Bythotrephes brevimanus Lilljeborg, 1901

Korovchinsky, Nikolai M., 2020, Description of a new species in the genus Bythotrephes Leydig, 1860 (Crustacea Cladocera: Onychopoda), supplements to selected species, and concluding remarks on the genus, Zootaxa 4789 (2), pp. 441-465 : 451

Bythotrephes brevimanus Lilljeborg, 1901

Material examined: Sweden, Jämtland: 1) sample SMNH N156573 labeled “ Sweden, lake Revsundssjön , 62°53’ N; 15° 08’ E ” (old label: “N 2470, Jämtland, Refsunden, Bythotrephes n. sp. Lilljeborg ”), 1 male ; Gävleborg: 2) sample SMNH N156665 labeled “ Bythotrephes longimanus , Sweden, near Gävle, lake Storsjön” (old label: “N2472, Gestrikland, Storsjön nâra Gafle , Bythotrephes longimanus Lilljeborg ”), 1 ad ; Stockholm: 3) sample SMNH N156675 labeled “ Bythotrephes longimanus , Sweden, Nacka, lake Källtorpssjön , 59° 17’ N; 18° 09’ E, 4 July 1939, leg. C. Puke ” (old label: “ Bythotrephes longimanus, Kallderssjön, Nacka , Stockholm, coll. and det. C. Pucke, 4/7 1909 ”), 1 ad ; 4) sample SMNH N 156574 labeled “ Bythotrephes longimanus , Sweden, 5 km west Hemfosa, Södertörn, lake Grindsjön , 59° 05’ N; 17° 52’ E, leg. 17 July 1939, C. Puke ”), old label: “ Bythotrephes longimanus Leydig, Grindsjö 5 km V Hemfosa, Südertorn, C. Puke coll. et det., 17/7 1909 ”), 1 ad ; Värmland: 5) sample SMNH N158346 labeled: “ Sweden, Vänern, Mälsvik between Karlstad and Kristinenhamn, Widegren ”, 4 ad ; 6) sample SMNH N158628 labeled “ Sweden, Värmland, Yngen , Hj Widegren ”, 3 ad ; 7) sample SMNH N158630 labeled “ Sweden, Värmland, Vermelen , ringadjup 1862, Widegren ”, 1 ad ; 8) sample SMNH N158852 labeled “ Sweden, Tanern, Dalbosjön , N om Hindens , 14.8.1942 ”, 5 ad ; Dalsland: 9) sample SMNH N 158861 labeled “ Sweden, St. Rorsjön, Dalarna , 2/8 1918, coll. O. Lundblad ”, 1 ad ;

Denmark: 10) sample SMNH N156663 labeled ”Denmark, Sjaelland, lake Esrum Sø, 56° 00’ N; 12° 22’E, Leg. P.E. Müller, Bythotrephes cederstroemi ” (old label: N 981, ” Denmark , Bythotrephes cederströmi Schödl ♂ Esrum Sø, P.E. Müller “, 3 males and 3 juv. males; 11) sample SMNH N 156664 labeled ” Bythotrephes cederstroemi , Denmark, Sjaelland, lake Esrum Sø, 56° 00’N; 12° 22’ E, leg. P.E. Müller “ (old label: “N 1014, Denmark, ♀ Bythotrephes cederströmii Schödl., Esrum Sø, P.E. Müller “), 16 ad ;

Germany: 12) sample SMNH N158441 labeled ” Bythotrephes longimanus , Germany, Starnbergersee, 1855” . 14 ad.

Remarks: The old label of sample 1 unambiguously testifies that initially Lilljeborg considered the taxon under consideration a new species but later downgraded its status to a variety of B. longimanus (see Lilljeborg 1901). All specimens of this sample set are quite characteristic in respect of their diagnostic traits. In one sample (1), this species was found co-occurring with B. cederströmii but no individuals with intermediate morphological traits which are characteristic of hybrid forms were found.

The occurrence of B. brevimanus in Bavarian lake Starnbergersee (47°54’ N) ( Fig. 6 ) (if this is really that lake) seems unusual because the main range of the species is situated far in the north, in the Circumbaltic region reaching approximately 52° N in the south (see Flössner 1972) (according to the latest data, this species was also found in Austrian lakes (Korovchinsky, unpubl.)).

Figures

FIGURE 6. Geographical distribution of Bythotrephes species, circles (“?”= questionable locations): dark blue—B. longimanus; dark red—B. arcticus (SK—locality Sabanty-Kul in Northern Kazakhstan); yellow—B. brevimanus; white—B. cederströmii; purple—B. lilljeborgi; light blue—interspecific hybrid form B. brevimanus x B. cederströmii; asterisk—B. transcaucasicus; cross—B. centralasiaticus sp. nov.