Eucyclops taiwanensis, Sukhikh & Alekseev, 2015

Sukhikh, Natalia & Alekseev, Victor, 2015, Genetic and morphological heterogeneity within Eucyclops serrulatus (Fischer, 1851) (Crustacea: Copepoda: Cyclopidae), Journal of Natural History 49 (45), pp. 2929-2953 : 2941-2949

publication ID	https://doi.org/ 10.1080/00222933.2015.1056267
DOI	https://doi.org/10.5281/zenodo.4323698
persistent identifier	https://treatment.plazi.org/id/8C6EE858-FFEE-1134-FDB6-EFDCFDBCBB01
treatment provided by	Carolina
scientific name	Eucyclops taiwanensis
status	sp. nov.

Treatment

Eucyclops taiwanensis sp. n.

( Figures 5–9 View Figure 5 View Figure 6 View Figure 7 View Figure 8 View Figure 9 )

Type material

Holotype: ZIN RN 55090 View Materials , female dissected on 1 slide; from Abvil Lake , Taiwan (25.0333°N, 121.6333°W), collected by V. Alekseev, 4 October 2009. GoogleMaps

Paratypes: ZIN RN 55091 View Materials /3–13, 3 males dissected on 3 slides, 9 females from Abvil Lake , Taiwan (25.0333°N, 121.6333°W), dissected on 5 slides, collected by GoogleMaps V. Alekseev , 4 October 2009 .

Description of holotype

Female ( Figures 5–7 View Figure 5 View Figure 6 View Figure 7 ). Length measurements. Total body length without caudal setae 1015 μm, with caudal setae 1494 μm. Cephalothorax 295 μm, 4 free thoracic somites: 138/59/54/48 μm. Urosoma 317 μm: genital double-somite 63 μm, 3 following abdominal somites 54/50/46 μm, caudal rami 104 μm. Cephalothorax slightly longer than wide, with maximum width close to terminal part, frontal part of cephalothorax oval ( Figure 5A View Figure 5 ).

Caudal rami parallel, 4.2 times as long as wide, with longitudinal row of spinules (serrula) along most of outer edge of each ramus ( Figure 5B View Figure 5 ).

Antennules 12-segmented, reaching middle margin of second free thoracic somite, with denticulate hyaline membrane on 10th and 11th segments and smooth hyaline membrane on distal segment. Armament per segment as follows: 8/4/2/6/4/2/2/3/2/2/3/ 8. Most segments with 2 or more setae; segments 4 with 1 aesthetasc; 1 and 12 with 2 aesthetascs ( Figure 5C View Figure 5 ).

Antenna ( Figure 6A View Figure 6 ) with 1-segmented basipodite, 3-segmented endopodite. Exopodite represented by long, barbed seta. Antennary basipodite micro patterns (caudal face): apical group N1 consists of 3 long setules; group N2 absent, three diagonal and parallel rows of spinules (N3–5) are reduced and row N4 with gap; group of marginal spinules N17 consists of 8–10 setules.

Mandible ( Figure 6B View Figure 6 ) with six teeth distally, palp and rudimentary endopod with two long and one short setae.

Maxillula ( Figure 6C View Figure 6 ) comprising praecoxopodite with six strong teeth and two strong setae; palp with 6 long hair-like setae of different length.

Maxilla ( Figure 6D View Figure 6 ) uniramous 4-segmented: praecoxopodite with two strong median setae; syncoxopodite with two endites; proximal endite with one, distal endite with two setae; next segment with two very strong spines and small seta near to fusion of rudimentary endopodite. Latter with 2 strong spines and 3 slender setae.

Maxilliped ( Figure 6E View Figure 6 ) uniramous of four segments: syncoxopodite with two strong setae in middle part and 1 seta in distal part; basipodite with two setae of different length; first segment of endopodite with strong spine and hairless seta, rudiments of other endopodite segments with strong spine and 1 seta.

Swimming legs P1–4 ( Figure 7 View Figure 7 ) consisting of coxopodite and basipodite, bearing 3-segmented exopod and endopod. Swimming legs P1–4 spine (Arabic numerals) and seta (Roman numerals) formulae as in Table 7.

Both basipodite P1 to P4 edges with long hair-like setae. Basipodite P1 with inner spine reaching middle of third segment of End ( Figure 7A View Figure 7 ).

Coxopodite of P4 ( Figure 7D View Figure 7 ) with strong inner spine like other legs, dense hairlike setae on inner side, and without gap among short hair-like setae on inner side. Posterior side of coxopodite with tiny spinules on inner side, not organized in groups, and groups of spinules and setules, giving formula A – I – B – E – C + D – H.

Coxopodite connected with coxal membrane. Intercoxal plate of P1–4 as in ( Figure 8 View Figure 8 ) with wide protuberances, but not protruding beyond free edge of plate. Coxopodites and intercoxal sclerites P1–P3 as in Figure 8 View Figure 8 .

Intercoxal plate of P4 with two groups of hair-like, long setules on free edge ( Figure 7D View Figure 7 , groups 1–2) and 3 groups of setules on plate ( Figure 7D View Figure 7 , groups 3–5). Distal spine Exp P4 about half of nearest seta and segment length ( Figure 7D View Figure 7 ).

Leg P5 ( Figure 6B View Figure 6 ) 1-segmented with strong knife-like inner spine and two setae; outer seta about 1.2 times as long as spine and about 1.7 times as long as medial.

Eggs packed into 2 rounded sacs.

Male ( Figures 8 View Figure 8 , 9 View Figure 9 ). Body length 723 μm without caudal setae ( Figure 8A View Figure 8 ), and 1125 μm with caudal setae. Cephalosome 1.3 times as long as wide, with maximal width close to posterior end. Last segment of prosome smooth, last urosomal segment with row of denticles on caudal side.

Caudal rami ( Figure 8B View Figure 8 ) 2.9 times longer than wide, without lateral spinules. Slender innermost caudal seta about 2.3 length of spine-like outermost caudal seta.

Antennule 14-segmented with 9 setae on first segment ( Figure 9A View Figure 9 ).

Antennary basipodite basically as in female. Morphology of mouthparts and P1– 3 basically as in female.

Inner edge of basipodite P4 ( Figure 9B View Figure 9 ) with short setules, coxopodite of P4 with strong spine, bearing strong hair-like setae without gaps. Coxopodite of P4 with several groups of spinules A + I – B – G – C + D – H, as in female, but fewer spinules in each group. Intercoxal plate of P4 with small protuberances, strong hairlike setae on free edge, and three groups of setules on both sides. Distal segment of P4 endopodite 1.2 times longer than outer spine and 3 times longer than terminal inner seta.

P5 ( Figure 8B View Figure 8 ) with inner spine 1.2 times shorter than in female, outer seta 1.2 times longer than inner spine, medial seta 1.7 times as long as spine.

P6 ( Figure 8B View Figure 8 ) with inner spine and two setae with length proportions, beginning from outer seta, 1/0.85/1.

Etymology

The name of the species originates from the name of the type locality: Taiwan.

Remarks

As for intraspecific variability within the type population, we did not observe significant differences among the 13 analysed individuals. This low variability is reflected in the small standard errors of the mean in Tables 4 and 5. In general, the variation among individuals is rather small, especially for females – mean values of 0.9–2.7%. Relative standard errors of the mean for males are greater than for females, with values from 2.1 to 3.7%. The relatively high standard errors of the mean for males are most likely a result of the small sample (3 specimens).

Differential diagnosis

The Taiwanese females differed from the Zakarpattia and Dniester females simultaneously in the following indexes: caudal rami length/width (L/W); innermost caudal seta/dorsal setae (IN/ DORseta); P4 distal exopodite segment length/apical spine length (P4 exo Lseg/Sp1) ( Table 4).

Additionally the Taiwanese females differed from the Dniester females in: innermost caudal setae/outermost caudal setae (IN/OUTseta); P4 length of inner setae of distal endopodite segment/segment length (P4 endo Inseta/Lseg); and from the Zakarpattia females in P4 apical spine of distal endopodite segment/segment length (P4 endo Sp1/Lseg) ( Table 4).

Reliable differences in caudal indexes IN/OUTseta and IN/L are shown in Table 5 and were obtained for the males from Taiwan and Dniester Liman. The Taiwanese males differed from the type population males in caudal ratio L/W ( Table 5).

In general we did not observe differences in the indexes used among Taiwanese and the type populations, but the males and females of Eucyclops taiwanensis sp. n. differed from all studied Eucyclops serrulatus populations and from E. agiloides (G. O. Sars) in antennular hyaline membrane structure and in the coxal seta of P4 ( Figure 10A–D View Figure 10 ). Eucyclops taiwanensis sp. n. as Eucyclops macruroides presents wide serrated hyaline membrane (but not so strongly serrated as in E. denticulatus (Graeter)) on the last antennular segment and a P4 coxal seta without a gap in setules ( Figure 10A, B, E, F View Figure 10 ). The micropatterns of Eucyclops taiwanensis sp. n. antennary basipodite also differ from those of Eucyclops serrulatus as it has reduced rows of spinules ( Figures 3C, D View Figure 3 , 6A View Figure 6 ). At the same time Eucyclops taiwanensis sp. n. is clearly different from E. macruroides by a combination of characters: only antennular segments 10 and 11 have serrated hyaline membrane (not 10–12) ( Figure 10A, E View Figure 10 ), and the caudal rami are significantly shorter – L/ W index not more than 4.5 (not 7–9 for females and 5–6.5 for males of E. macruroides according to Monchenko 1974). Eucyclops taiwanensis sp. n. differs from E. procerus Dussart, 1981 in the caudal rami (L/W index 6–7).

The female of Eucyclops taiwanensis sp. n. can be separated from E. macrurus (Sars) , E. speratus (Lilljeborg) , E. glaber Kiefer , E. borealis Ishida , and E. arcanus Alekseev by serrula along most of outer edge of each caudal ramus. Eucyclops taiwanensis sp. n. can be separated from E. miracle Alekseev , E. roseus Ishida , E. hadjebensis Kiefer , E. romaniensis Alekseev , E. serrulatus serrulatus (Fischer) , E. albuferensis Alekseev and E. vandouwei (Brehm) by the absence of group N2 on the posterior side of the antennal basipodite ( Figure 6A View Figure 6 ).

Eucyclops taiwanensis sp. n. can also be separated from other congeneric females by the antennula with finely serrated hyaline membrane along segments 10–11, and the smooth hyaline membrane on the distal segment, in combination with other above-mentioned characters.