Cyclops abyssorum divergens Lindberg, 1936

Hołyńska, Maria, 2008, On the morphology and geographical distribution of some problematic South Palearctic Cyclops (Copepoda: Cyclopidae), Journal of Natural History 42 (29 - 30), pp. 2011-2039 : 2024-2037

publication ID	https://doi.org/ 10.1080/00222930802140160
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scientific name	Cyclops abyssorum divergens Lindberg, 1936
status

Treatment

Cyclops strenuus divergens Lindberg 1936: p.3 –5, Figures 3–7 View Figure 3 View Figure 4 View Figure 5 View Figure 6 View Figure 7 ; Monchenko 1972: p.82 –83. Cyclops rubens divergens: Lindberg 1956: p.113 ; Lindberg 1957: p.38 –40, Figures 5–8 View Figure 5 View Figure 6 View Figure 7 View Figure 8 , Table II; Cyclops abyssorum divergens: Einsle 1975: p.134 , Figure 16, Table 25; Einsle 1996a: p.40 –41, Figure 24.

Cyclops bohater ponorensis Naidenow and Pandurski 1992: p.27 –30, Figure 1 View Figure 1 . Synonymized by Pandourski (1997) as Cyclops abyssorum divergens .

Cyclops singularis Einsle, 1996b: p.170 , p.172–176, Figures 2–6 View Figure 2 View Figure 3 View Figure 4 View Figure 5 View Figure 6 ; Einsle 1996a: p.33 – 36, Figure 21; Hołyńska and Dahms 2004: p.178 –196, Figures 1 View Figure 1 , 3A View Figure 3 , 6A,B View Figure 6 , 7F View Figure 7 , 10D View Figure 10 , 11C View Figure 11 , Table 1. New synonymy.

Cyclops strenuus: Kiefer 1955: p.112 –114, Figure 1 View Figure 1 .

? Cyclops strenuus forma vranae Koźmiński 1927: p.71 –72, Figure 6 View Figure 6 ; Cyclops strenuus subsp. vranae: Koźmiński 1933: p.107 , p.112, p.125; Koźmiński 1936: p.205, p.221. Cyclops abyssorum vranae: Lindberg 1957: p.79 –80, Table XIIb.

Material examined

Cyclops abyssorum divergens . Iran: Fars Province, Shiraz, 29 ° 339N 52 ° 309E, underground cisterne at tomb of Hafiz , 6 October 1935, two ♀♀, syntypes ( KBIN: COP7146 A–C; COP7147 A–B) .

Bulgaria: Sofia District, Ponor Mountains, cave Katzite, near Zimevitsa village, 43 ° 019N 23 ° 189E, ca. 1300 m a.s.l., 11 February 1989, one ♀, one „, labelled as ‘‘ Cyclops abyssorum divergens ’’, originally described by Naidenow and Pandurski (1992) as Cyclops bohater ponorensis ( MIZ: 157880-81).

Croatia: Island Cres , Lake Vrana, northwestern part, 44 ° 529N 14 ° 229E, vertical haul from 20 m deep to surface, bottom covered with Chara , leg. I. Ternjej 23 August 1997, five ♀♀ (three ♀♀ dissected, two ♀♀ undissected) ( MIZ: 157882-86) .

France: Besse-sur-Issole , 43 ° 219N 6 ° 119E, Gavoti, marsh, 18 May 2001, three ♀♀ ( MNHN) .

Hungary: Tiszavasvári , 47 ° 579N 21 ° 219E, Alkaloida , Sewage Plants, Oxidation lakes, one ♀, leg. M. Hołyńska 26 November 1985. ( MIZ: 157887) – in Hołyńska & Dahms 2004 it was referred to as Cyclops singularis .

Italy: Sicily, Nebrodi Mountains Lake of Trearie , 37 ° 579180N 14 ° 509150E, leg. F. Stoch & D. Vagaggini 7 October 2006, three ♀♀, two „„ ( MIZ: 157888-92) .

Lebanon: ‘‘ Chebaa , bei Chouaya’ ’, 1500 m, Lache 22 November 1951, labelled as ‘‘ Cyclops strenuus ’’, three ♀♀, two „„ ( SMNK: Glas 4169) .

Poland: Wojewódzkie Mazowieckie, Nowa Wieś ca. 20 km southwest of Warsaw , ditch [5], 52 ° 089N 20 ° 469E, leg. R. & M. Hołyńscy 3 April 2006, one ♀ ( MIZ: 157893) .

Portugal: Penilhos 1, 37 ° 389N 7 ° 519W, 07 February 2002, two ♀♀ ( MNHN) .

Spain: Pyrenees , Lake Estanya (Estans) ca. 1000 m a.s.l., leg. R. M. Miracle in May, identified by B. Dussart as C. abyssorum divergens , three ♀♀ ( MNHN)

Romania: Neamt, Lacu Roşu (Gyilkos-tó), lakeshore, 46 ° 489N 25 ° 479E, leg. M. Hołyńska 13 August 2003, one ♀ ( MIZ: 157894) .

Turkey, Eyüp , neighbourhood of Istanbul, 41 ° 029N 28 ° 559E, 8 March 1939, three ♀♀, one „ ( SMNK: Glas 1123); Demirköprü (Hatay) 36 ° 169N 36 ° 179E, leg. U. Demirhindi 24 March 1966, labelled as ‘‘ Cyclops strenuus ’’, four ♀♀ ( NHM) .

United Kingdom: Cheshire, Rostherne Mere, 53 ° 209N 2 ° 259W, leg. A.L. Galliford 17 May 1962 I, 440, labelled as ‘‘ Cyclops strenuus s. str. ’’ three ♀♀ ( NHM); London, Richmond Park, pond northwest of Pen Ponds , 51 ° 269N 0 ° 169W, leg. W. A. Smith 8 February 1970, labelled as ‘‘ Cyclops strenuus s. str. ’’ four ♀♀, one „ ( NHM) .

Yugoslavia (?): Petrina Mountains , puddle, leg. Hadzisce 29 October 1950, labelled as ‘‘ Cyclops strenuus ’’ one ♀, two „„ ( SMNK: Glas 4145).

Uzbekistan: near Samarqand , in puddle, bank of the river Chashma, 29 October 1962, identified by V. I. Monchenko as ‘‘ Cyclops strenuus divergens ’’, three ♀♀, three „„ ( MIZ: 157895-157900), gift of V. I. Monchenko .

‘‘ Cyclops singularis’’. Germany: Litzelsee / Markelfingen 47 ° 449N 9 ° 019E, ‘‘ Lake Konstanz’ ’, 4 April 1994, three ♀♀, one „, paratypes ( SMNK) .

Comparative material

Cyclops abyssorum s. str. Norway (terra typica). Oslo, Steinsfjord , 60 ° 029N 10 ° 109E, (28 km west of the type locality, Maridalsvann), slightly eutrophic, leg. Herbst 1972, three ♀♀ ( SMNK: Glas 5100) .

Mosvatn, 58 ° 589N 5 ° 439E, eutrophic lake: leg. J. P. Nilssen 7 September 1973, one ♀ ( MIZ: 157901) ; leg. Å. Molversmyr & S. B. Waervågen 15 October 1989, one ♀ ( MIZ: 157902) ; leg. Å. Molversmyr & S. B. Waervågen 28 April 1994, two ♀♀ ( MIZ: 157903-04) ; leg. Å. Molversmyr & S. B. Waervågen 19 July 1994, two ♀♀ ( MIZ: 157905-06) .

Lønavatn, 60 ° 419N 6 ° 289E, oligotrophic lake: 14 July 1969, one ♀ (UNOL); [23], leg. J. P. Nilssen 30 May 1973, three ♀♀ ( MIZ: 157907-09) .

Rockpool VS-XI, 58 ° 429N 9 ° 179E, leg. J. P. Nilssen 31 May 1983, two ♀♀ ( MIZ: 157910-11) .

Rockpool VS-III, 58 ° 429N 9 ° 149E, eutrophic, leg. J. P. Nilssen 13 September 1983, one ♀ ( MIZ: 157912) .

Frøylandsvatn, 58 ° 469N 5 ° 419E: [32], leg. Å. Molversmyr & S. B. Waervågen 30 March 1999 and 14 April 1999, two ♀♀ ( MIZ: 157913-14); [33], leg. Å. Molversmyr & S. B. Waervågen 10 September 1998 and 29 September 1998, one ♀ ( MIZ: 157915) .

Rockpool VS IX, 58 ° 429N 9 ° 149E, mesotrophic, leg. J. P. Nilssen 21 April 1983, two ♀♀ ( MIZ: 157916-17) .

Hellestveitvann, 59 ° 049N 9 ° 309E, oligotrophic lake, 1eg. J. P. Nilssen & S. B. Waervågen 09 August 2002, two ♀♀ ( MIZ: 157918-19) .

Lake Berse , 58 ° 199N 8 ° 139E, mesotrophic lake, leg. J. P. Nilssen 20 August 2002, two ♀♀ ( MIZ: 157920-21) .

Ljosevannet, 58 ° 319N 8 ° 089E, oligotrophic lake, leg. J. P. Nilssen 22 August 2002, three ♀♀ ( MIZ: 157922-24) .

Formuvann, 58 ° 399N 8 ° 129E, oligotrophic lake, leg. J. P. Nilssen 22 August 2002, one ♀, ( MIZ: 157925) .

Female. Morphometric data in Table 3. Posteriolateral lobes on pediger 2 sometimes present (e.g. Bulgaria cave Katzite), usually absent ( Figure 10F View Figure 10 ). Pediger 4 without posterior ‘‘wings’’ ( Figure 10F View Figure 10 , cf. Figure 1H View Figure 1 ). Pediger 5 pointed outwards ( Figure 9C,D View Figure 9 ), lateroventral lobes present ( Figure 6A View Figure 6 ). Symmetrical pattern of cuticular ridges present near large copulatory pore: pattern more complex in Turkish specimens (Demirköprü) ( Figure 7B–D View Figure 7 ), simple in female from UK (London) ( Figure 7A View Figure 7 ), restricted to single median ridge in female from Uzbekistan, but may vary even within population (Lake Vrana, Croatia). Genital double-somite usually adorned with shallow cuticular pits, extending also to succeeding urosomites. Anal operculum ( Figure 9E View Figure 9 ) not distinct, proctodeum without hair/spinule ornamentation. Posterior margin of anal somite with continuous row of spinules. Caudal ramus ( Figure 9A View Figure 9 ) medially pilose; tuft of hairs set perpendicular to ramus axis usually absent at anterior end; dorsal keel present. Spinules present at implantation of lateral and lateralmost terminal caudal setae.

Antennule 17-segmented, length varies between hardly reaching posterior margin of cephalothorax and extending to distal margin of pediger 2. Last three terminal segments with hyaline membrane. Armature formula as in C. ankyrae . Aesthetasc on segment 12 reaches proximal third or beyond distal margin of segment 14 ( Figures 6B View Figure 6 , 10C View Figure 10 ). Aesthetasc on segment 16 reaching to or slightly beyond middle of segment 17. First antennular segment with proximal row of spinules. Majority or at least the more proximal segments of antennule adorned with shallow cuticular pits on posterior surface.

Antenna bearing three setae on coxobasis, and one, nine, seven setae on endopodal segments 1 to 3, respectively. Exopodite seta reaching to or beyond distal margin of third endopodal segment. Medial setae ( Figure 10B View Figure 10 ) of coxobasis without long setules. Caudal ornamentation of coxobasis ( Figures 10B View Figure 10 ) composed of long spinules on lateral margin near base; robust spinules (5–11) in longitudinal row near lateral margin; double oblique row proximal to longitudinal row, spinules in more proximal row often smaller; oblique field of small spinules below insertion of medial setae; and small spinules on medial margin near base. Frontal surface of antennal coxobasis similar to that in C. ankyrae ( Figure 1C View Figure 1 ), adorned with few spinules near lateral margin, at 4/10 of segment, and group of long or small spinules medioproximally to former group.

Lateral protuberances of labrum ( Figure 10A View Figure 10 ) with few (two to four) small teeth, epistoma and labrum, except for usual distal fringe hairs, without ornamentation. Paragnaths with long spinules on mediodistal lobe (verified in specimens from Eyüp in Turkey and Nebrodi in Sicily). Mandible ( Figure 10D View Figure 10 ) without ornamentation near palp, setation as in C. ankyrae . Maxillula with setation typical of family, palp with transverse row of large spinules ( Figures 6C View Figure 6 , 11F View Figure 11 ) near base and tiny spinules more distally, very rarely ornamentation missing ( Figure 10D View Figure 10 ). Long setules present on proximal half of proximalmost seta of palp ( Figures 10D View Figure 10 , arrowed). Maxilla setation as in C. ankyrae , endopodite two-segmented. Frontal surface of syncoxopodite without spinule or hair ornamentation. Maxilliped segmentation and setation as in C. ankyrae . On frontal surface of syncoxopodite ( Figure 10E View Figure 10 ) group of medium-sized or small spinules between the level of insertion of distalmost and median setae, tiny spinules in two or three groups more proximally, and sometimes row of small spinules near distal margin of segment. Collar-shaped membranous element ( Figure 10E View Figure 10 , arrowed) near lateral margin of segment.

Spine formula on terminal exopodal segment of P1–P4, 3433; other armature elements as in C. ankyrae . P1 medial spine with long and stiff setules in proximal half ( Figures 6D View Figure 6 , 9B View Figure 9 ) and short spinules more distally, reaching between half and slightly beyond enp 2. Large spinules arranged in arc between insertions of exopodite and endopodite on frontal surface of basipodite. Medial expansion of basipodites of P1– P3 with fine hairs, those on P4 bare or with fine or thick hairs (this character can be variable within one population, or even in the same specimen on two sides of P4 ( Germany, Litzelsee/Markelfingen). Couplers frontally bare, caudally pilose on P4 only. Obtuse protuberances of P4 coupler ( Figure 11C View Figure 11 ) usually slightly emerging beyond distal margin of coupler, protuberances sometimes more conspicuous, or not emerging beyond distal margin. P4 coxopodite seta not bulbous. Spinule ornamentation on caudal surface of P4 coxopodite ( Figures 11C View Figure 11 ) composed of: 6– 13 spinules of similar size along distal margin, distal row often intermittent and arranged in two or three groups; long spinules in group at laterodistal angle; and long oblique row starting near proximal margin. Hairs or spinules usually absent (in 34 of 35 specimens examined) on lateral margin of coxopodite, very small spinules present in single female from Petrina ( Yugoslavia?). Proximolateral angle usually (in 31 of 34 females) without ornamentation; spinules present on one side of leg 4 in female from Hungary and one specimen from France, spinules appear both sides of leg 4 in a female from Cheshire, UK. Lateral hairs on first endopodal segment usually shorter than those on second and third endopodites ( Figure 11C,E View Figure 11 ). Short row of spinules at insertion of medial spine and apical seta of P5 ( Figure 9C View Figure 9 ), no spinules at implantation of lateral seta. P6 ( Figure 9D View Figure 9 ) with medial seta and two lateral spines, relative lengths from seta to lateral spines: 2.2–2.3, 1.1–1.5, 1.0.

Male. Body length 1240–1650 Mm. Cephalothorax length/width: 1.1–1.3. Pediger 5 not pointed outwards ( Figure 8A View Figure 8 ), lateroventral lobes absent. P6 flap without ornamentation, only 1-1 medial pore present, mediodistal angle rounded. Caudal ramus 4.7–5.6 times as long as wide, no dorsal keel. Lateral caudal seta 0.19–0.25 times as long as ramus, and inserted at 0.21–0.25 length of caudal ramus. Dorsal caudal seta 0.9–1.5 times as long as lateralmost terminal caudal seta. Relative length of terminal caudal setae from medialmost to lateralmost 1.7–2.1, 3.4–4.5, 2.7–3.4, 1.0 (seta length/ramus length: 1.0–1.4, 2.2–2.9, 1.7–2.2, 0.55–0.69). Longest terminal caudal seta about 0.65–0.8 times as long as urosome.

Antennule 16-segmented, with compound (segments 16 and 17 anteriorly fused) terminal segment, armature formula: 8+3 aesthetascs, 4, 2, 2+aesthetasc, 2, 2, 2, 2, 1+spine+aesthetasc, 2, 2, 2, 2+aesthetasc, 2, 1+aesthetasc ( Figure 8B View Figure 8 ), [4+aesthetasc, 7+aesthetasc]. Plate-like structures (one large on segment 14, and two smaller on segment 15) ( Figure 8B View Figure 8 ), and short conical elements (one each on segments 14 and 15) at distal geniculation. Second endopodal segment of antenna with seven or eight setae. Spine on P2 exp1 slender and straight, spinules on spine longer than those on other spines of swimming legs. Medial expansion of basipodite of P1–P4 pilose. Spinule ornamentation on caudal surface of P4 coxopodite as in female, only somewhat less (six to nine) spinules in distal row. Proportional lengths of P6 setae from medialmost to lateralmost 1.0, 1.6–2.3, 2.9–4.2.

Comments

Lindberg (1936) described C. strenuus divergens from cisterns and wells in the Zagros Mountains at 1600–1700 m a.s.l. (Borujerd, Esfahan and Shiraz), and compared it to C. abyssorum , as a form morphologically closely allied to the Iranian Cyclops . Lindberg mentioned four characters in which the two taxa differed: the shorter caudal ramus (six or seven times as long as wide in C. s. divergens compared with eight times as long as wide in C. abyssorum ), inner median caudal seta shorter than urosome in C. s. divergens (about as long as urosome in C. abyssorum ), A1 shorter (reaching middle of pediger 2 in C. s. divergens but reaching beyond pediger 2 in C. abyssorum ), number of eggs fewer in C. s. divergens. In a later publication, Lindberg (1942) added several new Iranian records from the Caspian Sea region to the Persian Gulf, from localities near sea level to sites at almost 1700 m a.s.l., both fresh and saline habitats, predominantly small and/or ephemeral waterbodies (cistern, water basin, well, puddle, marsh, ricefield). In his monograph of the genus Lindberg (1957) defined the range of C. ‘‘ rubens divergens’’ [the name C. rubens (Jurine 1820) , preoccupied by a diaptomid Cyclops rubens Müller 1785 , was erroneously used as an older synonym of C. strenuus Fischer 1851 ] as stretching from Turkey to northern/ northwest Afghanistan and probably also including Iraq, Syria, Israel and some part of the former Soviet Union. Cyclops strenuus divergens was found in a puddle in the Samarqand region ( Uzbekistan) ( Monchenko 1972), which so far represents the easternmost record of the taxon. Einsle (1975, 1996a) considered the ‘‘ divergens - form’’ to be a subspecies of C. abyssorum , and thought all populations of the latter species in North Africa (Maghreb) and Asia ( Turkey, Iran and Afghanistan) belonged to C. a. divergens. Naidenow and Pandurski (1992) described C. bohater ponorensis from subterranean habitats, small ponds and pools near the entrance of a cave at 1300 m a.s.l. in the Western Balkans Mountains ( Bulgaria). This form was later synonymized by Pandourski (1997) as C. abyssorum divergens , and the author explained its presence by possible transport by the Ponor river, which flows through the cave at high water. Subterranean occurrences (in wells) are also known from Sicily ( Pesce and Galassi 1987). Cyclops abyssorum divergens has been reported from Tunisia ( Dumont et al. 1979) and the Spanish Pyrenees ( Dussart 1979).

In the recent past, two new Cyclops species , C. heberti and C. singularis , have been described ( Einsle 1996b) from some ephemeral ponds in Southern Germany. In diagnoses of the new taxa, which for a long time were misidentified as C. furcifer, Einsle put emphasis on the differences in the electrophoretic traits and timing of the chromatin diminution. Separation of the morphological characters in C. furcifer , C. heberti and C. singularis seemed to be less distinct. Some years later C. singularis was found in Belgium ( Alekseev et al. 2002), UK (Green, in a letter to G. A. Boxshall), Slovakia and Hungary ( Hołyńska and Dahms 2004), and in northeastern and Central Italy ( Stoch 2006).

Hołyńska and Dahms (2004) compared the morphology of the cephalothoracic appendages in 12 Cyclops taxa, and revealed unique ornamentation of the maxillular palp in C. singularis . The presence of large spinules on the base of the maxillular palp ( Figure 6C View Figure 6 ) is a rarely variable character and appears in both sexes. This specific ornamentation (absent in C. abyssorum abysssorum ), is present in almost all the specimens examined here from Western Europe to Central Asia. In one of the three males from Uzbekistan, and one of the two females from Iran the maxillular palps do not have large spinules ( Figure 10D View Figure 10 ). In one Iranian female the characteristic ornamentation appears on the maxillule of the right side ( Figure 11F View Figure 11 ) and is missing on the left side. All the other qualitative and morphometric characters ( Table 3) of the females of ‘ C. strenuus divergens ’ from Shiraz ( Iran) agree with those in specimens with a maxillular palp of singularis - type. The occurrence of non-typical morphology might be explained by the fact that Southern Iran and the Samarqand region in Central Asia are at the limit of the taxon range. Nevertheless, shared morphology and biology (frequent occurrence in small ephemeral waterbodies) support the view that our Iranian form is conspecific with, and is a senior synonym of C. singularis . The geographic distribution ( Figure 12 View Figure 12 ) of C. a. divergens, as we now understand this taxon, extends at least from the southern part of the UK and Poland in the north to South Iran in the south, and from Portugal in the west to Uzbekistan in the east.

Cyclops abyssorum divergens can be distinguished from congeners by combinations of characters: lack of posterior wings on pediger 4 ( Figure 10F View Figure 10 ); presence of lateroventral lobes on pediger 5 ( Figure 6A View Figure 6 ); inner median caudal seta short, usually 0.5–0.7 times as long as urosome; 17-segmented antennule; transverse row of large spinules on the maxillular palp ( Figures 6C View Figure 6 , 11F View Figure 11 ), and presence of long setules on the proximal half of the proximalmost seta of the palp ( Figure 10D View Figure 10 , setules arrowed); the ornamentation of the frontal surface of the maxilliped syncoxopodite (small or medium-sized spinules between median and distalmost setae, tiny more proximally and sometimes near the distal margin) ( Figure 10E View Figure 10 ); lack of hairs or spinules on the lateral margin of P4 coxopodite ( Figure 11C View Figure 11 ); couplers caudally bare on P1–P3, and pilose on P4; absence of spinules at the insertion of lateral setae of P5 ( Figures 6A View Figure 6 , 9C View Figure 9 ); spine formula 3433 on P1–P4 exopodites; presence of large spinules on the frontal surface of P1 basipodite ( Figure 9B View Figure 9 , spinules arrowed); and long stiff setules on the proximal half of P1 medial spine ( Figures 6D View Figure 6 , 9B View Figure 9 ).

Cyclops abyssorum divergens differs from C. abyssorum s. str. in the relative length of the median terminal caudal seta ( Table 3), the spinules on the lateral margin and at the proximolateral angle on the caudal surface of P4 coxopodite usually missing in C. a. divergens ( Figure 11C View Figure 11 ), but often present in C. a. abyssorum [lateral spinules present in 19 of 28 ♀♀, proximolateral spinules present in 19 of 24 ♀♀, see Figure 11A,B View Figure 11 ], large spinules on the maxillular palp usually present in C. a. divergens but absent in C. a. abyssorum . From these observations it seems that there is tendency rather than clear-cut separation in the morphological characters, which indicates relatively recent divergence and would support a subspecific relationship of these taxa. Cytogenetic studies ( Einsle 1996a,b) in Cyclops revealed differences in the embryonic cleavage division during which chromatin diminution occurs and in the size of the eliminated heterochromatin particles between C. abyssorum and C. singularis (synonymized here with C. a. divergens). Einsle (1996a), however, supposed the timing of the chromatin diminution to be variable in C. abyssorum , and interpopulation variation of this trait was already reported in other Cyclops species ( Dorward and Wyngaard 1997; Grishanin and Akif’ev 1999). The diagnostic significance of the cytogenetic characters in these Cyclops taxa (are they speciesspecific or variable within species) needs to be tested.

The geographical distribution of C. abyssorum s. str. is not fully understood yet. Lindberg (1957) and Einsle (1996a) applied the name C. abyssorum s. str. to the northern European populations (Scandinavia, Spitzbergen, northern Poland, Baltic States and northern European part of Russia as far as the Sverdlovsk region near the Ural Mountains; I identified C. abyssorum s. str. also from northern UK, Shetlands, Iceland and from Eastern Greenland) only. In Norway, C. abyssorum occurs in both large and small waterbodies at various trophic states. Interestingly, the variation of the morphometric traits in C. abyssorum s. str. from Norway (terra typica) alone is comparable to those in C. a. divergens collected from the huge area between UK and Central Asia (for comparison see Table 3). The systematics of the abyssorum -group in Central and Southern Europe is very confusing and still needs clarification. From this relatively small region as many as 20 local forms, ecotypes and subspecies of questionable taxonomic value have been described ( Dussart and Defaye 2006). Further research may reveal synonymies of some of these forms with C. abyssorum s. str. or C. a. divergens, and find more geographic overlap of the distributional areas of the two taxa. The available data on habitat preferences nevertheless suggest that at least in Central and Southern Europe, C. a. divergens populates small waterbodies or lakes in lowland area and mountains of medium height, while other forms of C. abyssorum , usually referred to as C. a. tatricus and C. a. praealpinus, and different local forms described from the Apennines, Alps and Pyrenees, live in the high mountain lakes. In the contact zone, C. a. divergens may hybridize with the high-altitude forms, and specimens with intermediate morphology can appear. From the Pyrenees, Dussart (1979) reported the occurrence of C. abyssorum pyrenaicus Dussart, 1979 , C. abyssorum forma tatricus Kozminski, 1927, and two forms of C. a. praealpinus Kiefer, 1939 from lakes at 1600–2400 m a.s.l., and also found C. a. divergens at 1000 m a.s.l. The females collected at this latter site have a mixed character set. The inner median caudal setae are relatively short (0.6–0.7 times as long as urosome); the lateral margin of the P4 coxopodite bears short lateral spinules in all three specimens examined (ornamentation at proximolateral angle could not be verified); and the large spinules on the maxillular palp, the main diagnostic character of C. a. divergens, were apparently present only in one female and only on one side of the body. As this sample dried out, and the preparations were made after a trisodium phosphate treatment, the possibility that lack of ornamentation on the maxillular palp is a result of damage cannot be excluded.

The occurrence of C. a. divergens in a deep karstic lake, Lake Vrana, in Island Cres, Croatia is very interesting. The five females available have relatively small body length (range: 1535–1775 Mm; mean: 1634 Mm), relatively short caudal rami (length/width: 5.5–6.0 Mm, mean: 5.7 Mm), and longer inner median caudal setae (seta length/urosome: 0.65–0.80 Mm, mean: 0.76 Mm), but match C. a. divergens in all meristic and qualitative characters. This finding suggests that those lake populations in lowlands and mountains of medium height, which are often referred to as C. abyssorum divulsus in the literature, may actually be C. a. divergens. Koźmiński (1927) described Cyclops strenuus forma vranae from the plankton of Lake Vrana. Unfortunately the depository of the type of this taxon is unknown, and the original description does not allow safe identification of the specimens here examined from Lake Vrana with the form of Koźmiński. In addition we do not know if the Cyclops collected from underwater meadows of the macroalga Chara is the only representative of the genus in Lake Vrana. Synonymization of C. a. divergens with C. a. vranae lacks convincing morphological data and would at this moment be premature.