| CYCLOPINAE Rafinesque, 1815
DIACYCLOPS Kiefer, 1927
emend. Morton, 1985; Reid et al., 1989
The genus Diacyclops is the most
specious and the most problematic cyclopoid genus
(Monchenko and Von Vaupel Klein, 1999; Monchenko,
2000; Stoch, 2001).
Historically, there has been taxonomical confusion and instability regarding the systematic status of the genus Diacyclops. Some authors (Rylov, 1948; Damian-Georgescu, 1963), due to a morphological overlap between the genera Acanthocyclops and Diacyclops, included both genera into the genus Acanthocyclops.
Considering the structure of leg 5 as the main unifying generic feature of the family Cyclopidae, Kiefer (1927, 1967) subdivided the genus Acanthocyclops into two genera: Acanthocyclops, with the subgenera Acanthocyclops s.str. and Megacyclops, and Diacyclops.
Validity of the separation of these genera was questioned by Mazepova (1978) who recognized only Acanthocyclops in her monograph devoted to the Baikal cyclopids.
Following Kiefer's suggestion, Monchenko (1985), Dussart & Defaye (1985) and, more recently, Einsle (1993) definitely accepted both Acanthocyclops and Diacyclops as valid taxa.
Nevertheless, recent progress in cyclopoid research in North America and the discovery of new species with unusual structure and armature of leg 5 (Reid, 1994; Boxshall et al., 1993) have further confused the status and definition of the genus, proving as well that the systematic relationship and biogeographical patterns within the family Cyclopidae should be further elucidated. Recently Reid (1999) transferred Diacyclops virginianus to the new established genus Rheocyclops; Reid & Ishida (2000) moved as well Diacyclops yezoensis to the new genus Itocyclops; later on Karanovic (2000) established a new genus, Reidcyclops, to accomodate the species Diacyclops trajani, Diacyclops dimorphus and Diacyclops imparilis, characterized by a 2-segmented fiftyh leg and sexual dimorphism in all the swimming legs, suggesting as well that
the species D. incolotaenia, D. jasnitskii, D. intermedius, D. spongicola and D. eulitoralis from lake Baikal, on account of the peculiar armature of leg 5, and specific shape of the antenna, could form a distinct genus, endemic to lake Baikal.
At present the systematic "status" of the genus is undecided, due to its close affinities with the genus Acanthocyclops, and a revison of the "Diacyclops-Acanthocyclops" complex is strongly suggested.
The genus shows a worldwide distribution, with a few strictly cosmopolitan species. Most members are widespread in Eurasia and North America, a few species and subspecies are known from the tropics and the temperate Southern Hemisphere.
The genus seems to be particularly diversified in the Palaearctic but the high concentration could be probably due to the historically intensive research in the surface and subterranean habitats of that area rather than of any zoogeographical meaning: likewise, the lack of exhaustive information for the Oriental and Australian regions could be realated to inadequate and deficient collecting efforts in those countries
From an ecological point of view, the genus Diacyclops is the most successful and diverse of cyclopid genera. It includes land species inhabiting a wide variety of shallow fresh waters, distrophic ponds, temporary water bodies, riverine wetlands, mosses and brackish inland waters; other species occur in large and small natural and artificial lakes and reservoirs, occasionally in rivers; it is also widely distributed in cave and interstitial waters and in groundwater related habitats, whre numerous stygobitic species and subspecies, for the most part belonging to the "Diacyclops languidus-languidoides" group, can be found.
There are presently more than 100 named species and subspecies of Diacyclops, most of them stygobitic or stygophilic inhabitants of different groundwater systems.
Diacyclops abyssicola Lilljeborg, 1901 [Europe; ground waters] *
Diacyclops alabamensis Reid 1992 [north America, wells] 
Diacyclops albus Reid 1991 [north America, hyporheic]
Diacyclops alticola Kiefer, 1935 [India, China; fresh surface and ground waters] *******
 | | | |
Diacyclops andinus Locascio de Mitrovich & Menu-Marque, 2001 [Argentina; pools] (left)
Diacyclops antrincola Kiefer 1967 [Europe; ground waters]
Diacyclops arenosus (Mazepova, 1950) [Baikal Lake]
[= Acanthocyclops arenosus Mazepova, 1950]
Diacyclops balearicus Lescher-Moutoué 1978 [Balearic Islands; caves]
Diacyclops belgicus (Kiefer 1936) [Europe; fresh surface and ground waters]
Diacyclops bernardi (Petkovski 1986) [north America, Mexico; ponds, caves]
Diacyclops bicuspidatus bicuspidatus (Claus, 1857) [cosmopolitan, except Australia; fresh waters] *****
Diacyclops bicuspidatus lubbocki (Schmankevitch, 1875) [palaearctic, Iran; surface and ground waters]
Diacyclops bicuspidatus lucanus Pesce & Galassi 1985 [Italy; wells]
Diacyclops bisetosus (Rehberg, 1880) [cosmopolitan; fresh surface and ground waters] |
Diacyclops biwensis Ishida, 2005 (syn. Monchenkocyclops biwensis (Ishida, 2005)
Diacyclops brevifurcus Ishida, 2006 [Japan]
Diacyclops cantonatii Stoch, in prep.
Diacyclops chakan Fiers & Reid., 1996 [Mexico, Yucatan; wells]
Diacyclops chappuisi Naidenow & Pandourski 1992
[Bulgaria; ground waters] ******
Diacyclops charon Kiefer 1931 [Bosnia, Italy; ground waters]
Diacyclops chrisae Reid 1992 [north America; ground waters]
Diacyclops clandestinus (Kiefer 1926) [Europe, Asia; ground waters]
Diacyclops cockingi Karanovic, 2006 [Australia; bores]
Diacyclops cohabitatus Monchenko, 1980 [Ukraine, Austria; wells, caves]
Diacyclops conversus Reid, 2004 [U.S.A.; ground waters]
Diacyclops crassicaudis crassicaudis (G.O. Sars, 1863) [cosmopolitan; fresh surface and ground waters]
Diacyclops crassicaudis brachycercus Kiefer, 1927 [Europe, north America; fresh waters]
Diacyclops crassicaudis cosana Stella & Salvadori 1954 [Italy; caves]
Diacyclops crassicaudis cretensis (Kiefer 1928) [Greece, China, Korea; fresh surface and ground waters]
Diacyclops crassicaudis lagrecai Pesce & Galassi 1987 [Italy, Sicily; wells]
Diacyclops crassicaudis trinacriae Pesce & Galassi 1987 [Italy, Sicily; wells]
Diacyclops crassicaudoides (Kiefer, 1928) [New Zealand, Tasmanie; fresh waters]
Diacyclops cristinae Pesce & Galassi 1987 [Italy; wells]
Diacyclops cryonastes Morton, 1985 [Australia, Tasmania; temporary and permanent pools]
Diacyclops disjunctus (Thallwitz, 1927) [Europe; fresh surface and ground waters]
Diacyclops dispinosus Ishida, 1994 [Japan; springs]
Diacyclops dyabdar Novikov et al., 2024 [Siberia]
Diacyclops ecabensis Fiers & Ghenne, 2000 [Mexico, Yucatan; wells ]
Diacyclops einslei De Laurentiis et al., 1999 [Australia; ground waters]
Diacyclops ekmani (Lindberg, 1950) [Sweden; fresh waters] *
Diacyclops fontinalis Naidenov, 1969 [Bulgaria; fresh waters]
Diacyclops galbinus (Mazepova, 1961) [Baikal Lake]
[= Acanthocyclops galbinus Mazepova, 1961]
Diacyclops gauthieri Green, 1962 [Africa; fresh waters]
Diacyclops haemusi Naidenow & Pandourski 1992 [Bulgaria; karst waters] (= Acanthocyclops iskrecensis Pandourski, 1992)
Diacyclops harryi Reid 1992 [north America; hyporheic, wells]
Diacyclops haueri Kiefer, 1931 [north America; fresh waters]
Diacyclops hispidus Reid,1988 [Colombia; fresh waters]
Diacyclops humphreysi humphreysi Pesce & De Laurentiis 1996 [Australia; wells]
Diacyclops humphreysi unispinosus Karanovic, 2006 [Australia; river bore]
Diacyclops hypnicola (Gurney 1927) [Europe; ground waters, mosses]
Diacyclops hypogeus Kiefer, 1930 [Yugoslavie; caves] *
Diacyclops ichnusae Pesce & Galassi 1985 [Italy, Sardinia; wells]
Diacyclops ichnusoides Petkovski & Karanovic, 1997 [Balkan Peninsula, lake Ohrid; interstitial]
Diacyclops incolotaenia (Mazepova, 1950) [Baikal Lake]
[= Acanthocyclops incolotaenia Mazepova, 1950]
Diacyclops indianensis Reid, 2004 [U.S.A.; ground waters]
Diacyclops insularis Monchenko 1982 [Caspian Sea, interstitial]
Diacyclops intermedius (Mazepova, 1952) [Baikal Lake]
Diacyclops iranicus Pesce & Maggi 1982 [Iran; wells]
Diacyclops italianus (Kiefer, 1931) [Italy; ground waters]
Diacyclops jeanneli jeanneli (Chappuis 1929) [north America, fresh waters]
Diacyclops jeanneli putei Yeatman 1943 [north America, fresh waters]
Diacyclops joycei karanovic et al., 2013
Diacyclops karamani (Kiefer 1932) [Bosnia, Herzegovina; ground waters]
Diacyclops kaupi karanovic et al., 2013
Diacyclops kyotensis Ito 1964 [Japan; ground waters]
Diacyclops laurisilvae Holinska et al., 2024 [Portugal]
languidoides-group
Diacyclops languidoides languidoides (Lilljeborg 1901) s.l. [cosmopolitan, except Australia; fresh surface and ground waters]
Diacyclops languidoides anatolicus Pesce 1992 [Turkey; wells]
Diacyclops languidoides aprutinus Pesce & Fabrizi 1979 [Italy; wells]
Diacyclops languidoides cavernicola (Lindberg 1950) [Iran; caves]
Diacyclops danielopoli Pospisil & Stoch, 1999 [Europe; phreatic]
Diacyclops felix Pospisil & Stoch, 1999 [Europe; phreatic]
Diacyclops languidoides elegans Mazepova, 1961 [Baikal; lakes]
Diacyclops languidoides eriophori (Gurney, 1927) [Czecho-Slovakia; fresh waters] *
Diacyclops languidoides goticus (Kiefer, 1931) [Austria, Slovenia; ground waters (caves, wells)]
Diacyclops languidoides gracilirostris Smirnov, 1932 [URSS; fresh waters]
Diacyclops languidoides hiberniae (Gurney, 1927) [Europe; fresh waters]
Diacyclops languidoides gracilicaudatus (Smirnov, 1930) [URSS; fresh waters]
Diacyclops hanguk Karanovic et al., 2013 [Korea; subterranean waters]
Diacyclops languidoides improcerus (Mazepova, 1950) [Baikal Lake]
Diacyclops ishidai Karanovic et al., 2013 [Japan; subterranean waters]
[= Acanthocyclops improcerus Mazepova, 1950]
Diacyclops hisuta Karanovic et al., 2013 [Japan; subterranean waters]
Diacyclops languidoides italianus [Italy, URSS; ground waters]
Diacyclops leeae Karanovic et al., 2013 [Korea; subterranean waters]
Diacyclops languidoides jasnitskii (Mazepova, 1950) [Baikal Lake]
[= Acanthocyclops jasnitskii Mazepova, 1950; = D. jasnitskii (Karanovic, 2000) ]
Diacyclops languidoides japonicus Ito 1952 [Japan; ground waters]*
Diacyclops languidoides konstantini Mazepova, 1961 [Baikal; lakes]
[= Acanthocyclops konstantini Mazepova, 1961]
Diacyclops languidoides moravicus Sterba 1956 [Czecho-Slovakia, Baikal; fresh waters]
[= Acanthocyclops galbinus Mazepova, 1961]
Diacyclops languidoides nagysalloensis Kiefer, 1927 [Europe; fresh surface and ground waters]
Diacyclops parasuoensis Karanovic et al., 2013
Diacyclops parahanguk Karanovic et al., 2013 [Japan; subterranean waters]
Diacyclops languidoides pragensis Sladecek & Rehackova, 1951 [Czecho-Slovakia; fresh waters] *
Diacyclops pseudosuoensis Karanovic et al., 2013 [Japan; subterranean waters]
Diacyclops languidoides putealis (Chappuis 1928) [France; wells] *
Diacyclops languidoides spelaeus Plesa, 1956 [Romania; caves]
Diacyclops languidoides suoensis Ito 1954 [Japan; ground waters] *
Diacyclops languidus languidus (G.O. Sars, 1863) [Europe, north America, Asia; fresh waters]
Diacyclops languidus badeniae Kiefer, 1933
Diacyclops languidus deminutus Sterba, 1955 [Czecho-Slovakia; fresh waters] ***
Diacyclops languidus linneanus (Lindberg, 1949) [Sweden; fresh waters] ***
Diacyclops languidus maisi (Plesa & Buzila, 1998) [Austria; cave waters]
Diacyclops leeae Karanovic et al., 2013 [Korea; Ondal-gul cave]
Diacyclops lewisi Reid, 2004 [U.S.A.; ground waters]
Diacyclops limnobius (Kiefer, 1978) [Europe, URSS; lakes]
Diacyclops lindae Pesce 1986 [Italy; wells]
Diacyclops longifurcus Shen & Sung, 1963 [China; fresh waters]
Diacyclops maggii Pesce & Galassi 1987 [Italy; wells]
Diacyclops michaelseni (Mrazek, 1901) [south America; fresh waters] **
Diacyclops mirnyi Borutzky & Vinogradov, 1957 [Antarctic Sea] **
Diacyclops nagatoensis Ito 1964 [Japan; ground waters]
Diacyclops nanus nanus (G.O. Sars, 1863) [palaearctic; fresh waters]
Diacyclops nanus incertus (Wolf, 1905) [Europe; fresh waters]
Diacyclops navus Herrick, 1882 [north America; fresh waters]
Diacyclops nearcticus Kiefer, 1934 [U.S.A.; fresh waters]
Diacyclops neglectus Flossner, 1984 [Baikal Lake]
Diacyclops nikolasarburni Suarez Morales et al., 2013 [Mexico; caves]
Diacyclops nuragicus Pesce & Galassi 1985 [Italy, Sardinia; wells]
Diacyclops palustris Reid, 1988 [USA; flooded marsh]
Diacyclops paolae Pesce & Galassi 1987 [Italy. Albania; wells]
Diacyclops paralanguidoides Pesce & Galassi 1987 [Italy; wells]
Diacyclops pelagonicus pelagonicus Petkovski 1971 [Yugoslavia; surface and ground waters]
Diacyclops pelagonicus saetosus Pandourski 1993 [Bulgaria; hyporheic]
Diacyclops pilosus Fiers & Ghenne, 2000 [Mexico, Yucatan; wells ]
Diacyclops puuc Fiers, 1996 [Mexico, Yucatan; cenotes]
Diacyclops reidae De Laurentiis et al., 1999 [Australia; ground waters]
Diacyclops ruffoi Kiefer, 1981 [Italy; hyporheic]
Diacyclops rupestris Mazepova, 1950 [Baikal Lake]
Diacyclops salisae Reid, 2004 [U.S.A.; ground waters]
Diacyclops sardous Pesce & Galassi 1987 [Italy, Sardinia; wells]
Diacyclops scanloni Karanovic, 2006 [Australia; bores]
Diacyclops skopljensis (Kiefer 1932) [Yugoslavie; ground waters]
Diacyclops slovenicus Petkovski, 1954 [Herzegovina; ground waters]
Diacyclops sobeprolatus Karanovic, 2006 [Australia; large bores]
Diacyclops sororum Reid 1992 [USA; streams]
Diacyclops spongicola (Mazepova, 1961) [Baikal Lake]
[= Acanthocyclops spongicola Mazepova, 1961]
Diacyclops strimonis Pandourski 1994 [Bulgaria; ground waters] ****
Diacyclops stygius stygius (Chappuis 1924 [Europe; ground waters] ******
Diacyclops stygius deminutus (Chappuis 1925) [Romania; ground waters] ******
Diacyclops stygius macedonicus Petkovski 1954 [Yugoslavia; ground waters] ******
Diacyclops talievi (Mazepova, 1970) [Baikal Lake]
[= Acanthocyclops talievi Mazepova, 1970]
Diacyclops tantalus (Kiefer 1937) [Herzegovina, Bosnia, Italy; ground waters]
Diacyclops tenuispinalis Shen & Sung, 1963 [China; fresh waters]
Diacyclops thomasi (Forbes, 1882) [Europe?, north America, China; fresh waters] *
Diacyclops uruguayensis Kiefer, 1935 [Uruguay, Brazil; temporary pools, culture of leaf litters]
Diacyclops versutus (Mazepova, 1961) [Baikal Lake]
[= Acanthocyclops versutus Mazepova, 1961]
Diacyclops yeatmani (Yeatman, 1964) [north America; fresh waters]
Diacyclops yezoensis Ito, 1954 [Japan; ground waters] *
Diacyclops walkeri karanovic et al., 2013
Diacyclops zhimulevi Sheveleva & Timoshkin, 2012
Diacyclops zschokkei (Graeter 1910) [Europe; ground waters]
* questionable taxon
** should be included in the genus Acanthocyclops according to Dussart & Defaye (1985)
*** according to Stoch & Pospisil (2000) the taxonomic status of these subspecies is uncertain, and only the following species (formerly subspecies of Diacyclops languidus) are to be ascribed to the languidus-group: Diacyclops languidus, Diacyclops disjunctus and Diacyclops belgicus
**** Recently Pandourski (2000) moved this species to Acanthocyclops.
***** Recent crossbreeding studies (Monchenko, 2000) suggest the presence of cryptic species within D. bicuspidatus.
****** Recently Pandourski (1997) transferred these species to the genus Acanthocyclops.
******* According to Mirabdullayev & Rustamova (2007) D. Alticola could be conspecific with D. logifurcus.
The species jurenei (Khalida et al., 1988) , landei (Mahoon & Zia (1985) and the subspecies bicuspidatus jurinei (Najam-Un-Nisa & Mahoon (1987) are not Diacyclops, and are to be considered as nomina dubia.
Recently Reid (1992) and De Laurentiis et al. (1999) pointed out a "crassicaudis-complex" characterizing the Diacyclops species with a 12-segmented antennula and swimming legs 1-4 with both exopodite and endopodite 3-segmented. The complex presently includes 17 named species and subspecies, viz.: D. alticola Kiefer, 1935; D. antrincola Kiefer, 1967; D. crassicaudis crassicaudis G. O. Sars, 1863; D. crassicaudis brachycercus Kiefer, 1927; D. crassicaudis cosana Stella & Salvadori, 1954; D. crassicaudis cretensis Kiefer, 1928; D. crassicaudis lagrecai Pesce & Galassi, 1987; D. crassicaudis trinacriae Pesce & Galassi, 1987; D. fontinalis Naidenov, 1969 (syn. Acanthocyclops (Diacyclops) fontinalis ; D. dyabdar Novikov et al., 2024 D. karamani Kiefer, 1932; D. iranicus Pesce & Maggi, 1982; D. longifurcus Shen & Sung, 1963; D. ruffoi Kiefer, 1981; D. skopljensis Kiefer, 1932; D. talievi (Mazepova, 1970); D. reidae De Laurentiis et al., 1999; D. einslei De Laurentiis et al.; Cyclops (Diacyclops) crassicaudis taipehensis syn. nov. Navikov. 2024) , 1999.
Within the above complex, some subspecies, such as D. crassicaudis cretensis and D. crassicaudis brachycercus Navikov 2024 , which are very similar to each other, have been much discussed (Dussart, 1969; Monchenko, 1974; Rylov, 1948; Pesce & Galassi, 1987), and recently Reid (1992) hypothesized that there is no good reason for distinguishing these nominal taxa, at least not in North America.
For the most part, species of the "crassicaudis-complex" are stygophilic or stygoxen inhabitants of local (ground) freshwater systems of Asia, North America, Western Australia and Africa. The others are known from subterranean (caves, wells) habitats of Europe (D. antrincola, D. crassicaudis var. cosana, D. crassicaudis cretensis, D. fontinalis, D. karamani, D. ruffoi, D. skopljensis) or in Iran (D. iranicus) but, with the exception of D. antrincola and D. ruffoi, they do not exibit peculiar stygomorphies. Recently Karanovic & Krajicek (2012) considered an alticola-group of species among Australian taxa of Diacyclops, as well as two lineages
on the basis of the presence/absence of inner seta on the first exopodal segments
of all swimming legs although
this character was not considered as phylogenetically informative, and the monophyly
of the Australian taxa was advocated. The first group, with the inner seta
present, should include Diacyclops einslei, Diacyclops reidae and Diacyclops scanloni;
the second group Diacyclops cockingi, Diacyclops humphreysi s. str., Diacyclops
humphreysi unispinosus and Diacyclops sobeprolatus.
KEY FOR ASIAN SPECIES OF THE GENUS DIACYCLOPS
[RELEVANT LITERATURE]
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