Dikerogammarus istanbulensis, Özbek, Murat & Özkan, Nurcan, 2011

Özbek, Murat & Özkan, Nurcan, 2011, Dikerogammarus istanbulensis sp. n., a new amphipod species (Amphipoda: Gammaridae) from Turkey with a key for the genus, Zootaxa 2813, pp. 55-64 : 56-64

publication ID	https://doi.org/ 10.5281/zenodo.201896
DOI	https://doi.org/10.5281/zenodo.6193002
persistent identifier	https://treatment.plazi.org/id/A97287D2-0606-EF6B-FF58-D060FB22FB94
treatment provided by	Plazi
scientific name	Dikerogammarus istanbulensis
status	sp. nov.

Treatment

Dikerogammarus istanbulensis View in CoL sp. nov.

( Figs. 1−7 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 View FIGURE 7 )

Material examined. Holotype male, 15 mm (ESFM-MALI/00-02); Çanta Reservoir (41°10ʹ 23ʹʹN, 28°01ʹ12ʹʹE), Silivri District, İstanbul, Turkey (fig. 1), 16 Sept. 2000; collected by Dr. N. Özkan. Allotype female, 9 mm (ESFM- MALI /00-03), ovigerous (with 14 eggs), same data as holotype. 15 paratypes (some extremities are absent): 6 juveniles (4 to 5 mm), 6 males (8 to 17 mm) and 3 females (7 to 9 mm) (ESFM-MALI/00-04).

Diagnosis. Body large. Similar to D. bispinosus Martynov, 1925 except for the presence of setae on inner surface of basal segment of pereopod 7 in both sexes and absence of long setae on the ventral side of second peduncle segment of A1. In addition, epimeral plate 2 has many setae along the ventral margin in both sexes.

Description. Head (fig. 5G): inferior antennal sinus deep. Eyes present, well developed, reniform.

Antenna 1 (figs. 2A): slightly longer than half of the body length; setation weak, peduncular segments bearing a few groups of distal and ventral setae shorter than the diameter of the segment where they are implanted; peduncle segment 1 bears 2 spines in antero-distal part; primary flagellum with 32 segments; accessory flagellum with 6 segments.

Antenna 2 (figs. 2C): antennal gland-cone short, not reaching distal end of peduncular segment 3; peduncular segments 4 and 5 armed with 8−10 groups of setae shorter than the diameter of segment on which they insert; setae on dorsal side of the peduncular segments shorter; flagellum comprising of up to 10 segments; flagellar segments with many longer setae (slightly longer than the diameter of the segments where they are implanted) on their ventral sides; flagellar segments not swollen; calceoli absent.

Upper lip (fig. 2G): convex, with minute setae on distal part.

Right mandible (fig. 3E): incisor 4-dentate, lacinia mobilis bifurcate; molar triturative; segment 2 of palp bearing 17 setae; segment 3 armed with 29 D-setae, 4−5 E-setae; one group of A-setae, and 2−3 groups of B-setae; Csetae present.

Left mandible (fig. 3C): incisor with 5 teeth; lacinia mobilis 4-dentate.

Lower lip (fig. 2H): inner lobe absent.

Maxilla 1 (figs. 2D, E): inner plate of right maxilla 1 with 14 plumose setae, outer plate with 10 serrated spines, segment 2 of palp with 5 blunt spines and 1 stiff in distal part and 4 setae along outer margin; segment 2 of left palp with 5 sharp spines and 2 stiff setae.

Maxilla 2 (fig. 2B): inner plate with diagonal row of 13 plumose setae.

Maxillipede (fig. 4A): inner plate with 3 apical spines and 1 subapical spine; outer plate with row of 11−12 spines on medial margin and 4−6 pectinate apical setae.

Coxal plate 1 (fig. 3A): slightly dilated on distal margin, with 5 setae along the ventral margin. Coxal plates 2 and 3 subrectangular (figs. 3B, 4B). Coxal plate 2 with 1 short seta on anterodistal corner and 2 setae on posterodistal corner. Coxal plate 3 with 3 short setae on posterodistal corner. Ventral margin of coxal plate 4 slightly convex (fig. 4C), with 2 setae on anteriorodistal corner and 5−6 setae on posterior margin. Coxal plates 5−6 (figs. 5A, B) bilobate. Anterior lobe of coxal plate 5 small with 1 seta, posterior lobe with 1 seta on posterodistal corner. Coxal plate 6 with 1 seta on anterodistal and 1 spine on posterodistal corner. Coxal plate 7 (fig. 5C) with 4 setae on posterior margin. Coxal gills 2−7 present.

Gnathopod 1 (fig. 3A): smaller than gnathopod 2; basis with long setae (as long as diameter of the segment) on posterior margin; carpus and propodus elongate; propodus with 3 groups of setae on anterior margin, palm oblique, median spine absent, with 5 palmar angle spines; dactylus with 1 seta on its outer margin.

Gnathopod 2 (fig. 3B): basis with long setae (up to 1.3 times as long as diameter of the segment) on anterior and posterior margins; carpus and propodus elongate; propodus subrectangular, with 1 group of setae on anterior margin; median spine absent, with 5 spines on posterodistal margin; dactylus with 1 seta on outer margin. Inner side of propodus bears 13 groups of setae.

Pereopod 3 (fig. 4B): posterior margins of basis bearing many long setae (up to 1.6 times as long as diameter of the segment); merus and carpus sparsely setose along their posterior margins, the setae on posterior margins are short (shorter than the diameter of the segment where they are implanted); dactylus robust, with 1 serrated seta on outer margin and 2 setae at joint of unguis.

Pereopod 4 (fig. 4C): posterior margins of basis with many long setae (up to 1.6 times as long as diameter of the segment); posterior margins of merus and carpus bearing a few setae (shorter than the segment where they are implanted, not curled); dactylus robust, with 1 serrated seta on outer margin and 2 setae at joint of unguis.

Pereopods 5−7 (figs. 5A–C): subequal in length; without long setae along anterior margins of segments; basis of pereopod 5 subrectangular, with slightly projecting posterodistal lobe, posterior margin with small setules in addition to a spine on postero-distal corner, inner surface without setae, anterior margin with 4 short spines; basis of pereopod 6 quadrangular, anterior margin with 4−5 short spines, posterior margins with 10−11 short setae in addition to spine on postero-distal corner; basis of pereopod 7 with small, slightly overhanging, posterodistal lobe, bearing 7−8 setae on its inner surface; postero-distal corner without spines; segments 4−6 robust, with 2−4 groups of spines on anterior and posterior margin of each segment; dactylus with 1 seta on outer margin and 2 setae at joint of unguis.

Epimeral plates 1−3 (figs. 4D −F): epimeral plate 1 with 3−4 setae on anterior corner and with 2 setae on ventral side; epimeral plate 2 posterodistal corner slightly pointed, with 5 goups of setae and 1 group of setae together with spine on ventral side; epimeral plate 3 posterodistal corner slightly pointed, with 4 spines on ventral margin.

Pleopods 1−3 (fig. 2I): subequal; peduncle with some setae, bearing 2 retinaculae accompanied by a few setae; rami with about 20 segments, fringed with plumose setae.

Urosomites 1−3 (fig. 5F): urosomites 1 and 2 with large elevated process (both of them spinose); urosomite 1 bears dorsomedian (2 spines and 2 setae) and 2 dorsolateral groups of short spines (1-1) on posterior margin; urosomite 2 with a dorsomedian group of spines (2 spines) and without dorsolateral armaments; urosomite 3 without elevated process, with a dorsomedian group of setae (2 setae) and 2 dorsolateral groups of short spines (1-1) on posterior margin.

Uropod 1 (fig. 5D): peduncle longer than rami, with basofacial spine; 1-1 spines on outer margin and 1-1-1 spines on inner margin; outer ramus slightly shorter (about 0.97 times as long as inner ramus) than inner ramus, inner margin bare, outer margin with 2-1 spines and 1 seta; inner ramus with 1 spine on inner margin, outer margin bare.

Uropod 2 (fig. 5E): peduncle with 1 spine on inner and outer margins; outer ramus slightly shorter than inner ramus (about 0.72 times as long as inner ramus); outer ramus with long setae on both margins in addition to spine on outer margin; inner ramus with 2 spines on inner margin.

Uropod 3 (fig. 2F): extended; parviramous type; peduncle with 4−6 distal spines; inner ramus with 1 distal spine and 1 seta on outer margin; segment 1 of outer ramus with 3 groups of spines on outer margin together with many plumose and simple setae; inner margin with 1 group of spines and many plumose setae, first segment of outer ramus bearing 1−2 distal spines, segment 2 slightly longer than adjacent spines.

Telson (fig. 3D): deeply cleft; apically tapered; each lobe with 2 distal spines together with 2−3 shorter distal setae.

Female. Antenna 1 (fig. 6C): peduncle segments with few short setae (not longer than diameter of the segment where they implanted); primary flagellum with 25−26 segments; accessory flagellum with 5 segments. Antenna 2 (fig. 6D): peduncle segments bearing some groups of short setae on dorsal margin; setae on ventral margins almost as long as (some longer) diameter of segment where they implanted; primary flagellum with 10 segments; setation of flagellar segments weaker than that of male; calceoli absent. Gnathopod 1 (figs. 6A, B): basis with many long setae on both anterior and posterior margins; setae usually more than 2 times as long as diameter of basal segment; propodus ovate with 2 groups of setae on anterior margin, palm with 3 spines on posterior corner, dactylus with 1 seta on outer margin. Gnathopod 2 (figs. 6E, F): merus and carpus elongate, propodus subrectangular, medial palmar spine absent, bearing 5 spines on posterior corner and groups of setae on inner surface. Pereopods 3−4 (figs. 7A, B) similar to those of male in setation; pereopod 3 bearing longer setae on posterior margins of merus and carpus than those in males. Pereopods 5−7 (figs. 7C −E) similar to those of male in setation along anterior margins of ischium and merus segments; basal segment of pereopod 7 bearing 8−9 setae on inner surface. Epimeral plates 1−3 (figs. 6G −I) similar to those of male in setation. Uropods 1−2 (figs. 6J, K) seem like similar to that of males except presence of long setae on both margins of outer lobe of uropod 2. Uropod 3 (fig. 7F) and telson (fig. 6L) similar to that of male in setation. Oostegites broad, ovate, on pereopods 2 to 5.

Etymology. The epithet istanbulensis is derived from the name of the type locality, Silivri, İstanbul province in the North-Western Turkey.

Habitat. Type specimens were collected from a reservoir with muddy sediment.

Variability. In males, setation of flagellar segments of antenna 2 and gnathopod 2 are age dependent; larger specimens have more setose flagellar segment of antenna 2 and palm of gnathopod 2. Larger male specimens have more elevated process on their urosomites. Number of setae on inner surface of pereopod 7 can be increase by age.

Remarks. At first sight, this species looks similar to D. bispinosus Martynov, 1925 except for the presence of setae on inner surface of basal segment of pereopod 7 in both sexes and absence of long setae on the ventral side of second peduncle segment of A1. In addition, epimeral plate 2 has many setae along the ventral margin in both sexes.

This species also resembles D. villosus (Sowinsky, 1893) , D. caspius (Pallas, 1771) and D. oskari Birstein, 1945 in the presence of elevated process on urosomites 1 and 2. The new species differs from D. villosus , by the presence of many setae on the inner surface of pereopod 7 in males and by the presence of shorter setae along the posterior margins of segments 4 to 6 of gnathopod 1 and 2, and on the peduncular segments of antenna 1 and on the flagellar segments of antenna 2 in males ( Cârâuşu, 1943; Cârâuşu et al., 1955). The new species differs from D. balatonicus and D. fluviatilis in the presence of many setae on inner surface of basal segment of pereopod 7 in both sexes and in having less elevated dorsal process on urosomites 1 and 2 ( Ponyi, 1958). D. istanbulensis sp. n. differs from D. caspius by the absence of toothed carinae on the metasome segments. The new species differs from D. oskari by the presence of lobation on the basal segment of pereopod 5 and by the armament of the elevated process ( Barnard & Barnard, 1983). The new species differs from D. haemobaphes by presence of 8−10 setae on the inner surface of basal segment of pereopod 7 in both of the males and females. D. istanbulensis sp. n. differs from D. gruberi by the shape of peduncle segments of antennae 1 and 2 and pereopod 3 ( Mateus & Mateus, 1990). The new species differs from D. aralychensis by absence of mid-palmar spine on gnathopod 1 in males.