Eucyclops ishidai, Mercado-Salas & Suárez-Morales & Silva-Briano, 2015

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 : 128-136

Eucyclops ishidai sp. nov. Mercado-Salas and Suárez-Morales ( Figures 67 – 72 )

Material examined

Holotype. Adult ♀ specimen dissected, mounted in glycerin sealed with Entellan (ECO- CH-Z-05049).

Allotype. Adult ♂, dissected, mounted in glycerin sealed with Entellan (ECO-CH- Z-05050).

Paratypes. Seven adult ♀♀ undissected, ethanol-preserved (ECO-CH-Z-05051). Samples from type locality collected 19 February 1989 by Marcelo Silva-Briano.

Type locality

Creek at Sierra Fria, 21 km from La Labor, Calvillo, Aguascalientes, Mexico.

Etymology

This species is dedicated to Dr. Teruo Ishida, who pioneered the exploration of new morphological characters to distinguish closely related species of Eucyclops .

Distribution

Central and Northern Mexico (Aguascalientes, Zacatecas, Chihuahua).

Description

Female. Habitus as in Figure 69A . Average length excluding caudal setae = 788 µm. Body surface (including caudal rami) ornamented with small pits. Prosome widest at end of cephalosome and second pediger, representing 62% of total body length, symmetrical in dorsal view. Prosomal fringes finely serrate in dorsal surface. Five-segmented urosome, slightly elongated; first urosomite with long setules on lateral margin; urosomal fringes serrate dorsally and ventrally; posterior margin of anal somite with row of strong spinules. Genital double somite symmetrical ( Figure 69B ), representing 13.4% of total body length; anterior half of genital somite slightly expanded. Seminal receptacle with rounded, slender lateral arms on posterior margin, typical of the serrulatus -complex. Anal somite subequal in length to preanal somite, anal operculum rounded ( Figures 67G , 69D ). Length/width of caudal ramus = 4.1; inner margin of caudal rami naked; strong spinules covering 64% of total length of ramus. Dorsal seta (VII) 0.8 times as long as caudal ramus and 1.2 times as long as outermost caudal seta (III). Length ratio of innermost caudal seta (VI)/outermost caudal seta (III) = 1.5. Lateral caudal seta (II) inserted at 76% of caudal ramus. All terminal setae plumose.

Antennule ( Figures 67B–C , 69F , 70A–B ). Twelve-segmented, tip barely reaching beyond posterior margin of cephalosome; smooth, slender hyaline membrane on segments 10 – 12, antennules ornamented with small pits. Armature per segment as follows: 1(8s), 2(4s), 3(2s), 4(6s), 5(3s), 6(1s+1sp), 7(2s), 8(3s), 9(2s+1ae), 10(2s), 11(3s), 12(7s),

Transverse row of strong spinules on first segment. Spine on sixth segment reaching medial margin of seventh segment.

Antenna ( Figures 67D–E , 70C–E ). Coxa (unarmed), basis (2s+Exp), plus three-segmented Enp (1s, 9s, 7s, respectively). Basis with row of spinules on frontal surface: N1(V), N2(4), N3(6), N4(6), N5(9), N15 (4), N17(10); on caudal surface: N7(5), N8(6), N9+10(8), N11(8), N12(8), N13(4), N14(7), N16(6), N22(8). Caudal surface of first Enp with B2(7). Mouthparts as in Figure 70F .

Leg 1 ( Figures 68A , 70A–D ). Frontal surface of intercoxal sclerite with row I bearing small spinules arranged in a semicircular pattern, caudal surface with rows I and II bearing minute spinules, row I continuous, row III divided in three sections. Inner coxal seta biserially setulated, caudal coxal surface with spinule formula = A-B-C. Row of minute spinules along insertion of basipodite. 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 0.7 times as long as Enp.

Leg 2 ( Figures 68B–C , 71E ). Frontal surface of intercoxal sclerite with row I bearing hairs arranged in circular pattern; caudal row II continuous, bearing 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 = 1.8, apical spine of Enp3 1.2 times as long as Enp3. No modified setae observed.

Leg 3 ( Figures 68D–F , 71F , 72A–B ). Frontal surface of intercoxal sclerite with row I armed with hairs arranged in a circle on each side; caudal surface with row I bearing 10 – 12 long and very slender spinules on each side, small gap between it (row not continuous), row II continuous with strong short spinules (17 – 19) and; row III continuous bearing 20 – 26 long but strong spinules. Distal margin of sclerite with two rounded chitinised projections. Coxa with strong biserially setulated inner coxal seta, basally with long hairs and distally with strong spinules at both edges. Caudal coxal surface with spinule formula A-B-C. Small spinules along insertion of basipodite (frontal surface). Length/width ratio of Enp 3 = 2.1, apical spine slightly shorter than Enp3 (about 0.9 times). No modified setae observed.

Leg 4 ( Figures 68G , 72C–E ). Distal margin of intercoxal sclerite with two low, rounded, chitinised projections. Frontal surface of sclerite with row I bearing hairs arranged in semicircular pattern in both sides of surface. Caudal row I with seven long and slender spinules on each side and a small gap in the middle, row II bearing very long spinules, divided into three sections: two on outer margins and one medial; row III bearing long, slender spinules, also divided into three sections, two on outer margins and one in medial margin. 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 and with strong spinules distally, outer margin with one distal spinule basally setulated, gap in middle margin. Caudal coxal surface with spinule formula = A-C + D-E- F-H-J. Length/width ratio of Enp3 = 3.1, inner spine of Enp3 as long as Enp3 (1.0), length ratio of outer spine of Enp3/length Enp3 = 0.7; length ratio inner/outer spines of Enp3 = 1.4. Lateral seta of Enp3 inserted at 67% of segment. No modified setae observed.

Leg 5 ( Figure 72F ). Free segment subrectangular, 1.1 times as long as wide, bearing one strong inner spine and two setae, medial seta 1.7 times longer than outer seta and 1.6 times longer than inner spine. Inner spine 2.3 times longer than segment.

Male. Unknown.

Remarks. Records of E. ishidai sp. nov. were previously assigned to E. pectinifer ( Mercado-Salas and Suárez-Morales, 2012) ; however, significant differences were found among these closely related species. The two species share the presence of N1 bearing long hairs on the frontal surface of antennal Bsp and the presence of spinules on N2 and the absence of N6, while they differ because of the presence of N 22 in E. ishidai sp. nov. while it is absent in E. pectinifer . Both species share as well a typical seminal receptacle of the serrulatus -complex and a rounded and smooth anal operculum. Main differences can be found in the ornamentation of the intercoxal sclerites of the swimming legs. Eucyclops ishidai sp. nov. presents an intercoxal sclerite of P1 with rows I and II present and bearing minute spinules, while in E. pectinifer row I is absent and row II bears long spinules. The intercoxal sclerite of P2 is similar in both species, row I being absent and row II present; in E. ishidai sp. nov. it is represented by small spinules while in E. pectinifer it bears long hairs. Another species that seems to be closely related to E. ishidai sp. nov. is E. tziscao . In the former species the anal operculum is rounded and smooth, while in E. tziscao it is serrated. Ornamentation of the frontal surface of the antennal basis of E. ishidai sp. nov. is more complex than it is in E. tziscao . In E. ishidai sp. nov. rows N7, N13, N14, N16, N18 and N22 are present, while in E. tziscao they are absent. Ornamentation of the intercoxal sclerites is similar in both species.

Morphometrics and binary characters

In order to test the taxonomic value of the morphometric variables traditionally used in the separation of the species ( Lindberg 1955; Reid 1985; Suárez-Morales 2004; Alekseev and Defaye 2011) we performed a statistical analysis using boxplots with the aid of the statistical program R 3.0.2. (R Development Core Team 2008). We included 22 morphometrical characters measured in the 17 species included herein. We observed ( Figure 73 ) a lack of significant variation and a remarkable overlap of data in the morphometric characters used in the separation of species of the genus. The only characters that appear to have a consistent variation among species and that could be deemed useful in the separation of species are the length/width ratio of the caudal ramus (2), the length/ width ratio of P4 Enp3 (14) and the spine and setae proportions of the fifth leg armature (19 – 22), but even in these characters, variation is relatively weak, so they should not be used as defining characters.

The cluster analysis was performed using Euclidean distance in order to classify and verify dissimilarities among species in relation to the shared characters ( Figure 73 ). It included all characters (morphometric and binary) examined. The cluster in Figure 73B shows the results obtained using morphometrical data only.

Figures

Figure 67. Eucyclops ishidai sp. nov. Adult female. (A) Urosome, ventral; (B) antennule, segments 1–6; (C) antennule, segments 7–12; (D) antenna, caudal; (E) antennal basis, frontal; (F) maxilla; (G) anal operculum, dorsal.

Figure 68. Eucyclops ishidai sp. nov. Adult female. (A) P1, frontal; (B) endopod P2; (C) coxa and intercoxal sclerite P2, frontal; (D) endopod P3; (E) coxa, basis and intercoxal sclerite P3, frontal; (F) coxa, basis and intercoxal sclerite P3, caudal; (G) P4, frontal.

Figure 69. Eucyclops ishidai sp. nov. Adult female. (A) Habitus, dorsal; (B) genital somite, ventral; (C) urosome, dorsal; (D) anal operculum, dorsal; (E) caudal rami, dorsal; (F) antennule.

Figure 70. Eucyclops ishidai sp. nov. Adult female. (A) Antennule, segment 6; (B) antennule, segment 9; (C) antenna, caudal; (D) antennal basis, caudal; (E) antennal basis, frontal; (F) mouthparts.

Figure 71. Eucyclops ishidai sp. nov. Adult female. (A) P1; (B) basis P1, frontal; (C) intercoxal sclerite P1, frontal; (D) intercoxal sclerite P1, caudal; (E) P2, frontal; (F) P3, caudal.

Figure 72. Eucyclops ishidai sp. nov. Adult female. (A) Coxa P3, caudal; (B) intercoxal sclerite P3, caudal; (C) P4, caudal; (D) coxa P4, caudal; (E) intercoxal sclerite P4; caudal; (F) P5.

Figure 73. Boxplot of morphometric variation of Mexican species of Eucyclops. Abbreviations on the x-axis indicate the character used: TB, total body size; VII/CR, proportion seta VII/length caudal rami; VI/III, proportion seta VI/seta III; P1B.E, basipodal spine/Enp P1; P1S.E, spine/W Enp3 P1; P2S.L, spine/ Enp P2; P3S.L, spine/Enp3 P3; P4I.L, inner spine/L Enp3 P4; P4I.O, inner spine/outer Enp3 P4; P5L.W, proportion length/width; P5M.S, proportion medial seta/inner spine.