Extant leptostracans (Crustacea: Phyllocarida: Leptostraca) have been extensively studied in the last years in the Iberian Peninsula, with nine species reported or described from the northern and western coasts: Nebalia bipes (Fabricius, 1780), N. herbstii Leach, 1814, N. strausi Risso, 1826, N. troncosoi Moreira, Cacabelos & Domínguez, 2003, N. kocatasi Moreira, Koçak & Katagan, 2007, N. reboredae Moreira & Urgorri, 2009 in Moreira et al., 2009, Sarsinebalia typhlops (G.O. Sars, 1870), S. cristoboi Moreira, Gestoso & Troncoso, 2003 and S. urgorrii Moreira, Gestoso & Troncoso, 2003 (Aguirrezabalaga et al., 1988; Moreira et al., 2003a, 2003b, 2004, 2009a, 2009b; Martínez et al., 2007; Moreira, 2015; Sampaio et al., 2016). Most of previous records corresponded to N. bipes but its presence in southern European latitudes and Iberian waters is doubtful (Dahl, 1985; Moreira, 2015). In comparison, records of leptostracans from the southern and the Mediterranean coasts are scarce and mostly correspond to N. strausi (e.g., Dahl, 1985); recently, Taboada et al. (2016) recorded N. kocatasi from Blanes and Moreira & Junoy (2017) also reported the genus Paranebalia Claus, 1880 for the Balearic Islands.

Examination of leptostracans collected in Ebro Delta offshore has revealed the presence of N. troncosoi that was originally described from Galicia, and later reported from the Bay of Biscay (Martínez et al., 2007), Portugal (Sampaio et al., 2016), Morocco (Bayed & Bazairi, 2017) and from both Atlantic and Mediterranean French coast (Latry & Droual, 2020). This record fills, therefore, the gap in the distribution of N. troncosoi in the eastern Iberian Peninsula.

The study area (40°38'53.8"–40°39'36.48" N / 0°51'59.1"–0°51'38.01" E) was located in the inner continental shelf at 4.71 miles offshore from the Ebro Delta river mouth, 2.04 miles offshore the coast and at depths between 11 and 14 m. Sampling was part of the DELTA campaigns, which aimed to monitor the community structure of macrofauna (among others) along a 3-year period and to relate it to their environment. Different types of samples were taken, e.g., macrofauna, benthic fish (Solea solea (Linnaeus, 1758), S. senegalensis Kaup, 1858 and Mullus spp.), and sediments. Macrofauna sampling was carried out using a Van Veen grab (KC DENMARK A/S) of 0.05 m² on soft bottoms. Grab samples were carefully sieved over a 0.5-mm mesh and stored in >90% ethanol. Samples were examined under a Leica EC3 stereomicroscope with camera, and digital images were captured by the LAS-EZ V2 software (Leica Microsystems). Drawings were done with the aid of a camera lucida connected to a compound microscope and measurements were made with an ocular micrometer. The following measurements were considered: total length (TL; distance from the articulation between the rostrum and carapace to the posterior end of the uropods not considering setation), rostrum length (RL; distance along the midline), dorsal carapace length (DCL; distance between the articulation of the rostrum and the margin of the posterodorsal cleft), lateral carapace length (LCL; distance along lateral surface between the anterior-most and posterior-most margins) and carapace height (CH; distance between the dorsal and ventral margin). The abbreviated description corresponds to two mature females (Dahl, 1985; Martin et al., 1996) and focuses in diagnostic characters. Specimens are deposited in the Museo Nacional de Ciencias Naturales (MNCN), Madrid.

Family Nebaliidae Samouelle, 1819

Genus Nebalia Leach, 1814

Nebalia troncosoi Moreira, Cacabelos & Domínguez, 2003

Figs. 1–4

Nebalia troncosoi Moreira et al., 2003a: 341–350, figs. 1–8; 2009b: 271, fig. 1D. — Latry & Droual, 2020: 95–97, figs. 1–3, tab. 1.

Material examined. Ebro Delta continental shelf. 1 ovigerous ♀ (dissected; TL 3.45 mm, RL 0.69 mm, DCL 1.37 mm, LCL 1.82 mm, CH 1.47 mm), MNCN 20.04/13701, DELTA 1, St. 2, 40°38'53.8"N – 0°51'59.1"E, 8 April 2014, 11.8 m depth, muddy sediment. – 1 ovigerous ♀ (TL 3.85 mm, RL 0.80 mm, DCL 1.40 mm, LCL 2.02 mm, CH 1.57 mm; MNCN 20.04/13702), 1 preovigerous ♀ (TL 2.92 mm, RL 0.67 mm, DCL 1 mm, LCL 1.60 mm, CH 1.17 mm; MNCN 20.04/13703), 1 immature ♂ (TL 3.22 mm, RL 0.67 mm, DCL 1.25 mm, LCL 1.80 mm, CH 1.27 mm; MNCN 20.04/13704), 1 juvenile (TL 1.56 mm; MNCN 20.04/13705), DELTA 1, St. 3, 40°39'36.4"N – 0°51'38.0"E, 8 April 2014, 11 m depth, muddy sediment.

Short description of females

Carapace, rostrum and eye: Carapace covering at least lateral sides of pleonites 1–3; LCL 1.24–1.28 times CH. Rostrum long, with parallel margins, length about 4.1 times width, 0.5–0.55 times length of DCL (Figs. 1A, 2A, C). Eye 0.4 times length of rostrum; ommatidia numerous, distributed along eye distal half (Figs. 1A, 2B), with conspicuous dark pigment, more concentrated in central part with ommatidia; two small protuberances on distal inferior margin (Fig. 2B).

Antennae: Antennule peduncle fourth article with medial row of 7 simple setae and one distal thick spine (Figs. 1A, B, 2D); antennular scale length 2.2 times width; flagellum shorter than peduncle, with seven articles. Antenna peduncle third article lateral margin with eight similar spine-like setae (Figs. 1A, 2F); flagellum slightly shorter than peduncle, with 8–9 articles (Figs. 1C, 2E).

Mouthparts: Mandible with well-developed molar and incisor processes; incisor with sharp teeth along inner border, ending in acute process (Fig. 3A); mandibular palp second article with two setae, distal-most the longest and about 0.5 times length of article; third article slightly longer than second. Maxilla I palp well-developed, about four times length of protopod (Fig. 3B). Maxilla II endopod proximal article about 1.45 times length of distal article; exopod clearly surpassing level of articulation of endopod articles (Fig. 3C); distal-most setae of endopod and exopod longer each than entire limb.

Thoracopods: Thoracopods I–VII with endopod longer than exopod (Fig. 4A, B); endopod distal article slightly enlarged, with several long plumose setae (Fig. 1C); endopod segmentation weak; exopod and epipod with several setae along posterior margin, less numerous on epipod (1–3). Thoracopod VIII epipod smaller than in other thoracopods and lacking setae (Fig. 4C).

Pleonites and pleopods: Pleonite IV epimeron posterolateral corner forming triangular process acutely pointed (Fig. 4E). Pleonites VI–VII posterodorsal border bearing denticles acutely pointed (Figs. 1D, 3D, E). Pleopod I exopod 0.75 times length of endopod; lateral border with ‘comb-row’ of ca. 12 bi-pectinate setae (sensu Walker-Smith, 2000) (Fig. 4D); protopod with long seta near posterior base of exopod, surpassing middle of ‘comb-row’. Pleopod IV protopod posterior border with four serrations, posterodistal corner acute (Fig. 4E).

Anal somite, anal plates and uropods: Anal somite about as long as pleonite VII (Fig. 1D). Anal plates acutely tapering distally, lateral and medial margins sloping, ‘shoulder’ not developed (Fig. 4F). Uropods 0.85 times length of pleonite VII + anal somite; terminal seta at least two times length of ramus.

Male

About 15 articles in antenna flagellum, showing incomplete divisions in proximal half; carapace slightly longer than in females: LCL 1.4 times CH; furca similar in length to pleonite VII + anal somite.

Distribution and ecology. SW European Atlantic, from Normandy (France) to Figueira da Foz (Portugal) (Latry & Droual, 2020), Morocco (Bayed & Bazairi, 2017); French Mediterranean coasts (Latry & Droual, 2020); Ebro Delta coast (present work). Mainly in fine sand to muddy sand with Zostera marina L.; also reported in maërl, gravel, coarse and medium sand; at depths of 4.5–54 m (Martínez et al., 2007; Moreira et al., 2009b; Latry & Droual, 2020). In this work, specimens were found within a typical macrofaunal community from marine muddy bottoms, numerically dominated by amphipods of the genus Ampelisca Kroyer, 1842.

Remarks. The features of the specimens collected mostly agree with the original description. This species is mainly characterized by having a longer rostrum than other European Nebalia species (up to four times as long as wide), the antennule peduncle fourth article is only provided with one distal spine instead of two or more, the carapace in females is much shorter in comparison to height, the antennule flagellum is shorter than the peduncle and composed by up to seven articles, the maxilla II exopod is longer than the endopod proximal article and the anal plates lack defined ‘shoulders’ along lateral margin. The denticles of the posterodorsal borders of pleonites VI–VII are conspicuously acute distally; this character is only shared in European latitudes with N. strausi, that is a much larger species, whereas other species bear rounded to truncated denticles. The present findings fill the gap in the known distribution of N. troncosoi in the Iberian Peninsula; it is likely that this species might be also present through the coasts of northern Africa (Bayed & Bazairi, 2017) and the European western Mediterranean. However, more data are needed to truly assess the diversity and distribution of leptostracans in the eastern and southern Iberian Peninsula.