Hydraena (Hydraena) pygmaea Waterhouse , 1833

Bilton, David T., Ribera, Ignacio & Villastrigo, Adrián, 2023, The colonisation of the Tyrrhenian Islands by Hydraena water beetles, with Hydraena reflexa Rey, 1884 reinstated as a valid species endemic to Corsica and Sardinia (Coleoptera, Hydraenidae), Organisms Diversity & Evolution (New York, N. Y.) 23 (4), pp. 881-900 : 891-895

Hydraena (Hydraena) pygmaea Waterhouse, 1833

Hydraena pygmaea Waterhouse, 1833: 295 .

Hydraena (Hadraena) pygmaea Waterhouse ; Ganglbauer,

1904: 215.

Hydraena (Hadraena) pygmaea Waterhouse ; Reitter,

1909: 356.

Hydraena (s.str.) pygmaea Waterhouse ; Orchymont,

1936: 64; Balfour-Browne, 1958: 194; Valladares et al.,

2018; 189.

Hydraena Sieboldii Rosenhauer, 1847: 28 .

Hydraena (Hadraena) Sieboldi [!] Rosenhauer; Rey,

1886: 110.

Hydraena (Grammhydraena) Sieboldi [!] Rosenhauer;

Kuwert, 1888: 120.

Hydraena lata Kiesenwetter, 1849: 188 .

Type locality. Hebden Bridge , Yorkshire, UK .

We have not been able to locate the type series, which is not in Waterhouse’s material in the Natural History Museum, London (M. Barclay pers. comm.). Waterhouse based his description on specimens collected by a Samuel Gibson, whose collection was, at one time, in the Peel Museum, Manchester. Enquiries at Manchester, Liverpool and Salford Museums all failed to locate any H. pygmaea likely to emanate from Gibson, and this material may be lost. There is no doubt about the identity of this widespread species, however, the name having being used consistently by almost all authors since its introduction. See Valladares et al. (2018) for a thorough, modern description with figures .

Material examined. Great Britain: 3 ♂ 3 ♀ ( CBP) “ 10/v/2009 England S Devon // Ruddycleave Water nr.// Buckland in the Moor// D T Bilton leg.”; 1 ♂ 1 ♀ ( CBP) “ 15/x/2005 ENGLAND// S Devon River Gara @// Gara Mill above Strete// D T Bilton leg.”; 1 ♀ ( CBP) “D. T. Bilton// H. pygmaea // seepage near// Bewcastle 11/iv/83” [Hw.]; 1 ♂ ( CBP) “D. T. Bilton// H. pygmaea // Conic Hill// Lochlomondside// 28/vi/1983 ” [Hw.]; 5 ♂ 5 ♀ ( CBP) “ 4/ vi/2021 Wales Black Mountains// Nant Bwch at junction with Nant Ganol// SO232333 530 m, river moss// D T Bilton leg.”. France: 1 ♂ ( NHMW) “Guillebeau// Frankreich” “ ♂ ” “sieboldi” [Hw.]; 1 ♂, 3 ♀ ( NHMW) “Fauvel// Calvados”; 2 ♂, 2 ♀ ( NHMW) “ Elsass ” “ Hydraena // sieboldi” [Hw.] “pygmaea ” [Hw.] “ Hydraena // pygmaea Waterh. // det. M Jäch”. Germany: 1 ♂ ( NHMW) “sieboldi// Rochenh.” [Hw.] “ ♂ ” “c. Epplsh.// Steind.d.” [Hw.] “107” [Hw., green label] “alleged Paralectotype // H. sieboldi Rosenhauer// vid. Jäch & Diaz 2000 ” [Hw., red label]; 1 ♀ ( NHMW) “sieboldi// Erlangen// Rosenhauer” [Hw.] “106” [Hw., green label] “c. Epplsh.// Steind.d.” “sieboldi” [Hw.]; 1 ♀ ( NHMW) “Coll.// Hampe” “sieboldi// Rosh. Bav” [Hw]; 1 ♂ ( NHMW) “sieboldi Rosh.// Baden-Baden.// Sept. 79” [Hw.] “ ♂ ” “401” [Hw., green label] “c. Eppelsh.// Steind.d.” “sieboldi” [Hw.]; 1 ♂, 1 ♀ ( NHMW) “Oberbayern// leg. Hebauer” “St. Heinrich// 4.4.1976 ” “Hydr.// pygmaea” [Hw.]; 2 ♀ ( NHMW) “D-BAYERN: 2.11.1996 // E. Stuttgart// Weinstadt-Baach// leg. M. Jäch (D2)”; 1 ♂, 1 ♀ ( NHMW) “DDR 22.5.86// Drachenschlucht// bei Eisenach// leg. Jäch [Hw.]; 1 ♂ ( NHMW) “Dresden” [Hw.]; 1 ♂, 1 ♀ ( NHMW) “Seis, TL// Schuster”. Austria: 1 ♂ ( NHMW) “Austria VLBG 13229// Schwarzach 410 m // 13.6.1995 // Unterwassermoos// leg. C.M. Brandstetter” “ H. pygmaea ” [Hw.]; 1 ♂ ( NHMW) “A-VLBG: Bez. Dornbirn// N Dornbirn, 3.6.2001 // Haselstauder Bach, 410 m // leg. Jäch (2)”; 1 ♀ ( NHMW) “A-VLBG: Bez. Bregenz// ca. 1, 5 km N Hörbranz// 2.6.2002, ca. 425 m // leg. Jäch (1)”; 1 ♂ ( NHMW) “A-VLBG: Bez. Bregenz// 0, 7 km NNW Hohenweiler// 2.6. 2001, 460 m// leg. Jäch (2)”; 1 ♂ ( NHMW) “ SALZBURG: Flachgau// SW Seidenfeld, 600 m // NNE Plainfeld, 27.7.1999 // leg. Jäch et al. (6)”; 1 ♂, 1 ♀ ( NHMW) “A-KÄRNTEN: Klugenfurt/Land// 1 km SW Stuttern, 26.8.2001 // Stutterner Moos, 475 m // leg. Raunig (1)”; 4 ♂, 3 ♀ ( NHMW) “Umg. Linz O. Ö.// H. Priesner”; 1 ♀ ( NHMW) “A- Styria, Bez. Weiz// Raubklamm ca. 5 km NW Weiz// 15°33′28”E 47°14′08”N 540 m // 28.7.2000 leg. Jäch (5)” “ Hydraena // pygmaea Waterh. // det. M. Jäch”; 2 ♂ ( NHMW) “ Vorarlberg // Hohenweiler// Richenbach 470 m // 5.5.1993 Detritus// Wasserwehr// leg. Ing A Kapp 1680” “ Hydraena // pygmaea Waterh. // det. M. Jäch”; 10 ♂, 6 ♀ ( NHMW) “ Vorarlberg // Hohenweiler// Richenbach 470 m // 5.5.1993 Detritus// Wasserwehr// leg. Ing A Kapp 1680” “ Hydraena // pygmaea// Jäch det. 1994” [pygmaea & 4 Hw.]; 1 ♂, 1 ♀ ( NHMW) “AUSTRIA Vorarlberg // Hohenweiler// Rohrach 29.4.1993 // 590 m Detritus unter// wasserfall// leg. Ing A Kapp 1669” “ Hydraena // pygmaea// Jäch det. 1994” [pygmaea & 4 Hw.]. Slovenia: 4 ♀ ( NHMW) “ YU – Slovenija// 20 km N Kranj // leg. Jäch 27.6.88”; 1 ♀ ( NHMW) “ YU – Slov. Jäch// Selščica 23.6.84// W. Želenzniki” [Hw.]; 1 ♂ ( NHMW) “ YU – Slov. 25.6.88// PaulitschS.// Steiner A.// Jäch” [Hw.]. Bosnia and Herzegovina: 1 ♂ ( NHMW) “BOSNIA// Banja Stijena// 1931. VII. 2–24. // leg. Dr. J. Fodor”. North Macedonia: 1 ♂ ( NHMW) “ YU – Maked. 12.8.88// nw Gergeljia// leg. Jäch (85)”; 1 ♂ ( NHMW) “ YU – Maked. 27.7.88// Pelister bei// Bitola: Jäch (11)”. Spain: 1 ♂ ( NHMW) “ESPANA: Granada, 24.10.1998 // Sierra Nevada, 1100 m // Rio Maitena// leg. M. Jäch (19)”; 1 ♀ ( CBP) “ 17/vi/2006 Spain Albacete// Rio de las Hoyas @ Puerto// de Madera D. T. Bilton leg.”; 1 ♂ 2 ♀ ( CBP) “ 27/ vii/2012 Spain Albacete// Rio de las Hoyas @ Cortige// de Torta D T Bilton leg.”; 1 ♀ ( CBP) “ 10/vi/2013 Spain Guip.// PN de Aralar – stream// 1 km SE of Osinbeltz// D T Bilton leg.”; 1 ♀ ( CBP) “ 4/ix/2013 Spain Albacete// Rio de las Hoyas// en el Cortijo de Tortas// D T Bilton leg.”. Slovakia: 1 ♂ ( NHMW) “ CSFR – Slowakei// Muran (1)// 17.10.1991 Jäch” “ Hydraena // pygmaea Waterh. // det. M. Jäch”; 1 ♂ ( CBP) “ 8/vi/2009 Slovakia// River above Jablonové// 362 m D T Bilton leg.”. Greece: 1 ♂ ( NHMW) “GR mt. Ossa// Stomion 19.6.86// leg. H. Hebauer”; 4 ♂, 1 ♀ ( NHMW) “GR- Rodopi 8.8.88// Dipotama// leg. Jäch (75)” [same card]; 1 ♂ ( NHMW) “GR – Thassos 1991// Potamias (1)// leg. M. Jäch 9.IX.” “ Hydraena // pygmaea Waterh. // det. M. Jäch”; 1 ♂ male Calabria, Sila, Camigliatello, aedeagus dorsal and lateral; E) Hydraena pygmaea male Calabria, Sila, Camigliatello, mid and hind legs; F) Hydraena reflexa male Sardinia, Aritzo, aedeagus dorsal and lateral; G) Hydraena reflexa male Sardinia, Talàna, mid and hind legs

( NHMW) “GR – Euböa (6)// Steni-Stroponas// 650 m 30.IX.// leg. Jäch 1992”; 1 ♂ ( NHMW) “GR: Ioannina , 21.9.1999 // unterh. Metsovo, ca. 1000 m // 39.78886N 21.21666E // leg. Hess & Heckes (1)” “ HYDRAENA // pygmaea WAT. // A. Skale, 2003” ; 1 ♂ ( NHMW) “GR – Ioannina : 29.4.2000 // NE Ioannina, 3 km NNE Grevenniti // 39° 49.7’N 21° 00.8E // ca. 950 m, leg. Komarek // Schillhammer, Schönmann (23)” “ HYDRAENA // pygmaea WAT. // A. Skale, 2004” ; 1 ♂ ( CBP) “ 3/viii/2012 GR Peloponnese// Taygetos Mts. Loga Bk. @// 800 m above Anoghia // D T Bilton leg.”. Bulgaria : 3 ♂ 2 ♀ ( CBP) “ 5/vii/2005 Bulgaria// Rila Mts. Stream @ 1,500 m // Above Bacevo// D. T. Bilton leg.” ; 2 ♂ ( CBP) “ 9/vii/2005 Bulgaria// Rhodope Mts. Stream @ 800 m // Above Filipovo// D. T. Bilton leg.”. Turkey : 5 ♂, 2 ♀ ( NHMW) “TR – THRAKIA 28.7.// Istranca (30)// leg. Jäch 1998” ; 1 ♂, 1 ♀ ( NHMW) “TR – ORDU 28.5.// Gölköy (18)// leg. Jäch 1989” ; 2 ♀ ( NHMW) “TR – ERZINCAN 10.6.// sö Refahiye // leg. Jäch 89 (77)” ; 1 ♂ ( NHMW) “TR: ARTVIN // ca/ 25 km // NNW Borçka ” “ Kargöl // leg. A. Kasapoğlu // 16.IX.2000 ” “ Hydraena // pygmaea WAT. // det. Jäch 2001” ; 3 ♂ ( NHMW) “TR – ARTVIN 5.6.// Savsat (54)// leg Jäch 1989” ; 1 ♂, 1 ♀ ( NHMW) “TR – ARTVIN 98// W. Borcka (45)// leg. Jäch 4.6.” ; 1 ♂ ( NHMW) “TURKEY: Artvin // Karagöl // 1470 m // leg. N. Ertorum ” “ HYDRAENA // pygmaea WAT. // A. Skale , 2011” ; 1 ♂ ( NHMW) “TR – ERZURUM 9.6.// Tortum (76) leg. Jäch 1989” ; 1 ♀ ( NHMW) “TR – ERZURUM 31.5.// Ovitgagi P. 2000 m // leg. Jäch 89 (35)”. Armenia : 2 ♀ ( NHMW) “ARMENIA: E Yerevan // 40° 08.39’N 44° 49.12’E // nr. Gekhard, 5.5.2001 // ca. 1600 m, leg. Shaverdo // & Schillhammer (16)” “ HYDRAENA // pygmaea W.// A. Skale, 2009” ; 1 ♂ ( NHMW) “ARMENIA: N Yerevan // 40° 30.04’N 44° 36.86E // nr. Arzakan, 5.5.2001 // ca. 1900 m, leg. Shaverdo // & Schillhammer (23)” “ HYDRAENA // pygmaea W.// A. Skale, 2009” ; 1 ♀ ( NHMW) “ARMENIA: N Yerevan // 40° 37.35’N 44° 28.02’E // ca. 30 km NW Hrazdan // 19.5.2001, ca. 2050 m // Shaverdo & Schillhammer (54)” “ HYDRAENA // pygmaea W.// A. Skale, 2009”. Italy, typical pygmaea : 1 ♂ ( MSNG) “Cividale UD-// T. Patok 300 m-// leg. Ferro IX 75.” “ Hydraena // (s.str.) pygmaea // det. G. Ferro ” “ MUSEO GENOVA // coll. G. Ferro // (dono 2013)” ; 1 ♀ ( MSNG) “f#” “Cividale UD-// T. Patok 300 m-// leg. Ferro IX 75.” “ Hydraena // (s.str.) pygmaea // det. G. Ferro ” “ MUSEO GENOVA // coll. G. Ferro // (dono 2013)” ; 1 ♀ ( MSNG) UD. Tramonti // di Sotto. maro [?]// loc. Campone // 23.10.99. Ferro ” [Hw.] “Tor. Chiarzò” [Hw.] “ Hydraena // (s.str.) pygmaea // det. G. Ferro ” “ MUSEO GENOVA // coll. G. Ferro // (dono 2013)” ; 2 ♂ ( MSNG) “POFFABRO PN.// T- Colvera // leg. Ferro ” “m.448// 15 IV 77// leg. Ferro ” “ Hydraena // (s.str.) pygmaea // det. G. Ferro ” “ MUSEO GENOVA // coll. G. Ferro // (dono 2013)” ; 1 ♂, 1 ♀ ( MNSG) Pinzano // PN. 24.4.89// lg Ferro ” [Hw.] “ Hydraena // (s.str.) pygmaea // det. G. Ferro ” “ MUSEO GENOVA // coll. G. Ferro // (dono 2013)” on same pin ; 1 ♀ “[illegible] 82// COLVERE, M. Suf// Pre ALPI CARNICHE // leg. Seriani M. ” [Hw. Ecept ALPI CARNICHE // leg. Seriani M.] “pygmaea ” [ Hw. ] “ Hydraena // (s.str.) pygmaea // det. G. Ferro ” “ MUSEO GENOVA // coll. G. Ferro // (dono 2013)” ; 2 ♂ ( MNSG) “cascata// V-Veneto TV-// Leg. Ferro IV.76” “ Hydraena // (s.str.) pygmaea // det. G. Ferro ” “ MUSEO GENOVA // coll. G. Ferro // (dono 2013)” on same pin ; 1 ♀ ( MSNG) “ Bassano // Torrente // 27.9.79 Ferro” [Hw.] “ Hydraena // (s.str.) pygmaea // det. G. Ferro ” “ MUSEO GENOVA // coll. G. Ferro // (dono 2013)” ; 1 ♂, 1 ♀ ( MNSG) “Cascata Seravalle// V-Veneto TV.// 5. VI.75// Ferro” [ Hw. ] “ Hydraena // (s.str.) pygmaea // det. G. Ferro ” “ MUSEO GENOVA // coll. G. Ferro // (dono 2013)” on same card ; 3 ♂ ( MSNG) “Cascata Seravalle// V. Veneto TV // 5. VI.75// Ferro” [ Hw. ] “ Hydraena // (s.str.) pygmaea // det. G. Ferro ” “ MUSEO GENOVA // coll. G. Ferro // (dono 2013)” on same pin ; 2 ♂ ( MNSG) “ Feltre BL// Val. Canzal [?]// T. ce ordine [?]//2.8.90 Ferro ” [Hw.] “ Hydraena // (s.str.) pygmaea // det. G. Ferro ” “ MUSEO GENOVA // coll. G. Ferro // (dono 2013)” on same pin ; 1 ♀ ( MSNG) “ Toscana PI // Vallombrosa// T. Paradisino// m 1100. 20.8.02” [Hw.] “Protomagno// Papi R. leg.” [Hw.] “ Hydraena // (s.str.) pygmaea // det. G. Ferro ” “ MUSEO GENOVA // coll. G. Ferro // (dono 2013)” ; 1 ♂ ( MSNG) “Rossina// T. Sacutlo // AR. 1992” [Hw.] “ Hydraena // (s.str.) pygmaea // det. G. Ferro ” “ MUSEO GENOVA // coll. G. Ferro // (dono 2013)” ; 1 ♀ ( MSNG) “Montemigniaio// AR – 10c. Liconia// T. Scheffia m 863// 15.IX.05 Papileg.” [Hw.] “ Hydraena // (s.str.) pygmaea // det. G. Ferro ” “ MUSEO GENOVA // coll. G. Ferro // (dono 2013)” ; 1 ♀ ( MSNG) “Montemigniaio// AR. LICONIA// T. Scheffia m 841// leg Papi 29. VI.05.” [ Hw. ] “ Hydraena // (s.str.) reflexa [sic.]// det. G. Ferro ” “ MUSEO GENOVA // coll. G. Ferro // (dono 2013)” ; 1 ♂ ( MSNG) “ PIEMONTE // illegible [Hw., faded]// Coll. Demarchi ” “ Hydraena (s.str.)// pygmaea Waterh. // det. G. Binaghi ” “ MUSEO GENOVA // coll. G. Binaghi // (acquisto 1976)” ; 1 ♂ ( MSNG) “NAVA// Alpi Maritime // 20.30- VIII-1924 F. Solari” “ Hydraena // sieboldi// det. Dodero ” [Hw.] “pygmaea // det. E. Pretner ” [ pygmaea Hw. ] “ Hydraena (s.str.)// pygmaea Waterh. // det. G. Binaghi ” “ MUSEO GENOVA // coll. G. Binaghi // (acquisto 1976)” ; 1 ♀ ( MSNG) “NAVA// Alpi Maritime // 20.30- VIII-1924 F. Solari” “pygmaea // det. E. Pretner ” [ pygmaea Hw. ] “ Hydraena (s.str.)// pygmaea Waterh. // det. G. Binaghi ” “ MUSEO GENOVA // coll. G. Binaghi // (acquisto 1976)” ; 1 ♀ ( MSNG) “BIELLA C. Code // ( Sagliano ) 24–9// Capellaro 58” [date Hw.] “ Hydraena (s.str.)// pygmaea Waterh. // det. G. Binaghi ” “ MUSEO GENOVA // coll. G. Binaghi // (acquisto 1976)” ; 2 ♂ ( MSNG) “BIELLA C. Code // (Sagliano) 24–9// Capellaro 58" [date Hw.] “Rio affl.// T. CERVO ” [Hw.] “ Hydraena (s.str.)// pygmaea Waterh. // det. G. Binaghi ” “ MUSEO GENOVA // coll. G. Binaghi // (acquisto 1976)” on same pin ; 1 ♂ ( MSNG) “ Friuli // Torr. Suolrio // 2.VIII.1962.// G. Binaghi ” [Hw.] “località// podestra” [Hw.] “pygmaea ” [Hw.] “ Hydraena (s.str.)// pygmaea Waterh. // det. G. Binaghi ” “ MUSEO GENOVA // coll. G. Binaghi // (acquisto 1976)” ; 2 ♀ ( MSNG) “ Friuli // Torr. Cosizza // m. 310 Palinch // ( Drenchia ) [ Hw. ] “ 26.VII. 1962 // G. Binaghi ” [Hw.] “pygmaea ” [Hw.] “ Hydraena (s.str.)// pygmaea Waterh. // det. G. Binaghi ” “ MUSEO GENOVA // coll. G. Binaghi // (acquisto 1976)” on same pin ; 1 ♂ ( MSNG) “pygmaea // Wather [sic.]” [Hw.] “Masaralis// Udine. 26. 3.// 52. Bucciarelli” [Hw.] “ Hydraena (s.str.)// pygmaea Waterh. // det. G. Binaghi ” “ MUSEO GENOVA // coll. G. Binaghi // (acquisto 1976)” ; 1 ♀ ( MSNG) “ Friuli // Torr. Iuolrio// m. 310. 8.VIII.// 62. Binagi” [Hw.] “località// podestra” [Hw.] “ Hydraena (s.str.)// pygmaea Waterh. // det. G. Binaghi ” “ MUSEO GENOVA // coll. G. Binaghi // (acquisto 1976)” ; 1 ♂ ( MSNG) “ Friuli // aff. Narisone// Pulfero. 22.VII.// 962. Binaghi [Hw.] “località// Lock.” [Hw.] “pygmaea ” [Hw.] “ Hydraena (s.str.)// pygmaea Waterh. // det. G. Binaghi ” “ MUSEO GENOVA // coll. G. Binaghi // (acquisto 1976)” ; 1 ♂ ( MSNG) “ Friuli // valle Ampa// m. 650. 4.VIII.// 62. Binaghi” [Hw.] “località// Gallizzis” [Hw.] “pygmaea ” [Hw.] “ Hydraena (s.str.)// pygmaea Waterh. // det. G. Binaghi ” “ MUSEO GENOVA // coll. G. Binaghi // (acquisto 1976)” ; 1 ♂ ( MSNG) “ Friuli // Arbida. Aff.// Torr. Cosizza” [ Hw ] “m. 310. 25// VII. 1962 // G. Binaghi ” [Hw.] “pygmaea ” [Hw.] “ Hydraena (s.str.)// pygmaea Waterh. // det. G. Binaghi ” “ MUSEO GENOVA // coll. G. Binaghi // (acquisto 1976)” ; 1 ♀ ( MSNG) “ Friuli // Savogna. Torr.// Alberone. 23. VII.// 962. G. Binaghi ” [Hw] “pygmaea ” [Hw.] “ Hydraena (s.str.)// pygmaea Waterh. // det. G. Binaghi ” “ MUSEO GENOVA // coll. G. Binaghi // (acquisto 1976)” ; 1 ♂, 1 ♀ ( MSNG) “REZZOAGLIO d’// AVETO (Liguria)// IX – 1918 // A. Dodero” “ Hydraena // sieboldi// Rosh.” [Hw.] “ Hydraena (s.str.)// pygmaea Waterh. // det. G. Binaghi ” “ MUSEO GENOVA // coll. G. Binaghi // (acquisto 1976)” on same pin ; 6 ♂, 7 ♀ ( MSNG) “ Liguria // Rovegno. val. Treb. // bia. Rio del Riccio // m. 600. 4.V.1958 // G. Binaghi ” [Hw.] “ Hydraena (s.str.)// pygmaea Waterh. // det. G. Binaghi ” “ MUSEO GENOVA // coll. G. Binaghi // (acquisto 1976)” on same pin ; 4 ♂ ( MSNG) “ Liguria // alt aval Trebbia // Rovegno. Fosso del// Riccio. M. 600. 4.// V. 1958. G. Binaghi [Hw] “pygmaea ” [Hw.] “ Hydraena (s.str.)// pygmaea Waterh. // det. G. Binaghi ” “ MUSEO GENOVA // coll. G. Binaghi // (acquisto 1976)” on same pin ; 2 ♂ ( MSNG) “App. Ligure// Rovegno. val// Trebbia. 16.VIII.// 60. G. Binaghi ” [Hw.] “ Hydraena (s.str.)// pygmaea Waterh. // det. G. Binaghi ” “ MUSEO GENOVA // coll. G. Binaghi // (acquisto 1976)” on same pin ; 1 ♀ ( MSNG) “ Liguria occ.// Alto (Savona)// 17. V.64. Binaghi” [Hw.] “ Hydraena (s.str.)// pygmaea Waterh. // det. G. Binaghi ” “ MUSEO GENOVA // coll. G. Binaghi // (acquisto 1976)” ; 2 ♂, 1 ♀ ( MSNG) “ Liguria occ.// Passo Melogno // 23.IX.64. 1000// m. G. Binaghi” [Hw.] “ Hydraena (s.str.)// pygmaea Waterh. // det. G. Binaghi ” “ MUSEO GENOVA // coll. G. Binaghi // (acquisto 1976)” on same pin ; 1 ♂, 2 ♀ ( MSNG) “App. Tosco. Emiliano// Bosco del Teso. Campan // none. m. 1050. 16.VII.// 1959. G. Binaghi ” [Hw.] “Museo Genova// Coll. Binaghi ” “ Hydraena // pygmaea” [Hw.] “ Hydraena (s.str.)// pygmaea Waterh. // det. G. Binaghi ” “ MUSEO GENOVA // coll. G. Binaghi // (acquisto 1976)” on same pin ; 1 ♀ ( MSNG) “App. Tosco-Emiliano// Bosco del Teso. Torr. // Maresca. 15.18.VII.// 959. G. Binaghi ” [Hw.] “pygmaea ” [Hw.] “ Hydraena (s.str.)// pygmaea Waterh. // det. G. Binaghi ” “ MUSEO GENOVA // coll. G. Binaghi // (acquisto 1976)” ; 1 ♂ ( MSNG) “ Abruzzo // Passo Caparinelle // sorg. F. Vomano ” [ Hw. ] 20. VII. 1878 // G. Binaghi ” [Hw.] “pygmaea ” [Hw.] “ Hydraena (s.str.)// pygmaea Waterh. // det. G. Binaghi ” “ MUSEO GENOVA // coll. G. Binaghi // (acquisto 1976)” ; 1 ♀ ( MSNG) “ Cireggio // Bagnella // 28 settembre1900 ” [Hw]” Hydraena // pygmaea// Sieboldi Rsnh.” [Hw., green label] “ MUSEO GENOVA // coll. G. Binaghi // (acquisto 1976)” ; 1 ♂ ( NHMW) “S Ti Brixen// Umg. Kohlen” “Teis 27.5.73// Schnekenbach” [Hw.] “pygmaea ” [ Hw. ] ; 1 ♂, 1 ♀ ( NHMW) “ Italia-Adamello // Val di Daone ” “ Hydraena // pygmaea” ; 1 ♀ ( NHMW) “I – Lombardia I Varese dist. // 10 km NW Varese, nr. Orino // 13.6. 2001, 475 m// Komarek & Schönmann (2)” “ Hydraena // pygmaea// det. Jäch ” [Hw.] ; 1 ♂ ( NHMW) “ Abruzzen // Italien” [ Hw. ] ; 1 ♂, 1 ♀ ( NHMW) “I – Lazio (RI)// Mti della Laga // Amatrice – Capr. ” “ Bach in 1.400 m // 25.VIII.1992 // leg. Schönmann ”. Italy, form with reflexed elytra : 1 ♂ ( NHMW) “ ITALY: Calabria, 3.5 km // SW Serra San Bruno // 850 m stream” “ 38° 33′ 15.3″N 16° 18′ 34.8″E // 27.VIII.2018, leg. Gold-/ Schmidt (It 18-8a)” used for DNA extraction and sequencing (specimen voucher IBE- AN1129) ; 1 ♂, 1 ♀ ( NHMW) “ SILA (Calabria)// Camigliatello // VII 1933 // A. Dodero” “reflexa ” [Hw.] “det. E. Prettner // H. pygmaea ssp.// reflexa” [species name Hw.] ; 1 ♂ ( NHMW) “ SILA (Calabria)// Camigliatello// “det. E. Pretner // pygmaea// reflexa Rey ” [species name Hw. ] ; 2 ♀ ( NHMW) “ SILA (Calabria)// Camigliatello // 5.VIII.1933 // A. Dodero” ; 1 ♂ ( NHMW) “ SILA (Calabria)// Camigliatello // VII-VIII.1933// A. Dodero ” ; 1 ♂ ( MSNG) “ Calabria 115b 08.10.90// CS Pellegrino. Saracena. // Fte. Cannello, Quellbach // 1385 m WE 902 040 GER” reverse “ Hydraena ” [Hw.] “ Hydraena // (s.str.) reflexa // det. G. Ferro ” “ MUSEO GENOVA // coll. G. Ferro // (dono 2013)” ; 1 ♂, 1 ♀ ( MSNG) “ Sila (Calabria)// CAMIGLIATELLO// 25.VII. 1933 // A. Dodero” [Hw.] “ Hydr. Pygmaea // ssp. reflexa Rey // det. G. Binaghi ” “ MUSEO GENOVA // coll. G. Binaghi // (acquisto 1976)” ; 1 ♂ ( MSNG) “ Calabria, Sila// Camigliatello// Dodero” [Hw.] “ Hydr. Pygmaea // ssp. reflexa Rey // det. G. Binaghi ” “ MUSEO GENOVA // coll. G. Binaghi // (acquisto 1976)” mounted between perspex ; 3 ♂, 2 ♀ ( MSNG) “ SILA (Calabria)// Camigliatello // 25.VII.1933 // A. Dodero” [day and month Hw.] “ Hydr. Pygmaea // ssp. reflexa Rey // det. G. Binaghi ” “ MUSEO GENOVA // coll. G. Binaghi // (acquisto 1976)” on same pin ; 4 ♂ ( MSNG) “ SILA (Calabria)// Camigliatello // 25.VII.1933 // A. Dodero ” [day and month Hw.] “ H. PYGMAEA // S. REFLEXA // det. Dr. CHIESA// BOLOGNA// Via S. Stefano 1″ [species name and det. Hw.] “ Hydraena // s. str.// pygmaea ssp.// reflexa” [Hw.] “ Hydr. Pygmaea // ssp. reflexa Rey // det. G. Binaghi ” “ MUSEO GENOVA // coll. G. Binaghi // (acquisto 1976)” on same pin ; 1 ♂ ( MSNG) “ Basilicata 1093 30.09.90// PZ Pollino. Terranova.// Qu. 3 Piano delle Mandre.// 1330 m XE 073 234 GER” reverse “ Hydraenidae ” [Hw.] “ s. reflexa // Rey// det. Ferro 1993” [species, describer and 93 Hw. ] .

Differential diagnosis. The short habitus, with broad, rounded elytra, together with the male leg modifications and aedeagal design make this species unmistakable with any others in the genus except H. reflexa . For characters separating the two species see above. With the exception of southern Italian populations, H. pygmaea appears to be morphologically almost uniform across its wide geographical range, including male characters (e.g. aedeagus, Fig. 4C–E ).

Distribution and ecology. One of the most geographically widespread Hydraena in the Western Palaearctic, known throughout much of central and southern Europe and Western Asia, from Ireland to Anatolia and Armenia, and from

Scotland in the north to southern Spain, the southern Italian Apennines and the Peloponnese ( Greece) in the south ( Jäch & Skale, 2015). Absent from Scandinavia and North Africa. H. pygmaea is most common in small, stony headwater streams, where it can be found in moss and in association with clay exposures. In some areas (e.g. Bulgaria) it can also be frequent on rotting wood in streams. All specimens examined from throughout the range have been micropterous, a highly unusual finding for such a widespread water beetle ( Foster et al., 2020). The species has shown evidence of decline over the past half century in the UK ( Foster et al., 2020), usually in association with agricultural pollution, but also recently lost from some apparently unmodified catchments, for example at Conic Hill in Lochlomondside, Stirlingshire, Scotland.

Figures

Fig. 4 Hydraena species aedeagi. A–B Hydraena reflexa Rey, Monte d’Oro, Corsica; C–E Hydraena pygmaea Waterhouse; C Rio de las Hoyas, Albacete, Spain; D stream above Bacevo, Rila Mts., Bulgaria; E Ruddycleave Water, South Devon, UK. Scale bar=100 μm