Eucyclops chihuahuensis, 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 : 15-18

Eucyclops chihuahuensis sp. nov.

( Figs 9 , 10 )

Material examined. Holotype. Adult female, dissected, mounted in glycerine sealed with Entellan, deposited in the zooplankton collection of ECOSUR (ECO-CHZ- 3589), collected from Presa Chihuahua, a reservoir near the city of Chihuahua, northern Mexico (28° 34.540 N; 106°09. 932 W), July 7, 2006; coll. Elizabeth Walsh and colleagues. Paratypes. One undissected adult female, mounted in glycerine, slide sealed with Entellan (ECO-CHZ-3590), same date, site, and collector. Four undissected adult females, ethanol-preserved (ECO-CHZ-3590), same locality and date. Additional, non-paratype specimens and original zooplankton sample in the laboratory of E. Walsh, University of Texas at El Paso.

Type locality. Presa Chihuahua, Chihuahua, Mexico (28° 34.540 N; 106°09. 932 W), a man-made reservoir located 12 km from the city of Chihuahua, Mexico.

Etymology. The name of this species makes reference to the reservoir and the arid environmental system from which this species was collected. The name is an adjective for place, using the Latin suffix “-ensis”.

Description. FEMALE ( Fig. 9 A): Total body length = 0.640 ± 0.043 mm (n= 6) from anterior end of cephalothorax to posterior margin of caudal rami. Body as in E. pseudoensifer Dussart, 1984 .

Antennule ( Fig. 9 B): As in E. pseudoensifer except for absence of proximal row of spinules on first segment, one seta less on segment 2 and 6, and last segment 1.15 times as long as penultimate one. Antenna ( Fig. 9 C): As in E. pseudoensifer except for lighter ornamentation of caudal surface of basipod. Mouthparts including mandible, maxillule, maxilla, and maxillipeds as in E. conrowae ( Reid 1992) except for mandibles armed with only 6 blunt bicuspidal teeth.

Leg 1 ( Fig. 10 A): As in E. pseudoensifer except for coupler with curved rows of 5–8 spinules on medial surface plus rows of long hair-like elements on distal margin ( Fig. 6 E), coxa with rows of spinules on outer proximal surface, medial row of 6–8 spinules plus subdistal row of 4–6 short hair-like elements along outer margin. Basis with long, pinnate spiniform basipodal seta reaching distal margin of second endopodal Leg 2 ( Fig. 10 B): As in E. pseudoensifer except for coupler strongly pilose, with transverse clusters of long hair-like elements on anterior, medial and distal surfaces ( Fig. 6 F), coxa with outer margin ornamented with proximal and subdistal rows of long hair-like elements. Basis with slender basipodal seta on outer margin reaching beyond distal margin of first exopodal segment.

Leg 3 ( Fig. 10 C): As in E. pseudoensifer except for coupler with 2 transverse rows of 8–10 long hair-like elements.

Leg 4 ( Fig. 10 D): As in E. pseudoensifer except for longer coxal seta, reaching well beyond distal margin of basipodite, coxa ornamented with outer row of long spinules. Outer and inner terminal endopodal spines finely serrate along outer margin only; inner margins smooth. Length ratio of inner/outer terminal spines of Enp 3= 1.5. Length/width ratio of third endopodal segment= 2.4. Insertion point of outer seta of Enp 3= 66%. Length of inner endopodal spine/endopod 3= 1.3.

Leg 5 ( Fig. 9 E): As in E. pseudoensifer except for outer seta as long as or slightly shorter than inner spine.

Vestigial leg 6 ( Fig. 9 E): As in E. pseudoensifer .

Urosome ( Figs 9 A, E): As in E. pseudoensifer except for genital double somite representing 12.2–12.8 % of total body length.

Caudal rami ( Fig. 9 D): As in E. pseudoensifer except for rami representing 14.5 % of total body length. Length/width ratio= 4.3–4.5. Outer margin armed with row of slender spinules arranged in tight pattern increasing in size distally. Lateralmost terminal spiniform seta relatively long, 0.50 times as long and 3.1 as wide as caudal ramus. Dorsal seta 0.43–0.45 times as long as caudal ramus. Inner medialmost terminal seta longest, proximal half smooth, followed by regular plumose pattern. Innermost terminal seta 0.85 times as long as ramus.

MALE: Unknown.

Remarks. The new species is similar in general proportions, habitus, and structure of the leg 5 to the general morphological pattern of E. pseudoensifer Dussart, 1984 (see Dussart 1984). Following Reid’s (1985) work on the Neotropical Eucyclops Claus , this new species keys out to the South American E. silvestrii (Brian, 1927) , both species share some important characters such as: length/width ratio of the caudal rami around 4.0, outer margin of caudal rami mostly serrate, short dorsal seta, outer spiniform caudal seta more than two times as wide as ramus, spine of the fifth leg as long as outer seta, last antenular segment longer than penultimate one. The new species differs from E. silvestrii in several characters including: the relative length of the last antennular segment (1.3 in E. chihuahuensis sp. nov. vs. more than 1.5 in E. silvestrii ) (see Reid 1985), the length of the middle seta of the fifth leg is twice as long as the outer seta in the new species, whereas both elements are equally long in E. silvestrii (see Reid 1985, fig. 128). The serration pattern of the caudal rami is different in both species, elements are smaller and more numerous in E. silvestrii (see Reid 1985, fig. 127) than in the new species, in which the distal spinules of the serra are elongate, the length/width ratio of the caudal rami is less than 4.0 in E. silvestrii , thus differing from the figure in the new species (4.3– 4.6). Additional morphometric differences between these species are presented in the Table 2 .

This species has, of course, a strong resemblance with E. pseudoensifer Dussart, 1984 because of the similar body proportions, lateral margins of the thoracic somites 2–4 produced posteriorly and overlapping the succeeding somites, the length/width ratio of the caudal rami, the relative lengths of the caudal setae, and the general structure of the fifth leg (see Table 2 ). There are, however, several subtle differences between these two species. Among the most conspicuous is the structure of the serra on the caudal rami; in E. pseudoensifer it is formed by stout, relatively short spinules arranged in a loose pattern (see Figs 5 C-E; Dussart 1984, fig. 14), whereas the elements in the new species are clearly slender, longer, arranged in a tighter pattern, and more numerous. The outer terminal spiniform caudal seta is clearly shorter in the new species, 0.50 times as long as ramus vs. 0.63-0.67 in E. pseudoensifer (see Figs 5 C-E; Dussart 1984). Also, the length of the antennules differs in both species; they are clearly shorter in E. pseudoensifer (see Dussart 1984 fig. 14), even stretched backwards it barely reaches the middle of the first thoracic somite, whereas in the new species it reaches the posterior margin of the third thoracic somite ( Fig. 9 A). The inner basipodal spine of the first leg is shorter in the new species than in E. pseudoensifer ; in E. chihuahuensis it barely reaches the distal margin of the second exopodal segment, whereas it stretches to the distal margin of the third segment in E. pseudoensifer (see Figs 6 B, 7B; Dussart 1984). The length ratio of the inner/outer spines of the fourth leg endopod differs in these species, 1.5 in the new species vs. 1.1 in E. pseudoensifer (see Figs 7 A, 8B). Also different is the length ratio of the inner spine/ third endopodal segment: 1.3 in the new species, 1.1 in E. pseudoensifer . In the fifth leg the outer seta is as long as the inner spine in E. chihuahuensis and it is about 50% shorter in E. pseudoensifer (see Fig. 5 B, Table 1 ). The body size of these species differs slightly, females: 0.64 mm in E. chihuahuensis vs. 0.77 in E. pseudoensifer .

Figures

FIGURE 5. Eucyclops pseudoensifer Dussart, 1984, adult female paratype (MNHN- 2547) from Laguna Mucubajì, Venezuela. A) antennule; B) leg 5; C) caudal rami, ventral view; D) same, dorsal view; holotype female, E) right caudal rami, ventral view. E from D. Defaye’s drawing of the holotype specimen (in litt.). Scale bars A = 50 μm, B = 25 μm, C – E = 50 μm.

FIGURE 6. Eucyclops pseudoensifer Dussart, 1984, adult female paratype (MNHN- 2547) from Laguna Mucubajì, Venezuela. A) antenna; B) leg 1; C) leg 2; D) leg 3. Scale bars A – D = 50 μm.

FIGURE 7. Eucyclops pseudoensifer Dussart, 1984, A adult female paratype (MNHN- 2547) from Laguna Mucubajì, Venezuela. B-D from D. Defaye’s drawings of the holotype specimen (MNHN-Cp 663) (in litt.). A) leg 4; B) leg 1, coupler and inner margin of coxa and basipod; C) leg 4, ornamentation of coupler; D) leg 3, same. Scale bars A = 50 μm, B – D = 25 μm.

FIGURE 9. Eucyclops chihuahuensis sp. nov., adult female holotype from Presa Chihuahua, northern Mexico. A) habitus, dorsal view; B) antennule; C) antenna; D) caudal rami and anal somite, ventral view; E) genital double and fifth pedigerous somites, ventral view. Scale bars A = 100 μm, B – D = 50 μm.

FIGURE 10. Eucyclops chihuahuensis sp. nov., adult female holotype from Presa Chihuahua, northern Mexico. A) leg 1; B) leg 2; C) leg 2; D) leg 4; E) coxal plate of leg 1; F) coxal plate of leg 1; G) coxal plate of leg 3; H) coxal plate of leg 4. Scale bars A – G = 50 μm. All appendages shown in frontal view.