Spirogammarus, COPILAS-CIOCIANU, PALATOV, MARIN & GRABOWSKI, 2023

Copilaș-Ciocianu, Denis, Palatov, Dmitry, Rewicz, Tomasz, Sands, Arthur F., Arbačiauskas, Kęstutis, Haaren, Ton Van, Hebert, Paul D. N., Grabowski, Michał & Marin, Ivan, 2023, A widespread Ponto-Caspian invader with a mistaken identity: integrative taxonomy elucidates the confusing taxonomy of Trichogammarus trichiatus (= Echinogammarus) (Crustacea: Amphipoda), Zoological Journal of the Linnean Society 198, pp. 821-846 : 831-832

GENUS SPIROGAMMARUS COPILAȘ-CIOCIANU,

PALATOV, MARIN & GRABOWSKI GEN. NOV.

Z o o B a n k r e g i s t r a t i o n: u r n: l s i d: z o o b a n k. o r g: a c t: D 5 2 6 9 6 B 2 - A E B A - 4 0 D B - A 7 C C - BF712AAD3780

Type and only species: Chaetogammarus tenellus major CărăuȘu, 1943 .

Diagnosis: Large Echinogammarus -like gammarid amphipods (≤ 16 mm). Body smooth and non-carinate. Head anterolateral lobe straight. Antenna 1 poorly setose, accessory flagellum well developed (up to nine articles). Antenna 2 flagellum and peduncle segments densely set with tufts of setae twice as long as the width of underlying segment (distally coiled in males), calceoli absent. Gnathopod 1 propodus subequal to gnathopod 2 propodus. Posterior margin of carpal and meral (sometimes ischial) articles of pereopod 3 set with dense and distally coiled setae as long as/longer than the width of underlying segment; pereopods 4–7 with sparse and short setae, dominated by spines. Uropod 3 exopod with dense setae as long as/longer than the width of underlying segment (coiled in males); endopod short and rudimentary; pleonites unarmed dorsally; epimeral plates with spines only (second straight; third with produced inferoposterior corner); urosomites 1–2 without elevations, armed with four dorsolateral clusters of two to four spines. Telson fully cleft, as long as broad, armed with distal and lateral spines, with lobes abruptly tapering distally.

Etymology: From the Latin spira, meaning coil/ spiral, with reference to the coiled setae found on the antennae, gnathopods, pereopods and uropod 3 in males. The gender is masculine.

Remarks: Spirogammarus can be distinguished readily from any species of Chaetogammarus and Echinogammarus s.l. by the presence of dense, distally coiled setae on the carpus and merus of pereopod 3 that are as long as/longer than the width of the underlying segment in both sexes. To our knowledge, no Echinogammarus -like taxa have females with coiled setae on the carpus and the merus of pereopod 3 ( Pinkster, 1993). Spirogammarus is similar to Echinogammarus tibaldii Pinkster & Stock, 1970 with respect to the highly developed setosity of antenna 2, pereopod 3 and weakly setose pereopods 5–7 ( Pinkster, 1993). However, Spirogammarus is distinguished by the weak setation of antenna 1 (highly developed), higher number of articles in the accessory flagellum (nine vs. five), coiled setae on gnathopod propodi and uropod 3 (non-coiled), and absence of long setae along the distal margin of epimeres. For further comparisons, see Supporting Information, Table S4.