Nebalia abyssicola Fage 1929

Nebalia abyssicola Fage, 1929

Figs 1, 6–9

Nebalia bipes abyssicola Fage, 1929: 41, pl. III, figs 88–89.

Nebalia abyssicola – Ledoyer 1997: 29, fig. 1. — Moreira et al. 2012: 352, figs 1–5.

Material examined

MOROCCO • 1 preovigerous ♀, 6 ♂♂, 1 juvenile; 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; DBUA0001676.01.W • 4 preovigerous ♀♀, 5 ♂♂, 3 juveniles; same locality and coordinates as for preceding; 3 Mar. 2008; St 64PE284_12752A, experimentally deployed alfalfa substrate; DBUA0001676.02.A • 1 ♂, 3 juveniles; Gulf of Cadiz, Meknès MV; 34°59.091′ N, 07°04.424′ W; 698 m depth; 20 May 2009; St B09-14b_03A, experimentally deployed alfalfa substrate; DBUA0002350.02.A • 3 ovigerous ♀♀, 1 ♂, 1 juvenile; Gulf of Cadiz, Darwin MV; 35°23.523′ N, 07°11.513′ W; 1100 m depth; 19 May 2009; St B09-14b_02A, experimentally deployed alfalfa substrate; DBUA0002350.01.A • 2 ♀♀, 2 ♂♂, 25 juveniles; same locality and coordinates as for preceding; 1109 m depth; 21 May 2007; St JC10_032-SUS01, suction sample from Bathymodiolinae bed; DBUA0002392.01 • 2 ♀♀, 8 ♂♂, 11 juveniles; same locality and coordinates as for preceding; 1110 m depth; 22 May 2007; St JC10_032- SUS02, suction sample from Bathymodiolinae bed; DBUA0002392.02 • 3 juveniles; same locality and coordinates as for preceding; 1110 m depth; 1 Jun. 2007; St JC10_076-SUS01, suction sample from Bathymodiolinae bed; DBUA0002392.03.

Description of female

MEASUREMENTS. Ovigerous ♀♀: TL 6.0– 6.625 mm, RL 1.05–1.125 mm, DCL 2.375–2.5 mm, LCL 3.0– 3.125 mm, CH 2.125–2.25 mm; preovigerous ♀♀: TL 4.6–6.5 mm, RL 0.75–0.925 mm, DCL 1.75– 2.25 mm, LCL 2.125 –2.875 mm, CH 1.5–1.925 mm.

CARAPACE, ROSTRUM AND EYE. Carapace covering at least lateral sides of pleonites 1–4 (Fig. 6A); LCL about 1.4 times CH. Rostrum long, with parallel margins, length about 2.5 times width, 0.45 times DCL (Fig. 6 B–C). Eye about 0.4–0.5 times as long as rostrum; some ommatidia irregularly distributed on distal half or second third (Fig. 6C); inferior distal border slightly produced downwards.

ANTENNAE. Antennule peduncle fourth article with anterior row of 9–10 simple setae and one distal robust seta (one preovigerous female with two) (Fig. 6D); antennular scale length 2.15–2.5 times width; flagellum with up to 10–11 articles. Antenna peduncle third article lateral margin with 4–5 proximal plumose setae and three distal thin long spine-like setae (Fig. 6 E–F); flagellum with up to 12–14 articles (Fig. 6E).

MOUTHPARTS. Mandibular palp second article with two simple setae: one simple seta on distal third and one simple slightly longer seta on lateral margin at mid-length; third article 1.15 times as long as second (Fig. 7A). Maxilla I palp well-developed, about six times as long as protopod (Fig. 7B). Maxilla II endopod proximal article about 1.6 times as long as distal; exopod as long as endopod first article (Fig. 7C).

THORACOPODS. Endopod longer than exopod (Fig. 7 D–E); endopod distal article slightly enlarged, with several (> 10) long setae; endopod segmentation weak. Thoracopod 8 epipod smaller than in other thoracopods and lacking setae (Fig. 7F).

PLEONITES AND PLEOPODS. Pleonite IV epimeron posterolateral corner forming triangular proccess acutely pointed (Fig. 8C). Pleonites VI–VII posterodorsal border bearing distally rounded to slightly pointed denticles (Fig. 8 F–G). Pleopod I protopod with long seta near base of exopod, reaching first half of exopod ‘comb-row’; exopod about 0.7 times as long as protopod and endopod; lateral margin with ‘comb-row’ of about 25–30 bi-pectinate setae (Fig. 8A). Pleopods II–IV exopod with row of 4–6 smooth setae (‘spine pairs’) (Figs 6A, 8B). Pleopod IV protopod posterior border with 3(4?) serrations. Pleopod V distal article 4.0 times as long as wide, with five simple setae along distolateral and terminal margins, proximal-most the shortest (Fig. 8D). Pleopod VI 2.7 times as long as wide, with five simple setae along lateral and terminal margins, distal-most the longest (Fig. 8E). Pleopod V–VI pairs with acute triangular process between rami bases.

ANAL SOMITE, ANAL PLATES AND UROPODS. Anal somite 1.15–1.4 times as long as pleonite VII. Anal plates acutely tapering distally, lacking distinct ‘shoulder’ (Fig. 8H). Uropods 1.15–1.28 times as long as pleonite VII +anal somite (Fig. 6A); terminal seta two times as long as ramus.

Description of male

TL 3.5–6.25 mm, RL 0.675 –1.075 mm, DCL 1.375 –2.425 mm, LCL 1.875–3.25 mm, CH 1.375 – 1.875 mm. Carapace slightly longer than in females (Fig. 9A), LCL about 1.7 times CH. Ommatidia irregularly distributed along distal ¾ of eye (Fig. 9B). Antennular scale proportionally longer than in females (2.7–2.75 times as long as wide) (Fig. 9C); flagellum with up to 9–12 articles, thicker than in females. Antenna peduncle third article lateral margin with similar setation as in females; flagellum with many articles (> 40) but not surpassing TL (Fig. 9D). Pleonites VI–VII denticles more pointed distally than in females. Pleopod IV protopod posterior border with four serrations. Small males (<4.8 mm TL) with uropods about as long as pleonite VII +anal somite; proportions in larger males (1.14–1.23) similar to females.

Remarks

Nebalia abyssicola is mostly characterized by the shape of the eye and the number and distribution of ommatidia, as discussed by Fage (1929), Ledoyer (1997) and Moreira et al. (2012). Fage (1929) also highlights the differences in setal armature of the fourth article of antennule, that includes one distal robust seta and a larger number of medial simple setae (up to 10) in comparison to other species of

similar body length, such as N. herbstii Leach, 1814, N. strausi and N. mediterranea Koçak & Moreira, 2015, that bear 5–7 simple setae.

The specimens from the Gulf of Cadiz agree well with the full description of the species by Ledoyer (1997), including diagnostic characters such as eye features, antennular scale proportions, setae of the fourth article of antennule peduncle (one distal robust seta and row of 9–10 setae on anterior margin), proportions of the articles of the maxilla 2 endopod and exopod, and shape of pleonites 6–7 denticles. The second article of the mandibular palp is provided with two setae whereas Ledoyer (1997: fig. 1) only illustrates one; two setae are present as well in specimens from the Aegean Sea but the proximal seta is provided with short setules instead of being naked (Moreira et al. 2012: fig. 3A). Furthermore, one specimen had two robust setae on the fourth article of antennule peduncle instead of one as found in all other specimens and those reported elsewhere; such variation may occur, however, in other species as discussed above for N. strausi.

Ecology

This species has been reported at depths between 410 and 2368 m; specimens from the Aegean Sea have been found in mud-clay sediments (Moreira et al. 2012). Specimens from MVs were found at depths of 354 to 1100 m in experimentally deployed wood and alfalfa substrata and associated with Gigantidas mauritanicus aggregations in cracks between large carbonate slabs at Darwin MV (1100 m depth).

Distribution

There are few records of this species; its known distribution ranges from the western Mediterranean (Monaco: Fage 1929; Corsica and Provence, France: Ledoyer 1997) and the Ionian Sea (Froglia 2010) to the Aegean Sea (Moreira et al. 2012). Darwin, Meknès and Mercator MVs, Moroccan continental slope, Gulf of Cadiz (Fig. 1); this is the first record for the Atlantic Ocean.