Eucyclops torresphilipi Suárez­Morales, 2004

Suárez-Morales, E., 2004, A new species of Eucyclops Claus (Copepoda: Cyclopoida) from Southeast Mexico with a key for the identification of the species recorded in Mexico, Zootaxa 617, pp. 1-18 : 3-15

Eucyclops torresphilipi Suárez­Morales , n. sp.

( Figs. 2–5 )

Material examined

Holotype. Adult Ψ, dissected, mounted in glycerine sealed with Entellan (ECOCH­Z­ 01809), pond in Ejido El Aguila, Cacahoatán, near Tapachula, Chiapas, Mexico (15° 05’ 33” N; 92° 10’ 46” W), January 1, 2004; coll. Felipe Hernández­Bravo.

Paratypes. 1 dissected adult Ψ, mounted in glycerine, slide sealed with Entellan (ECOCH­Z­01808), same locality and date as holotype, coll. Felipe Hernández. 12 undissected adult ΨΨ, ethanol preserved (ECOCH­Z­01807), same locality and date as holotype, coll. Felipe Hernández­Bravo. Allotype. One partially dissected adult %, mounted in glycerine, slide sealed with Entellan (ECOCH­Z­01806), same locality and date as holotype; coll. Felipe Hernández­Bravo. Additional paratypes. Five undissected adult ΨΨ, one undissected adult %, ethanol­preserved, vial deposited in the Muséum National d'Histoire Naturelle, Paris, France (MNH­Cp­2182). Additional, non­type specimens in collection of E. Suárez­Morales.

Type locality

Pond in Ejido “El Aguila”, Cacahoatán, Chiapas, Mexico.

Etymology

The species name is a latinized composite formed by the surname and the first name of the two colleagues who collected this new species, José Luis Torres and Felipe Hernández­ Bravo, respectively.

Descriptions

Female ( Fig. 2B ): Total body length = 0.680 0.127 mm (n= 20) from anterior end of cephalothorax to posterior margin of furcal rami. Body elongated, cephalothorax relatively long, slightly expanded laterally 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 end of first pediger. Rostrum strong, wide, with two rows of spinules on lateral surfaces of rostral base converging near anteriormost end. Urosome slender, except for genital double­somite, lateral margins almost straight; urosome, excluding caudal rami, representing 34% of body length. Antennule ( Fig. 2A ): As usual in female Eucyclops , 12­segmented; armament per segment as follows (s= seta, ae= aesthetasc): 1(7s + ventral row of 10–12 unsocketed spines and two additional rows of spinules), 2(4s+ dorsal row of spinules), 3(1s), 4(4s+ two rows of spinules), 5(4s), 6(s+ 1 spine), 7(2s), 8(3s), 9(2s), 10(2s), 11(2s), 12(7s+1ae). Narrow hyaline membrane finely serrated on segments 10–12. Antennule reaching middle of second thoracic somite. Antenna ( Fig. 3D ): Foursegmented, basis with several groups of unsocketed spines on caudal surface. Largest spines on subdistal position, near insertion point of two anterodistal setae. Basis with long exopodal seta biserially pinnate. Second segment with 1 outer seta and inner row of 5–6 spinules. Third segment with 5 lateral and 3 outer distal setae; inner margin with row of spinules. Distal segment with 5 terminal and 2 subterminal setae. Labrum ( Fig. 5 F): Distal margin with 8 rounded teeth. Two rounded ventral plates in area where 2 groups of longer hair­like setae are medially conjoined. Mandible ( Fig. 3A ): Gnathobase with 5 strongly chitinized teeth. Palp reduced, with 2 long plumose setae. Maxillule ( Fig. 3B ): Praecoxal arthrite with 3 strong chitinized claws and 2 spiniform setae on frontal side. Proximal part of inner margin with thick, biserially plumose seta; row of 5 or 6 long spines near insertion point of thick seta. Maxillular palp with usual structure for family, with 3 setae on distal article and with 3 setae on proximal article, plus 1 long basal seta. Maxilla ( Fig. 3C ): Praecoxa and coxa separated; precoxal endite armed with 2 biserially setulated setae. Coxa with single long seta on distal inner margin; coxal caudal surface naked. Proximal basipodal endite well developed, with 2 apical seta furnished with spinules. Claw­like basal endite bearing 12–15 stout teeth along inner margin, row of fine denticles on distal 1/3 of outer margin, plus short, slender seta on frontal side. Endopod 2­segmented, proximal segment with 2 strong, long spiniform setae. Distal endopodal segment armed with 3 spiniform setae. Maxilliped ( Fig. 3E ): Four­segmented. Coxa with 3 setae bearing spiniform setules, 2 on midlength of coxa, 1 on distal position. Basis with 2 setae, both spinulate. One group of long spines on caudal surface. Endopod reduced, 2­segmented, first segment with wide­based, stout basal spine furnished with uniserial row of spinules on inner margin; row of 6–7 long spines on segment near insertion of stout seta. Second endopod armed with 1 proximal strong, spiniform seta armed with inner row of denticles and some setules along inner margin. Distal part of segment with 2 subequal, slender setae.

Leg 1 ( Fig. 4A ): Intercoxal sclerite (coupler) with 2 frontal rows of 4–6 and 7–10 unsocketed spines on each side plus proximal row of short spinules, distal margin with 2 rounded chitinized projections. Coxa with strong inner coxal seta. Basis with 1 slender seta on outer margin; inner margin with spines on insertion point of strong, biserially setulated spiniform basipodal seta; spiniform seta reaching beyond distal margin of second endopodal ramus. Endopod and exopod 3­segmented. Endopod slightly longer than exopod. Armature as in Table 1 . Leg 2 ( Fig. 4B ): Intercoxal sclerite (coupler) with 2 frontal, transverse rows of 7–10 spinules, plus 2 asymmetrical groups of spines, 1 on each side of coupler. Distal margin with 2 rounded chitinized projections ( Fig. 5A ). Coxa with strong inner coxal seta plus 2 rows of spinules along distal margin. Basis with 1 slender seta on outer margin; inner corner of basis forming sharp spiniform expansion. Distal margin with small spinules on disto­medial expansion between insertion point of exopod and endopod. Endopod and exopod 3­segmented. Endopod nearly as long as exopod. Armature as in Table 1 . Leg 3 ( Fig. 4C ): Intercoxal sclerite (coupler) with 2 frontal rows both of 4–6 unsocketed spines on each side, distal margin with 2 rounded chitinized projections each armed with 4 long unsocketed spines ( Fig. 5D ). Coxa with inner coxal seta. Basis with 1 relatively strong, biserially setulated seta on outer margin; inner corner of basis forming sharp spiniform expansion. Endopod and exopod 3­segmented. Endopod slightly longer than exopod. Armature as in Table 1 . Leg 4 ( Figs. 5 B,C , H): Intercoxal sclerite (coupler) with light ornamentation on frontal surface, represented by row of 4–5 short unsocketed setiform elements on each side of plate; distal margin with 2 rounded chitinized projections ( Fig. 5 E). Coxa with strong inner coxal seta. Basis with 1 slender seta on outer margin. Endopod and exopod 3­segmented. Endopod slightly longer than exopod. Armature as in Table 1 . Outer and inner terminal endopodal spines finely spinulate along most of margins. Length ratio of outer and inner terminal spines of Enp 3= 1.22–1.25. Length/width ratio Enp 3= 2.1. Insertion point of seta on outer margin of Enp 3= 68%. Length of inner endopodal spine/endopod 3= 1.08–1.1. Leg 5 ( Figs. 2C , 5 G): Leg consisting of broad article armed with 2 regular setae and 1 spiniform seta, middle seta longest, 2 remaining (inner and outer) setae subequal in length; inner spiniform seta biserially pinnate, particularly slender. Fifth leg article with cluster of 2–3 spinules along distal inner margin (arrowed in Fig. 5 G). Leg 6 ( Fig. 2E ): Small, low plate near lateral margin of genital double­somite with laterally directed dorsal seta and tiny lateral spinules. Pediger 5 ( Fig. 2C ): Armed with tuft of hair­like setae on outer distal margin. Urosome ( Figs. 2C, 2E ): Formed by 4 somites, relative ratio of each urosomite as: 47.5: 22.5: 18.7: 11.2= 100. Genital double­somite representing 15–16.5 % of body length (excluding caudal rami). Genital double­somite smooth on ventral and dorsal surfaces. Anterior half of genital double­somite expanded laterally forming subtriangular processes with terminal short setae representing leg 6 ( Fig. 2E ). Paired eggsacs carried dorsolaterally. Each sac with 4– 6 eggs. Seminal receptacle with 2 short, rounded lateral arms; lateral channels straight. Posterior margin rounded, sac­like. Ventral surface of anal somite smooth; distal ventral and dorsal margins with rows of 10–12 stout spines at insertion points of caudal rami ( Figs. 2D,E , 5 I). Caudal ramus ( Figs. 2D,E ): Ramus representing 11.7 % of total body length and 0.35 times as long as urosome. Length/width ratio= 4.1–4.5. Inner margin smooth. Outer margin armed with row of spinules from proximal 1/3 to distal margin; spines increasing in size distally. Cluster of spines at base of lateral terminal spiniform seta. Lateral terminal spiniform seta noticeably long, 0.75 times as long as caudal ramus. Dorsal seta relatively short, 0.72–0.85 times as long as caudal ramus. Lateral seta inserted subterminally, near the insertion point of the terminal setae. Dorsal seta inserted at about distal ¾ of caudal ramus length. Inner terminal seta longest, about 30% longer than outer terminal seta.

Male ( Fig. 6A ): Body elongated, without hairs or pits on dorsal surface. Noticeably smaller than female. Total body length of allotype = 0.652 mm, cephalothorax length = 0.429 mm, representing almost 67% of total body length, abdomen length = 0.223 mm. Body and appendages as in females except for sexual dimorphism. Antennule ( Fig. 6B ): Geniculate, 17­segmented; article armament per segment as follows: 1(8s + proximal row of spinules), 2(3s), 3(1s), 4(1s), 5(3s), 6(1s), 7(1s), 8(0), 9(1s,1ae), 10(0), 11(2s), 12(2s + 1 sp), 13(1s+1 sp), 14(1s), 15(0), 16(1s, 1sp), 17(10s+1ae). First geniculation between segments 8 and 9, second one between segments 14 and 15 ( Fig. 6B ). Leg 6 ( Fig. 6C ): consisting of broad subquadrate plate with long medial seta reaching beyond succeeding posterior urosomite. Article with 2 outer seta subequal in length and breath. Innermost seta 2.1 times longer than 2 lateral setae. Urosome ( Fig. 6C ): Five­segmented, genital double­somite largest of urosome; relative lengths of urosomites as: 40.4: 19.2: 17.3: 17.3: 5.8=100. Ventral and dorsal surface of anal somite smooth; distal margin with continuous dorsoventral row of spines. Anal plate smooth.

Remarks. The general body shape, the structure of the seminal receptacle, the armature of the swimming legs, and the setation of the fifth leg of the new species resembles other members of the genus Eucyclops . Some of the main characters used to include these specimens under Eucyclops were 1) the presence of a fifth leg represented by a single segment armed with 2 setae and an inner spiniform seta, 2) the segmentation of the female (12 articles) and male (16 articles) antennules, the 2 distal antennular segments with a hyaline membrane, 3) outer margin of the caudal rami with spinules, and 4) the presence of hairlike setules on each side of the fifth pedigerous somite ( Reid 1985; Dussart & Defaye 2001).

Following the criteria proposed by Lindberg (1954, 1955) and Reid (1985), one of the most useful characters to separate some of the American species of Eucyclops is the spinulation pattern of the outer margin of the caudal rami. In some species the coverage of the spinules includes only the distal half of the rami and can be very sparse, represented by a few spinules only. Another group of species have a complete, tight spinulation pattern; this character has proved to be useful in many cases, but some species (i.e. E. bondi Kiefer, 1934 ) show intraspecific variations (see Suárez­Morales et al. 1996). The new species could be included in the second group, because nearly ¾ of the length of the outer margin is covered by spinules (see Figs. B,D,E; Table 2 ). With some exceptions (i.e. Eucyclops neotropicus Kiefer, 1936 ), most species of Eucyclops , including E. torresphilipi n.sp., have the inner margin of the caudal rami naked. A third discriminating feature is the insertion point of the outer seta of the fifth leg, which can be at the same level of the inner spiniform seta or at a different level ( Reid 1985). The new species has both elements inserted at the same level (see Fig. 5 G). An additional character used to separate the species of Eucyclops is the length/width proportions of the caudal rami, which can be very long (more than 6.5 times longer than it is wide) as in E. solitarius Herbst, 1959 or E. festivus Lindberg, 1955 , or relatively short (between 3.6–4 in E. leptacanthus 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 over 4 (4.3–4.5).

Among the American species that share with the new species at least three of these characters are: E. delachauxi ( Kiefer, 1925) , E. agilis (Koch, 1838) , E. conrowae Reid, 1992 , E. leptacanthus Kiefer, 1956 , E. ensifer Kiefer, 1936 , E. pseudoensifer Dussart , E. prionophorus Kiefer, 1931 , and E. bondi Kiefer, 1934 . The new species differs from this group of congeners by evaluating additional characters. The fifth leg in the new species has a particularly slender inner spiniform seta, a character that diverges from the general pattern in Eucyclops , in which this seta is normally stout, noticeably thicker than the other setae of the fifth leg, and heavily armed (spinulated). There are only two American species with a relatively long, slender inner spiniform seta are: E. delachauxi and E. leptacanthus , plus E. permixtus Kiefer, 1929 from India and Java ( Lindberg 1955; Reid 1985; Collado et al. 1984). The new species can be distinguished from E. delachauxi by the spinule ornamentation pattern on the outer margin of the caudal rami. In E. delachauxi this pattern is somewhat variable ( Reid 1985), only a few distal spinules can be present in some specimens and in others there is a sparse row of spinules that can stretch beyond half the length of the caudal rami ( Lindberg 1955; Reid 1985); its coverage of the corresponding margin is between 16–52% (see Table 2 ). The spinulation pattern in the new species is consistently homogeneous, covering between 67–70% and arranged in a relatively tight pattern. The caudal rami proportions are similar in both species, around 4 times longer than it is wide; however, in E. torresphilipi n.sp. the dorsal seta is relatively longer with respect to the caudal ramus than it is in E. delachauxi (0.85 vs 0.64, respectively). The ratio of the inner/outer terminal spines of the third exopodal segment of the fourth leg is different in both species, 1.1 in E. delachauxi vs 1.3–1.5 in the new species. These spines are distally curved in E. delachauxi and straight in the new species ( Figs. 5B,C ). The ratio of the inner spiniform seta/ outer seta of the fifth leg is different in both species, (1.1 in E. delachauxi , 0.8 in the new species). Also, in E. delachauxi the insertion points of the inner and outer elements of the fifth leg are not at the same level (see Reid 1985, fig. 101), thus differing from the symmetrical insertion in the new species. Eucyclops delachauxi seems to be restricted to South America ( Kiefer 1925, 1926; Dussart & Defaye 1985; Reid 1985).

The new species differs from E. leptacanthus in the structure of the fifth legs, the insertion point of the inner spiniform seta and the outer seta is not at the same level ( Reid 1985). Also, the spiniform seta is about half the length of the outer seta in E. leptacanthus ( Collado et al. 1984; Table 2 ) whereas both setal elements are equally long in E. torresphilipi n.sp. The inner/outer spines ratio of the third endopodal segment of the fourth leg is 1.8, whereas this ratio is 1.3–1.5 in the new species (see Table 2 ). The ornamentation of the fourth leg coxal plate is different in these species, with a single row of 4–5 setiform elements in the new species and a much denser pattern of 8–10 elements in E. leptacanthus . Eucyclops leptacanthus is closely related to E. pseudoensifer (see Collado et al. 1984) and some comparative comments are: the latter has a short dorsal caudal seta (0.37– 0.44 times as long as ramus), whereas this seta is longer in the new species (0.84 times as long as the ramus). Also, the hyaline membrane is characteristically well­developed and serrated in E. pseudoensifer ; the same structure is weakly developed in the new species. The male sixth leg is different in both species, the innermost seta is longest and naked in the new species and the same seta is as long as the others and is thicker and spinulated in E. pseudoensifer . The relative length of the dorsal seta is different in these species, with E. delachauxi showing a wide range of variation (0.3–0.65), followed by E. leptacanthus (0.5–0.69), and E. pseudoensifer (0.37–0.44); the new species showed a low variability (0.85–0–87) ( Table 2 ). Other morphometric differences to compare these and other American species of Eucyclops , including all the species recorded in Mexico, are shown in Table 2 .

This is the tenth record of species of Eucyclops in Mexico, after E. agilis (as E. serrulatus and E. cf. serrulatus ), E. bondi , E. conrowae , E. festivus , E. prionophorus , E. leptacanthus , E. cf. bondi , E. pseudoensifer , and E. cf. solitarius Herbst, 1959 (Grimaldo­ Ortega et al. 1998; Suárez­Morales & Reid 1998; Suárez­Morales et al. 2000; Gutiérrez­ Aguirre & Suárez­Morales 2001). The diversity of the Mexican fauna of Eucyclops could be underestimated. Some of the differences found in specimens identified as E. bondi and E. prionophorus from Central Mexico ( Grimaldo­Ortega et al. 1998) suggest that they could be undescribed species.

The new species seems to have ties with presumedly cosmopolitan forms (i.e. E. agilis ), but mainly with South American forms ( E. delachauxi , E. leptacanthus , E. pseudoensifer ) ( Reid 1985). This affinity could be explained as a result of an early northwards dispersal of a common ancestor from South America after the Pliocene, when the connection of the two subcontinents was consolidated; it has been suggested that the ancestors of many other freshwater cyclopoid copepods closely related to South American forms have speciated in Southern Mexico and have restricted distributional ranges ( Suárez­Morales et al. 2004).

Figures

FIGURES 2 A – G. Eucyclops torresphilipi n. sp .. adult female from Chiapas, Mexico. A) antennule; B) habitus, dorsal view; C) fifth pedigerous and genital double­somites, ventral view; D) caudal rami, dorsal view; E) urosome, dorsal view, another specimen.

FIGURES 3 A – E. Eucyclops torresphilipi n. sp. adult female from Chiapas, Mexico. A) mandible; B) maxillule and maxillular palp; C) maxilla; D) antenna; E) maxilliped.

FIGURES 4 A – E. Eucyclops torresphilipi n. sp. adult female from Chiapas, Mexico. A) first swimming leg showing coxal plate; B) second swimming leg; C) third swimming leg.

FIGURES 5 A – D. Eucyclops torresphilipi n. sp. adult female from Chiapas, Mexico. A) coxal plate of second swimming leg, caudal view; B) two terminal segments of endopod of fourth swimming legs; C) fourth swimming legs; D) coxal plate of third swimming leg, caudal view; E) coxal plate of fourth swimming leg, caudal view; F) labrum; G) fifth leg; H) fourth swimming leg, distal segment of exopod.

FIGURES 6 A – C. Eucyclops torresphilipi n. sp. adult male (allotype) from Chiapas, Mexico. A) habitus, dorsal view; B) left antennule showing armature; C) fifth pedigerous and genital doublesomites, lateral view, showing sixth legs (only setal armature represented).

Tables

TABLE 1. Armature of swimming legs 1 – 4 (spines in Roman numerals, setae in Arabic) of Eucyclops torresphilipi n. sp. Sequence follows outer to inner positions.

	coxa	basis	exopodite	endopodite
leg 1	0­1	1­1	I­1;I­1;III,2,3	0­0;0­0;1­I,2,2
leg 2	0­1	1­0	I­1;I­1;IV,1,4	0­1;0­2;1,I,1,3
leg 3	0­1	1­0	I­1;I­1;IV,1,4	0­1;0­2;1,I,1,3
leg 4	0­1	1­0	I­1;I­1;III,1,4	0­1;0­2;1,II,2

TABLE 2. Comparison of selected morphometric characters of adult females of some American species of Eucyclops, including E. torresphilipi n. sp. CR = caudal ramus; I = Inner terminal spine of third endopodal segment of fourth leg; IS = Inner spiniform seta of fifth legs; OS = Outer seta of fifth legs; O = Outer terminal spine of third endopodal segment of fourth leg; L 4 ED = Fourth leg endopod, third segment; L 4 EDS = Fourth leg endopodal terminal spine of third segment. LSD = Length of dorsal seta; SC = Coverage of serra on outer margin of caudal rami. (*) indicates South American forms. Data from Kiefer (1925), Reid (1985, 1992), Grimaldo­Ortega et al. (1998), Dussart & Defaye (1985, 2001).

Species L/W CR % SC	I/O L4EN3	I/ L4EN3	IS/OS L5	LSD/CR	L/W L4EN3
E. agilis 5–5.3 50–75	1.3	0.9	0.69–1.0	0.3	3.0–3.1
E. bondi 3.1–3.5 71	1.6–2	1.1–1.3	0.57–0.62	0.61–0.69	2.1–2.2
E. delachauxi * 4.0 16–52	1.1	1.1	1.1	0.65	2.3
E. conrowae 3.5 77	1.5	1.2	0.54	1.0	2.2
E. festivus 6.0 68	1.1	1.1	1.4–1.7	0.41	2.5
E. leptacanthus * 3.2–3.6 70–80	1.8	1.2–1.3	0.61–0.63	0.52–0.65	2.0
E. prionophorus 4–4.3 71	1.5	1.3–1.4	1.5–2.7	0.37–0.64	1.9–2.4
E. pseudoensifer * 3–3.8 63–74	1.5	1.0	0.6	0.37–0.44	2.3
E. solitarius * 6.5–8 73–90	1.2	0.85	1.5–1.6	0.39–0.61	2.9
E. torresphilipi 3.8–4.1 67	1.3–1.5	1.3	0.82	0.84–0.85	2.1