Pseudoniphargus djemoi Dole-Olivier & Hafid & Piscart 2018, sp. nov.

Pseudoniphargus djemoi sp. nov.

(Figs 1–5)

Material examined. A set of 37 specimens (5♂, 15♀, 17 juveniles & unidentifiable specimens) was used for dissection (maximum size 6.5 mm, ♀ 1). The five largest and less damaged specimens were selected for descriptions, as follows. Syntypes: 2 ♂♂ (♂1: 6 mm (MNHN-IU-2017-327), ♂2: 5.5 mm (MNHN-IU-2017-328)), and 3 ♀♀♀ (♀1: 6.5 mm (MNHN-IU-2017-329); ♀2: 6 mm (MNHN-IU-2017-330); ♀ 3: 6 mm (MNHN-IU-2017- 331) with non-setose oostegites. Each specimen was completely dissected on a single slide and deposited in the collections of the Museum National d’Histoire Naturelle (MNHN) of Paris. Additional specimens (N= 60) from the same well were deposited in the collections of the University of Lyon, CEntre de REssources pour les Sciences de l’Evolution (CERESE, n° UCBLZ 2017.4.1; UCBLZ 2017.4.2; UCBLZ 2017.4.3; UCBLZ 2017.4.4; UCBLZ 2017.4.5).

Type locality and ecological conditions. The sampled wells were situated in the Tamlouka plain (36°4’6”N 7°01'46"E), northwest of Oum El Bouaghi, Algeria. This plain essentially consists of quaternary fluvial alluvial filling. The aquifer is oriented southwest-northeast with a thickness varying between 9–12 m (upstream) and 5–8 m (downstream). Eleven wells out of 16 prospected harbored the new species (Merzoug et al. 2010). When present in a well, the species was rather abundant (total abundance 736 specimens, varying from 13 to 305 individuals per well) compared to another co-occurring species belonging to the same genus (P. africanus), which was collected in two wells only (total abundance: 24 specimens). Amphipod diversity of the sampling area included also a new, not yet described genus observed in five wells (96 specimens; Merzoug et al. 2010). Physicochemical conditions were characterized by very high water mineralization (Electric Conductivity ranging from 1344 µS.cm -1 to 2211 µS.cm - 1), temperatures varying from 19°C to 21,7°C and oxygen content from 6,8mg.L -1 to 8,3 mg.L -1. Detailed analyses also demonstrated that most of the wells were polluted by organic contaminants (Merzoug et al. 2010).

Etymology. The specific name djemoi refers to Prof. Djemoi Merzoug (University Larbi Ben H'idi), who worked on the groundwater invertebrate fauna of the area and discovered the species. It can be treated as a noun in apposition.

Diagnosis. Antenna 1 short, with accessory flagellum shorter than first article of main flagellum. Antenna 2 flagellum 6- or 7-articulate, shorter than peduncle articles 4+5 combined. Male gnathopod 1 carpus about as long as corresponding propodus. Coxal plate 4 with posterior excavation. Basis of pereopods 6–7 without posterodistal lobe. Pereopod 7 propodus not elongated. Uropod 1 without basofacial spine(s). Uropod 3 elongate in both sexes, sexually-dimorphic. Male uropod 3 with peduncle slightly elongate, about 2.54 times as long as broad; exopod strongly elongate and upcurved, about 14.5 times as long as broad. Female uropod 3 peduncle subrectangular, 1.7 times as long as broad; exopod moderately elongate, about 11.1 times as long as broad. Telson short and wide with 2 (♂) and 3 (♀) spines at each distal corner, and with poorly marked and shallow mediodistal notch.

Description. Body aspect as in Fig.1; colorless, eyeless. Head lacking rostrum, with broadly rounded lateral plates, anteroventral margin weakly recessed. Pereopodal coxal plates 1–3 slightly longer than wide.

Antenna 1 (Fig. 3F, G): short, less than half body length with fairly slender peduncle; accessory flagellum 2- articulate, shorter than first article of main flagellum (at least half its length); main flagellum composed of 14–16 articles; most articles bearing one aesthetasc and 3–4 setae in apical position. Distal-most aesthetasc longer than terminal article of flagellum. A few flaccid sensorial tufted setae present on third peduncle article in both sexes (Fig. 3F 1, G 2) and on terminal article of male main flagellum (compare Fig. 3F 2 vs. Fig. 3G 1).

Antenna 2 (Fig. 2E): Less than half length of antenna 1. As in most Pseudoniphargus species, peduncle article 4 longest; peduncle articles 3–5 relative length as: 0.35: 1: 0.82. Flagellum 6- or 7-articulate, shorter than peduncle articles 4+5 combined.

Upper lip (Fig.4G): Distal margin rounded, bearing two symmetrical tufts of short and fine setules.

Left mandible (Fig. 4B): incisor 5-denticulate, lacinia mobilis 4-denticulate, spine row composed of 5 pappose setae; molar process well developed, with long molar seta.

Right mandible (Fig. 4C): incisor 4-denticulate, pars molaris bifid, each branch with row of numerous (~7 and 4 respectively) small rounded denticles; setal row composed of only 3 pappose setae; molar process as in left counterpart; molar seta lacking. Left and right palps similar, 3-articulated. Article 1 naked; article 2 longer, as long as article 3, bearing 4–5 simple setae; article 3 with 3 long E-setae, one of them with a row of small and delicate setules proximally; distal most inner margin of article with row of plumose D-setae; 1 simple A-seta and 1 B-seta on dorsal and lateral faces of article as figured (see Karaman 1969).

Lower lip (= Labium) (Fig. 4H): inner lobes smooth, weakly developed, fused proximally (only in ♂ 2), with the two lobes distinctly separated only in the distal part. Outer lobes well developed, with relatively long and narrow lateral processes.

Maxilla 1 (Fig. 4I): inner plate with 2 long apical plumose setae. Outer plate slightly curved and bearing 7 apical stout spines, most of them bifid, some simple (all bifid in ♂1); inner margin partially covered with few fine setules. Palp 2-articulated, with distal article slightly curved, bearing 6–8 (depending on specimens) terminal stout setae, and long setules (3–14, depending on specimens) on outer margin.

Maxilla 2 (not represented): inner plate with numerous (~12) long setae in disto-medial position, with additional fine setules on inner margin. Outer plate with ca. 10–15 long apical setae and 5 long curved plumose setae on outer subdistal margin; both groups of setae separated by a short spinule.

Maxilliped (Fig. 4A): inner plate ~ 4x longer than wide, distal margin with with 3 plumose and 1 long simple setae, and 2 lanceolate ciliated teeth (Fig. 4A 1); distal part of plate covered with fine setules and bearing 1 lateral seta on outer margin. Outer plate with lateral margin evenly rounded, naked; distomedial margin fringed with~10 knife-like teeth; teeth progressively larger towards distal. Slight variation in form of teeth observed between left and right outer plates, the left bearing more spatule-like teeth. Each teeth row continuing with 1–2 long simple and 2 plumose curved setae. Additional setae are scattered close to the dental row. First article of palp short, bearing a single distal seta on distomedial angle; article 2 long, bearing numerous setae (~15) on inner margin, some of them bifid. Article 3 slightly expanded distally, with numerous (~10) setae (some of them bifid) on distal margin. Dactylus with single seta on outer margin; unguis shorter than dactylus.

Gnathopod 1 (Fig. 5A): Basis wider from proximal to median region, with a row of 8 very long setae on posterior margin, plus another row of 4 similar setae proximally on lateral surface of article. Ischium and merus of similar length, bearing 2 (ischium) and <10 (merus) simple setae on posterior margin. Carpus length similar to propodus, with 6 or 7 (♀) rows of 3–6 long and bifid setae on posterior margin, most of them bearing tiny setules along distal half of their length (only the longest), and 4 setae of variable lenght on anterior margin. Propodus 1,38 times longer than wide with about 11 setae irregularly distributed in 4 clusters over anterior margin of article, 4–6 strong bifid spines of variable length at palm angle (Fig. 5 A-detail); palm margin weakly armoured.

Gnathopod 2 (Fig. 5C): Basis with 7 (♂ 1) or 11 (♀) setae on posterior margin and 4 (♂ 1) or 9–10 (♀) setae on anterior margin. Ischium, merus and carpus all of similar length. Carpus bearing 2 groups of bifid setae on posterior margin and 2 groups of shorter setae on distolateral margin. Propodus 1,5 times longer than wide and more twice longer than carpus; 3 (♂ 1) or 4 (♀) groups of bifid setae on posterior margin; palmar margin convex, weakly armoured; palm angle with 3 unequal conical spines.

Pereopod 3 (not figured): similar to pereopod 4, but with coxal plate narrow and high, lacking concave posterior margin.

Pereopod 4 (Figs 2A; 5B): coxal plate as high as wide, with convex anterior and concave posterior margins, and 5 short setules on ventral border. Basis armed with 5 (♂) or 9 (♀) long setae on posterior margin, 2 (♂) or 6 (♀) anterior setae and 1 distal seta. Carpus shorter than both merus and propodus. Dactylus 30–35% of propodus length; unguis shorter than dactylus.

Pereopod 5 (Fig. 2C, C 1): remarkably shorter than pereopods 6 and 7 (about half as long as their length). Basis large with anterior and posterior margins convex, and with a reduced posterodistal lobe. Merus and carpus similar in length, propodus slightly longer. Dactylus short (34% of propodus) with a short claw (40% of dactylus length).

Pereopods 6–7 (Fig. 2 B-B2, D-D2): pereopod 7 longer than pereopod 6. Basis with truncated posteroventral angle giving article a trapezoidal aspect. Articles progressively longer from merus to propodus (merus length = 43% of propodus). Pereopod 7 propodus not elongated (less than 7 times as long as broad). Dactylus with a short claw (25–30% of dactylus length).

Epimeral plates 1–3 (Fig. 4D–F): posteroventral angle straight; ventral border of plate 2 slightly rounded; ventral margin armature of plates as: 1-3-3/4).

Metasomites 1–3 smooth (Fig. 1), without denticulated posterodorsal spur.

Pleopods 1–3 (not represented): protopods bearing each 2 retinacles. Exopods 9, 8, and 6-articulate, respectively; endopods 7, 6, and 6-articulate, respectively.

Uropod 1 (Fig. 3E, H) peduncle longer than both exopod and endopod, basofacial spine lacking; 2 unequal spines on posterolateral angle and single spine on posteromedial angle of article; posterolateral margin with 3(♂)- 4(♀) spines, posteromedial margin smooth. Exopodi slightly shorter than endopodi, both articles each with 5 apical spines (2 of them very short) and without marginal armature.

Uropod 2 (Fig. 3E, H): peduncle with 1 (♂)-3 (♀) distal spines and 1 lateral spine; rami each with 5 apical spines.

Male Uropod 3 (Fig. 3B): peduncle slightly elongate, about 2.54 times as long as broad; exopod strongly elongate and upcurved, about 14.5 times as long as broad; bearing 5 external and 7 internal group of 1–4 spines; 4– 6 short apical spines.

Female Uropod 3 (Fig. 3A) peduncle subrectangular, 1.7 times as long as broad; exopod moderately elongate, about 11.1 times as long as broad; bearing 5 external and 4 internal group of 1–4 short spines; 4–6 short apical spines.

Telson (Fig. 3C, D): subrectangular, slightly broader than long, shallowly excavate. Cluster of 2–3 subequal spines subdistally at each side, plus pair of flaccid sensorial tufted seta (plumose setules) on lateral margin; spines shorter than telson itself in both sexes. Sexual dimorphism apparent in telson being larger in the female, with emargination extremely shallow, and three spines at each side compared to only two in the male. Lateral sensorial tufted setae are also in a more distal position in the male than in the female.

Remarks and affinities. Pseudoniphargus djemoi belongs to a group of species characterized by the common display of a male uropod 3 exopod strongly elongate (more than 10 times as long as broad) but with the corresponding peduncle only moderately elongate (between 2.1 and 3.5 times as long as broad), combined with a pereopod 5 - pereopod 7 basis lacking a strongly overhanging posterodistal lobe in the male (Stokkan et al. 2018). These species include: P. fragilis Notenboom, 1987, and P. nevadensis Notenboom, 1987, both from southern Spain; P. associatus Sánchez, 1991, from Tenerife (Canaries); and P. longipes Coineau & Boutin, 1996, from northern Morocco (see Notenboom 1987; Sánchez, 1991; Coineau & Boutin 1996). Of them, only P. associatus shares with the new species the absence of basofacial spine on the peduncle of uropod 1. But it can be readily differentiated from the new taxon on the basis of the much shorter female uropod 3 exopod, up to 6.3 times longer than wide (versus up to 11.1 times longer than wide in P. djemoi sp. nov.), and male gnathopod 1 carpus shorter than the corresponding propodus (versus carpus and propodus about equal length in P. djemoi sp. nov.).

Three species of Pseudoniphargus are known only from the female: P. duplus Messouli, Messana & Yacoubi- Khebiza, 2006, and P. italicus Karaman & Ruffo, 1989, both from Sicily; and P. unispinosus Stock, 1988, from Tenerife (Canaries). Again, they display a basofacial spine on the peduncle of uropod 1, in sharp contrast with the condition exhibited by the new species described herein.

A key to the species of Pseudoniphargus present in Africa and the Mediterranean islands, including the new species, is presented below (see also Table 1).

Distribution of the genus Pseudoniphargus in continental Africa. The genus Pseudoniphargus is widely distributed around the Western Mediterranean coasts and along the Atlantic coasts of the Iberian Peninsula and Morocco (see Notenboom 1988 and references herein). The genus is also very diversified in Mediterranean (e.g. Balearic, Corsica, Sicily) and Atlantic islands (e.g. Açores, Canaries, Madeira) as far as Bermuda (Stock et al. 1986). This wide distribution likely results in the ability of Pseudoniphargus species to colonize a wide range of environmental conditions (Notenboom 1988). For instance, the genus is known to inhabit a very wide range of salinity (from anchihaline caves in marine coastal areas to purely freshwater springs) as well as a wide range of altitude (from 0 to 1000 m a.s.l. for Pseudoniphargus unisexualis Stock, 1980 in Spain) or temperatures (up to 44°C, Messouli et al. 2001). Recently, the finding of Pseudoniphargus in Benin extended significantly the African distribution of the genus from the Maghreb to western Africa and south to the Sahara (Lagnika et al. 2016).

However, the wide distribution of the genus does not reflect the dispersal ability of species, that remains very low. The narrow geographic range of most Pseudoniphargus species, which are highly endemic and frequently known only from one or two locations (Stock 1980; Notenboom 1987; Coineau & Boutin 1996; Messouli et al. 2006) strengthens this idea. In North Africa, only P. longiflagellum (in Morocco) and P. africanus (in Algeria and Tunisia) seem to have a relatively wide distribution (Fig. 6). However, very few samples have been collected at this part of the world. Consequently, without more intensive sampling, it is still hazardous to conclude definitively on these aspects, considering also that some misidentifications may have occured. For example, the wide distribution of P. africanus, previously reported to occur in the Balearic Islands, Croatia, France, Italy, Sicily, and Yugoslavia, is now considered to be reduced to Algeria, from where it was first described (Messouli et al. 2006).

TABLE 1.

Uropod 3 pedunculus elongated NO YES YES slightly slightly NO slightly slightly

lengh: sexual dimorphism? moderate YES YES? NO NO moderate YES

groups of exopod marginal spines 9-12 5- 12 5-12 14 5- 6 9-10 10 7

number of distal spines on endopod 1 1 1 1 1-2 2 2 1

……continued on the next page ……continued on the next page

Species from Mediterranean Islands Benin

Pseudoniphargus species --> pityusensis racovitzai pedrerae planasiae obritus beninensis Antenna 1 flagellum: number of articles 18 12>21 12-16 16 14

accessory flagellum longer than first flagellar

= NO = NO YES YES

article

Uropod 3 pedunculus elongatedYESNO NOYES YESNO lengh: sexual dimorphism?? NO NOYES YES? groups of exopod marginal spines 11 1-3 7-8 7-14 8 7 number of distal spines on endopod 1 1 1 1 1 1

0: absent; +: poorly marked; ++: marked; +++: strongly marked (V-shaped)

Bold cases indicate apomorphic characters

The high level of endemism, associated to a high species diversity, is likely to be the result of the successive and independent colonization of inland waters by several marine ancestors in the Late Tertiary between the Eocene and the Pliocene (Stock 1980; Coineau & Boutin 1996). The origin of continental African species is old compared to the species inhabiting the Atlantic and Mediterranean Islands. The colonization of freshwater likely started during the early Miocene (around -20 MYA) from littoral sands of the Tethys. P. africanus and P. macrotelsonis, found in Algeria and Tunisia, were for a long time considered to be the oldest species in North African inland waters (Boutin & Coineau, 1988) until the recent discovery of P. beninensis, for which the ancestors could have colonized the northeastern part of Benin at the beginning of the Eocene (Lagnika et al. 2016). However, the lack of knowledge about the freshwater stygofauna of Africa (Tuekam Kayo et al. 2012) and the fact that at least ten species from northern Morocco (Messouli et al. 2001) and four from Algeria and Tunisia remain undescribed (Stock 1980, C.P. personal observations), do not allow us to establish a sound hypothesis on the origin and the geographical distribution of the genus Pseudoniphargus in Continental Africa. Further investigations using both additional samples and DNA analysis are hence required to disentangle the global and local distribution pattern of the genus.