Synonymy in Dussart and Defaye (1985)

Cyclope serrulatus, Fischer, 1851

Eucyclops serrulatus, Claus, 1893a

Cyclope agilis, Gurney, 1933

Eucyclops agilis, Comita, 1951

Eucyclops serrulatus, Dussart, 1969; Kiefer, 1978

Synonymy in Dumont (1979)

Eucyclops asymmetricus, Dumont and Pensaert, 1979

Based on habitus, morphotype 3 of Eucyclops serrulatus group was the smallest one (Table 2), morphotype 1 is characterised by external articulation of its abdominal segments (Fig. 2a), while morphotype 2 is identified by its elongated lateral thoracic segments which envelop the following segment and its fourth thoracic segment has cilia on its lateral angles (Fig. 4a).

Figure 2.  

Eucyclops cf. serrulatus (Fischer, 1851). Morphotype 1; a Habitus (dorsal view); b caudal rami; c A1; d A2 basipodite (posterior surface); e A2 basipodite (anterior surface).

Figure 3.  

Eucyclops cf. serrulatus (Fischer, 1851). Morphotype 1

a first leg (P1) with coxopodite and intercoxal plate (with fine denticules), arrow show external seta of exopodite 3 with a row of little spinules along outer margin and with setules on inner edge; b fourth leg (P4) with coxopodite and intercoxal plate, arrows showing two apical setae of exopodite 3 stylet-shaped; c fifth leg (P5).

Figure 4.  

Eucyclops cf. serrulatus (Fischer, 1851). Morphotype 2; a habitus (dorsal view); b caudal rami; c A1 basipodite; d A2 basipodite (posterior surface); e A2 basipodite (anterior surface).

Figure 5.  

Eucyclops cf. serrulatus (Fischer, 1851). Morphotype 2; a first leg (P1) with coxopodite and intercoxal plate, arrow showing external seta of exopodite 3 with a row of little spinules along outer margin and with setules on inner edge; b fourth leg (P4) with coxopodite and intercoxal plate; c fifth leg (P5).

Figure 6.  

Eucyclops cf. serrulatus (Fischer, 1851). Morphotype 3; a habitus (dorsal view); b caudal rami; c A1 basipodite; d A2 basipodite (posterior surface); e A2 basipodite (anterior surface).

P5 with a spine as long as outer seta in all morphotypes, slender and long in morphotypes 1 and 3 (Fig. 3c, Fig. 7c) and large in morphotype 2 (Fig. 5c).

Figure 7.  

Eucyclops cf. serrulatus (Fischer, 1851). Morphotype 3; a first leg (P1) with coxopodite and intercoxal plate, arrow showing external seta of exopodite 3 with a row of little spinules along outer margin and with setules on inner edge; b fourth leg (P4) with coxopodite and intercoxal plate; c fifth leg (P5).

Caudal rami somewhat divergent: morphotype 1:4–4.5 times longer than wide (Fig. 2b), morphotype 2:4.5–5 times longer than wide (Fig. 4b), morphotype 3:3.5–4 times longer than wide (Fig. 6b). Serra (longitudinal row of spinules) with 51 denticules in morphotype 1, 28 denticules in morphotype 2 and 22 denticules in morphotype 3, spine-like outermost seta with spinules along outer margin and long setules on inner edge in all the morphotypes. Innermost seta with long setules on both sides, about 1.3–1.4 times longer than spine-like outermost seta in morphotypes 2 and 3, but almost equal in morphotype 1.

Antennule 12-segmented, reaching middle of first free thoracal somite in morphotypes 1 and 2 and the beginning of the third one in morphotype 3 (Fig. 2a, Fig. 6a), the last three articles with hyaline membrane, the first segment with curved row of spinules at its base; outermost spinules the longest in morphotypes 1 and 2 (Fig. 2c, Fig. 4c). In morphotype 3, the longest ones were between two groups of little spines (Fig. 6c).

Antennary basipodite, posterior face: (N1) with three long setules in morphotypes 1 and 3 (Fig. 2d, Fig. 6d), five long setules in morphotype 2 (Fig. 4d); a group of two long spinules (N6) and three diagonal and parallel rows of spinules (N3–5) only in morphotype 1.

Antennary basipodite, anterior face: (N8) composed of three long spinules subdistally in morphotype 1 (Fig. 2e), five long spinules subdistally in morphotype 2 and three (Fig. 4e, Fig. 6e), (N11 + N12) formed of a long row of relatively small spinules with 17 spinules in morphotype 1, 13 spinules in morphotype 2. In morphotype 3 only (N11) exist with eight spinules, (N13) represented by a group of five little spinules only in morphotype 1, two groups of marginal spinules (N17) and (N15) only in morphotypes 1 and 2, in morphotype 3 only (N17) exist.

Endopodite and exopodite segments of P1–P4 were plumose.

P1: inner edge of basipodite with group of long hair only in morphotypes 1 and 2 (Fig. 3a, Fig. 5a), intercoxal plate with two groups of finest spinules on body of protuberances, only in morphotype 1, external seta of exopodite 3 in all morphotypes with a row of little spinules along outer margin and with long setules on inner edge (Fig. 3a, Fig. 5a, Fig. 7a).

P4, innermost apical spine of endopodite 3 was 1.3–1.4 times as long as outermost apical spine in all morphotypes and about 1.5-1.6 times as long as supporting segment in morphotype 1 (Fig. 3b) and as long as supporting segment in morphotypes 2 and 3 (Fig. 5b, Fig. 7b), outer seta long reaching almost the top of outermost apical spine in all morphotypes, two apical setae of exopodite 3 stylet-shaped only in morphotype 1 (Fig. 3b), inner edge of basipodite with group of long setules only in morphotypes 1 and 3 (Fig. 3b, Fig. 7b). Coxopodite with a row of numerous fines spinules along internal distal side only in morphotype 1, several groups of spinules: (A – B - (C + D) –E-G-H-I) in morphotype 1, (A – B- (C + D) – G - H –I) in morphotype 2 and (A – B- (C + D) – E- G- H- I) in morphotype 3, morphotype 2 did not show group E. Group F did not exist in all morphotypes, intercoxal plate with dense setules, in all morphotypes, but in morphotypes 2 and 3, setules are two times longer than those in morphotype 1. On body of plate, I found two groups of little setules and spinules in morphotype 1, two groups of little spinules in morphotype 2 and one group of little setules in morphotype 3. Caudal setae had dense long setules, but those of morphotypes 1 and 3 had a strong spine.

This taxon was discovered in the mid-nineteenth century in a pond at Peterhof close to Saint Petersburg, Russia (Fischer 1851). In recent years, the distributional area of the species was revised and restricted to a Palearctic distribution. Previous data on geographical distribution of the species outside this area are critically analysed. It is hypothesised that records of E. serrulatus from Japan, Australia, North America and other zoogeographical zones could be a result of recent invasions, possibly via human activities in relation to ship transport.

Freshwater species (lakes, basins, ponds, wadis)

Eucyclops serrulatus (Fischer, 1851) has been reported from waterbodies around the world and, consequently, it has long been considered a cosmopolitan species until some species that look like Eucyclops serrulatus were separated from it. Some of these may indeed be valid species; others were forms of Eucyclops serrulatus.