Eucyclops torresphilipi Suárez-Morales, 2004

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 : 66-69

Eucyclops torresphilipi Suárez-Morales, 2004

( Figure 27 )

Description

Female. Average length excluding caudal setae = 680 µm. Prosome representing 66% of total body length, symmetrical in dorsal view. Prosomal fringes finely serrate in dorsal view. Urosomal fringes strongly serrate; posterior margin of anal somite with row of spinules. Genital double somite symmetrical, representing 16.5% 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 but posterior lobe slightly expanded. Anal operculum slightly rounded and smooth, with a small gap in the middle margin ( Figure 27A ). Length/width of caudal rami = 4.1; inner margin of caudal ramus smooth; strong spinules covering 47% with respect to the total length of ramus. Dorsal seta (VII) 0.7 times as long as caudal ramus, and 1.0 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 77% of total length of caudal ramus.

Antennule. Tip reaching middle margin of second 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(7s+1ae). One transverse row of spinules on first segment. Spine on sixth segment not reaching medial margin of seventh antennular segment.

Antenna ( Figure 27B ). Coxa (unarmed), basis (2s+Exp), plus three-segmented Enp (1s, 9s, 7s, respectively). Basis with rows of spinules on frontal surface: N1(V), N2(2), N3(3), N4(9), N5(6), N6(3), N15(3), N17(6), N18(3).

Leg 1 ( Figure 27C–D ). Frontal surface of intercoxal sclerite with row hair-spinules arranged in semicircular patternon each side, caudal surface with row II bearing spinules, row I absent. Inner coxal seta biserially setulated, caudal coxal surface with spinule formula = A-B-C. Inner basal seta (basipodal spine) not reaching midlength of Enp3, 0.6 times as long as Enp. Length/width ratio Enp3 = 1.5, apical spine of Enp3 being 1.2 times as long as Enp3.

Leg 2 ( Figure 27E–F ). Frontal surface of intercoxal sclerite with row I bearing hairs arranged in semicircular pattern; caudal surface lacking row I, row II continuous, with 21 strong 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 = 2.0, apical spine of Enp3 1.2 times as long as Enp3. No modified setae present.

Leg 3 ( Figure 27G–H ). Frontal surface of intercoxal sclerite with hairs – spinules arranged in circular pattern on each side; caudal surface with row I bearing long hairs (gap at middle section), row II with 24 strong spinules, divided into two sections arranged in semicircular pattern; row III continuous, with 19 strong spinules. Distal margin with two rounded, chitinised projections. Coxa with strong biserially setulated inner coxal seta, proximal section with long hairs; distal section with strong spinules long both margins. Caudal coxal surface with spinule formula = A-B-C. Length/width ratio of Enp = 2.3, apical spine of Enp3 being 1.0 times as long as Enp3. No modified setae present.

Leg 4 ( Figure 27I–J ). Distal margin of intercoxal sclerite with two low, rounded, chitinised projections. Frontal surface of sclerite with row I bearing small hair – spinules arranged in a semicircular pattern, caudal surface with row I bearing long, strong spinules, row II with spinules close to outer margins of sclerite; row III with strong and slightly longer spinules close 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 margin with strong spinules; outer margin with one distal spinule, proximal section with setules, gap in middle margin. Spinule formula on caudal surface = C + D-G-H-J. Length/width ratio Enp3 = 2.1, length ratio inner spine of Enp3/length Enp3 = 1.2; length ratio outer spine of Enp3/length Enp3 = 0.8; length ratio inner/outer spines Enp3 = 1.5. Lateral seta of Enp3 inserted at 70% of segment. No modified setae in Enp and Exp.

Leg 5. Free segment subrectangular, 1.6 times longer than wide; bearing one strong inner spine and two setae; medial seta 1.6 times longer than outer seta and 1.6 times longer than inner spine. Inner spine twice longer than segment.

Male. Length range excluding caudal setae = 652 µm. Prosome symmetrical in dorsal view, representing 67% of total body length. Urosome six-segmented, slightly elongated, urosomal fringes strongly serrate. Caudal ramus smooth along both inner and outer margins, with strong spinules at insertion of lateral seta.

Antennule. 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. Basis ornamented 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. End and Exp of all swimming legs three-segmented and armed as in female.

Leg 5. Free segment subrectangular, 1.7 times longer than wide, bearing one inner spine and two setae; medial seta longer than outer seta (about 1.6 times) and inner spine (1.5 times). Inner spine 1.5 times longer than segment.

Remarks. As stated by Suárez-Morales (2004), E. torresphilipi resembles the South American species E. leptacanthus and E. delachauxi because they share a particularly slender inner P5 spine and relatively short caudal rami. The morphometric values obtained from our analysis of E. leptacanthus and E. torresphilipi revealed that there are no significant differences between these species, but the ornamentation of the swimming legs and the antennae provide useful characters to distinguish them. In the P1 coxa of E. torresphilipi row C bears long hair – spinules whereas this row has small but strong spinules in E. leptacanthus . In the P2 coxa small differences were found: row D of E. torresphilipi bears long hair – spinules but in E. leptacanthus this row has strong and long spinules which are also fewer than in E. torresphilipi . In P3 differences in the caudal surface of the intercoxal sclerite are remarkable; in E. leptacanthus row I bears long hairs while in E. torresphilipi this row is armed with long hair – spinules. In both species row II is divided in two sections, each close to the outer margin, but in E. leptacanthus it has small but strong spinules whereas in E. torresphilipi this row covers all the medial surface of the intercoxal sclerite and bears strong and slightly longer spinules. In both species row III has long spinules along the sclerite.

Eucyclops prionophorus is another species that seems to be closely related to E. torresphilipi but can be easily distinguished because of its possession of row I on the caudal surface of P1 and P2 intercoxal sclerites; this row is absent in E. torresphilipi . One of the main characteristics of E. torresphilipi is the coxal ornamentation of the fouth swimming leg which is remarkably reduced when compared with that known in other congeners like E. delachauxi , E. leptacanthus , E. prionophorus , E. pectinifer and E. bondi . In E. torresphilipi row A is not present as it is in all the other mentioned species, but also E. torresphilipi presents a unique pattern in row J which is divided into three rows bearing minute spinules. This pattern is similar to that present in E. albuferensis from Spain ( Alekseev 2008), with the difference that in E. albuferensis the groups of spinules are not clearly separated as they are in E. torresphilipi . Another distinctive feature of E. torresphilipi is the shape of its anal operculum; in the Mexican Eucyclops we found two general types: (1) rounded and smooth and (2) rounded and serrate ( E. elegans , E. tziscao and E. defayeae sp. nov.); E. torresphilipi is the only species whose anal operculum is smooth and rounded but has a small gap in its middle section. This character is known only in E. neumani s. str., a South American species and otherwise clearly different to E. torresphilipi because of the ornamentation of the caudal rami, the length/width of the caudal ramus, and the body size, among other characters.

Eucyclops delachauxi and E. torresphilipi share a short caudal ramus and a particularly long lateral seta in Enp3 P4 as compared to other species of Eucyclops . In these two species this seta reaches or exceeds the apical margin of the outer spine, while in the rest of the species the seta does not reach beyond the midlength of the outer spine. A character that separates these two species is the ornamentation of the outer margin of the caudal ramus; in E. torresphilipi (as in most of species of the genus) spinules cover ¾ of the total length of the ramus, while in E. delachauxi the serra is reduced – it covers only 20 – 30% of the outer margin.

Figures

Figure 27. Eucyclops torresphilipi Suárez-Morales, 2004. Adult female. (A) Anal operculum, dorsal; (B) antennal basis, frontal; (C) coxa and intercoxal sclerite P1, frontal; (D) intercoxal sclerite P1, frontal; (E) coxa and intercoxal sclerite P2, caudal; (F) intercoxal sclerite P2, frontal; (G) coxa and intercoxal sclerite P3, caudal; (H) intercoxal sclerite P3, frontal; (I) intercoxal sclerite P4, frontal; (J) coxa, intercoxal sclerite and coxal spine P4, caudal.