Gammarus tazekkaensis, Piscart & Mabrouki & Taybi, 2025

Piscart, Christophe, Mabrouki, Youness & Taybi, Fouzi A., 2025, Description of two new species of freshwater Gammarus Fabricius, 1775 (Amphipoda: Gammaridae) from the Middle Atlas of Morocco, European Journal of Taxonomy 1026, pp. 123-146 : 136-142

Gammarus tazekkaensis sp. nov.

urn:lsid:zoobank.org:act:

Figs 1–3, 9–13, Tables 1–2

Diagnosis

A relatively large species of freshwater Gammarus with long setae on Antenna 2 but no calceoli. Epimeral plate 2 with spinules only on the ventral margin, pereopods 5–7 without setae on the anterior margin of the merus and carpus, pereopod 5 being shorter than the others. The endopodite of uropod 3 is relatively short, never exceeding 60% of the exopodite, and the telson has a lateral spine on each lobe.

Etymology

The specific epithet refers to Tazekka National Park, where the new species was discovered.

Holotype

MOROCCO • ♂ ( 15.4 mm); Raz el Oued or Ras El Ma waterfalls near Taza, 34°08′51.2″ N, 4°00′36.2″ W; alt. 880 m; 20 Dec. 2022; small stream, collected by handnet; MNHN-IU-2025-2613.

Paratypes

MOROCCO • 5 ♂♂; same data as for holotype; MNHN-IU-2025-2614 • 3 ♀♀; same data as for holotype; MNHN-IU-2025-2615 .

Other material examined (used for molecular analysis)

MOROCCO • 5 incomplete specs ( ♂♂, ♀♀ or juvs); same data as for holotype; DNA extracts stored in the personal collection of Christophe Piscart, University of Rennes (France); CP690, CP693 to CP696 .

Description

Male

Habitus slender, up to 17 mm length ( Fig. 3B). Head with truncated lateral cephalic lobe; eyes relatively small, always less than 2 × as long as wide; inferior antennal sinus deep ( Fig. 9A). First antenna as long as half body length, with few setae ( Fig. 9B). First article of peduncle is longer than second, itself longer than third. Flagellum more than 2 × as long as peduncle, with 31 relatively long articles and accessory flagellum of 3 articles. Second antenna as long as ½ of first antenna ( Fig. 9C). Gland cone about ⅔ × as long as third article of peduncle. Peduncle article 4 armed with simple setae on all sides, longer than or as long as diameter of article. Peduncle article 5 as long as, but thinner than, peduncle article 4 and armed with 4–5 groups of setae as long as or slightly longer than diameter of article. Flagellum with 13 articles and armed with transverse rows of setae longer than articles and decreasing in length distally. Calceoli absent.

Mouthpart not showing distinctive characteristics ( Fig. 10). Mandible incisor 5-toothed, lacinia mobilis 4-toothed ( Fig 10A). Mandibular palp with three developed articles ( Fig. 10B). First article unarmed; second armed with ~10–12 long ventral setae. Third article with one row of A-setae and B-setae, row of more than 40 regular D-setae, and 4–5 long apical E-setae. Right maxilla 1 asymmetric relative to left ( Fig. 10C). Inner plate triangular and longer than wide, with simple apical setae on right maxilla and plumose setae on left. Outer lobe bearing 11 pectinate setae. Palp longer than outer lobe with relatively long apical setae. Palps two articulate, fine, and curved, with 5 thin terminal spines for right maxilla 1 and enlarged, with 6 stout terminal spines, for left maxilla 1. Maxilla 2 inner and outer lobes with one row of apical and subapical simple setae; outer lobe slightly larger than inner lobe ( Fig. 10D). Lower and upper lips similar to those of Gammarus , with setose inner surface and without inner lobe ( Fig. 10E–F). Maxilliped similar to that of G. latispinus ( Fig. 10G). Maxilliped inner lobe ~3 × as long as wide, distal margin with 3 stout teeth and long subapical spine; distal part of lobe covered with few fine setules and bearing lateral simple setae on outer margin. Outer lobe with lateral margin evenly rounded, distomedial margin fringed with ~20 knife-like teeth; teeth progressively thinner towards distal part, apex with 7–8 plumose setae. First segment of palp short, trapezoidal and bearing few distal robust setae on distomedial angle; segment 2 long, bearing numerous setae (> 20) on inner margin and 2–3 groups of simple setae on outer margin. Segment 3 slightly expanded distally, with many groups of facial and marginal setae. Dactylus with few setae; unguis shorter than dactylus.

Gnathopod 1 more slender and slightly shorter than gnathopod 2, subchelate ( Fig. 11A); basis longer than depth of coxa 1; carpus shorter than propodus, with hind margin furnished with setae and several rows of setae on outer face. Propodus pyriform, with 2–3 groups of simple dorsal setae and many ventral setae. Palm armed with medial palmar spine, variable number of palmar angle spines and few smaller spines along posterior margin; dactylus shorter than palm width.

Gnathopod 2 carpus shorter than propodus ( Fig. 11B). Palm more transverse and stronger than in first gnathopod, with more groups of longer dorsal and ventral setae and only 2–3 rows of lateral setae on outer face. Palm also with thin medial palmar spine and several strong and small spines toward palmar angle; dactylus as long as or slightly longer than palm width.

Pereopod 3 slightly longer than pereopod 4 ( Fig. 11C). All segments armed with many groups of long setae on posterior margin and few spines on anterior margin. Propodus with 4–5 spines on posterior margin. Dactylus relatively short with one distal seta. Pereopod 4 similar to pereopod 3, but setation reduced in both density and size ( Fig. 11D).

Coxal plates 1–4 with rounded ventral corners, set with short ventral and lateral setules ( Fig. 11). Coxal plate 4 wide and deep reaching ~0.75 × the length of basis.

Pereopods 5–7 similar in shape, but pereopod 5 15% shorter than pereopods 6 and 7 ( Fig. 12); meri, carpi and propodi with very few setae, sometimes longer than spines along anterior margin, especially on pereopod 5. Pereopod 5 with short subrectangular basis less than 1.7 × as long as wide ( Fig. 12A). Pereopods 6 and 7 bases 2 × as long as wide ( Fig. 12B–C). Pereopod 7 similar to pereopod 6, but basis different and constricted near distal end.

Uropod 1 longer than uropod 2; basis with 3 lateral spines on each side and few terminal spines ( Fig. 13A). Endopodite as long as exopodite, armed with 1–3 lateral spines and 3 terminal spines. Uropod 2 similar to uropod 1 but much shorter ( Fig. 13B), endopodite and exopodite with one lateral spine on each side. Uropod 3 basis with long distal spines ( Fig. 13C); endopodite length 0.5–0.6 × that of exopodite, both bearing mainly plumose setae on inner and outer margins and few spines on outer margins.

Dorsal surface of metasome unarmed, except for few setules on distal margin of last segment. Urosome segments with rare dorsal setae, as long as spines; each urosomite armed with 2 pairs of spines on each side. Epimeral plates postero-inferior corner rounded on plate 1 and subrectangular on plates 2 and 3 ( Fig. 13D). Epimeral plate 1 with relatively long setae along anterior part. Epimeral plates 2 and 3 armed with 2–3 spinules on ventral margin; epimeral plate 2 with diagonal ridge. Pleopods 1–3 similar in shape with 2 coupling hooks on basis and very long plumose setae on flagellum ( Fig. 13E–G).

Telson lobes elongate, each lobe about 2 × as long as wide ( Fig. 13H). Armature of lobes consisting of two apical spines, one lateral spine and several long dorsal and lateral simple setae.

Female

Females shorter than males, maximal observed size 12 mm. Antenna 2 with more and sometimes longer setae than in males. Telson lobes similar to those of males, with lateral spines and several lateral and dorsal setae. Exopodite of uropod 3 shorter but similar in structure to that of males.

Ecology and distribution

Despite additional sampling in the study area, the species has never been found outside the type locality in the Ras El Oued River, located in Tazekka National Park. Gammarus tazekkaensis sp. nov. seems to require habitats with good water quality and relatively high ionic concentration ( Table 2).

Differential diagnosis

Gammarus tazekkaensis sp. nov. is characterized by the presence of long setae and by the lack of calceoli on antenna 2, the lack of long setae on pereopod 7 and a telson with a lateral spine on each lobe. Among members of the North African Gammarus , few species share these characteristics. Gammarus tazekkaensis resembles G. acalceolatus , G. latispinus sp. nov. and G. marmouchensis in lacking calceoli, but it differs from these species in several characters. It differs from G. acalceolatus by having long setation on antenna 2 and short setation on pereopods 5–7. It differs from G. latispinus in the absence of lateral spinules on epimeral plate 2, a pereopod 5 that is slightly shorter than pereopods 6 and 7, the presence of a lateral spine on the telson, and the number of A- and B-setae rows on the mandibular palp. Finally, it differs from G. marmouchensis in having a flat urosome, subrectangular epimeral plates 2 and 3, and telson armature bearing a lateral spine on each lobe. It resembles G. gauthieri , G. rifatlensis and G. marmouchensis in lacking long setae on pereopods 5–7, but differs from these species by the presence of long setae on antenna 2.