Eucyclops tziscao Mercado-Salas 2013

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 : 77-84

Eucyclops tziscao Mercado-Salas 2013

( Figures 31 – 33 and Gutiérrez-Aguirre et al. 2013)

Description

Female. Average length excluding caudal setae = 620 µm. Prosome representing 61% of total body length, symmetrical in dorsal view. Urosomal fringes strongly serrate. Genital double-somite symmetrical ( Figure 31A ), carrying paired egg sacs. Seminal receptacle with rounded, lateral arms on posterior margin typical of the serrulatus - complex. Anal somite with hair – seta in anal opening, anal operculum serrate. Length/ width of caudal ramus = 4.0; inner margin of caudal ramus naked; outer margin with strong spinules covering 40% with respect to the total length of ramus. Dorsal seta (VII) short: 0.65 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) = 1.2. Lateral caudal seta (II) inserted at 71% of caudal ramus.

Antennule ( Figure 31C–F ). Tip reaching from middle to distal margin of third pediger. 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 strong long spinules, second row with minute spinules. Spine on sixth segment reaching midlength of seventh segment.

Antenna ( Figures 32A ). Coxa (unarmed), basis (2s +Exp), plus three-segmented Enp (1s, 9s, 7s, respectively). Basis with rows of spinules on frontal surface: N1 (IV), N2 (5), N3(5), N4(6), N5(12), N15(4), N17(10); on caudal surface: N8(4), N9+10(5), N11(5), N12(5). Caudal surface of Enp 1 with B3(4).

Leg 1 ( Figure 32C–D ). Frontal surface of intercoxal sclerite with row I bearing spinules arranged in semicircular pattern on each side; caudal surface with row I bearing 17 minute spinules and row II with 14 minute spinules, 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 Enp3 = 1.0, apical spine of Enp3 being1.4 times as long as Enp3.

Leg 2 ( Figure 32E–F ). Frontal surface of intercoxal sclerite with row I bearing minute spinules arranged in semicircular pattern; caudal surface with row II continuous, with 20 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 = 1.9, apical spine of Enp3 1.0 times as long as Enp3. No modified setae present.

Leg 3 ( Figure 33A–B ). Frontal surface of intercoxal sclerite with row I armed with minute spinules arranged in semi-circle on each side; caudal surface with row I bearing long hair-like spinules (small gap in middle section), rows II and III continuous, with minute spinules. Distal margin with two low, rounded projections. Coxa with strong, biserially setulated inner coxal seta, basally with long hairs and distally with strong spinules along both margins. Caudal coxal surface with spinule formula = A-B-C. Length/ width ratio of Enp = 2.2, apical spine of Enp3 being 1.2 times as long as Enp3. Modified setae present in both Enp and Exp.

Leg 4 ( Figure 33C–E ). Distal margin of intercoxal sclerite with two low, rounded, chitinised projections. Frontal surface of intercoxal sclerite with row I bearing minute spinules arranged in semicircular pattern; caudal surface of sclerite with row I bearing strong spinules on each side and small gap, row II with small spinules divided into three sections, with small gap between them and row III divided into three sections, first section with five long spinules, middle section with six small, strong spinules, and third section with five long spinules. Inner coxal spine with heteronomous setulation: proximally with long hair-like setules, distally with spinule-like setules; outer edge of coxal spine with three spinule-like setules distally, naked proximally. Caudal surface of coxa with spinule groups A-C + D-E-F-H-J. Length/width ratio Enp3 = 3.0; length ratio inner spine/ length Enp3 = 0.70; length ratio outer spine Enp3/length Enp3 = 1.0; proportion inner/outer spines Enp3 = 1.4. Lateral seta of Enp3 inserted at 66% of segment. Modified setae on Enp3 and Exp3.

Leg 5 ( Figure 33F ). Free segment subrectangular, 2.1 times longer than wide, bearing one inner spine and two setae; medial seta about 1.3 times longer than outer seta and 1.8 times longer than inner spine. Inner spine 1.7 times as long as segment.

Male. Body length excluding caudal setae = 509 µm. Prosome symmetrical in dorsal view, representing 65% of total body length. Urosome relatively short, representing 35% of total body length. Anal operculum slightly rounded, smooth. Caudal ramus 3.5 times longer than wide; medial margin naked, strong spinules at insertion of lateral caudal seta (II) and outermost terminal caudal seta (III). Dorsal seta (VII) short, 0.35 times as long as caudal ramus, and 0.75 times as long as outermost caudal seta (III). Ratio of innermost caudal seta (VI)/outermost caudal seta (III) = 1.6. Lateral caudal seta (II) inserted at 70% of caudal ramus. All terminal caudal setae plumose.

Antennule. Armature per segment as follows: 1(7s+2ms); 2(3s+1ms); 3(1s+2ms); 4(1s+1ms +1ae); 5(0); 6(2s); 7(1s); 8(1s); 9(0); 10(3s); 11(2s); 12(0); 13(0); 14(0); 15(3s); 16(8s).

Antenna. Coxa (unarmed), basis (2s+1 seta representing Exp) plus three-segmented Enp (first to third Enp with 1, 8, and 7 setae, respectively). Basis ornamented with: N1 (four hair – setae), N2 (four small spinules), N3, N4, N5, N15, and N17 on frontal surface ( Figure 4E ); and N9+N10, and N12 on caudal surface.

Legs 1–4. Endopods and exopods of all swimming legs three-segmented; P1 – P3 armed as in females.

Leg 4. Coxa, Bsp, and intercoxal sclerite as in female, except for distal row of spinules of intercoxal sclerite, which has nine spinules, all longer and more slender than in female. Enp3 P4 being 2.6 times as long as width; inner spines 1.2 times as long as outer spine, and 1.2 times as long as segment. No modified setae on fourth leg. Lateral seta of Enp3 P4 inserted at 64.7% of segment length, lateral seta reaching midlength of outer spine.

Leg 5. Free segment subrectangular, 1.5 times longer than wide, bearing one inner spine and two setae: outer seta about 1.3 times longer than medial seta and 1.3 times longer than inner spine. Inner spine 1.8 times as long as segment.

Leg 6. Represented by small, low plate near lateral margin of genital somite with one strong and long inner spine and two unequal setae. Inner spine reaching distal margin of fourth urosomite. Inner spine about 2.3 times longer than median seta and about 1.6 longer than outer seta.

Remarks. This species, recently described in Gutiérrez-Aguirre et al. (2013), closely resembles Eucyclops bondi . Morphometric values are similar but the lack of data on the ornamentation of the antennal basis of E. bondi did not allow a complete comparison. Other characters that are useful to separate these species include the length of the lateral seta on Enp3 P4, which in E. bondi exceeds half the length of the outer apical spine and is not modified, while in E. tziscao the same seta is shorther, not reaching half the length of the outer apical spine, and it is modified as a strong, heavily sclerotised blunt seta. The male secondary characters have been deemed useful in the separation of species among the Eucyclopinae . Since its original description by Kiefer (1931a), one of the main characteristics of E. bondi (and constantly ignored thereafter in the identification of the species) is the sixth leg of the male, which bears a very small inner spine; it does not reach the posterior margin of the third urosomite and it is smaller than the outer seta and as long as the medial seta. The opposite pattern is present in males of E. tziscao , in which the inner spine is 1.5 times longer than the outer seta and 2.5 longer than the medial seta.

Another species that resembles E. tziscao is E. pectinifer , but strong differences clearly separate these taxa. Among the differences advanced by Gutiérrez-Aguirre et al. (2013) to distinguish these two species, the ornamentation of the anal operculum (smooth in E. pectinifer , serrate in E. tzicao ) is one of the strongest. A serrate operculum is shared also with E. elegans and E. defayeae sp. nov. The ornamentation of the antennal basis is simple in both species, but differs mainly by the presence of N18 on the caudal surface and N7, N13 and N14 on the frontal surface of E. pectinifer ; these rows are absent in E. tziscao . The ornamentation of the intercoxal sclerites also differs between these two species: E. tziscao is the only species distributed in Mexico in which the sclerite spinules of row I of P1 (frontal surface) are remarkably small, while in the rest of the species these spinules (or in some cases hairs) are always long, conspicuous elements. On the caudal surface of the same P1 sclerite, row I bears minute spinules in E. tziscao but is absent in E. pectinifer . Row II is present in both species but in E. pectinifer it bears long hairs and in E. tziscao it has small spinules. Row I of the P4 intercoxal sclerite has some additional differences; in E. pectinifer this row bears long spinules vs strong and short spinules in E. tziscao . Another species resembing E. tziscao by the presence of modified setae on P3 and P4 and similar length/width proportions of the caudal ramus is E. conrowae . However, they are easily distinguished because E. conrowae is not a member of the serrulatus -group – it lacks groups N1 and N2 on the frontal surface of the antennal basis – whereas in E. tizcao both groups are present in all the specimens examined ( Gutiérrez-Aguirre et al. 2013)

Eucyclops angeli Gutiérrez-Aguirre and Cervantes-Martínez, 2013 (see figures in Gutiérrez-Aguirre et al. 2013)

Description

Female. Average length excluding caudal setae = 600 µm. Representing 58% of total body length, symmetrical in dorsal view. Prosomal fringes serrate dorsally; fourth pediger with long, lateral, hair-like setae. First urosomite with long spinules on lateral margin; urosomal fringes strongly serrate. Posterior margin of anal somite with large spinules on ventral and dorsal surfaces, except for the medial section. Genital double somite symmetrical, lateral arms of proximal part of seminal receptacle rounded; distal section forming sinuous sac. Anal somite subequal in length to preanal somite, with hairlike setae adjacent to anal pore. Length/width of caudal ramus = 2.1; inner margin of caudal ramus naked, strong spines covering 62% with respect to the total length of ramus. Dorsal seta (VII) 0.8 times as long as caudal ramus, and 1.1 times as long as outermost terminal caudal seta (III). Ratio of innermost caudal seta (VI)/outermost caudal seta (III) = 1.5. Lateral caudal seta (II) inserted at 71.6% of caudal ramus.

Antennule. Tip reaching between middle and distal margin of second pediger. 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(2s+1ae); 12(7s+1ae). Row of spinules on first segment: inner spinules shorter than outer spinules. Long spine on sixth segment, reaching distal 1/3 of seventh antennular segment.

Antenna. Coxa (unarmed), basis (2s+1s representing Exp), plus three-segmented Enp (1s, 9s, 7s, respectively). Basis with rows of spinules on frontal surface: N1(4), N2(3), N3(4), N4(7), N5(11), N15(3), N17(6); on caudal surface: N7(5), N8(5), N10(5), N11(6), N12(6), N13(11), N16(4), N18(2).

Leg 1. Frontal surface of intercoxal sclerite with row I bearing long spinules arranged in semicircular pattern, caudal surface with row II bearing 21 small, strong spinules, row I absent. Inner coxal seta biserially setulated, caudal surface with spinule formula = A – C. Inner basal seta (basipodal spine) reaching beyond apical margin of Enp3, 0.9 times as long as Enp. Length/width ratio Enp3 = 1.4, apical spine of Enp3 being 1.3 times as long as Enp3.

Leg 2. Frontal surface of intercoxal sclerite with row I bearing long hair – spinules arranged in circular pattern; caudal surface with row I divided in two groups of 10 minute spinules on each side; row II continuous, armed with 10 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 Enp3 = 1.6, apical spine of Enp3 being 1.4 times as long as Enp3. No modified setae observed.

Leg 3. Frontal surface of intercoxal sclerite with row I bearing hair – spinules arranged in circular pattern on each side; caudal surface with row I bearing long hairs (small gap in middle section), row II continuous, bearing long hair – spinules; row III discontinuous, with long hair – spinules (small gap in middle section). Distal margin with two rounded, chitinised projections. Coxa with strong, biserially setulated inner coxal seta, basally with long hairs and distally with strong spinules along both margins. Caudal coxal surface with spinule formula = A-B-C. Modified setae in both Enp and Exp.

Leg 4. Distal margin of intercoxal sclerite with two low, rounded, chitinised projections. Frontal surface with row I bearing long spinules arranged in circular pattern (on each side), caudal surface of sclerite with row I bearing seven long denticles (gap in middle section), rows II and III with long hair – spinules on outer margins. Frontal coxal surface with row of small spinules at insertion of Bsp. Inner coxal spine with heterogeneous ornamentation; basally, inner margin with long hairs; distally, with strong spinules. Outer distal margin naked, proximal section setulated. Spinule formula on caudal surface of coxa = A-B-C + D-E-F-G-H-J. Length/width ratio Enp3 = 1.8; length ratio inner spine of Enp3/length Enp3 = 1.3; length ratio outer spine of Enp3/length Enp3 = 0.9; length ratio inner/outer spines Enp3 = 1.3. Lateral seta of Enp3 inserted at 68% of segment. Modified setae present in both, Enp and Exp.

Leg 5. Free segment 1.4 times longer than wide, bearing one inner spine and two setae; medial seta 2.0 times longer than outer seta and 1.3 times longer than inner spine. Inner spine twice as long as segment.

Male. Body length excluding caudal setae = 540 – 580 µm (n = 4); average body length = 552.9 ± 15.56 µm. Prosome symmetrical in dorsal view, representing 60 – 63% of total body length. Urosome relatively elongated; lateral margin of first urosomite naked; posterior margin of anal somite with continuous (dorsally and ventrally) row of spinules. Anal region armed with two parallel rows of hair-like setae; anal operculum slightly rounded, smooth. Caudal ramus 2.3 times longer than wide; medial margin of caudal ramus naked, strong spines at insertion of lateral caudal seta. Dorsal seta (VII) 0.9 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 = 1.8. Lateral caudal seta (II) inserted at 75% of ramus length.

Antennule. Armature per segment as follows: 1(6s+2ms+1ae); 2(3s+1ms); 3(1s+1ms); 4(1s+1ms+1ae); 5(2s+1ms); 6(1s+1ae); 7(1s); 8(2s); 9(2s); 10(2s); 11(1s); 12(1s); 13(3s); 14(0s); 15(1s); 16(9s). Row of spinules on first segment, inner spinules shorter than outer spines.

Antenna. As in female except for absence of groups N7, N13 and N16 on caudal surface of antennal Bsp. Basis ornamented with: N1 (IV), N2 (II) N3, N4, N5, and N17 on frontal surface.

Leg 5. Free segment 1.6 times longer than wide, bearing three elements; outer seta slightly longer than in female (subequal in length to inner spine). Inner spine 1.8 times as long as segment.

Leg 6. Represented by small, low plate adjacent to lateral margin of genital somite, armed with one inner spine, 1.87 times longer than median seta, and 0.6 times longer than outer seta. Inner spine of sixth leg reaching distal margin of fourth urosomite.

Remarks. Eucyclops angeli is easily distinguishable from the other species of Eucyclops distributed in Mexico because of its remarkably short caudal rami and the unique ornamentation on the P4 coxa. There are other species in the Americas that share with E. angeli short caudal rami such as E. breviramatus and E. siolii , but these species are restricted to South America. As mentioned by Gutiérrez-Aguirre et al. (2013), Löffler ’ s description of E. breviramatus did not include the new, currently used characters, but some other characters are useful to distinguish them. The length/width ratio of Enp3 P4 differs between these species; in E. angeli the ratio range is 1.8 – 2.0 while in E. breviramatus the segment is shorter (1.4 – 1.5). Another character that could be useful to separate these species is the armature of the male sixth leg; in E. angeli the inner spine is almost twice as long as the medial and outer setae, while in E. breviramatus the inner spine is clearly shorter, only 1.2 times longer than both the outer and medial setae. Eucyclops angeli can be distinguished from E. siolii by the shape and size of P5; in both species the medial seta is longer than the outer seta and the inner spine but in E. siolii the inner spine is remarkably short, being as long as or slightly shorther than the segment. Other species resembling E. angeli but from other geographic regions are the recently described E. albuferensis from Spain ( Alekseev 2008), E. dumonti Alekseev, 2000 distributed in Mongolia (and not belonging to the serrulatus -group; Alekseev 2000; Alekseev and Defaye 2011) and E. echinatus Kiefer, 1926 with a distribution restricted to Africa ( Angola, Democratic Republic of Congo, Ivory Coast, Kenya, and Madagascar; Dussart and Defaye 2006).

Figures

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 31. Eucyclops tziscao Mercado-Salas, 2013. Adult female. (A) Genital somite, ventral; (B) caudal rami, ventral; (C) antennule; (D) antennule segment 6; (E) antennule segment 9; (F) antennule segment 12.

Figure 32. Eucyclops tziscao Mercado-Salas, 2013. Adult female. (A) Antennal basis; (B) mouthparts; (C) P1, caudal; (D) intercoxal sclerite P1, caudal; (E) P2, frontal; (F) intercoxal sclerite P2, frontal.

Figure 33. Eucyclops tziscao Mercado-Salas, 2013. Adult female. (A) P3, caudal; (B) intercoxal sclerite P3, caudal; (C) P4, caudal; (D) coxa P4, caudal; (E) intercoxal sclerite P4, caudal; (F) P5.