convex, setose, corner defined by two small protuberances; dactyl slightly overhangs palm and is inserted in about the middle of the distal margin.

Pereopod 3: Coxa subrectangular. Dactyls short, broad, strongly curved.

Pereopod 4 ( Fig. 1 ): Coxa length ~1.5 × largest width; posterior margin strongly excavate, with strong, subtriangular posterodistal lobe, angle with a small rounded pointed lobe, posterior corner located at distal 72% of the length.

Pereopod 5 ( Fig. 1 ): Coxa 5 strongly posterolobate, with posterodistal margin regularly convex. Basis shorter (~0.85×) than coxa; posterior margin regularly convex and minutely serrated, with posterodistal lobe regularly convex.

Pereopod 6 ( Fig. 1 ): Basis with posterior margin regularly convex and minutely serrated; anterior margin nearly straight; posterodistal lobe regularly convex and not reaching distal margin of ischium.

Pereopod 7 ( Fig. 1 ): Basis with posterior margin regularly convex and minutely serrated; anterior margin nearly straight; posterodistal lobe regularly convex and reaching about the distal margin of ischium.

Uropod 1 ( Fig. 11 ): Peduncle ~2.16 × length of outer ramus, with 12 dorsolateral and 15 dorsomedial slender spines. Rami subequal, poorly spinose, with two or three slender spines.

Uropod 2 (Fig. 11): Peduncle ~2.20 × the length of outer ramus, with six or seven dorsolateral and six or seven dorsomedial slender spines. Rami subequal, with few (two to six) short, thin spines on lateral margins.

Uropod 3 ( Fig.11 ): Peduncle very slightly shorter (0.97×)than outer ramus. Rami with numerous plumose setae (8–10) on inner margins. Inner ramus reaching 70% of the length of outer ramus. Outer ramus second article very short, 15% of the length of first article.

Telson ( Fig. 11 ): 1.14 × longer than wide, cless wide, 50% of telson length, lobes weakly tapering distally, with ~10 surface, submarginal, and lateral fine setae, one distal spine, and one or two distal setae.

Gills 5 and 6: With one long, tubular accessory lobe, inserted basally.

Gill 7: Present, ovate, well developed.

Stomodeum: Extending to the fissh pereonite.

Description: male

Based on four males: 19.3, 17.8, 16.6, and 11.3 mm (SR-PhC micro-CT).

Very similar to female (in particular, with regard to size of eyes, size of antennae, and shape and spination of uropods and telson), but differing as follows.

Antenna 1 ( Figs 1–3 ): Callynophore slightly longer and stronger than in female, as long as the three following articles. Calceolus on each flagellar article.

Antenna 2 ( Fig. 1 ): Of similar size to female. Calceolus on each flagellar article.

Distribution/depth

Southern Ocean: Terra Nova Bay, Ross Sea, Antarctica, depth 3 m.

Phylogenetic analysis

In the unrooted tree for all available Lysianassoidea species clustered by genera, Orchomenella rinamontiae is placed within the same clade as the genera Orchomenella , Orchomenyx , Abyssorchomene , and Pseudorchomene , being supported by multiple sequences ( Fig. 12 ).

Taking a closer look at the Orchomene s.l. tree ( Fig. 13 ), we were able to resolve the phylogenetic position of Orchomenella rinamontiae beưer.All the COI sequences, including the sequence of the SR-PhC micro-CT male, clustered together (bootstrap 100%). Ŋe clade including Orchomenella rinamontiae is well supported within the tree (bootstrap 99%), and the new species is highly supported as a sister group of all the other sequences, with a bootstrap of 92%. Ŋe laưer clade include, in addition to Orchomenella rinamontiae , the following species: Abyssorchomene charcoti (Chevreux, 1912) , Abyssorchomene cheoreuxi (Stebbing, 1906) , Abyssorchomene distinctus (Birstein % Vinogradov, 1960), Abyssorchomene gerulicorbis (Shulenberger % Barnard, 1976), Abyssorchomene nodimanus (Walker, 1903) , Abyssorchomene scotianensis (Andres, 1983), Cheirimedon femoratus (Pfeffer, 1888), Falklandia reducta (Schellenberg, 1931), Orchomenella acanthura (Schellenberg, 1931), Orchomenella caoimanus (Stebbing, 1888) , Orchomenella ssanklini Walker, 1903 , Orchomenella pinguides Walker, 1903 , Orchomenella rotundissons Barnard, 1932 , Orchomenyx macronyx (Chevreux, 1905) , Orchomenyx schellenbergi (Ŋurston, 1972) , Orchomenyx tabarini (Ŋurston, 1972) , Pseudorchomene coatsi (Chilton, 1912) , Pseudorchomene debroyeri (d’Udekem d’Acoz and Havermans, 2012), Pseudorchomene plebs (Hurley, 1985), and Pseudorchomene rossi (Walker, 1903).

Figures

Figure 1. Synchrotron radiation X-ray phase-contrast micro-tomography of Orchomenella rinamontiae. Paratype, ♂, 11.3 mm. Volume renderings of lateral less view (A) and ventral view (B). Abbreviations:A1, antenna 1; A2, antenna 2; Gn1, gnathopod 1; Gn2, gnathopod 2. Scale bar: 4.0 mm.

Figure 2. Scanning electron microscopy of antenna 1 of Orchomenella rinamontiae. Paratype, ♂, 11.3 mm. Scale bar: 200 µm.

Figure 3. Scanning electron microscopy of antenna 1 of Orchomenella rinamontiae. Paratype, ♂, 11.3 mm. Calceoli (white arrows) are present on each flagellar article. A–C, neighbouring calceoli are orientated the same on the proximal part of the flagellum (A, B) and rotated by ~90° on the distal part (C). D, a higher magnification of a lateral view of a calceolus.Abbreviation:a, callynophore.Scale bars: 100 µm in A; 20 µm in B, C; 10 µm in D.

Figure 4. Synchrotron radiation X-ray phase-contrast micro-tomography of Orchomenella rinamontiae. Paratype, ♂, 11.3 mm. Volume renderings of the mouth in ventral view (A), higher magnification of the right mouthparts in ventral view (B), right mouthparts in median view (C), and mouth in dorsal view with the observation point inside the animal (D). Abbreviations: a, outer plate maxilliped; b, inner plate maxilliped; c, outer plate maxilla 2; d, inner plate maxilla 2; e, palp maxilla 1; f, outer plate maxilla 1; g, inner plate maxilla 1. Scale bars: 200 µm.

Figure 5. Scanning electron microscopy of mandibles of Orchomenella rinamontiae. Paratypes, ♂♂, 15.4 and 16.8 mm. A, B, less palp median view (A) and lateral view (B). C, D, less mandible in median view (C) and dorsal view (D). Abbreviations: i, incisor; l, lacinia m, molar process. Scale bars:200 µm in A, B; 50 µm in C; 40 µm in D.

Figure 6. Scanning electron microscopy of maxillae of Orchomenella rinamontiae. Paratypes, ♂♂, 15.4 and 16.8 mm.A, right maxilla 2 in median view. B, right maxilla 1 in median view.C, less maxilla 1 in median view. D, right maxilla 1 inner plate in median view. E, F, outer plates of right maxilla 1 (E) and less maxilla 1 (F) in median view.G, tip of maxillular palp. Scale bars: 100 µm in A–C; 40 µm in D–G.

Figure 7. Scanning electron microscopy of maxillipeds of Orchomenella rinamontiae. Paratypes, ♂♂, 15.4 and 16.8 mm.A, anterior/dorsal view. B, less dorsal view.C, dorsal view of outer and inner plates. D, higher magnification of the tip of the right outer plate.E, dorsal view of right palp.Scale bars: 200 µm in A–C; 20 µm in D; 100 µm in E.

Figure 8. Orchomenella rinamontiae. Holotype, ♀, 24.4 mm. Right maxilliped (Mxpd) and less inner plate (L inner pl). Scale bars: 0.1 mm for L inner pl; 0.5 mm for Mxpd.

Figure 9. Synchrotron radiation X-ray phase-contrast micro-tomography (A, B) and scanning electron microscopy (C–F) of gnathopods of Orchomenella rinamontiae. Paratypes, ♂♂, 11.3 mm (A, B) and 11.3 and 15.4 mm (C–F). A, lateral view of right gnathopod 2. B, medial view of right gnathopod 2. C, lateral view of less gnathopod 1. D, medial view of right gnathopod 1. E, lateral view of less gnathopod 2. F, medial view of right gnathopod 2. Abbreviations: a, gnathopod 1 lateral spine; b, gnathopod 1 medial spine; c, gnathopod 2 tip of dactyl. Scale bars: 200 µm.

Figure 10. Orchomenella rinamontiae. Holotype, ♀, 24.4 mm. Medial view of less gnathopod 2 (Gn2). Scale bars: 1 mm.

Figure 11. Orchomenella rinamontiae. Holotype, ♀, 24.4 mm. Less uropods (U1, U2, and U3) and telson (T) in dorsal view. Scale bars: 0.5 mm.

Figure 12. Unrooted non-redundant maximum likelihood tree of the Lysianassoidea COI. Leaves represent individual specimens, coloured by genus where this information was available in the NCBI database. Our samples of Orchomenella rinamontiae, from both RNA sequencing and DNA sequencing, are coloured in red. Ŋe area of the tree illustrated in Figure 13 is enclosed by a grey doưed line. A complete list of sequences in each genus group can be found in the Supporting Information (Table S1).

Figure 13. Rooted maximum likelihood tree of the Orchomene s.l. complex COI. Bootstrap support is shown for each branch. Hirondellea gigas was used as the outgroup. Ŋe position of Orchomenella rinamontiae is shown in yellow.