Eucyclops cuatrocienegas Suárez-Morales and Walsh, 2009

Mercado-Salas, Nancy F., Suárez-Morales, Eduardo & Silva-Briano, Marcelo, 2015, Taxonomic revision of the Mexican Eucyclops (Copepoda: Cyclopoida) with comments on the biogeography of the genus, Journal of Natural History 50, pp. 25-147 : 73-76

Eucyclops cuatrocienegas Suárez-Morales and Walsh, 2009 ( Figures 29 – 30 )

Description

Female. Average length excluding caudal setae = 818 µm. Body elongate, prosome representing 63% of total body length, symmetrical in dorsal view. Urosome representing 37% of body length, urosomal fringes strongly serrate. Genital somite ( Figure 29A ) symmetrical, representing 13.9% of total body length; proximal third of genital double somite expanded laterally. Seminal receptacle with rounded lateral arms on posterior margin. Length/width ratio of caudal rami = 3.7; inner margin of caudal ramus naked, outer margin with strong spines covering 65% with respect to the total length of ramus. Dorsal seta (VII) relatively short: 0.4 times the length of caudal ramus, and 1.1 times as long as outermost caudal seta (III). Ratio of innermost caudal seta (VI)/ outermost caudal seta (III) = 1.3. Lateral caudal seta (II) inserted at 68% of total length of caudal ramus.

Antennule ( Figure 29B–C ). Tip reaching distal margin of cephalothorax. Armature per segment as follows: 1(8s), 2(4s), 3(2s), 4(6s), 5(4s), 6(1s+1sp), 7(2s), 8(3s), 9(2s+1ae), 10(2s), 11(3s), 12(7s+1ae). Two rows of spinules on first segment, basal row bearing minute spinules, second row with longer and stronger spinules than those in basal row. Spine on sixth segment reaching midlength of seventh antennular segment.

Antenna ( Figure 29D–E ). Coxa (unarmed), basis (2s + Exp), plus three-segmented Enp (1s, 9s, 7s, respectively). Basis with rows of spinules on frontal surface: N1(VII), N2 (5), N3(9), N4(5), N5(13), N17(8), N18(5); on caudal surface: N7(7), N8(7), N9+10 (7), N11(8), N12(8), N13(4), N14(4), N15(4). Caudal surface of Enp1 with B1(7).

Leg 1 ( Figure 30A–B ). Frontal surface of intercoxal sclerite with row I bearing strong spinules arrenged in semicircular pattern on each side; caudal surface smooth, distal margin with two rounded, chitinised projections. Inner coxal seta biserially setulated, caudal coxal surface with spinule formula = A-B-C. Inner basal seta (basipodal spine) reaching middle margin of Enp3, 0.8 times as long as Enp. Length/width ratio of Enp3 = 1.4, apical spine of Enp3 being 1.1 times as long as Enp3.

Leg 2 ( Figure 30C–F ). Frontal surface of intercoxal sclerite with row I bearing small, strong spinules arrenged in a semicircular pattern on each side; caudal surface with row II continuous, with 16 minute spinules, distal margin with two rounded, chitinised projections. Inner coxal seta biserially setulated, caudal coxal surface with spinule formula = A-B-C-D. Small spinules along insertion of basipodite. Length/width ratio of Enp 3 = 2.0, apical spine of Enp3 being 1.2 times as long as Enp3. Modified setae present in Enp and Exp.

Leg 3 ( Figure 30G–I ). Frontal surface of intercoxal with row I bearing spinules arranged in semi-circular pattern on each side, proximal spinules longer than the others; caudal surface with row I bearing 13 minute spinules (small gap in the middle), row II continuous, bearing 18 minute spinules; row III with 14 strong, long spinules, with gap in the middle (seven spinules on each side). Distal margin with two rounded projections. Coxa with strong biserially setulated coxal seta, both margins with long setules along proximal section and strong spinules along distal section. Caudal coxal surface with spinule formula = A-B-C. Length/width ratio of Enp3 = 2.2, apical spine of Enp3 being 1.1 times as long as Enp 3. Modified setae in Enp and Exp.

Leg 4 ( Figure 30J–M ). Distal margin with two low, rounded, chitinised projections. Frontal surface of intercoxal sclerite with row I bearing minute spinules in semi-circular

pattern on each side; caudal surface of intercoxal sclerite with row I bearing nine strong but small spinules on each side, with small gap, row II continuous, bearing 22 spinules, outer spinules slightly longer than inner ones; row III with seven spinules on each side, with wide gap. Frontal surface of coxa with row of small spinules at insertion of Bsp. Inner coxal spine with heterogeneous ornamentation; proximal inner margin with long hairs, distal margin with spinules; outer margin with two distal spinules, proximal section with three hairs, gap in middle margin. Caudal coxal surface with spinule formula = A-B-C + D-E-F-H-J. Length/ width ratio Enp3 P4 = 2.5; length ratio inner spine of Enp3 P4/length Enp3 P4 = 1.3; length ratio outer spine of Enp3 P4/length Enp3 P4 = 0.9; proportion inner/outer spine Enp3 = 1.4. Lateral seta of Enp3 inserted at 61% of segment. Modified setae in Enp and Exp.

Leg 5. Free segment subrectangular, 2.2 times longer than wide, bearing one inner spine and two setae; medial and outer setae equal in length. Setae 2.1 times longer than inner spine. Inner spine 1.3 times as long as segment.

Remarks. Eucyclops cuatrocienegas was recognised as a new species by Suárez-Morales and Walsh (2009) based on the peculiarity of its fifth leg, which, diverging from most of its congeners, has a remarkably short inner spine and an outer seta as long as the medial seta. Eucyclops siolii Herbst, 1962 resembles E. cuatrocienegas because of the general shape and armature of the fifth leg, but in E. siolii the outer seta is clearly shorter than the medial seta, and it also has a shorter caudal ramus (2.5 times longer than wide) than that of E. cuatrocienegas (3.7 – 3.9). It is noteworthy to consider that E. siloii has been recorded only from the Brazilian Amazon. Among the species known from Mexico, only E. pectinifer has a fifth leg resembling that of E. cuatrocienegas . These species can be easily distinguished by the length of the outer and medial setae of the fifth leg; in E. cuatrocienegas these setae are equally long, while in E. pectinifer the medial seta is always longer than the outer seta (about 1.3 times). These two species also share a relatively weak ornamentation of the antennal basis caudal surface when compared with species like E. prionophorus , E. leptacanthus and E. chihuahuensis , bearing rows N20 and N22. Eucyclops cuatrocienegas differs from E. pectinifer by the presence of N13, the absence of N6, N16 and the fusion of N9+N10. Many differences were found in the caudal surfaces of intercoxal sclerites of the two species; E. cuatrocienegas is the only species distributed in Mexico with a completely naked caudal surface of P1, while in the rest of the species row II is always present and row I is present only in E. elegans , E. prionophorus , E. tziscao , E. festivus , E. mittmanni sp. nov. and E. wixarica sp. nov. The ornamentation of the caudal surface of the P2 intercoxal sclerite differs between E. cuatrocienegas and E. pectinifer : in the former species this row bears minute spinules (as in E. leptacanthus ) while in E. pectinifer the row has long hair – spinules. Another distinctive character of E. cuatrocienegas is the ornamentation of the caudal surface of the P3 sclerite; most of the species distributed in Mexico have long hairs or hair – spinules in row I, but in E. cuatrocienegas this row bears small but strong spinules, a character shared only with E. mittmanni sp. nov. and E. defayeae sp. nov., both of which differ from E. cuatrocienegas in the ornamentation of the antennal basis, with row N2 (frontal) bearing long hairs as in E. serrulatus , but in E. cuatrocienegas this row has short spinules as in E. pectinifer .

Figures

Figure 29. Eucyclops cuatrocienegas Suárez-Morales and Walsh, 2009. Adult female. (A) Urosome, ventral; (B) antennule, segment 1–8; (C) antennule, segment 9–12; (D) antenna, frontal; (E) antennal basis, caudal.

Figure 30. Eucyclops cuatrocienegas Suárez-Morales and Walsh, 2009. Adult female. (A) P1, frontal; (B) exopod P1; (C) P2, caudal; (D) exopod P2; (E) intercoxal sclerite P2, frontal; (F) intercoxal sclerite P2, caudal; (G) exopod P3; (H) intercoxal sclerite P3, caudal; (I) intercoxal sclerite P3, frontal; (J) P4, frontal; (K) exopod P4; (L) intercoxal sclerite P4, frontal; (M) coxa and intercoxal sclerite P4, caudal.