Spirogammarus major, 1943

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 : 833

SPIROGAMMARUS MAJOR ( CĂRĂUȘU, 1943) COMB. & STAT. NOV.

Chaetogammarus tenellus major CărăuȘu, 1943 .

Diagnosis: Same as for genus (see above).

Remarks: Spirogammarus major can be distinguished from C. trichiatus (in parentheses) by: its larger size (16 vs. 12 mm; Fig. 5C ), absence of setae on the basal segment of mandibular palp, subequal gnathopod propodi (propodus 2 longer than propodus 1), straight anterolateral head lobes (acutely produced; Fig. 6B ), denser setation along the inner side of the gnathopod palm ( Fig. 6C ), urosomites armed with clusters of two to four spines (solitary spines; Fig. 6A ), uropod 3 exopod with dense setation in both sexes (only males have dense setation; Fig. 6D ), and uropod 3 endopod in males is armed with spines and long setae (setae absent in both sexes; Fig. 6D ). Both taxa are similar with respect to the setosity of antennae ( Fig. 7A, B ) and pereopod 3 ( Fig. 7D ).

Distribution: Lagoons, estuaries and lower stretches of rivers that drain along the north-western to western shore of the Black Sea. Our morphomolecular analyses confirm that S. major is a widespread invasive species in European inland waters, being widely distributed along the Danube, lower Rhine, Oder and Dnieper rivers ( Fig. 4 ).

Type locality: Lake Shabla (Shablensko Ezero), Bulgaria .

Figures

Figure 4. Distribution of focal taxa. Small dots represent distribution records from the literature (after CopilaȘ-Ciocianu et al., 2023); large dots represent sequenced localities (black outline, literature data; white outline, present study). Arrows represent the type localities of Chaetogammarus trichiatus (orange) and Spirogammarus major (purple). The question mark represents a doubtful distribution record of Chaetogammarus ischnus. Green dashed lines indicate the native range.

Figure 5. Morphological differentiation among the focal taxa. A, principal components analysis showing variability in morphospace across the first three axes (PC 1–PC 3) for males (top) and females (below). B, dendrogram based on squared Mahalanobis distances. C, boxplots depicting variation in length of selected morphological traits (corrected for body size).

Figure 6. Scanning electron micrographs. A, dorsal side of urosome. B, lateral head lobes. C, gnathopod 2 propodus. D, uropod 3. Scale bars: 0.2 mm.

Figure 7. Scanning electron micrographs. A, antenna 1. B, antenna 2. C, basis of pereopod 7. D, pereopod 3. Scale bars: 0.2 mm.