Sarsinebalia ledoyeri, Moreira, Juan, Esquete, Patricia & Cunha, Marina R., 2021

Moreira, Juan, Esquete, Patricia & Cunha, Marina R., 2021, Leptostracans (Crustacea: Phyllocarida) from mud volcanoes at the Gulf of Cadiz (NE Atlantic) with description of a new species of Sarsinebalia Dahl, 1985, European Journal of Taxonomy 736, pp. 102-136 : 117-128

Sarsinebalia ledoyeri sp. nov.

urn:lsid:zoobank.org:act:6203DB5B-D428-494D-AE12-96671063F37A

Figs 1 , 10–16 , Table 2

Diagnosis

Rostrum length 2.4–2.5 times width. Compound eye provided with 10–20 spaced ommatidia along distal half; pigment not observed; eye distal half with concave ventral margin; distal third gradually compressed laterally. Antennular scale length about 2.2 times width. Antennule peduncle fourth article with one distal robust seta. Antenna peduncle third article with 2–3 slightly plumose setae and three similar spine-like setae on lateral margin. Mandibular palp second article with two setae: 1) proximal seta on lateral surface, setulose along distal half inferior margin, about 0.5 times as long as article; 2) subdistal simple seta, longer than third article. Maxilla II endopod weakly segmented, distal article 1.8 times as long as proximal article; exopod 1.4 times as long as endopod proximal article. Pleonite IV epimeron posterolateral corner as triangular acute process. Pleonite IV posterolateral border with denticles distally acute; pleonites V–VII posterodorsal border with denticles distally rounded to pointed, never acutely produced. Pleopod I exopod lateral margin lacking setae. Pleopod IV protopod posterior border with three serrations; posterolateral corner acutely pointed. Uropods 0.7–0.85 times as long as pleonite VII+ anal somite.

Etymology

The new species is named after the French carcinologist Michel Ledoyer because of his many contributions to leptostracan taxonomy.

Type material

Holotype MOROCCO • postovigerous ♀, TL 4.0 mm, RL 0.675 mm, DCL 1.65 mm, LCL 2.15 mm, CH 1.4 mm; Gulf of Cadiz , Gemini MV; 35°16.88′ N, 06°45.35′ W; 418 m depth; 6 Oct. 2006; St 64PE253_06, MV crater, mud breccia; MNCN 20.04/13706 .

Allotype MOROCCO • ♂, TL 3.9 mm, RL 0.625 mm, DCL 1.6 mm, LCL 1.975 mm, CH 1.3 mm; same locality and station as for holotype; MNCN 20.04/13707 .

Paratypes MOROCCO • 4 postovigerous ♀♀; same locality and station as for holotype; MNCN 20.04/13708 to 20.04/13711 • 10 preovigerous ♀♀; same locality and station as for holotype; MNCN 20.04/13712 to 20.04/13721 • 6 ♂♂; same locality and station as for holotype; MNCN 20.04/13722 to 20.04/13727 • 3 juveniles; same locality and station as for holotype; MNCN 20.04/13728 to 20.04/13730 • 4 postovigerous ♀♀, 10 preovigerous ♀♀, 5 ♂♂, 3 juveniles; same locality and station as for holotype; DBUA0002351.01 .

Description of female

MEASUREMENTS. Postovigerous ♀♀: TL 3.625–4.0 mm, RL 0.575–0.70 mm, DCL 1.50–1.75 mm, LCL 1.90–2.375 mm, CH 1.325–1.50 mm; preovigerous ♀♀: TL 3.375–3.85 mm, RL 0.575 –0.625 mm, DCL 1.125–1.60 mm, LCL 1.625 –2.075 mm, CH 1.125–1.40 mm.

CARAPACE, ROSTRUM AND EYE. Carapace roughly oval, margins convex or rounded, covering laterally most of pleonites III–IV ( Fig. 10A ); LCL about 1.5–1.6 times CH. Rostrum long, extending well beyond eyestalk, length 2.4–2.5 times width, 0.4–0.45 times DCL ( Fig. 10A, D ); tapering gradually on distal half and turning downwards ( Fig. 10B ); paired ventral keels present; tip of rostrum provided with terminal spine, segmented proximally. Compound eye slightly longer than high, distal third becoming gradually compressed laterally ( Fig. 10C ); dorsal and distal margins almost straight, ventral margin straight proximally and concave on distal half ( Fig. 10B ); 10–20 spaced ommatidia, present mostly along distal half; pigmentation not observed in fixed specimens; supra-orbital plate with acute tip, reaching at least end of distal half of eye dorsal surface.

ANTENNULE. Peduncle composed of four articles ( Fig. 11A ). First article shorter than second, naked. Second article widest at midpoint, length almost 3.0 times width, with (1) one plumose seta on anterior margin at mid-length, (2) cluster of about 12 smooth and plumose setae arising from posterolateral distal third surface, (3) cluster of about 10 short and long simple setae and one plumose seta on anterodistal margin. Third article 0.5 times as long as second, wider distally, with terminal cluster of about 12 simple setae on anterodistal and posterodistal margins, one long simple seta on external surface and two shorter setae on inner surface. Fourth article shorter than third, with (1) anterior row of 5–6 simple setae, (2) one distal robust seta, (3) lateral row of 2–3 simple setae on external surface, distal-most the longest, (4) one simple seta on inner surface, (5) one simple seta arising from posterodistal margin, longer than article and antennular scale combined. Antennular scale roughly oval, length 2.2 times width; anterior margin slightly convex; anterior and terminal margins with (1) row of shorter setae recurved distally and provided with blunt teeth along distal half (asb in Fig. 11A ), (2) numerous simple setae of different lengths with thinner teeth, setae arising from posteroterminal margin the longest (ast in Fig. 11A ); row of three spaced simple setae on inner surface. Flagellum long, well-developed, shorter than peduncle, with 7 articles (6–7 in preovigerous females), proximal article as long as following three combined; each article with (1) cluster of 2–8 aesthetascs and (2) 2–4 simple setae on distal margin ( Fig. 11B ), distal article with 5–6 setae and lacking aesthethascs.

ANTENNA. Peduncle composed of three articles ( Fig. 11C ). First article anterior margin with process ending in small acute spine. Second article about as long as first, anterior margin with subdistal acutely pointed process. Third article about 2.0 times as long as second; plumose seta arising proximally from inner surface, associated to four simple short setae; medial and lateral anterior margins with several rows of setae ( Fig. 11D ): (1) five sparsely plumose setae, (2) two rows of simple thin spine-like setae, of 5–6 setae each (most arranged in pairs), (3) five simple, thin setae, (4) terminal row of eight simple setae, increasing in length distally, (5) 2–3 slightly plumose setae and three spine-like similar setae along lateral margin, distal-most seta associated to 5–7 simple setae; posterior margin with long, densely plumose seta ( Fig. 11F ); cluster of 8–9 plumose setae along distal margin inner surface; posterodistal margin with two short simple setae of different length. Flagellum well-developed, composed of 11 articles (12 in one postovigerous female) ( Fig. 11E ); each article with four terminal setae, one shorter than others ( Fig. 11G ).

MANDIBLE ( Fig. 12A ). Molar process well-developed, about as long as first palp article, with several rows of teeth on distal third and several distal simple setae; incisor process smaller, broadest basally, with row of acute teeth on medial margin and acute terminal process. Mandible palp composed of three articles; second article slightly longer than first, widest on proximal third; two setae: one at mid-length on lateral surface, setulose on inferior margin of distal half, about 0.5 times as long as article, and one subterminal simple seta, longer than third article. Third article 1.3 times as long as second, with almost parallel sides, slightly tapering distally; inferior margin with (1) a row of plumose setae extending from ending of proximal third to distal end, first four setae increasing gradually in length, (2) a row of six subdistal dentate setae, (3) two terminal setae, one as long as those of (1); superior margin proximal half with a row of minute setae.

MAXILLA I. First endite (proximal) with rounded medial margin bearing row of plumose setae ( Fig. 12B ). Second endite (distal) larger than first; inner margin with several distal simple setae; medial margin with several types of setae arranged in two rows: first row with (1) about 9 setae of increasing size with several teeth along distal half and one large tooth on distal superior margin (tcs in Fig. 12C ) and (2) two pappose setae (pas in Fig. 12C ); second row with (3) about ten spatulate setae (sps in Fig. 12C ) and (4) six setae with several teeth (2–4) along distal superior margin, thinner than those of type (1) (tns in Fig. 12C ); setae of types (1), (3) and (4) with one margin provided with long, spaced setules ( Fig. 12C ). Palp well-developed, about 4.0 times as long as protopod, with about 7–9 long setae along its entire length; setae provided with minute setules along distal third and with apex recurved distally ( Fig. 12B ).

MAXILLA II ( Fig. 12D ). Protopod with four endites; first (proximal) and third endite the largest, fourth endite much shorter; first to third endites bearing numerous plumose setae arranged in two rows; fourth endite with five longer plumose setae. Endopod weakly segmented, longer than exopod, distal article 1.8 times as long as proximal; medial margin of both articles with one row of spaced plumose setae, proximal with two additional longer setae with long setules along distal half; distal article with one plumose seta, longer than endopod. Exopod 1.4 times as long as endopod proximal article; lateral margin with plumose setae, two distal-most setae as long as exopod.

THORACOPODS. Endopod longer than exopod, segmentation weak; with numerous plumose setae along anterior margin arranged in two rows and one long sparsely plumose seta ( Fig. 13A ); distal article expanded, in postovigerous females lacking long setae, in preovigerous females with several setae shorter than exopod ( Fig. 13 B–C). Exopod posterior margin with 6–9 plumose setae, 1–2 distal-most the longest ( Fig. 13A ). Epipod posterior margin with two plumose setae. Thoracopod VIII shorter than

others, with epipod comparatively reduced and lacking setae ( Fig. 13D ); exopod posterior margin with about 5 plumose setae comparatively longer than those of other thoracopods.

PLEONITES. Pleonite I posterior border lacking denticles. Pleonites II–VII bearing denticles along posterior border, at least dorsally and laterodorsally ( Fig. 10A ). Pleonite II with denticles along dorsal border and extending to dorsolateral border ( Fig. 14A ); denticles thin, distally acute. Pleonite III with denticles along dorsal border extending well into lateral border, ending at mid-length ( Fig. 14B ); denticles distally pointed with more or less parallel sides (dorsal) to triangular (laterodorsal). Pleonites IV–VII with posterior border fully provided with denticles. Pleonite IV with dorsal and dorsolateral denticles pointed to rounded becoming distally acute and triangular in shape along lateral border ( Fig. 14C ); epimeron posterolateral corner forming large tooth with triangular distal end, acutely pointed. Pleonites V–VII dorsal and dorsolateral denticles similar in shape to those of pleonite III, distal end roughly pointed to rounded but never acutely produced ( Fig. 14 D–F); some denticles on ventrolateral border distally acute ( Fig. 14D ).

PLEOPODS 1–4. Pleopod 1 protopod with posterior margin even ( Fig. 15A ); with one short simple seta proximally on posterior margin and four distal simple setae: one seta on anterior margin arising subdistally and one seta between rami, posterior margin with long seta near exopod base and hardly reaching exopod distal half plus one shorter subdistal seta. Exopod about 0.6 times as long as protopod; lateral margin lacking ‘comb-row’; distolateral margin with one short simple seta and four stout simple setaes, distal-most the longest; long plumose setae (> 15) along medial margin. Endopod of two articles, 1.25 times as long as exopod; proximal article shorter, with appendix interna provided with three short recurved hooks; lateral and medial margins of distal article each with one row of> 10 plumose setae, distal margin with acute process at apex and long, robust terminal seta.

PLEOPODS II–III. Similar in appearance. Protopod inner surface with 1–2 simple setae on proximal third, and cluster of 2–6 long simple setae at mid-length, posterior margin with cluster of three long simple setae on distal third, and two simple setae near rami bases: one near appendix interna and one thicker seta close to exopod ( Fig. 15 B–C); acute triangular process between rami; posterior margin even. Exopod shorter than endopod; lateral margin with row of four smooth setae (‘spine pairs’), each pair consisting of two setae subequal or one slightly shorter (sometimes one lacking in proximal pair), with short setulose seta in between; medial margin with about 10 long plumose setae; distal margin with three simple setae, distal-most the longest. Endopod of two articles; proximal article short, provided with appendix interna; lateral and medial margins of distal article each with one row of>15 plumose setae; terminal margin with one long, robust distal seta.

PLEOPOD IV. Protopod posterior margin with three serrations ( Fig. 14C ); posterolateral corner acutely pointed. Rami similar to pleopods II–III.

PLEOPODS V–VI. Pleopod V–VI pairs with acute triangular process between rami bases. Pleopod V uniramous, length 4.3 times width, with three terminal stout simple setae, proximal-most much shorter ( Fig. 15D ); approximately 12–13 simple setae of different lengths along medial and terminal margins, appearing jointed at mid-length. Pleopod VI uniramous, length 3.0 times width ( Fig. 15E ); with three terminal simple setae, one longer than entire ramus; medial, distolateral and terminal margins with about eight ‘jointed’ setae of different lengths.

ANAL SOMITE, ANAL PLATES AND UROPODS. Anal somite 1.15–1.35 times as long as pleonite VII ( Fig. 10A ). Anal plates with broad bases and acutely tapering distally ( Fig. 14G ); medial margins convex defining a Y-shaped invagination between plates; lateral margins gently sloping, lacking ‘shoulder’. Uropods tapering distally, 0.7–0.85 times as long as pleonite VII+anal somite ( Fig. 10A ); lateral margin with 15–18 simple setae gradually increasing in length towards distal end; terminal margin with two longer robust setae, broken in all specimens but distal-most at least as long as uropods ( Fig. 15F ); medial margin with one row of simple setae similar to those on lateral margin but fewer and thinner plus one row of long plumose setae; distomedial margin with cluster of three short simple setae.

Description of male

TL 3.3–3.925 mm, RL 0.525 –0.675 mm, DCL 1.275 –1.675 mm, LCL 1.6–2.05 mm, CH 1–1.3 mm. Carapace proportions similar to females ( Fig. 16A ), LCL about 1.5–1.6 times CH. Ommatidia irregularly distributed along distal half or ¾ of eye ( Fig. 16B ). Antennular scale proportionally longer than in females (2.2–2.45 times as long as wide) ( Fig. 16C ); flagellum with up to 6–7 articles, thicker than in females. Antenna peduncle third article lateral margin with similar setation as in females; flagellum with many articles (> 30) but not surpassing TL ( Fig. 16D ). Pleopod IV protopod posterior margin with three serrations. Pleonites VI–VII denticles elongated, more pointed than in females.

Remarks

Known species of Sarsinebalia can be distinguished by whether or not eyes are provided with ommatidia / pigment and lateral margin of pleopod I exopod is provided with setae, as well as by the eye shape, features of maxilla II exopod and endopod and pleonites denticles ( Table 2 ). Sarsinebalia ledoyeri sp. nov. is characterised by the following combination of characters: the rostrum is about 2.4– 2.5 times as long as wide, the eye is provided with ommatidia (10–20) and lacks pigment, the eye is gradually compressed laterally along distal third and towards anterior margin, the eye ventral margin is concave along distal half, the antennular scale is about 2.2 times as long as wide, the second article of the mandibular palp bears one seta on lateral surface about 0.5 times as long as article and one subterminal seta longer than the third article, the distal article of the endopod of the maxilla II is about 1.8 times as long as the proximal article, the exopod of the maxilla II is clearly longer than the proximal article of the endopod, the posterodorsal border of pleonites VI–VII are provided with distally rounded to pointed denticles, the protopod of pleopod IV has three serrations along the posterior border and the posterolateral corner is acutely pointed, and the uropods are shorter than the pleonite VII and anal somite combined.

Sarsinebalia ledoyeri sp. nov. mainly differs from S. typhlops , S. biscayensis and S. pseudotyphlops in having eyes provided with ommatidia. Furthermore, S. typhlops also differs in that the two articles of the maxilla II endopod are subequal ( Sars 1896: fig. 14), the proximal seta of the mandibular palp second article is more than two thirds of the length of the article whereas in S. ledoyeri sp. nov. is only half the length of the article, and the pleopod V–VI have more stout distal/distolateral setae according to Sars (1896) (V: 5, VI: 5 vs 3/ 3); S. typhlops also seems a larger species, reaching 9 mm in length ( Sars 1896) whereas the largest mature specimens of S. ledoyeri sp. nov. only reach 4 mm. In turn, S. biscayensis has elongated eyes, the fourth article of the antennule peduncle lacks the distal robust seta bearing instead one long simple seta similar to those along the medial margin, the pleopod I exopod is provided with ‘spines’ along the lateral border (as it happens in S. kunyensis Ledoyer, 2000 and S. pseudotyphlops ) and the pleopod I protopod bears a row of simple, long setae along the proximal half of the posterior border instead of only one shorter seta (cf. Ledoyer 1998: fig. 2 vs Fig. 15A ); S. pseudotyphlops has a comparatively longer antennular scale, the proximal article of the maxilla II endopod is longer than the distal one, the pleopod IV protopod has an even posterior margin and the posterodorsal denticles of pleonites VI–VII are acute distally. On the other hand, S. kunyensis is also provided with ommatidia but differs from S. ledoyeri sp. nov. in having oval elongated eyes, the two articles of the maxilla II endopod are subequal, the proximal seta of the mandibular palp second article is comparatively longer and the denticles along the lateral border of the pleonite IV epimeron are distally rounded instead of being acute. Sarsinebalia ledoyeri sp. nov. differs from the shallow-water species, S. cristoboi and S. urgorrii , in lacking eye pigment and in the shape of the eyes, that has distal and ventral margins parallel in S. urgorrii and convex in S. cristoboi ; the aforementioned species also bear proportionally shorter denticles along posterodorsal borders of pleonites VI–VII that are always distally rounded, the distal long seta of the mandibular palp second article bears short setules along distal half instead of being naked, and the proximal article of the maxilla II endopod is longer than the distal one in S. cristoboi while the distal article is, in turn, only slightly longer in S. urgorrii . Finally, the description of S. typhlops occidentalis is brief but it shows that the rostrum is wider basally than that of S. ledoyeri sp. nov. and the furca is about as long as the pleonite VII and the anal somite combined instead of the former being clearly shorter; Hessler & Sanders (1965) also mention that the mandible is provided with “two large setae on second segment of palp” whereas in Sarsinebalia ledoyeri sp. nov. the length of the proximal seta is about one third of the distal one.

On the other hand, S. typhlops has been previously recorded in the Mediterranean at deep-sea depths ( Lo Bianco 1903). Ledoyer (1997) also reports S. typhlops from southern France in Posidonia beds at a shallow depth (11 m); the only examined specimen corresponded to one ovigerous female but this mostly differs from the description by Dahl (1985) in having eyes that are provided with many ommatidia (ca 40 each), the maxilla II has an endopod with the two articles clearly defined, the distal one being slightly longer than the proximal, and the maxilla II exopod is clearly longer than the proximal article of the endopod. In fact, this description fits better with that of S. urgorrii , that is mostly present in shallow waters as well; the shape of the eyes and the denticulation of pleonite IV epimeron, as illustrated by Ledoyer (1997) is also very similar to that of S. urgorrii (cf. Ledoyer 1997: fig. 5 and Moreira et al. 2003b: figs 8f and 14g). Therefore, previous records of S. typhlops in shallow waters and into the Mediterranean might correspond to other taxa and deserve further revision ( McCormack et al. 2016; Latry & Droual 2020).

Ecology

This species was collected from the crater of the Gemini MV and was the most abundant species in a box core sample. The sediments (mud breccia) yielded a highly diverse macrofaunal assemblage (ca 50 species) characterized by the presence of mega-epifauna (Pennatulacea, Hydrozoans, Crinoids), the chemosymbiotic species Siboglinum spIb (as in Hilário et al. 2010), and numerous species of peracarid crustaceans.

Distribution

Only known from the type locality, Gemini MV (418 m depth), in the Moroccan margin of the Gulf of Cadiz (this study; Fig. 1 ).

Figures

Fig. 1. Location of sampling sites in the mud volcanoes (Darwin, Gemini, Meknès, Mercator) at the Gulf of Cadiz within the Moroccan EEZ. Codes refer to samples obtained at each site.

Fig. 10. Sarsinebalia ledoyeri sp. nov. Postovigerous females. A. Holotype (MNCN 20.04/13706). B–D. Paratypes (MNCN 20.04/13708, MNCN 20.04/13709). A. Complete specimen, lateral view. B. Rostrum and eye, lateral view. C. Eye and supra-orbital plate, ventral view. D. Rostrum, dorsal view. A: dashed lines marking distribution of denticles on posterior borders of pleonites II and III.

Fig. 11. Sarsinebalia ledoyeri sp. nov. Postovigerous female, paratype (MNCN 20.04/13708). A. Antennule, lateral view. B. Antennule, flagellum, fifth article. C. Antenna, lateral view, outline. D. Antenna, peduncle, third article, lateral view. E. Antenna, flagellum. F. Antenna, peduncle, third article, distal margin plumose setae. G. Antenna, flagellum, fifth article. A, C: letters in brackets refer to parts detailed in other drawings with same letters; B: only one aesthethasc out of five figured.

Fig. 12. Sarsinebalia ledoyeri sp. nov. Postovigerous female, paratype (MNCN 20.04/13708). A. Mandible. B. Maxilla I. C. Maxilla I, endites, detail. D. Maxilla II.

Fig. 13. Sarsinebalia ledoyeri sp. nov. Female, paratypes (MNCN 20.04/13708). A. Thoracopod III, showing setation. B. Thoracopod V. C. Thoracopod VII. D. Thoracopod VIII. A, D: postovigerous female; B–C: preovigerous female, same scale bar; B–D: only selected setae illustrated.

Fig. 14. Sarsinebalia ledoyerisp. nov. Postovigerous female, paratype (MNCN20.04/13708). A. Pleonite II, dorsal and laterodorsal posterior border, denticles. B. Pleonite III, dorsal and lateral posterior border, denticles. C. Pleonite IV (posterior border, denticles and epimeron) and pleopod IV (protopod), lateral view. D. Pleonite V, dorsal and lateral posterior border, denticles. E. Pleonite VI, dorsal and laterodorsal border, denticles. F. Pleonite VII, dorsal and laterodorsal border, denticles. G. Anal plates. A–B, E–F: same scale bars.

Fig. 15.Sarsinebalia ledoyerisp. nov. Postovigerous female, paratype (MNCN20.04/13708). A. Pleopod I, lateral view. B. Pleopod II, lateral view. C. Pleopod III, protopod and endopod appendix interna, inner side. D. Pleopod V, ventral view. E. Pleopod VI, ventral view. F. Right uropod, ventral view. A–B, D–E: same scale bars; A–B: plumose setae not illustrated; C: exopod and endopod plumose setose: setules not illustrated.

Fig. 16. Sarsinebalia ledoyeri sp. nov. Male. A. Allotype (MNCN20.04/13707). B–D. Paratype (MNCN 20.04/13722). A. Rostrum, eye and carapace outline, lateral view. B. Rostrum and eye, lateral view. C. Antennule, lateral view. D. Antenna, lateral view. C–D: only selected setae illustrated.