Eucyclops cuatrocienegas, Suárez-Morales, Eduardo & Walsh, Elizabeth J., 2009

Suárez-Morales, Eduardo & Walsh, Elizabeth J., 2009, Two new species of Eucyclops Claus (Copepoda: Cyclopoida) from the Chihuahuan Desert with a redescription of E. pseudoensifer Dussart, Zootaxa 2206, pp. 1-22 : 2-9

publication ID	https://doi.org/ 10.5281/zenodo.189729
publication LSID	lsid:zoobank.org:pub:1202C22B-15EF-4EF5-9A19-218AF4536C51
DOI	https://doi.org/10.5281/zenodo.5625824
persistent identifier	https://treatment.plazi.org/id/039D87D0-E940-FFD4-D5C2-F8A7C18EFE05
treatment provided by	Plazi
scientific name	Eucyclops cuatrocienegas
status	sp. nov.

Treatment

Eucyclops cuatrocienegas sp. nov.

( Figs 1–4 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 )

Material examined. Holotype. Adult female, dissected, mounted in glycerine sealed with Entellan, deposited in the zooplankton collection of ECOSUR (ECOCH-Z) (ECO-CHZ- 03586), collected from Poza Tortugas, a pond in the northern sector of the state of Coahuila, Mexico (26º 55.887’N; 102º 0 7.482 W), July 7, 2006; coll. Elizabeth Walsh and colleagues. Allotype. One dissected male, same date, site, and collector, mounted in glycerine, slide sealed with Entellan® (ECO-CHZ-03588). Paratypes. Five undissected adult females (ECO- CHZ-03587), same date, site, and collector, ethanol-preserved. Additional, non-paratype specimens and original zooplankton sample in the laboratory of E. Walsh, University of Texas at El Paso.

Type locality. Poza Tortugas, Cuatro Ciénegas, Coahuila, Mexico (26º 55.887’N; 102º 0 7.482 W), elevation 725 m. Shallow (~ 1 m deep) poza (pond with vertical walls) near Poza Azul. Poza Tortugas was a natural, small pond that was enlarged by previous owners for recreational swimming about 16 years ago. The pond is no longer used for swimming but is a site where visitors are shown features and fauna of Cuatro Cienegas from an observation deck. It is surrounded by grasses (spikerush, common reed, cordgrass, brittlegrass) and hairsedge. Aquatic vegetation includes stonewort and the dotleaf waterlilly. Physical parameters at the time of collection: water temperature 28.6°; pH 7.96; conductivity 1.69 milliS/cm; TDS 1.099 mg /L.

Etymology. The species name is a noun in apposition that makes reference to Cuatro Ciénegas, the Mexican protected area from which this species was collected.

Description. FEMALE ( Fig. 1 View FIGURE 1 A): Total body length = 0.818 ± 0.039 mm (n= 6) from anterior end of cephalothorax to posterior margin of caudal rami. Body elongate, cephalothorax relatively long, widest at midlength of cephalosome in dorsal view; lateral margins of pedigers 3 and 4 straight, slightly produced posteriorly. Cephalothorax length = 0.45 ± 0.08 mm (n= 15), representing 66 % of total body length. Dorsal surface smooth, antennules reaching anterior margin of first pediger. Rostrum strong, wide, with rows of spinules on lateral surfaces of rostral base converging near anteriormost end. Urosome, excluding caudal rami, representing 31% of body length.

Antennule ( Fig. 1 View FIGURE 1 B): 12-segmented, armament per segment as follows (s= seta, ae= aesthetasc): 1(8s + rows of spinules on proximal and distal position), 2(3s), 3(2s), 4(5s), 5(2s), 6(2s+ 1 spine), 7(2s), 8(3s), 9(2s), 10(2), 11(2s), 12(7s+1ae). Hyaline, smooth, slender membrane on segments 10–12.

Antenna ( Fig. 2 View FIGURE 2 D): 4-segmented, basis with several rows of spinules on caudal surface. Largest spinules on subdistal clusters, near insertion point of 2 anterodistal setae. Basis with long exopodal pinnate seta. Second segment with 1 short external seta and subdistal row of spinules. Third segment with 8 setae; inner margin with row of spinules from proximal 1/3 increasing size distally. Fourth segment with 5 terminal and 2 subterminal setae.

Labrum: Distal margin curved, with 11–12 rounded teeth. Two ventral plates in area where 2 groups of short spinules are medially conjoined.

Mandible ( Figs 2 View FIGURE 2 B, C): Gnathobase with strongly chitinized teeth; 4 ventral teeth bicuspidal, blunt, 3 dorsal ones acute. Palp with 2 long plumose setae and 1 naked seta of about half the length of the other two, row of 6–8 spinules on ventral surface.

Maxillule ( Fig. 2 View FIGURE 2 E): Praecoxal arthrite armed with 6 setae and spines. Palp with 3 setae on proximal article; distal article with 3 subequal setae.

Maxilla ( Fig. 2 View FIGURE 2 F): 5-segmented, praecoxa and coxa separated; precoxal endite protuberant, armed with 2 plumose setae, caudal surface naked. Coxa with single seta on middle inner margin. Proximal basipodal endite well developed, with 2 apical setae. Claw-like basal endite with 12–15 stout teeth, row of fine spinules on distal 1/3 of outer margin, plus short, slender seta on frontal side. Endopod 2-segmented, proximal segment with 2 long setae, distal segment with 3 stout setae.

Maxilliped ( Fig. 2 View FIGURE 2 G): 4-segmented. Coxa with 3 short pinnate setae; row of spinules on surface of coxa. Basis with 2 pinnate setae, with row of long spinules near insertion of basipodal setae. Endopod 2-segmented, first segment with wide-based, stout seta; row of 6–8 long spinules along distal margin of segment. Second endopod armed with strong spiniform seta and 2 distal setae.

Leg 1 ( Fig. 3 View FIGURE 3 A): Coupler with curved rows of 7–10 spinules on each side plus distal row of short spinules between pair of rounded chitinized projections. Coxa with strong coxal seta; row of spinules on outer proximal surface and row of 4–6 hair-like elements along outer margin. Basis with slender outer seta; inner margin with spinules and row of short hair-like elements on insertion point of strong, pinnate basipodal seta reaching beyond distal margin of second endopodal segment. Endopod and exopod 3-segmented. Armature as in Table 1 View TABLE 1 .

Leg 2 ( Fig. 3 View FIGURE 3 B): Coupler with transverse row of 10–13 minute spinules; distal margin with 2 low, rounded projections. Coxa with strong inner coxal seta; outer margin with proximal row of spinules. Basis with slender basipodal seta on outer margin, inner margin with hair-like ornamentation. Distal margin with disto-medial expansion between insertion point of exopod and endopod. Endopod and exopod 3-segmented; first and second exopodal segments with distal row of spinules. Armature as in Table 1 View TABLE 1 .

Leg 3 ( Fig. 3 View FIGURE 3 C): Coupler with 2 frontal, transverse rows of 25–30 tiny spinules, distal margin with 2 low, rounded chitinized projections, naked. Coxa with strong inner coxal seta; outer margin with proximal row of spinules. Basis with seta on outer margin; row of spines at insertion point of seta. Endopod and exopod 3- segmented. Armature as in Table 1 View TABLE 1 .

Leg 4 ( Fig. 3 View FIGURE 3 D): Coupler with medial row of 7–8 spinules on each side of plate; distal margin straight, armed with row of spinules. Coxa with strong inner coxal seta. Basis with slender basipodal seta and row of strong spines on outer margin. Endopod and exopod 3-segmented. Armature as in Table 1 View TABLE 1 . Outer terminal endopodal spine finely pinnate along both margins; inner seta with spinules on outer margin only, inner margin smooth. Length ratio of inner/ outer terminal spines of Enp 3= 1.50–1.54. Length/width ratio of third endopodal segment= 3.1. Insertion point of seta on outer margin of Enp 3= 58%. Length of inner endopodal spine/endopod 3= 1.1–1.3.

Leg 5 ( Figs 2 View FIGURE 2 A, 3E): Consisting of article armed with 2 setae and 1 spiniform seta, middle seta as long as outer one; inner spiniform seta pinnate, slightly curved, short, as long as bearing segment.

Vestigial leg 6 ( Fig. 2 View FIGURE 2 A): Small, low plate near lateral margin of genital somite with laterally directed dorsal seta and tiny lateral spinules.

Urosome ( Figs 1 View FIGURE 1 A, 2A): Urosome comprising fifth pedigerous somite, genital double somite and 3 free somites; posterior margin of genital double and postgenital somites serrate dorsally and ventrally. Fifth pediger armed with tuft of hair-like elements on outer distal margin. Genital somite representing 13.9–14.3 % of total body length; anterior half of genital somite expanded laterally forming subtriangular processes. Seminal receptacle wide, with short, rounded lateral arms; lateral channels curved. Posterior margin rounded, sac-like ( Fig. 2 View FIGURE 2 A). Anal somite armed with row of spinules along posterior margin; ventral row covering only half of margin ( Figs 1 View FIGURE 1 C, D).

Caudal rami ( Figs 1 View FIGURE 1 C, D): Rami relatively short, representing 8.5 % of total body length, 0.35 times as long as urosome. Length/width ratio= 3.1–3.4. Inner margin smooth. Outer margin armed with row of spinules from proximal to distal margin; spines increasing in size distally, distalmost spines of saw relatively long. Lateral seta noticeably short, peg-like, thick at base, tapering into acute end; inserted subterminally near insertion point of lateralmost terminal spiniform seta. Lateralmost terminal seta 0.63 times as long as caudal ramus. Dorsal seta noticeably short, 0.42–0.47 times as long as caudal ramus. Inner terminal seta longest, about 2 times longer than outer terminal seta, armed with a few spinules along proximal half, followed by regular plumose pattern ( Fig. 1 View FIGURE 1 A). Outer terminal setae with same ornamentation pattern, half their length with sparse spinulation, distal half with regular setulation.

MALE ( Figs 4 View FIGURE 4 A–E): Body elongate, without hairs or pits on dorsal surface. Noticeably smaller, more slender than female. Total body length of allotype = 0.68 mm, cephalothorax length = 0.42 mm, representing almost 64% of total body length, urosome length = 0.26 mm. Body and appendages as in females except for sexual dimorphism.

Antennule ( Fig. 4 View FIGURE 4 E): Geniculate, 14-segmented.

Vestigial leg 6: consisting of broad subquadrate plate with long medial stout spine reaching beyond succeeding posterior urosomite; cluster of spines on insertion of spine. Article with 2 outer seta subequal in length and breath. Spine twice as long as 2 lateral setae, reaching about proximal 1/3 of succeeding urosomite.

Urosome. 5-segmented, genital somite largest of urosome; relative lengths of urosomites as: 32.1: 24: 23.3: 13.3: 7.3=100. Ventral and dorsal surface of anal somite smooth; distal margin with continuous dorsoventral row of spines. Anal plate smooth. Caudal rami relatively shorter than in female, 2.8 times longer than wide ( Fig. 4 View FIGURE 4 C), margins smooth. Inner and outer terminal caudal seta with ornamentation as in female ( Fig. 4 View FIGURE 4 D). Innermost terminal seta relatively shorter than in female, 0.64 times as long as ramus.

Remarks. The specimens examined were assigned to the genus Eucyclops Claus, 1893 owing to their its possession of the combination of features defined by Reid (1985) and Dussart & Defaye (2001). One of the most useful characters used to separate some of the American species of Eucyclops is the length/width proportion of the caudal ramus; it can be long (more than 5.0 times longer than it is wide) as in E. serrulatus (Fischer, 1851) , E. pectinifer (Cragin, 1883) , E. solitarius Herbst, 1959 or E. festivus Lindberg, 1955 , or relatively short, less than 4 times longer than it is wide (i.e., between 3.6–4 in E. leptacanthus Kiefer, 1956 and E. serrulatus chilensis Löffler, 1961 , 3.5 in E. conrowae Reid, 1992 , 3.2 in E. ensifer Kiefer, 1936 , or 2–3 in E. siolii Herbst, 1962 , E. breviramatus Löffler, 1963 , and the Asian E. dumonti Alekseev, 2000 ). The length ratio of the caudal rami in the new species shows values around 3 (3.1–3.4).

Among the American species that share with the new species these characters (i.e., relatively short caudal rami, outer margin entirely spinulated) are: E. delachauxi ( Kiefer, 1925) , E. conrowae , E. leptacanthus Kiefer, 1956 , E. ensifer , E. pectinifer (sensu Alekseev et al. 2006), E. pseudoensifer Dussart, 1984 , E. prionophorus Kiefer, 1931 , E. bondi Kiefer, 1934 , E. serrulatus chilensis , and E. torresphilippi Suárez-Morales, 2004 . The new species can be distinguished from this group of congeners by evaluating additional characters. In the new species the fifth leg has a relatively short inner spine, as long as the bearing segment (ratio: 1.0). This character diverges from the pattern found in other congeners in which this element is clearly longer than the segment; the comparative length ratios (spine/segment) are: 1.37 in E. conrowae , 1.78 in E. ensifer , 1.28 in E. leptacanthus , 1.2–1.3 in E. pectinifer , 2.6 in E. prionophorus , 4.5 in E. pseudoensifer , 1.7–2.1 in E. serrulatus chilensis , and 1.31 in E. torresphilippi Suárez-Morales, 2004 ( Löffler 1961; Collado et al. 1984; Reid 1985, 1992; Suárez-Morales 2004; Alekseev et al. 2006). Only in one other American species, E. siolii , is the inner spine is smaller than the fifth leg segment ( Reid 1985). This character should be explored further in some of these species, particularly in those showing polymorphism such as E. serrulatus and E. prionophorus (see Alekseev et al. 2006). Conversely, the proportion of the outer and middle setae seems to be generally more stable in these species (see Alekseev et al. 2006, figs 6.1–7). In the new species these setae have the same length, thus diverging from most of these other congeners in which one of these setae is noticeably longer than the other, except for E. ensifer ; however, in this species the inner spine is thick, dagger-like, thus differing from the slender, slightly curved spine of the new species.

Overall, the new species shows the closest resemblance with E. pectinifer (sensu Alekseev et al. 2006), but there are a number of important differences between the two species. Eucyclops cuatrocienegas sp. nov.

can be easily distinguished from E. pectinifer mainly by the proportion of the caudal rami; in the latter species the length/width proportion is consistently around 5 ( Reid 1992; Alekseev et al. 2006), whereas it is clearly shorter in the new species (consistently less than 3.6). The dorsal seta is distinctly shorter in the new species, 0.36 times as long as ramus, vs 0.5 in E. pectinifer . The inner caudal seta is 0.5 times as long as ramus in E. pectinifer vs. a relatively longer seta (0.82) in the new species. Other differences include shorter antennules in the new species, reaching only halfway of the second pedigerous somite, whereas in E. pectinifer they reach beyond the third pedigerous somite (see Alekseev et al. 2006). The taxonomic value of the structure and ornamentation of the mouthparts has not been fully explored in the genus but some of the most complete, detailed descriptions allow a comparative analysis of some characters related to these appendages. The ornamentation of the antennular basis has been used as valuable discriminating characters in other genera (see Holynska 2006), and Alekseev et al. (2006) provided guidelines to evaluate these patterns in Eucyclops . A comparison of the characters of the mouthparts showed additional differences of E. cuatrocienegas with respect to E. pectinifer , including: 1) a weaker antennal ornamentation in E. cuatrocienegas sp. nov.; 2) in the new species the maxilliped has a stronger ornamentation on the basipod and on the first endopodal segment. In E. pectinifer the spinulation pattern of the coxal plate of leg 4 includes three rows of stout spines, whereas the pattern is reduced in E. cuatrocienegas , with only two rows of tiny spinules. In the new species the first coxal plate has a heavy ornamentation, with two frontal rows of slender spines and one distal row of spinules; the plate is smooth in E. pectinifer ( Alekseev et al. 2006, figs 17.14, 18.5).

The relative lengths and ornamentation of the distal spines of leg 4 endopodite are useful to separate some species of Eucyclops ( Reid 1985, Table 2 View TABLE 2 ). In the new species, the inner/outer spine length ratio is 0.64–0.66 vs. a 0.60 ratio in E. pectinifer (see Alekseev et al. 2006, fig. 18.7). In E. pectinifer both elements are bipinnate, whereas the inner margin of the inner spine is smooth in E. cuatrocienegas sp. nov. This character is present in other American species of the genus, such as E. solitarius , E. delachauxi , and E. demacedoi Lindberg, 1907 , all known only from South America (see Reid 1985). Also, in E. cuatrocienegas sp. nov. the insertion point of the outer seta of the third endopodal segment of leg 4 is at midlength (57%) of the segment vs. a more distal position in E. pectinifer (74%) (see Alekseev et al. 2006, fig. 18.8).

The medial spine of leg 6 of the male of E. pectinifer reaches beyond the proximal margin of the third urosomite ( Alekseev et al. 2006, fig. 17.11), whereas in the new species this element is shorter, barely reaching the posterior margin of the second urosomite. The male caudal rami of E. pectinifer are relatively shorter than in the female (length/width ratio= 3.9); the same is true in the new species (l/w ratio=2.7). The innermost terminal caudal seta is clearly shorter in E. cuatrocienegas sp. nov. than in E. pectinifer (0.64 times as long as ramus vs 1.0 in E. pectinifer ) (see Alekseev et al. 2006, fig. 17.10).

Eucyclops conrowae is another American species that has morphologic resemblance to E. pectinifer (see Reid 1992) and has some affinities with the new species too, mainly in having a relatively short caudal rami (length/width ratio=3.5); however it differs from E. cuatrocienegas sp. nov. in some important characters. Eucyclops conrowae has 1) relatively longer antenules, reaching posterior margin of pediger 2; 2) modified, sclerotized blunt setae on third endopodal segment of leg 4; 3) both terminal spines of leg 4 endopod are spinulate on both margins; 4) the inner spine of the fifth leg is clearly longer than the segment; 5) a set of lateralmost terminal caudal setae carried nearly at right angle to ramus; 6) dorsal seta 0.7 times as long as ramus; 7) anal somite relatively short, 0.35 times as long as caudal ramus; 8) medial spine of male leg 6 reaching beyond posterior margin of third urosomite. These characters are absent from or different in E. cuatrocienegas sp. nov. Another American form that has some resemblance with the new species is the Chilean subspecies Eucyclops serrulatus chilensis Löffler, 1961 ; both share several characters including a short dorsal seta, anal somite with spines along distal margin, a complete serra on the caudal rami, the outer and middle setae of the fifth leg are equally long, and the fourth leg has the same general structure (see Löffler 1961). Aside those mentioned before, the new species diverges in several other taxonomically relevant characters in Eucyclops , including a shorter caudal rami (length/width ratio= 3.1–3.4, vs 3.7–4.1 in E. serrulatus chilensis , although some specimens reported by Löffler have a ratio close to 3.5; however, additional specimens from the Patagonic region show a consistent range between 3.72 and 3.77 (Menu Marque in litt.). There is also a different proportion of inner/outer spines of leg 4 third endopodal segment (1.50–1.54 in the new species vs. 1.2–1.4 in the subspecies chilensis) ( Löffler 1961; Menu Marque in litt.), the distal ornamentation of the coxal plate of leg 4 (row of short spinules in the new species vs. single distal row of long hair-like elements in the form chilensis) ( Löffler 1961; Menu Marque in litt.), the dorsal seta is clearly shorter in the new species (0.35 times as long as ramus) than in the form chilensis (0.52–0.65) (see Löffler 1961, figs 77, 81, 84). Further, one of the main characters of the new species is the short spine of the fifth leg, which is as long as the segment; in the subspecies chilensis this spine is consistently almost twice as long as the segment in different populations (see Löffler 1961, figs 78, 82, Menu Marque in litt.).

	coxa	basis	endopodite	exopodite
leg 1	0-1	1-I	0-;0-0;0-2	I-0;I-0; 0,3
leg 2	0-1	1-0	1-0;2-0;3,1,I,1	I-1;I-1;IV,1,4
leg 3	0-1	1-0	1-0;2-0;3,1,I,1	I-1;I-1;IV,1,4
leg 4	0-1	1-0	1-0;2-0;2,II,1	I-1;I-1;III,1,4

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Taxonomy

Kingdom	Animalia
Phylum	Arthropoda
Class	Maxillopoda
Order	Cyclopoida
Family	Cyclopidae
Genus	Eucyclops