Nebalia strausi Risso, 1826

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 : 106-111

Nebalia strausi Risso, 1826

Figs 1–5

Nebalia straus Risso, 1826: 84 , pl. V, fig. 20.

Nebalia straus – Koçak & Katagan 2006: 321, figs 1–3. — Koçak et al. 2007: 449, figs 1–3.

Nebalia strausi – Dahl 1985: 155, figs 63–79. — Ledoyer 1997: 34, fig. 4. — Moreira et al. 2004: 84, figs 1–7; 2009b: 101, lam. 1, figs 1–3.

Material examined

MOROCCO • 1 preovigerous ♀, 4 ♂♂, 3 juveniles; Gulf of Cadiz , Mercator MV; 35°17.916′ N, 06°38.709′ W; 354 m depth; 2 Mar. 2008; St 64PE284_12750W, experimentally deployed wood substrate; DBUA0001677.01.W • 3 preovigerous ♀♀, 8 ♂♂, 4 juveniles; same locality and coordinates as for preceding; 3 Mar. 2008; St 64PE284_12752A, experimentally deployed alfalfa substrate; DBUA0001677.02.A .

Description of female

MEASUREMENTS. Preovigerous females measuring TL 5.275–5.8 mm, RL 0.925 –1.025 mm, DCL 2.15– 2.25 mm, LCL 2.675–3.0 mm, CH 1.825–1.95 mm.

CARAPACE, ROSTRUM AND EYE. Carapace covering at least lateral sides of pleonites 1–4; LCL about 1.5 times CH. Rostrum long, with parallel margins, length about 2.3 times width, 0.45 times DCL ( Fig. 2A, C ). Eye about 0.65 times as long as rostrum; ommatidia numerous, distributed about 5/6 of eye ( Fig. 2B ); dark pigment in most ommatidia.

ANTENNAE. Antennule peduncle fourth article with anterior row of 5–6 simple setae and two distal robust setae, proximal one shorter ( Fig. 2D ), juveniles (<4 mm TL) with one robust seta; antennular scale length 2.25–2.4 times width; flagellum with up to 11–13 articles. Antenna peduncle third article lateral margin with three proximal plumose setae on proximal half and three distal spine-like setae ( Fig. 2 E–F); flagellum with up to 11–14 articles ( Fig. 2E ).

MOUTHPARTS. Mandibular palp second article with two subequal setae: one seta setulose along distal half on lateral margin at mid-length and one simple seta on distal third; third article slightly longer than second ( Fig. 3A ). Maxilla I palp well-developed, about 4.5 times as long as protopod ( Fig. 3B ). Maxilla II endopod proximal article about 1.5–1.6 times as long as distal article; exopod longer than endopod first article ( Fig. 3C ).

THORACOPODS. Endopod slightly longer than exopod ( Fig. 3 D–E); endopod distal article slightly enlarged, with several (ca 10) setae; endopod segmentation weak. Thoracopod VIII epipod smaller than in other thoracopods and lacking setae ( Fig. 3F ).

PLEONITES AND PLEOPODS. Pleonite IV epimeron posterolateral corner slightly pointed ( Fig. 4C ). Pleonites VI–VII posterodorsal border bearing denticles acutely pointed ( Fig. 4 G–H). Pleopod I exopod about 0.72 times as long as protopod and endopod; lateral border with ‘comb-row’ of ca 30 bi-pectinate setae (sensu Walker-Smith 2000) ( Fig. 4A ); protopod with long seta near base of exopod, hardly reaching middle of ‘comb-row’. Pleopods II–IV exopod with row of 5–7 pairs of smooth setae (‘spine pairs’) ( Fig. 4B ). Pleopod IV protopod posterior border with four serrations. Pleopod V distal article 3.4 times as long as wide, with five simple setae along distolateral and terminal margins, proximal-most the shortest ( Fig. 4D ). Pleopod VI 2.0 times as long as wide, with five simple setae along lateral and terminal margins, distal-most the longest ( Fig. 4E ). Pleopod V–VI pairs with acute triangular process between rami bases.

ANAL SOMITE, ANAL PLATES AND UROPODS. Anal somite 0.8–0.95 times as long as pleonite VII. Anal plates acutely tapering distally, ‘shoulder’ well-defined ( Fig. 4F, I ). Uropods 0.8–0.92 times as long as pleonite VII+ anal somite; terminal seta 1.7 times as long as ramus.

Description of male

TL 3.95–5.375 mm, RL 0.825–1.05 mm, DCL 1.575 –2.125 mm, LCL 2.2–3.0 mm, CH 1.625 –1.925 mm. Carapace proportions (LCL: CH) similar to females ( Fig. 5A ). Ommatidia and dark pigment covering 5/6 of eye ( Fig. 5B ). Antennule peduncle fourth article with 1–2 distal robust setae; antennular scale proportions similar to females (2.25–2.30 times as long as wide) ( Fig. 5D ); flagellum with up to 10–12 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. 5C ). Pleonites VI–VII denticles acutely pointed. Pleopod IV protopod posterior border with four serrations. Uropods length similar to females.

Remarks

Nebalia strausi is a well-known species that is characterized by having ommatidia and dark pigment extending through most of the eye; the antennular scale is more than twice as long as wide; the fourth article of antennule peduncle bears two distal robust setae of different length; the exopod of maxilla II surpasses the level of articulation of endopod articles, and the endopod proximal article is clearly longer than the distal one; the posterolateral corner of the pleonite IV epimeron is not acutely produced; the posterior margin of pleopod IV protopod bears four serrations; and the posterodorsal denticles of pleonites VI–VII are acutely pointed ( Dahl 1985; Ledoyer 1997; Moreira et al. 2004). Furthermore, the terminal simple seta of the pleopod I protopod barely reaches half-length of the ‘comb-row’ and the uropods are at least as long as pleonite VII and anal somite combined, and slightly longer in mature specimens ( Dahl 1985).

Specimens from Mercator MV mostly agree with the diagnosis of the species. The only minor difference is that the uropods are slightly shorter, but this may be due to the state of development, i.e., no specimen was fully mature. Note that the organic substrates where the specimens were found were enclosed by a 2 mm mesh size net, and it is likely that the specimens settled on the substrates as juveniles just released from the brood pouch. The anal plates have an even more prominent shoulder than in the Mediterranean specimens described by Dahl (1985); those reported by Ledoyer (1997) bear, in turn, a gently sloping ‘shoulder’, whereas there is almost no ‘shoulder’ at all in those described by Moreira et al. (2004) from the NW Iberian Peninsula. Most specimens bear two robust setae on the fourth article of antennule peduncle but small males and juveniles bear instead only one. Moreira et al. (2004) reported similar observations in immature females whereas ovigerous and postovigerous females always had two robust setae of different length. Number of setae is known to vary during ontogeny ( Dahl 1985) and therefore this character should be considered with care for identification unless fully-grown specimens are available; this also applies for the number of articles in the antennae flagella that are fewer on juveniles. On the other hand, some minor variations have also been reported for specimens from the eastern Mediterranean ( Koçak et al. 2010) and therefore the possibility of a complex of species across its wide distribution range has been suggested ( Koçak et al. 2011).

Ecology

Recorded from the intertidal to depths of 140 m, in rocky substrates and sandy and muddy soft bottoms, and among the seagrasses Zostera marina L., 1753, Z. noltii Hornem., 1832 , Cymodocea sp. and Posidonia oceanica (L.) Delile, 1813 ( Dahl 1985; Ledoyer 1997; Moreira et al. 2004, 2009a, 2009b; Koçak et al. 2007; Latry & Droual 2020). The present findings of the species from experimentally deployed wood and alfalfa substrates at the Mercator MV extend its known bathymetric range to depths of 354 m.

Distribution

SW European Atlantic from north western Ireland to NW Iberian Peninsula ( Dahl 1985; Moreira et al. 2004, 2009a, 2009b; McCormack et al. 2016; Latry & Droual 2020); Mediterranean Sea ( Dahl 1985; Ledoyer 1997; Koçak & Katagan 2006; Koçak et al. 2011; Latry & Droual 2020); Canary Islands ( Dahl 1985; Moreira et al. 2009b), Madeira and St Helena ( Dahl 1985); 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. 2. Nebalia strausi Risso, 1826. Preovigerous female (DBUA0001677.01.W). A. Rostrum, eye and carapace outline, lateral view. B. Eye and supra-orbital plate, lateral view. C. Rostrum, dorsal view. D. Antennule, lateral view. E. Antenna, lateral view. F. Antenna, peduncle third article, lateral view. D–E: only selected setae illustrated.

Fig. 3. Nebalia strausi Risso, 1826. Preovigerous female (DBUA0001677.01.W). A. Mandibular palp. B. Maxilla I. C. Maxilla II. D. Thoracopod II. E. Thoracopod V. F. Thoracopod VIII. D–F: same scale bar; C: setules and endites’ setae not illustrated; D–F: only selected setae illustrated.

Fig. 4. Nebalia strausi Risso, 1826. Preovigerous female (DBUA0001677.01.W). A. Pleopod I, lateral view. B. Pleopod II, lateral view. C. Pleonite IV, epimeron and pleopod IV protopod, lateral view. D. Pleopod V, ventral view. E. Pleopod VI, ventral view. F. Anal plates, ventral view. G. Pleonite VI, posterior dorsal and laterodorsal border, denticles. H. Pleonite VII, posterior dorsal and laterodorsal border, denticles. I. Right uropod and anal plate, ventral view. A–C, D–E, G–H: same scale bars; A–B, I: plumose setae not illustrated.

Fig. 5. Nebalia strausiRisso, 1826. Male (DBUA0001677.01.W). A. Rostrum, eye and carapace outline, lateral view. B. Eye and supra-orbital plate, lateral view. C. Antenna, lateral view. D. Antennule, lateral view. C–D: only selected setae illustrated.