Eucyclops elegans ( Herrick, 1884 )

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 : 34-43

Eucyclops elegans ( Herrick, 1884)

( Figures 2 – 8 )

Description

Female. Habitus as in Figure 5A . Average length excluding caudal setae = 1061 µm. Whole body (caudal rami included) ornamented with small pits (see Figure 2A , 5 ). Prosome representing 58% of total body length, symmetrical in dorsal view. Prosomal fringes finely serrate in dorsal view ( Figure 5B ). Urosomal fringes strongly serrate. Genital double somite symmetrical ( Figure 5D ), representing 10% 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, weakly serrate ( Figure 5F ). Length/width of caudal rami = 7.0; inner margin of caudal ramus naked; outer margin with strong spinules covering 60% with respect to the total length of ramus. Dorsal seta (VII) 0.4 times as long as caudal ramus and 0.7 times as long as outermost caudal seta (III). Length ratio of innermost caudal seta (VI)/outermost caudal seta (III) = 1.2. Lateral caudal seta (II) inserted at 70% of ramus.

Antennule ( Figures 2B–C , 6A–B ). Tip reaching posterior margin of fourth 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 one with minute spinules, second row with stronger, longer spinules. Spine on sixth segment not reaching medial margin of seventh segment.

Antenna ( Figures 2D–E , 6E–F ; 7A ). Coxa (unarmed), basis (2s+Exp), plus three-segmented Enp (1s, 9s, 7s, respectively). Basis with rows of spinules on frontal surface: N1+N2(XVI), N3(9), N4(8), N5(5), N15(5), N17(16), N18(5) and on caudal surface: N7(7), N8(5), N9+10(7), N11(9), N12(12), N13(6), N16(14), 22(14). Caudal surface of Enp1 with B2(6) and B3(8).

Leg 1 ( Figures 3A–B , 7B–C ). Frontal surface of intercoxal sclerite with row I bearing spinules in semicircular pattern on each side, caudal surface with row I

continuous

bearing 14 minute spinules. Row II continuous, armed with 23 minute spinules. Inner coxal seta biserially setulated, caudal coxal surface with spinule formula = A-B-C. Inner basal seta (basipodal spine) reaching middle margin of Enp3, 0.7 times as long as Enp. Length/width ratio of Enp3 = 1.6, apical spine of Enp3 being 1.3 times as long as Enp3.

Leg 2 ( Figures 3C–G , 7D–E ). Frontal surface of intercoxal sclerite with row I with hairs arranged in circular pattern; caudal surface with rows I and II continuous, row I with 16 minute spinules and row II with minute spinules. 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 1.1 times as long as Enp3. No modified setae present.

Leg 3 ( Figures 3H–K , 7F , 8A ). Frontal surface of intercoxal sclerite with row I formed by hair-like elements arranged in circular pattern on each side caudal surface with row I bearing slender spinules, row II continuous with 28 minute spinules and row III with 21 strong spinules. Distal margin with two rounded, chitinised projections. Coxa with strong, biserially setulated inner coxal seta, ornamented basally with long hair-like elements and distally with strong spinules along both margins. Caudal coxal surface with spinules formula A-C. Length/width ratio of Enp = 2.6, apical spine of Enp3 being 1.1 times as long as Enp3. No modified setae present.

Leg 4 ( Figures 4A–D , 8B–E ). Distal margin of sclerite with two low, rounded, chitinised projections. Frontal surface with row I bearing small, slender spinules arranged in circular pattern, caudal surface of intercoxal sclerite with row I bearing strong, small spinules, row II with small spinules at middle section and row III with strong, slightly longer spinules close to outer margins. Frontal surface of coxa with row of small spinules at insertion of basipod (Bsp). Inner coxal spine with heterogeneous ornamentation; inner margin with proximal row of long hairs, distal section with strong spinules. Outer margin with three distal spinules and proximal hair-like elements, gap in middle margin. Spinule formula of caudal surface of coxa: A-C + D-G-H-J. Length/width ratio Enp3 = 3.5, length ratio inner spine of Enp3/length Enp3 = 0.9; length ratio outer spine of Enp3/length Enp3 = 0.7; length ratio inner/outer spines Enp3 = 1.3. Lateral seta of Enp3 inserted at 62% of segment. No modified setae in Enp and Exp.

Leg 5 ( Figure 8F ). Free segment subrectangular, 1.9 times longer than wide, bearing strong inner spine and two setae; medial seta 1.7 times longer than outer seta and 1.4 times longer than inner spine. Inner spine 2.6 times longer than segment.

Male. Prosome symmetrical in dorsal view. Urosome slightly elongated, urosomal fringes strongly serrate. Caudal ramus smooth along both inner and outer margins, except for strong spinules at insertion of lateral seta. Length/width ratio of caudal ramus = 6.1, dorsal seta (VII) 0.5 times as long as caudal ramus and 1.2 times as long as outermost caudal seta (III). Innermost caudal seta (VI)/outermost caudal seta (III) ratio = 1.1. Lateral caudal seta (II) inserted at 71% of ramus length.

Antennule ( Figure 4E–F ). Armature as follows: 1(6s+3ms), 2(4s+1ms), 3(1+2ms), 4(1ms), 5(0), 6(2s), 7(3s), 8(0), 9(1s), 10(4s), 11(0), 12(0), 13(0), 14(1), 15(9s+1sp).

Antenna ( Figure 4G ). Basis with spinule groups on frontal surface: N1(VI), N2(V), N3(6), N4(7), N5(11), N15(4), N17(11), N18(4) and on caudal surface: N7(4), N8(4), N9+10(5), N11(4), N12(10).

Legs 1–4. Enp and Exp of all swimming legs three-segmented, armed as in females.

Leg 5 ( Figure 4L ). Free segment subrectangular, 1.8 times longer than wide, bearing inner spine and two setae; medial seta longer than outer seta (about 1.8 times) and inner spine (1.3 times).

Leg 6 ( Figure 4L ). Represented by small, low plate adjacent to lateral margin of genital somite armed with strong inner spine and two unequal setae. Inner spine reaching medial margin of third urosomite, as long as medial seta and 1.6 times longer than outer seta. Small, strong spinules present at insertion of inner spine.

Remarks. Eucyclops elegans was recently assigned as a member of the serrulatus -group by Mercado-Salas and Suárez-Morales (2014b) following the diagnostic characters established by Alekseev and Defaye (2011) to distinguish species of this group. The inclusion of E. elegans in the serrulatus -group precludes the idea of a synonymy with E. speratus and supports Reid and Marten ’ s (1995) assumption that American records of E. speratus should be assigned to E. elegans after an analysis of more material. It is important to consider that we observed differences between specimens of E. elegans from North and South America; the latter population could refer to another species (see Mercado-Salas and Suárez-Morales 2014b). We described a new species closely related to E. elegans (see remarks of E. mittmanni sp. nov.) from Mexico that must be considered in the identification of material related to E. elegans . Eucyclops elegans can be distinguished from E. serrulatus by the ornamentation of the frontal surface of the antennary basis: group N18, N1 and N2 are fused and row 22 is present on the caudal surface. Both species share rows N3, N4, N5, N15 and N17 on the frontal surface. The caudal surface of the antennary basis has some additional differences between these two species: row N8 is absent in E. serrulatus and sometimes N16 is absent too, but in E. elegans both rows are always present. The sixth leg of males of E. elegans is remarkably different from that of E. serrulatus , E. speratus , E. neumani titicacae , and most of the American species of the genus: it bears a small but strong inner spine which barely reaches the medial margin of the third urosomite, while in the rest of the species this spine is clearly longer than both the medial and outer setae and reaches at least the posterior margin of the third urosomite. Furthermore, the proportions of the P6 setae and spine should be considered important in separating the populations examined; together with the antennule ornamentations, this character was useful to distinguish species.

Other American Eucyclops with long caudal rami are E. neumani s. str. and E. neumani titicacae , both differing from E. elegans because the caudal ramus only bears spinules in the area adjacent to the lateral caudal seta (II). Among other characters, the former subspecies ( E. neumani s. str.) differs from E. elegans , E. serrulatus and E. neumani titicacae in details of the antennary ornamentation, with group N1 formed by spinules and not hair-like elements. Eucyclops neumani titicacae also differs from E. elegans and E. serrulatus in its unique ornamentation pattern of the intercoxal plate of P4 (see Figure 13 Kiefer 1957a; Fuentes and Suárez-Morales 2014).

Figures

Figure 2. Eucyclops elegans (Herrick, 1884). Adult female. (A) Urosome, ventral; (B) antennule segments 1–8; (C) antennule segments 9–12; (D) antenna, caudal; (E) antenna basis, frontal; (F) Scale bar = 100 μm.

Figure 3. Eucyclops elegans (Herrick, 1884). Adult female. (A) P1; (B) intercoxal sclerite P1, frontal; (C) endopod P2; (D) exopod P2; (E) coxa and basis P2, frontal; (F) intercoxal sclerite P2, frontal; (G) intercoxal sclerite P2, caudal; (H) coxa, basis and endopod P3, frontal; (I) exopod P3; (J) intercoxal sclerite P3, frontal; (K) intercoxal sclerite P3, caudal; (L) Scale bar = 100 μm.

Figure 4. Eucyclops elegans (Herrick, 1884). A–D, adult female; E–L, adult male. (A) Endopod P4; (B) exopod P4; (C) coxa, basis and intercoxal sclerite, frontal; (D) coxa, basis and intercoxal sclerite, caudal; (E) antennule segments 1–13; (F) antennule segments 14–15; (G) basis antenna, caudal; (H) caudal ramus; (I) endopod P4; (J) exopod P4; (K) coxa, basis and intercoxal sclerite P4, caudal; (L) P5 and P6.

Figure 5. Eucyclops elegans (Herrick, 1884). Adult female. (A) Habitus, lateral; (B) prosome, lateral; (C) cuticular patterns, dorsal; (D) genital somite and P5, ventral; (E) urosome, dorsal; (F) anal operculum, dorsal.

Figure 6. Eucyclops elegans (Herrick, 1884). Adult female. (A) Caudal rami; (B) antennule; (C) antennule segment 9; (D) antenna; (E) antenna basis, caudal; (F) antennal basis, frontal.

Figure 7. Eucyclops elegans (Herrick, 1884). Adult female. (A) Enp 1 antenna, frontal; (B) P1, frontal; (C) coxa, basis and intercoxal plate P1, frontal; (D) P2, frontal; (E) coxa, basis and intercoxal sclerite P2, frontal; (F) P3, frontal.

Figure 8. Eucyclops elegans (Herrick, 1884). Adult female. (A) Coxa, basis and intercoxal sclerite P3, frontal; (B) P4, frontal; (C) Enp3 P4; (D) coxa and basis P4, frontal; (E) intercoxal sclerite P4, frontal; (F) P5.

Figure 13. Eucyclops prionophorus Kiefer, 1931a. Adult female. (A) Coxa, basis and intercoxal sclerite P3, caudal; (B) intercoxal sclerite P3, caudal; (C) P4; (D) coxa, basis and intercoxal sclerite P4, frontal; (E) coxa P4, frontal; (F) P5.