Eucyclops leptacanthus Kiefer, 1956

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 : 59-65

Eucyclops leptacanthus Kiefer, 1956

( Figures 22 – 26 )

Description

Female. Average length excluding caudal setae = 792 µm. Prosome representing 63% of total body length, prosome symmetrical in dorsal view. Prosomal fringes finely serrate in dorsal view. Urosomal fringes strongly serrate, urosomites ornamented with pits (see Figure 22A ); posterior margin of anal somite with row of spinules. Genital double somite symmetrical ( Figure 24A ), representing 11% of total body length; proximal third of genital double somite expanded laterally. Seminal receptacle with rounded lateral arms on posterior margin, typical of the serrulatus -complex. Anal operculum slightly rounded, serrate ( Figure 22B ). Length/width of caudal rami = 3.7; inner margin of caudal ramus smooth; outer margin with strong spinules covering 60% with respect to the total length of ramus. Dorsal seta (VII) 0.7 times as long as caudal ramus and 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 71% of caudal ramus.

Antennule ( Figures 22C–D , 24D–F ). Tip reaching posterior margin of third pediger, antennules ornamented with pits. 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(8s). Two transverse rows of spinules on first segment, first row with long, strong spinules and adjacent second row with minute spinules. Spine on sixth segment reaching midlength of seventh segment.

Antenna ( Figures 22E–F , 25A–C ). Coxa (unarmed), basis (2s+Exp), plus three-segmented Enp (1s, 9s, 7s, respectively). Basis with rows of spinules on frontal surface: N1(5), N2(3), N3(3), N4(8), N5(5), N15(4), N17(5), N18(3) and on caudal surface: N7(4), N8(4), N9 + 10(6), N11(5), N12(6), N13(3) N14(4), N22(6). Caudal surface of Enp1 with B2(6) and B3(3).

Leg 1 ( Figures 23A–C , 25D ). Frontal surface of intercoxal sclerite with row I bearing hair-like spinules arranged in semicircular pattern; caudal surface with row II continuous, bearing 21 minute but strong spinules, row I absent. 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 Enp3 = 1.6, apical spine of Enp3 being 1.1 times as long as Enp3.

Leg 2 ( Figure 23D–E , 25E ). Frontal surface of intercoxal sclerite with row I bearing long hair-like elements arranged in circular pattern; caudal surface with row II continuous, with 20 minute spinules, row I absent. Distal margin of intercoxal sclerite with two rounded, chitinised projections. Inner coxal seta biserially setulated, caudal coxal surface

with spinule formula = A-B-C-D. Length/width ratio of Enp3 = 2.1, apical spine of Enp3 being 1.4 times as long as Enp3. No modified setae present.

Leg 3 ( Figures 23F–H , 25F , 26A ). Frontal surface of intercoxal sclerite armed with hairspinules arranged in a circle on each side; caudal surface with row I bearing hair-like elements, row II divided in two groups, each one with eight minute spinules (gap in middle); row III continuous, with 18 strong spinules, spinules adjacent to outer margins being longer. Distal margin with two rounded, chitinised projections. Coxa with strong, biserially setulated inner coxal seta, with long hair-like elements on proximal section and with strong spinules distally. Caudal coxal surface with spinule formula = A-B-C, group B with two rows. Length/width ratio of Enp = 2.3, apical spine of Enp3 being 1.3 times as long as Enp3. Modified setae present in both, Enp and Exp.

Leg 4 ( Figures 23I–L , 26B–E ). Distal margin of intercoxal sclerite with two low, rounded, chitinised projections. Frontal surface of sclerite with row I bearing small, strong spinules arranged in semicircular pattern. Caudal surface of intercoxal sclerite

with row I bearing strong small spinules, row II with strong spinules adjacent to outer margins and row III with strong, long hair-like spinules adjacent to outer margins. 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 section with strong spinules, outer margin with three distal spinules and with hairs on proximal section, gap in middle margin. Spinule formula on the caudal surface = A-B-C + D-E-F-G-J. Length/width ratio Enp3 = 2.7, length ratio inner spine of Enp3/length Enp3 = 1.1; length ratio outer spine of Enp3/length Enp3 = 0.9; proportion inner/outer spines Enp3 = 1.2. Lateral seta of Enp3 inserted at 61% of segment. Modified setae in Enp and Exp.

Leg 5 ( Figure 26F ). Free segment subrectangular, 1.9 times longer than wide, bearing one slender inner spine and two setae; medial seta 1.7 times longer than outer seta and 2.3 times longer than inner spine. Inner spine 1.7 times longer than segment.

Male. Not found.

Remarks. Based on our observations, we herein assign E. leptacanthus as a member of the serrulatus -group. A distinguishing character of this species is the presence of long hair-like spinules on N1, while this row possesses long hairs in all the other members of the group. We identified our specimens from Mexico as E. leptacanthus because it has the main morphologic and morphometric characters found in the holotype from Kiefer ’ s collection. This species is characterised by a long innermost caudal seta (VI) which is 1.3 times longer than the outermost caudal seta (III), long setae in the four swimming legs and a slender P5 spine. Among its congeners, E. leptacanthus can be easily distinguished from E. bondi by the possession of a shorter dorsal seta and a completely different ornamentation of the P4 intercoxal sclerite. Eucyclops leptacanthus resembles E. prionophorus , E. serrulatus and E. pectinifer but shows significant differences with respect to these species. In E. leptacanthus row N1 of the antennal Bsp has long hair-spinules, while in E. prionophorus , E. serrulatus and E. pectinifer this row bears long hair-like elements. In addition, N6 is absent in E. leptacanthus as it is in E. prionophorus and E. serrulatus , but it is present in E. pectinifer . The caudal surface of the antennal Bsp of E. leptacanthus resembles both E. prionophorus and E. pectinifer in the presence of row N18, but differs from both species by the unique presence of N13. The caudal surface of the coxal sclerite of the four swimming legs differs among these species as well. In P1 E. leptacanthus shares with E. serrulatus and E. pectinifer the absence of row I but differs from both species in its possession of a row II with minute spinules; it has long hairs in the other species and in E. prionophorus row I is always present. In P2, E. leptacanthus shares the absence of row I with E. serrulatus and E. pectinifer but differs in having row II with minute spinules vs long spinules in the other two species. Also, E. prionophorus differs by possessing a row I armed with minute spinules. The caudal surface of the P3 intercoxal sclerite is similar in the three species, but row II of E. leptacanthus is discontinuous, thus differing from the continuous pattern observed in E. prionophorus , E. serrulatus and E. pectinifer . The ornamentation pattern of the caudal surface of the P4 sclerite is similar in all species; in E. leptacanthus it has small but strong spinules on row I, whereas this row bears long spinules in the other species.

Figures

Figure 22. Eucyclops leptacanthus Kiefer, 1956. Adult female. (A) Urosome, ventral; (B) anal operculum, dorsal; (C) antennule, segments 1–11; (D) antennule, segment 12; (E) antennal basis, frontal; (F) antennal basis, caudal.

Figure 23. Eucyclops leptacanthus Kiefer, 1956. Adult female. (A) P1, frontal; (B) intercoxal sclerite P1, frontal; (C) coxa and intercoxal sclerite P1, caudal; (D) P2, frontal; (E) coxa and intercoxal sclerite P2; caudal; (F) P3, frontal; (G) endopod P3; (H) coxa and intercoxal sclerite P3, caudal; (I) P4, frontal; (J) exopod P4; (K) coxa and intercoxal sclerite P4, caudal; (L) coxal spine P4.

Figure 24. Eucyclops leptacanthus Kiefer, 1956. Adult female. (A) Genital somite, ventral; (B) urosome, ventral; (C) caudal rami, ventral; (D) antennule; (E) antennule segment 9; (F) antennule segment 12.

Figure 25. Eucyclops leptacanthus Kiefer, 1956. Adult female. (A) Antenna, frontal; (B) antennal basis, frontal; (C) antennal basis, caudal; (D) P1, frontal; (E) P2, frontal; (F) P3, frontal.

Figure 26. Eucyclops leptacanthus Kiefer, 1956. Adult female. (A) Coxa, basis and intercoxal sclerite P3, frontal; (B) P4, caudal; (C) coxa P4, caudal; (D) intercoxal sclerite P4, caudal; (E) coxal spine P4; (F) P5.