Pectenogammarus oliviiformis ( Greze, 1985 ) Marin & Palatov & Copilaș-Ciocianu, 2023

Marin, Ivan, Palatov, Dmitry & Copilaș-Ciocianu, Denis, 2023, The remarkable Ponto-Caspian amphipod diversity of the lower Durso River (SW Caucasus) with the description of Litorogammarus dursi gen. et sp. nov., Zootaxa 5297 (4), pp. 483-517 : 505-512

Pectenogammarus oliviiformis ( Greze, 1985) comb. nov.

Figs 14–17 , 18 c–f

Chaetogammarus oliviiformis Greze, 1985: 68 , fig. 30 [type locality—Sevastopol Bay, Crimea].

Material examined. 25 ÔÔ, 35♀♀ , LEMMI — Northeastern Black Sea, Russian Federation, southwestern Caucasus, Krasnodar Krai, Novorossiysk area , Durso village , pebble beach, 44°40’41.1”N 37°33’44.1”E, under the upper layer of pebble and stones, with hand net, coll. Palatov D.M. & Marin I.N., 20.07.2021 .

Additional material. Northeastern Black Sea , Crimean Peninsula: 12 ÔÔ, 25♀♀, LEMMI —the eastern part of Laspi Bay, 44°24’45.3”N 33°42’56.3”E, under the upper layer of pebble and stones, with hand net, coll. Marin I.N., 03.06.2020 ; 10 ÔÔ, 15♀♀, LEMMI — Northeastern Black Sea , Crimean Peninsula, Karadag Bay, 44°54’41.4”N 35°11’56.9”E, under the upper layer of pebble and stones, with hand net, coll. Marin I.N., 22.06.2020 ; Abkhazia : 14 ÔÔ, 12♀♀, LEMMI — Ochamchira district, Ochamchira, 42°42’27.6”N 41°27’47.2”E, in the pebble close to the sea mall, with hand net, coll. Marin I.N. & D.M. Palatov, 18.06.2022 ; Russian Federation, Sochi area : 16 ÔÔ, 18♀♀, LEMMI — Khosta, 43°30’29.2”N 39°52’02.0”E, in the pebble close to the sea mall, with hand net, coll. Marin I.N. & D.M. Palatov, 21.06.2022 .

Diagnosis. Head with concave anteroventral lobe. Pleon with urosomite I with a pair of submedian posterior stout spines and several marginal setae; urosomite II with 2 marginal spines on each side and a pair of median stout spines; urosomite III with 1 marginal spine of each side. Antenna I with 4-6-segmented accessory flagellum. Antenna II with short rounded calceoli in males. Gnathopod I with teardrop-shaped propodus (palm) with oblique palmar margin. Gnathopod II with trapezoidal propodus with oblique palmar margin in males and rectangular elongated with straight palmar margin in females. Pereopods V–VII with basis bearing feebly marked ventral lobes. Pleopods with 2 elongated hooks and 1–2 thick bristles in retinacules. Epimeral plates with sharp but not produced posteroventral angles.

Short re-description. Body unpigmented, generally smooth, non-carinate. Pleon with free urosomites, urosomite I with a pair of submedian posterior stout spines and several marginal setae; urosomite II with 2 marginal spines on each side and a pair of median stout spines; urosomite III with 1 marginal spine of each side. Head with distally concave anteroventral lobe. Eye reniform, well pigmented. Antenna I smooth, non-setose, with 4–6-segmented accessory flagellum, with small aesthetascs. Antenna II subequal to AI, densely covered with long setae in males, with short rounded calceoli in males. Upper lip (labrum) with convex distal part. Lower lip (labium) with mostly reduced inner lobes. Mandible with outer lobe subequal to inner lobe, not expanding distally, with long and distally flattened incisor teeth in some species. Maxilla I with outer plate bearing hairbrush-like distal setae, with outer lobe subequal to inner lobe, inner plate distally expanding or not, with a row of small marginal setae. Maxilla II with outer lobe wider than inner lobe, bluntly expanding distally. Maxilliped with outer and inner plates wide, distally bluntly rounded. Gnathopod I smaller than GnII, not sexually dimorphic, propodus (palm) teardrop-shaped with oblique palmar margin. Gnathopod II also not sexually dimorphic, trapezoidal with oblique palmar margin in males and rectangular elongated with straight palmar margin in females. Pereopods V–VII with basis (article 2) bearing feebly marked ventral lobes. Pleopods with 2 elongated hooks and 1–2 thick bristles in retinacules. Uropod III with outer ramus broad, about 3–4 times as long as wide, with reduced distal article furnished with numerous long simple distal setae. Epimeral plates with sharp but not produced posteroventral angles. Telson entirely cleft, with elongated suboval lobes armed with strong stout apical and submedian spines.

Coloration. Body and appendages translucent. Eyes cornea silver or brown (see Fig. 3 ).

Body size. The largest collected ♀ has tbl. 6.0 mm; the largest collected Ô has tbl. 9.0 mm.

GenBank accession numbers. OP466479, OP466456, OP466425 (Copilaș-Ciocianu et al. 2022).

Habitat and distribution. One of the most widely distributed coastal species presently known along the northeastern Black Sea coast, from Sevastopol area (type locality) (after Greze, 1985) to the eastern Abkhazia (present study). Rather small pebble-dwelling species, living together with Litorogammarus karadagiensis comb. nov. under the upper layer of the pebble, boulder and stones, where both species form sufficiently large aggregations of heterosexual and different-aged individuals. Probably this species was often confused with other coastal dwelling species, such as Echinogammarus foxi ( Schellenberg, 1928) and Echinogammarus olivii (H. Milne Edwards, 1830) (e.g., Greze, 1985; Grintsov, 2016).

Molecular-genetic analysis. Pectenogammarus oliviiformis ( Greze, 1985) comb. nov. is deeply nested within Atlantic-Mediterranean clade ( Pectenogammarus or Homoeogammarus sensu Hou & Sket 2018 ), forming a well-supported, but non-distinct phylogenetic lineage (see Fig. 3 ). Now, we are transferring the species with the genus polyphyletic Pectenogammarus s.l. (after García-París et al., 2023), because the taxonomy of the genus Chaetogammarus is rather well clarified recently (Copilaș-Ciocianu et al., 2023) and this species surely not belong to this genus. However, the taxonomic position will be verified in further studies.

Remarks. Pectenogammarus oliviiformis Greze, 1985 was originally described within the genus Chaetogammarus Martynov, 1924 (see Greze, 1985). In the original description, it was indicated that the species is closely morphologically similar to Pectenogammarus olivii (H. Milne Edwards, 1830) . In fact, our analyses indicate that these two species are not molecularly very close, while E. olivii could be a complex of distinct phylogenetic lineages ( Fig. 3 ).

From P. olivii , co-occurring along the Black Sea coast, the species can be separated by the armature of urosome with only a pair of median dorsal spines on UsI (vs. 2 marginal spines on each side and a pair of medial spines) and 1 marginal spine on each side of UsIII (vs. 2 marginal and a pair of median spines), as well as the presence of calceoli on AII (vs. absent in E. olivii ).

The species can be also separated from Pectenogammarus foxi ( Schellenberg, 1928) , by less concave anterolateral lobe on the head, the armature of urosome with only a pair of median dorsal spines on UsI (vs. 1 marginal spine on each side and a pair of medial spines) and 1 marginal spine on each side of UsIII (vs. 2 marginal and a pair of small median spines).

From the type species of the genus Echinogammarus Stebbing, 1899 , E. berilloni (Catta, 1878) , it could be separated by smooth, non-setose metasoma and urosome (vs. densely setose), shorter accessory flagellum of AI (3–4 segments vs. 6–8 segments), the presence of calceoli on AII (vs. absent) and different setation of urosome, epimeral plates and appendages (see Pinkster, 1973).

From the genus Chaetogammarus with the type species Ch. ischnus ( Stebbing, 1899) , it could be separated by shorter and compact body form, less armed urosome (vs. strongly armed with large spines), shorter accessory flagellum of AI (3–4 segments vs. 6–8 segments), the presence of calceoli on AII (vs. absent), non-produced posteroventral angles of EpI–III (vs. strongly and sharply produced), different shape of telson and basis of PpV–VII.

From the type species of the genus Pectenogammarus Reid, 1940 , P. planicrurus Reid, 1940 , P. oliviiformis can be distinguished by the significantly reduced setosity of PpIII–VII, coxal plates I–IV, and epimeral plate II. From P. simoni ( Chevreux, 1894) (= Echinogammarus simoni ( Chevreux, 1894)) , Schellenberg, 1937 it can be easily separated by the presence of calceoli on AII (vs. absent), concave anterolateral lobe of the head (vs. convex), and several minor features, such as setation of urosomal segments and epimeral plates (see (see Pinkster & Stock, 1972). Moreover, P. simoni is a strictly freshwater species living in wells/spring and the upper stream of the rivers, unlike P. oliviiformis ( Greze, 1985) comb. nov., which is a strictly marine (brackish water) species (see below).

Figures

FIGURE 3. Maximum-likelihood phylogenetic tree based on COI. Number above nodes represent ultrafast bootstrap (UFBS) and Shimodaira-Hasegawa approximate likelihood ratio test (SHaLRT) values. Number below nodes represent posterior probabilities (PP). Strongly supported nodes in all analyses are shown with green circles. Species from Durso River are indicated with red arrows. Taxonomically relevant taxa are shown with various colors. Species belonging to Chaetogammarus are shown with dotted branches.

FIGURE 14. Pectenogammarus oliviiformis (Greze, 1985) comb. nov., Ô (a, b, d, e, g, h, j, k), ♀ (c, f, i, l): a, c—antenna I; b—accessory flagellum of antenna I; d, f—antenna II; e—calceoli of AII; g, i—gnathopod I; h—palmar margin of chela of GnI; j, l—gnathopod II; k—palmar margin of chela of GnII.

FIGURE 15. Pectenogammarus oliviiformis (Greze, 1985) comb. nov., Ô: a—upper lip; b—lower lip; c—left mandible; d— same, incisor process and pars incisiva; e—right mandible; f—same, incisor process and pars incisiva; g—maxilla I; h—same, distal spines of outer lobe; i—maxilla II; j—maxilliped.

FIGURE 16. Pectenogammarus oliviiformis (Greze, 1985) comb. nov., Ô: a—pereopod III; b—dactylus of PIII; c—pereopod IV; d—dactylus of PIV; e—pereopod V; f—dactylus of PV; g—pereopod VI; h—dactylus of PVI; i—pereopod VII; j—dactylus of PVII.

FIGURE 17. Pectenogammarus oliviiformis (Greze, 1985) comb. nov., Ô (a, c, e, g, i, j, k, m, o), ♀ (b, d, f, h, l, n, p): a–f— epimeral plates I–III; g, h—telson I; i—pleopod I; j—retinacula of pleopod I; k, l—uropods I; m, n—uropod II; p, o—uropod III.