Eucyclops sibiricus, Novikov & Sharafutdinova & Abramova & Mayor & Chertoprud, 2025

Eucyclops sibiricus sp. nov.

Figs 9 View Figure 9 , 10 View Figure 10 , 11 View Figure 11 , 12 View Figure 12 , 13 View Figure 13 , 14 View Figure 14 , 15 View Figure 15 , 16 View Figure 16 , 17 View Figure 17 , 18 View Figure 18

Eucyclops speratus View in CoL : Ishida and Hiruta 1999 (part): 88, figs 1, 2 a – e; Lee et al. 2005: 146, fig. 5; Chertoprud et al. 2022: 6, table A 1.

Eucyclops sp. nov.: Chertoprud et al. 2024: 1014, supplemental material 1: table S 1.

Etymology.

The species was first discovered and has its main range in Siberia. The word sibiricus is an adjective in the masculine gender.

Type material.

Holotype: Russia • ♀ dissected on two slides; North Yakutia, Lena River Delta , Floodplain puddle; 72.38755 ° N, 126.48205 ° E; 8 Sep. 2020; E. Abramova leg; EMKSU VH 2000 / 1, VH 2000 / 2 (N ° 45) GoogleMaps . Paratypes: Russia • ♂ dissected on one slide; North Yakutia, Lena River Delta , Floodplain puddle; 72.36874 ° N, 126.47595 ° E; 20 Aug. 2019; A. Novikov leg; EMKSU VH 2000 / 3 GoogleMaps . • ♀ dissected on one slide; collection data as for holotype; EMKSU VH 2000 / 4 (N ° 47) GoogleMaps ; • ♀ dissected on one slide; collection data as for holotype; EMKSU VH 2000 / 5 (N ° 48) GoogleMaps ; • ♀ dissected on one slide; collection data as for holotype; EMKSU VH 2000 / 6 (N ° 49) GoogleMaps ; • 3 ♀ and 2 ♂ preserved in 4 % formalin; North Yakutia, Lena River Delta , Floodplain puddle; 72.36874 ° N, 126.47595 ° E; 20 Aug. 2019; A. Novikov leg; EMKSU VH 2000 / 13 GoogleMaps ; • 2 ♀ dissected on one slides; collection data as for preceding; EMKSU VH 2000 / 7 GoogleMaps ; • 1 ♂ dissected on one slide; collection data as for preceding; EMKSU VH 2000 / 8 GoogleMaps ; • ♀ dissected on one slide; collection data as for preceding; EMKSU VH 2000 / 9 (N ° 27) GoogleMaps ; • ♀ dissected on one slides; collection data as for preceding; EMKSU VH 2000 / 10 (N ° 88) GoogleMaps ; • ♀ preserved in 96 % ethanol; North Yakutia, Lena River Delta, Floodplain puddle; 72.38755 ° N, 126.48205 ° E; 18 July 2021; A. Novikov leg; GenBank: OR 917926, OR 941791, OR 918477; EMKSU VH 2000 / 14 (N ° ch 5) GoogleMaps ; • ♀ preserved in 96 % ethanol; collection data as for preceding; GenBank: OR 917925; EMKSU VH 2000 / 15 (N ° ch 6) GoogleMaps ; • ♀ preserved in 96 % ethanol; collection data as for preceding; GenBank: OR 917928; EMKSU VH 2000 / 16 (N ° ch 7) GoogleMaps ; • ♀ preserved in 96 % ethanol; collection data as for preceding; GenBank: OR 917929; EMKSU VH 2000 / 17 (N ° ch 8) GoogleMaps ; • ♀ dissected on one slides; North Yakutia, Lena River Delta , Floodplain puddle; 72.38755 ° N, 126.48205 ° E; 18 July 2021; A. Novikov leg; EMKSU VH 2000 / 11 (N ° 17) GoogleMaps ; • ♀ dissected on two slides; collection data as for preceding; EMKSU VH 2000 / 12 (N ° 19) GoogleMaps ;

Additional material.

Russia • ♀ dissected on one slides; North Yakutia, Lena River Delta , small river; 72.11877 ° N, 126.98782 ° E; 22 July 2021; A. Novikov leg; in collection of A. Novikov (N ° 21) GoogleMaps ; • 3 ♀ dissected on three slides; North Yakutia, lake; 69.97000 ° N, 125.60158 ° E; 28 June 2019; A. Novikov leg; in collection of A. Novikov (N ° 89, 90, 91) GoogleMaps ; • 2 ♀ dissected on two slides; Central Yakutia, temporary puddles; 64.94187 ° N, 124.84179 ° E; 22 June 2019; A. Novikov leg; in collection of A. Novikov (N ° 69, 73) GoogleMaps ; • ♀ dissected on one slides; Anabar Plateau , small lake; 70.64073 ° N, 105.90506 ° E; 25 July 2023; A. Novikov and E. Chertoprud leg; in collection of A. Novikov (N ° 79) GoogleMaps ; • ♀ dissected on one slides; Putorana Plateau , swampy lake; 68.60415 ° N, 94.05641 ° E; 7 Aug. 2021; E. Chertoprud leg; in collection of A. Novikov (N ° 32) GoogleMaps ; • ♀ preserved in 96 % ethanol; Putorana Plateau , swampy lake; 68.60415 ° N, 94.05641 ° E; 7 Aug. 2021; E. Chertoprud leg; GenBank: OR 917930; EMKSU VH 2000 / 18–20 (N ° ch 1) GoogleMaps ; • ♀ preserved in 96 % ethanol; collection data as for preceding; GenBank: OR 917924, OR 941789; EMKSU VH 2000 / 18–20 (N ° ch 2) GoogleMaps ; • ♀ preserved in 96 % ethanol; collection data as for preceding; GenBank: OR 917927, OR 941790, OR 918478; EMKSU VH 2000 / 18–20 (N ° ch 3) GoogleMaps ; • ♀ dissected on one slides; Putorana Plateau , swampy lake; 68.60344 ° N, 94.05875 ° E; 7 Aug. 2021; E. Chertoprud leg; in collection of A. Novikov (N ° 33) GoogleMaps ; • ♀ dissected on one slides; Putorana Plateau , swampy lake; 68.60029 ° N, 94.05300 ° E; 7 Aug. 2021; E. Chertoprud leg; in collection of A. Novikov (N ° 34) GoogleMaps ; • ♀ dissected on one slides; Tatarstan republic, Naberezhnie Morkvashi village , puddle on stream; 55.76324 ° N, 48.85700 ° E; 28 June 2020; A. Novikov and D. Sharafutdinova leg; in collection of A. Novikov (N ° 92) GoogleMaps ; • ♀ on the electron microscope stage no. 90134; Irkutsk region, Tulun district, Aleksandrovka village , river; 55.3905 ° N, 100.8231 ° E; 25 July 2021; T. Mayor leg; LI SB RAS T 13 GoogleMaps ); • ♀ preserved in 96 % ethanol; Irkutsk region, Kuitun District , pond; 54.34722 ° N, 101.52861 ° E; June 2021; G. Dzyba leg; GenBank: OR 941793, OR 918476; in collection of T. Mayor (N ° K 1-4) GoogleMaps

Diagnosis.

Proctodeum with rows of setules. Caudal ramus with serra and dorsal pore. Length / width ratio of caudal rami 5.2–7.0. Ratio of lengths of caudal seta VI to seta III 1.07–1.47. Antennule 12 - segmented, with hyaline membrane on three distal segments. Hyaline membrane finely serrated. Antennal coxobasis with groups of spinules 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16. Maxillular basis with group of spinules. P 1 – P 4 Exp 1 without spinules / setules on outer side. P 1 – P 4 Exp 2 with setules on outer side. P 4 Exp 1 with 8–17 inner setules. P 4 Exp 2 with 6–10 inner setules.

Description.

Female. Body elongated (Fig. 9 A – C View Figure 9 ). Total body length from anterior margin of rostrum to posterior margin of caudal rami: mean 1279 µm (n = 3). Cephalothorax wider than first and second free somites, largest width 408 µm (n = 1), surface with 251 pores and sensilla, with all groups, except group 36 (Fig. 8 A – D View Figure 8 ). Naupliar eye present, color red or orange (Fig. 9 D View Figure 9 ). Rostrum fused with cephalothorax. Posterior margin of cephalothorax and all pedigerous somites smooth. Body color yellowish, except second pedigerous somite, this somite white (Fig. 9 D View Figure 9 ).

Abdomen (Figs 10 A – C View Figure 10 , 11 A View Figure 11 ) consisting of genital double-somite, two free abdominal somites, and anal somite with caudal rami. Genital, second, and third abdominal somites on posterior margin serrated. Genital double-somite consists of last thoracic somite and first abdominal somite; longer than wide; anterior part with two dorsal pairs of sensilla, dorsal unpaired pore, lateral and ventral pairs of pores; posterior part with three pairs of sensilla, two pairs of pores and dorsal unpaired pore.

P 6 (Fig. 10 A, B View Figure 10 ) lateral, formed plate, partially fused with somite; with one long plumose seta, one short spine and small spiniform process. Genital field (Fig. 10 C View Figure 10 ) wide, bean-shaped. Copulatory pore medial, located on notable suture cord. Copulatory duct short, chitinised. Anterior and posterior chambers of seminal receptacle equal in wide, narrow. Two egg sacks attached to gonopore area.

Second abdominal somite (Fig. 10 A – C View Figure 10 ) with three pairs of sensilla, two pairs of pores, and dorsal unpaired pore. Third abdominal somite (Fig. 10 A – C View Figure 10 ) with dorsal unpaired pore, pairs of lateral and ventral pores. Anal somite with one dorsal pair of sensilla: one dorsal, one anterolateral, one lateral, and one ventral pairs of pores; with or without small posterior spinules near sides of proctodeum; with ventro-lateral posterior rows of spinules; proctodeum with rows of setules. Anal operculum slightly protruding.

Caudal rami (Figs 10 A – C View Figure 10 , 11 A View Figure 11 ). Length / width ratio 6, 5 in holotype (5.2–7.0, median 5.91, n = 19). Ramus with one ventral and two dorsal pores; with longitudinal row of small spinules (serra); with spinules at base of seta III. Serra extending from base of seta II to anterior 8 % of ramus in holotype (8 % – 30 %, median 16 %, n = 19). Seta I absent. Seta II dorsolateral, small. Seta III spiniform, with spinules on outer side and long setules on inner side. Apical setae IV and V (Fig. 10 D View Figure 10 ) long; bipinnate; with fracture planes; proximal part bare, medial part with rare long spinules, distal part with dense long spinules; length ratios 1 and 1.63, respectively. Seta VI with several inner setules and with or without outer setules; longer than seta III (ratio of lengths of seta VI to seta III 1.07–1.47, median 1.26, n = 19). Seta VII biarticulate.

Antennule (Fig. 11 B, C View Figure 11 ) 12 - segmented; extending to second pedigerous somite. Armature formula as follows: 1 - [8], 2 - [4], 3 - [2], 4 - [6], 5 - [4], 6 - [2], 7 - [2], 8 - [3], 9 - [2 + ae], 10 - [2], 11 - [2 + ae], 12 - [7 + ae]. Segment 1 with four rows of spinules. Segment 4 with one pore. Three distal segments with finely serrate hyaline membrane (Fig. 11 C View Figure 11 ); proximal part of membrane of distal segment with 90 small denticles. Aesthetascs located on segments 9, 11, and 12. One seta on segment 6 spiniform. One apical seta on segment 12 fused basally to aesthetasc.

Antenna (Fig. 12 A – D View Figure 12 ) four-segmented include coxobasis and three-segmented endopod. Coxobasis rectangular; with three setae, one of these exopodal long pinnate seta; with groups of spinules 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16. Number of spinules of group 7: 1–6 (median 3, n = 19). Number of spinules of group 8: 0–5 (median 1, n = 19). First endopodal segment with one naked seta; one postero-lateral and postero-medial rows of spinules. Second endopodal segment with nine naked setae on inner margin, these setae longer from proximal to distal; with row of spinules along outer margin. Third endopodal segment cylindrical, same length as second segment; with seven naked apical setae with claw-like tips; with two spinular rows on outer margin.

Labrum (Fig. 11 D View Figure 11 ) trapezoidal. Anterior surface with two groups of long spinules. Distal margin with lateral outgrowths with small denticles and 11 medial teeth.

Mandible (Fig. 12 E View Figure 12 ) composed of coxa and small palp. Coxal gnathobase with 14 distal elements: one serrate seta; eight strong teeth; five slender teeth, three of these fused in base; gnathobase distally with row of long spinules. Palp with three apical setae: two long and plumose and one short and naked.

Paragnaths (Fig. 11 E View Figure 11 ) with paired lateral lobes. Distal parts of lobes with folded outgrowths. Proximal part of lobes on posterior side with three transverse group of spinules; medial part on posterior side with two longitudinal rows of spinules; distal part with one dense longitudinal posterior, one longitudinal anterior and distal rows of spinules.

Ventral surface of cephalothorax posteriorly to paragnaths with groups of long hairs.

Maxillule (Fig. 13 A, B View Figure 13 ) composed of syncoxa and two-segmented palp: one-segmented basis and one-segmented endopod. Praecoxal arthrite medially with three distal strong teeth, distal pinnate seta, two strong medial spines, three medial setae, one short plumose proximal seta and one long pilose robust proximal seta. Basis with anterior group of spinules; distally with two setae and one spine. Exopod represented by one plumose seta on proximal part of basis. Endopod with three plumose setae.

Maxilla (Fig. 13 C View Figure 13 ) five-segmented, composed of syncoxa, basis and three-segmented endopod. Syncoxa with two rows of spinules on anterior side; with endite with two long pinnate setae. Basis with postero-lateral row of spinules and group of small spinules on posterior side; with two endites: proximal with one plumose seta; distal with one plumose and one bare setae. First endopodal segment with slender seta, strong subdistal plumose seta and strong claw with longitudinal row of spinules. Second endopodal segment with one strong serrate and one strong plumose setae. Third endopodal segment with one seta with small spinules, one bare and one strong serrate seta.

Maxilliped (Fig. 13 D View Figure 13 ) four-segmented, composed of syncoxa, basis and two-segmented endopod. Syncoxa elongated; on anterior side with proximal row of spinules, medial flap-like structure and medial group of small spinules; with three plumose setae. Basis with two outer rows of spinules; two rows of spinules on anterior side; with two plumose setae. First endopodal segment with row of spinules on anterior side and long plumose seta. Second endopodal segment with one plumose and two serrulate setae.

Setae / spine armature of P 1 – P 4 presented in Table 7 View Table 7 .

P 1 (Fig. 14 A View Figure 14 ) with three-segmented rami. Praecoxa with two rows of long spinules. Coxa rectangular; with two posterolateral, one anterolateral and one posteromedial rows of spinules; distal anterior margin with small spinules; anterior side with one pore and seven rows of tiny spinules; with long pinnate inner seta. Intercoxal sclerite almost square, with anterior distal paired and posterior medial continuous rows of spinules. Basis with pore; spinulose rows at base of endopod and inner seta; inner row of setules; outer row of small spinules; large number ungrouped tiny spinules on anterior side; with outer plumose and inner thick pinnate setae. All exopodal and endopodal setae plumose; all exopodal and endopodal spines spinulose. First exopodal segment with outer spine and inner seta; distal posterior, distal anterior rows of spinules, inner row of setules, spinules at base of outer spine. Second exopodal segment with inner seta and outer spine; with anterior pore, distal posterior, distal anterior rows of spinules; inner and outer rows of setules, spinules at base of seta and spine. Third exopodal segment with three outer spines, two apical and three inner setae; with inner setules and spinules at base of setae and spines. First endopodal segment with inner seta; with anterior distal rows of spinules and outer setules. Second endopodal segment with two inner setae; with one pore, distal anterior and distal posterior rows of spinules, outer and inner row of setules. Third endopodal segment with outer seta, apical spine, apical seta, three inner setae; with outer row of setules and spinules at base of spine and setae.

P 2 (Fig. 15 A View Figure 15 ) with three-segmented rami. Praecoxa with group of long spinules. Coxa rectangular; with two posterolateral, two anterolateral and one posteromedial row of spinules; distal anterior margin with small spinules; anterior side with one pore and six rows of tiny spinules; with pinnate inner seta. Intercoxal sclerite almost square, with anterior distal paired and posterior medial continuous rows of spinules. Basis with pore; spinulose rows at base of endopod and on outer side; inner row of setules; several ungrouped tiny spinules on anterior side; with outer plumose seta. All exopodal and endopodal setae plumose; all exopodal and endopodal spines spinulose. Segments with small spinules near base of all spines and setae, except inner seta of first exopodal segment. First exopodal segment with outer spine and inner seta; distal posterior, distal anterior rows of spinules, inner row of setules. Second exopodal segment with inner seta and outer spine; with anterior pore, distal posterior, distal anterior rows of spinules; inner and outer rows of setules. Third exopodal segment with three outer spines, one apical spine, one apical seta and four inner setae; with one pore and inner setules. First endopodal segment with inner seta; with distal anterior and distal posterior rows of spinules and outer row of setules. Second segment with two inner setae; with one pore, distal anterior and distal posterior rows of spinules, and outer and inner rows of setules. Third segment with one outer seta, one apical spine, one apical seta, and three inner setae; with one pore; with outer and inner row of setules.

P 3 (Fig. 15 B View Figure 15 ) similar to P 2. Intercoxal sclerite on posterior side with two rows of spinules.

P 4 (Fig. 16 A, B View Figure 16 ) with three-segmented rami. Praecoxa with group of long spinules. Coxa rectangular; with pinnate inner seta. Posterior side of coxa with three proximal straight rows, three medial groups, several lateral groups and rows, and one distal row of large spinules. Anterior side with one pore and six rows of tiny spinules; with spinules on distal margin. Intercoxal sclerite on posterior side with continuous distal row of setules and discontinuous medial and proximal rows of long spinules / setules. Basis with pore; spinulose rows at base of endopod and on outer side; inner row of setules; several ungrouped tiny spinules on anterior side; with outer plumose seta. All exopodal and endopodal setae plumose; all exopodal and endopodal spines spinulose. Segments with small spinules near base of all spines and setae, except inner seta of first exopodal segment. First exopodal segment with outer spine and inner seta; distal posterior, distal anterior rows of spinules; inner row of setules; number of inner setules 8–17 (median 12, n = 13). Second exopodal segment with inner seta and outer spine; with anterior pore, distal posterior, distal anterior rows of spinules; inner and outer rows of setules; number of inner setules 6–10 (median 7, n = 13). Third exopodal segment with two outer spines, one apical spine, apical seta, and four inner setae; with one pore, outer and inner setules; three distal setae with hyaline frill. First endopodal segment with inner seta; with distal anterior and distal posterior rows of spinules and outer row of setules. Second segment with two inner setae; with one pore, distal anterior and distal posterior rows of spinules, outer row of setules. Third segment with one outer and one apical seta, one apical spine, and three inner setae; with one pore; with outer and inner row of setules; with small proximal outgrowth; all setae with weakly expressed hyaline frill.

P 5 (Fig. 14 B View Figure 14 ) one-segmented, without intercoxal sclerite. Segment with large robust inner spine, one apical pinnate and outer pinnate setae; with row of spinules near base of inner spine and with or without outer row of spinules.

Male. Significantly smaller than female (Fig. 9 E – G View Figure 9 ). Total body length from anterior margin of rostrum to posterior margin of caudal rami: 870 µm (n = 1), largest width of cephalothorax 255 µm (n = 1). Sexual dimorphism expressed in the antennule, ornamentation of A 2, P 2 – P 4, genital segmentation and ornamentation, P 6, caudal rami. Pore pattern of cephalothorax and abdominal somites as in female.

Genital somite (Fig. 17 A, B View Figure 17 ) free; with two spermatophores visible inside; with P 6. Spermatophores (Fig. 17 B View Figure 17 ) bean-shaped. P 6 (Fig. 17 B View Figure 17 ) marked by two large flaps fused to the somite; with ventral pores; with outer and middle pinnate setae and inner long spinulose spine.

Antennule (Fig. 18 A – C View Figure 18 ) 16 - segmented, haplocer with two geniculations: first one between segments 7, 8, and 9; second one between segments 14 and 15. Segment 1 long; with three spinulose rows; one long setiform aesthetasc, six unmodified setae and two modified “ blowball-setae ” with abruptly breaking tip with dense bunch of setules. Segment 2 with three unmodified setae and one “ blowball-seta ”. Segment 3 with one unmodified seta and one “ blowball-seta ”. Segment 4 with one long setiform aesthetasc, one unmodified seta and one “ blowball-seta ”. Segment 5 with one unmodified seta and one “ blowball-seta ”. Segments 6, 7, 8 similar, short, each with two setae. Segment 9 with two unmodified setae and one aesthetasc. Segments 10 and 11 widened, each with two setae. Segment 12 with one small and one spiniform robust seta. Segment 13 with one robust serrate seta, one small seta and one aesthetasc. Segment 14 elongated, with one modified flattened laminar seta and three small finger-like modified setae. Segment 15 elongate; with two modified flattened setae; one long unmodified seta; one modified spiniform seta and one aesthetasc. Segment 16 with two aesthetascs, eleven setae, one of which fused in base with aesthetasc. Armature formula: 1 - [8 + ae], 2 - [4], 3 - [2], 4 - [2 + ae], 5 - [2], 6 - [2], 7 - [2], 8 - [2], 9 - [2 + ae], 10 - [2], 11 - [2], 12 - [2], 13 - [2 + ae], 14 - [4], 15 - [4 + ae], 16 - [10 + ae + (1 + ae)].

Antenna (Fig. 18 D, E View Figure 18 ). Endopod similar to that in female. Coxobasis rectangular; with three setae, one of these exopodal long pinnate seta; with groups of spinules 1, 3, 4, 5, 6, 7, 9, 10, 11, 12, 15, 16.

P 2 – P 4 (Fig. 17 C View Figure 17 ) similar to this in female, differences in relative length and shape of segments; smaller ornamentation; spines longer with strong spinules; setae shorter, with well-expressed hyaline frills.

Variability.

Eucyclops sibiricus sp. nov. var. brevis does not differ in the structure of the caudal rami (Fig. 11 A View Figure 11 ) and coxobasis of the antennae (Fig. 12 C, D View Figure 12 ). The differences concern only the relative length of the P 2 – P 4 segments (Fig. 16 B View Figure 16 ).