Eucyclops agiloides (G.O. Sars, 1909 )

Hołyńska, Maria, Sługocki, Łukasz, Ghaouaci, Souad & Amarouayache, Mounia, 2021, Taxonomic status of Macaronesian Eucyclops agiloides azorensis (Arthropoda: Crustacea: Copepoda) revisited - morphology suggests a Palearctic origin, European Journal of Taxonomy 750, pp. 1-28 : 15-22

Eucyclops agiloides (G.O. Sars, 1909)

Figs 7−11 ; Tables 4−5

Cyclops agiloides G.O. Sars, 1909: 59 , figs 183−188.

? Eucyclops agiloides − Alekseev & Defaye 2011: 61, fig. 7. — Alekseev 2019: 499.

Material examined

Holotype

TANZANIA • ♀ (undissected); Lake Victoria , Bukoba [Musila?] island (locality information is from Sars 1909); 1°19.9′ S, 31°48.7′ E; 25(?) Apr. 1905; W.A. Cunnington, Third Tanganyika exped.; labelled as “ Cyclops agiloides GOS , 269, Vict. Nyanza 437, Typical specimen, Type, ♀, 1909.6.24.303 ”; NHM.

Paratypes

TANZANIA • 1 ♀; same collection data as for holotype; labelled as “ Cyclops agiloides GOS , 437, 269 Vict. Nyanza, Syntype, Anatomy, ♀, 1909.6.24.300 ”; body parts were re-embedded in glycerine after solving the old (likely Hoyer) mounting medium in water; NHM .

ZAMBIA • 1 ♀ (undissected); Lake Tanganyika, Niamkolo [Kumbula] island; 8°45.3′ S, 31°5.9′ E; 19 Sep. 1904; W.A. Cunnington, Third Tanganyika exped.; labelled as “ Cyclops agiloides GOS , 437, Tanganyika 97, Syntype, ♀, 1909.6.24.302”; NHM. Collection data were retrieved from Sars (1909), information on the Sars collection deposited in Oslo Zoological Museum (Åse Ingvild Wilhelmsen, in litt. 21 June 2019), and a map showing the route of the W.A. Cunnington Expedition 1904−1905 in Lake Tanganyika, published by Karlsson & Karlsson (2019).

Other material

TANZANIA • 3 ♀♀; Lake Tanganyika , Kirando, river mouth ; 7°21.6′ S, 30°36.6′ E; 1926; S. Pask leg.; identified as Eucyclops agiloides by R. Gurney, 1930 II 6 4−8; NHM. ♀-1 and ♀-2 were fully dissected, while in ♀-3 the antennule, antenna, the mouthparts and P1 were removed from the corpus and embedded in glycerol medium, and rest of the body remained in ethyl-alcohol .

Comparative material

Eucyclops roseus

CHINA • 2 ♀♀; Xinjiang-Uygur Autonomous Region , Bogda-Shan Mountain Range, Tianchi Lake; 43°53.2′ N, 88°7.95′ E; 2000 m a.s.l.; 1 Jun.−1 Jul. 2011; E.S. Chertoprud, A.Y. Sinev and I. Dimante- Deimantovica leg.; MIZ 1/2021/23 , MIZ 1/2021/24 .

IRAQ • 3 ♀♀; South Iraq, Al Salal marsh, 20 km NW of Basra; 30°40′ N, 47°36′ E; 24 Mar. 2012; S.D. Salman and M. Hołyńska leg.; lake shore; MIZ 5/2014/1 to 5/2014/3 • 2 ♀♀; Shatt al Arab River, Basra; 30°31′ N, 47°49′ E; 21 Mar. 2012; S.D. Salman and M. Hołyńska leg.; MIZ 5/2014/4 , MIZ 1/2021/21 .

RUSSIA • 1 ♀; Siberia , Yakutia , Kobiyanskiy Ulus County, Anga River , Melnikov Island; 63°51.9′ N, 127°27.05′ E; 21 Aug. 2010; A.A. Kotov leg.; MIZ 1/2021/22 .

SUDAN • 1 ♀; Khartoum State; Oct. 2012 – Jul. 2013; G.M. Idris leg.; MIZ 1/2021/20 .

UKRAINE • 2 ♀♀; Arabatska Strilka [Arabat Spit], Strilkove Village; 45°54′ N, 34°52.8′ E; originally labelled as Eucyclops serrulatus ; V.I. Monchenko collection; IZAN .

1. = body length (μm); 2. = cephalothorax, length/ width; 3. = genital double-somite, length/ width; 4. = length of prosome/ length of urosome; 5. = length of caudal seta V/ length urosome; 6. = P5, length of medial spine/ length of segment; 7. = P5, length of apical seta /length of segment; 8. = P5, length of lateral seta / length of segment; 9. = caudal ramus, length/ width; 10. = length of caudal seta II/ length of caudal ramus; 11. = distance of insertion of caudal seta II, measured from posterior end of ramus/ length of caudal ramus; 12. = caudal setae, VII / III; 13. = caudal setae, VI/ III; 14. = caudal setae, V/ III; 15. = caudal setae, IV/ III; 16. = length of caudal seta VI/ length of caudal ramus; 17. = length of caudal seta V /length of caudal ramus; 18. = length of caudal seta IV/ length of caudal ramus; 19. = length of caudal seta III/ length of caudal ramus; 20. = P4, length of coxopodite seta /height of medial expansion of basipodite; 21. = P4 enp3, length/width; 22. = P4 enp3, medial terminal spine /lateral terminal spine; 23. = P4 enp3, medial terminal spine /segment length.

Description

Female

HABITUS. Total body length 0.9−1.1 mm (for morphometric characters see Table 4 ). Pediger 4 and pediger 5 posterolaterally bearing long fine hairs and thick (spinule-like) hairs, respectively ( Fig. 8 A−B) – pilosity of pediger 4 could only be verified in females from Kirando, Lake Tanganyika. Genital double-somite ( Fig. 8B ) as long or slightly shorter than wide. Seminal receptacle as common in genus ( Fig. 8B ), anterior and posterior parts short in length, posterior part wider than anterior, single large copulatory pore in anterior fifth of somite. Anal operculum ( Fig. 8D ) nearly straight, anal sinus with longitudinal rows of hairs, posterior margin bearing continuous row of robust spinules. Caudal rami ( Fig. 8D ) 4.0−6.0 times as long as wide, no hairs on medial margin. Serra extending from insertion of anterolateral (II) caudal seta to anterior ⅕−⅙ of rami. Seta II inserted in posterior ¼−⅕ of caudal ramus. Spinules present next to insertion of posterolateral (III) caudal seta. Relative length of caudal setae in Table 4 .

ANTENNULE. 12-segmented, reaching middle length to posterior margin of pediger 2. Setation formula same as in E. azorensis . Aesthetasc ( Fig. 7A ) on segment 9 short, ~12 μm in length, not reaching distal margin of segment. Segments 10−12 with smooth (very finely serrate) hyaline membrane. First antennular segment bearing spinules on ventral surface, spinules absent on other segment. Terminal antennulary segment 5.0−7.1 times as long as wide.

ANTENNA. Composed of coxobasis and three-segmented endopodite, and bearing 3, 1, 9 and 7 setae, respectively. Exopodite seta reaching slightly (paratype, Lake Victoria) or distinctly (Kirando, Lake Tanganyika) beyond enp3, proximal setules can be similar in length or distinctly longer than setules in distal section of seta ( Figs 7B , 8F ). Caudal surface ornamentation of antennal coxobasis ( Figs 7B , 8E ) with same groups of spinules as those in E. azorensis in lateral half of segment, except for additional group of spinules next to distal margin (group marked with arrow in Fig. 7B ). Medial half of segment with reduced ornamentation: few spinules sometimes present at height of insertion medial setae ( Fig. 7B ), or below setae ( Fig. 8E ). Frontal surface ( Figs 7C , 8F ) adorned with spinule-like hairs next to distal margin, hairs absent mediodistally, longitudinal/oblique row of spinules (8−13) along lateral margin, and oblique rows of large and small spinules near proximal margin.

MOUTHPARTS. Labrum ( Fig. 8G ) with naked epistoma, distal fringe hairs arranged in two groups, teeth acute on distal rim, obtuse lateral lobes with tiny spinules. Paragnaths ( Fig. 8H ) bearing longitudinal rows of hairs on outer (ventral) surface, longitudinal row of spinules more dorsally (indicated by dotted line in Fig. 8H ), mediodistal lobe with group of spinules. Four medial claw-like elements (three inserted close to each other and one inserted more distally) located slightly dorsally to hairs on outer (ventral) surface (not shown in figure). Long spinules present posterior to paragnaths. Mandible ( Figs 7D , 9A ) bearing two long and one short seta. Near palp transverse row of long spinules and smaller spinules arranged in row rather than oval pattern present on anterior surface of gnathobase. Maxillulary palp ( Figs 7D , 9 B−C) with few spinules arranged in discontinuous row/arc. Setation of maxilla ( Fig. 9 D−E) as common in Eucyclops , endopodite 2-segmented. Praecoxopodite and coxopodite separated on caudal surface and partially fused on frontal surface; short transverse row of spinules present near lateral margin on caudal surface ( Fig. 9E , marked with arrow). Armature of maxilliped ( Fig. 9 F−G) as common in Eucyclops , arthrodial membrane between terminal endopodal segment and its medialmost seta failed to form. Basipodite with two rows of spinules on caudal surface. Tiny dents on free margin of flap-like structure ( Fig. 9G , marked with arrow) sometimes present (maxilliped could be verified in specimens from Kirando, Lake Tanganyika).

P1−P4. Setation formula same as in E. azorensis ( Table 2 ). P1 intercoxal sclerite ( Fig. 9H ) naked on both frontal and caudal surfaces in all specimens examined (one paratype from Lake Victoria and three females from Kirando, Lake Tanganyika). P2−P3 intercoxal sclerites ( Fig. 10 B, D ): hairs arranged in two groups present on frontal surface in both legs; transverse row of spinules present or absent on caudal surface in P2 and present in P3. P4 intercoxal sclerite ( Figs 7E , 10E ) caudally bearing hairlike spinules in two (three) rows, free margin avoid of hairs in middle; frontal surface naked. Coxopodite setae with long and fine setules in P1, and short and thick setules in P2−P4 ( Figs 9H , 10B , D−E). P4 coxopodite seta lacking setules in short proximal section on lateral margin (two ♀♀, Kirando, Lake Tanganyika) – whole length (continuous) setulation shown in Sars (1909). Caudal surface ornamentation of P4 coxopodite ( Figs 7E , 10E ) as common in genus; number of spinules 20, 21 (two ♀♀, Kirando, Lake Tanganyika) in transverse row along distal margin. Medial expansion of basipodites pilose in P1−P4. Medial seta of P1 basipodite ( Fig. 9H ) with short setules, seta reaching beyond distal margin of enp2. Second exopodal segment laterally pilose, exp1 and exp3 laterally naked in P1−P4 ( Figs 7 E−F, 9H−I, 10A, C, E−F). P4 enp3 ( Figs 7G , 10G ) 2.2−2.4 times as long as wide, medial terminal spine 1.4−1.5 times as long as lateral spine, and about as long as segment ( Table 4 ). None of setae of P4 enp3 reaching beyond tip of longer (medial) terminal spine.

P5 ( Fig. 8C ). One-segmented, with three appendages. Medial spine distinctly longer than segment ( Table 4 ), small spinules present at insertion of spine. Apical seta 1.4 (paratype, L. Victoria) to 2.3 (Kirando, Lake Tanganyika) times as long as medial spine, lateral seta and medial spine subequal in length.

Male

Unknown.

Geographic distribution and habitat preferences

Eucyclops agiloides has been reported from various regions of Africa, Asia and even Eastern Europe: Lake Malawi ( Alekseev & Defaye 2011), Ethiopia ( Defaye 1988), Nigeria ( Boxshall & Braide 1991), Northern Algeria ( Hamaidi et al. 2010), Crimea, Lesser Caucasus and Talysh region (South Azerbaijan) ( Monchenko 2003), China ( Tai & Chen 1979 − E. agiloides was considered by these authors as a synonym of E. serrulatus ), India ( Kiefer 1939; Lindberg 1939; Dev Roy & Venkataraman 2018), Sumatra and Java ( Kiefer 1933), and Borneo ( Alekseev et al. 2016). Part of these records may refer to other taxa (e.g., E. roseus ), and the geographic distribution of the species is still poorly understood ( Fig. 11 shows only the verified records). The same holds true for the habitat preferences of E. agiloides . The specimens examined here were collected in large lakes and a river mouth in Lake Tanganyika, yet precise information on the collection sites is missing.

Figures

Fig. 7.Eucyclops agiloides (G.O. Sars, 1909) (Lake Victoria, paratype, ♀; NHM). A. Antennulary segment 9−12, ventral surface (terminal setae of segment 12 are not figured). B. Antennal coxobasis and first and second endopodal segments, caudal view – note the group of spinules next to distal margin (arrow). C. Antennal coxobasis and first endopodal segment, frontal view. D. Mandible (Md) and maxillule (Mxl). E. Leg 4, protopodite and first exopodal and endopodal segments, caudal view. F. Leg 4, second and third exopodal segments, caudal view. G. Leg 4, second and third endopodal segments, caudal view. Scale bars: A−G = 50 μm.

Fig. 8. Eucyclops agiloides (G.O. Sars,1909), ♀ (Lake Tanganyika, Kirando; NHM). A. Pediger 4, dorsal view. B. Pediger 5 and genital double-somite (leg 5 is not figured), ventral view. C. Leg 5. D. Anal somite and caudal rami, dorsal view. E. Antennal coxobasis and first endopodal segment, caudal view. F. Antennal coxobasis, frontal view. G. Labrum – ʻepiʼ shows epistoma, laterodistal lobe is indicated by arrow. H. Paragnaths, ventral view (3+1 medial claws inserted on opposite surface of both paragnaths are not figured). A, D−H show ♀-1; B−C show ♀-2. Scale bars: A−H = 50 μm.

Fig. 9. Eucyclops agiloides (G.O. Sars,1909), ♀ (Lake Tanganyika, Kirando; NHM). A. Mandible, anterior view.B−C. Variation of the spinule ornamentation of the maxillulary palp. B. ♀-1 (one apical seta is broken off). C. ♀-3. D. Maxillar basipodite and two-segmented endopodite, caudal view. E. Maxillar syncoxopodite, caudal view – note short transverse row of spinules near lateral margin (arrow). F. Maxilliped, basipodite and two-segmented endopodite, frontal view. G. Maxilliped, syncoxopodite and basipodite, frontal view – note the flap-like structure (arrow). H. Leg 1, protopodite and first exopodal and endopodal segments, frontal view (coxopodal seta is figured separately). I. Leg 1, second and third exopodal segments, frontal view. J. Leg 1, second and third endopodal segments, frontal view. A shows ♀-2; B, D–E, G−J show ♀-1; C, F show ♀-3. Scale bars: A−J = 50 μm.

Fig. 10. Eucyclops agiloides (G.O. Sars,1909), ♀ (Lake Tanganyika, Kirando; NHM). A. Leg 2 exopodite, caudal view. B. Leg 2 intercoxal sclerite, caudal view – ornamentation on the frontal surface is indicated by dotted line. C. Leg 3 exopodite, caudal view. D. Leg 3 intercoxal sclerite, caudal view − ornamentation on the frontal surface is indicated by dotted line. E. Leg 4, protopodite and first exopodal and endopodal segments, caudal view (coxal seta is figured separately). F. Leg 4, second and third exopodal segments, caudal view. G. Leg 4, second and third endopodal segments, caudal view. All drawings show ♀-1. Scale bars: A−G = 50 μm.

Fig. 11. Verified records of Eucyclops agiloides (G.O. Sars,1909). Filled red circles show occurrences verified by the authors, and open circle shows a record taken from the original description of the species (Sars 1909).