Paracyclops hirsutus, Mercado-Salas & Suárez-Morales, 2009

Mercado-Salas, Nancy & Suárez-Morales, Eduardo, 2009, A new species and illustrated records of Paracyclops Claus, 1893 (Copepoda: Cyclopoida: Cyclopinae) from Mexico, Journal of Natural History 43 (45 - 46), pp. 2789-2808 : 2790-2801

Paracyclops hirsutus sp. nov.

( Figures 1–5 )

Material examined

Adult female holotype specimen from La Chica Dam (22°22′ N, 102°18′ W), state of Aguscalientes , central Mexico, coll. Marcelo Silva-Briano, 21 July 1990. Specimen dissected, slide in collection of Zooplankton at ECOSUR-Chetumal (ECO-CHZ-03989) . Allotype adult male from La Chica Dam, Aguascalientes, central Mexico, coll. Marcelo Silva-Briano, 21 July 1990, specimen dissected, slide in collection of Zooplankton at ECOSUR-Chetumal (ECO-CHZ-03990) . Paratypes: three adult females, same site and date of collection, ethanol-preserved, vial deposited at ECOSUR (ECO-CHZ-03991) .

Description – adult female holotype

Body length 0.794 mm from anterior end of cephalothorax to posterior margin of anal somite. Average length of type specimens: 0.810 mm. Habitus compact, with prosome longer than urosome, cephalothorax widely rounded anteriorly, 1.4 times longer than wide.

Antennule ( Figure 1A ). Eight-segmented, armature per segment as follows (s, seta; ae, aesthetasc): 1(8s), 2(10s), 3(5s), 4(3s), 5(2s+ae), 6(2s), 7(2s+ae), 8(5s+ae). Ventral surface of first antennular segment with row of six to eight spinules on proximal half. Third segment with incomplete suture line.

Antenna ( Figure 1B ). Four-segmented, comprising coxobasis and three-segmented endopod. Coxobasis with five groups of spinules on proximal half, with two biserially spinulated basipodal setae and long exopodal seta. First segment of endopod without outer setae, but ornamented with a transversal group of hair-like setules and with one group of hair-like setules on inner surface, close to the insertion. Second segment of endopod with four lateral and four terminal outer setae; inner margin with row of spinules. Third endopodal segment with seven terminal setae, inner margin with row of spinules.

Mandible ( Figure 1C ). Gnathobase with five strongly chitinized teeth and long dorsal seta armed with inner row of spinules, fifth tooth tricuspidal. Coxa with row of spinules on outer margin between palp and gnathobase. Palp with 2 long biserially setulated setae.

Maxillule ( Figure 1D ). Precoxa with surface armed with spiniform process on proximal half; distal half with three strong chitinized claws, five spiniform setae and one strong setulated seta on frontal side. Proximal segment of palp with three subequally long apical setae and long, biserially setulated seta on dorsal surface. Distal segment of palp with three apical setae.

Maxilla ( Figure 1E ). Precoxa with row of strong spinules on dorsal surface; precoxal endite with two biserially setulated setae, one clearly shorter. Coxa with single stout seta, coxal endite armed with two setae, one strongly spinulated, one naked. Basis with usual claw and strong spine, both elements bearing spinules on outer margin. First endopodal segment armed with two subequal setae; second segment bearing three setae.

Maxilliped ( Figure 1F ). Four-segmented. Syncoxa with three equally long setulated setae along inner margin with transverse row of spinules near insertion of setae. Basis with two subequal setulated setae and two transverse rows of spinules on outer margin. Endopod two-segmented, first segment with one stout spine with strong spinules along inner margin. Second endopod armed with three elements, two strong spiniform spinulated setae plus a slender, naked seta.

Swimming legs 1–4 biramous, all endopodal and exopodal rami three-segmented; armature is described in Table 1.

Leg 1 ( Figure 2A ). Coupler (not illustrated) with two groups of hairs on each side of anterior surface, distal margin with two rounded chitinized projections. Coxa with one group of long spinules close to outer margin, row of 10–12 long spiniform elements perpendicular to medial margin of coxa. Basis with one slender basipodal seta on outer margin, inner margin with one strong, spiniform basipodal seta reaching proximal onethird of third endopodal segment; group of spinules at insertion of seta. Endopod slightly longer than exopod. Three segments of exopod armed with long spines.

Leg 2 ( Figure 2B ). Coupler with one row of spinules on each side of anterior surface, row of hair-like elements along anterior margin, with two rounded chitinized projections. Coxa with one row of 9–11 spinules on outer margin. Coxal spiniform seta long, strong, spinulated. Basis with one row of hair-like elements on inner margin; outer margin with cluster of spinules close to insertion of basipodal seta. Endopod as long as exopod.

Leg 3 ( Figure 2C ). Coupler with two rows of spinules on middle anterior surface, one tight row of long spinules and one of short spinules; distal margin with row of hairlike elements. Coxa with two groups of spinules, one row on outer margin and short, diagonal row of long spinules close to proximal outer corner; strong spiniform, spinulated coxal seta. Basis with row of hair-like elements on inner margin; outer margin with basipodal seta, group of four spinules on insertion of basipodal seta. Endopod slightly longer than exopod.

Leg 4 ( Figure 3A ). Coupler with three rows of small spinules, two on middle anterior surface and one on distal margin. Coxa with row of spinules on outer margin and strong, relatively short coxal spinulated seta on inner margin. Basis with row of four spinules on outer margin close to insertion of basipodal seta. Exopod slightly longer than endopod. Outer and inner terminal endopodal spines serrate. Outer spine reaching about half the length of inner spine. Length ratio of outer/inner terminal spines of Enp 3 = 0.52. Length: width ratio Enp 3 = 1.73.

Leg 5 ( Figure 3C ). Leg consisting of one free subquadrate segment, bearing one strong inner bilaterally serrate spine, one slender seta and one biserially setulated

outer seta. Outer seta slightly longer than inner spine. Row of three to four spinules at insertion of inner spine.

Urosome ( Figure 3C ). Consisting of fifth pediger, genital-double somite plus three free somites. Posterior margins of genital double somite and succeeding urosomites crenulated both dorsally and ventrally; relative ratio of each urosomite as: 17.7: 36.7: 14.4: 16.7: 14.5 = 100. Anterior half of genital double-somite not expanded laterally; somite ornamented on ventral surface with short rows of spiniform cuticular projections on distal half. First and second postgenital somites with two ventral rows of spinules on ventral surface and three on dorsal surface. Anal somite with distal row of strong spinules close to the insertion of caudal rami. Anal operculum with longitudinal row of small spinules on each side.

Caudal rami ( Figure 3C,D ). Rami representing 34% of urosome length. Length: width ratio = 3.8. Inner margin weakly hairy. Row of transversal spinules near insertion of lateral setae. Cluster of strong spinules at base of lateral spiniform seta and near base of outer terminal seta. Ramus armed with six setae. Lateral seta short, 0.5 times as long as caudal ramus, inserted at about 70% of outer margin of ramus. Dorsal seta short, 0.35 times as long as caudal ramus. Inner terminal seta 0.64 times as long as caudal ramus, longer than dorsal seta.

Description – adult male

Antennule ( Figure 4A–C ). Geniculate, 11-segmented, armature per segment as follows (s, seta; ae, aesthetasc): 1(12s), 2(2s), 3(5s), 4(5s+ae), 5(0), 6(1s), 7(1s), 8(3s), 9(2s), 10(1s), 11(5s+ae). First segment with one modified seta, dorsal surface of same segment with two rows of spinules.

Antenna. As in female except for relatively longer coxobasis.

Mandible. As in female, except for larger cluster of spinules near palp.

Maxillule. As in female.

Maxilla. As in female.

Maxilliped. As in female except for additional row of spinules on outer surface of syncoxa.

Legs 1–4. Biramous, all endopodal and exopodal rami three-segmented, ramal armature as in female.

Leg 1 ( Figure 4D,E ). As in female except for looser arrangement of row of spinules on middle surface of coxa.

Leg 2 ( Figure 4F,G ). As in female except for additional row of spinules along distal margin of coxa.

Leg 3 ( Figure 5A ). As in female except for longer hair-like elements on distal margin of coupler and distal row of short spinules on coxa.

Leg 4 ( Figure 5B ). As in female except for weaker ornamentation of coupler.

Leg 5 ( Figure 5D ). As in female. Leg 6 ( Figure 5D ). Small, low plate at distal corner of genital somite with one long, strong spine, one short middle seta and one outer seta as long as inner spine. Row of strong spinules at insertion of leg.

Urosome ( Figure 5C,D ). Genital somite subrectangular, length: width ratio = 0.71. Posterior margins of genital somite and succeeding three urosomites crenulated both dorsally and ventrally. Genital somite ornamented on dorsal surface, with rows of spiniform cuticular projections. Postgenital urosomites with ventral and dorsal rows of spiniform projections. Anal somite with patch of short hair-like elements on ventral and dorsal surfaces; anal operculum with row of small spinules at each side. Row of spinules close to insertion of caudal rami.

Caudal rami ( Figure 5C,D ). Rami representing 24% the length of urosome. Length: width ratio = 2.3. Inner margin, dorsal and ventral surfaces hirsute. Row of transverse spinules close to insertion of lateral setae. Cluster of strong spinules at base of lateral spiniform seta and near base of outer terminal seta. Lateral terminal spiniform seta short, 0.34 times as long as caudal ramus, inserted at about three-quarters of the outer margin of ramus. Dorsal seta 0.72 times as long as caudal ramus. Inner terminal seta 0.87 times as long as caudal ramus; seta longer than dorsal seta.

Type locality

La Chica Dam (22°22′19.63′′ N, 102°18′46.69′′ W), Cosío Municipality , Aguascalientes, central Mexico. This is a small reservoir (surface ca. 26,000 m 2) in a high-altitude (2021 m) semi-desert area with scarce vegetation .

Etymology

The specific name is the Latin adjective hirsutus meaning hairy; it makes reference to the unique condition of the caudal rami of the male, completely covered with pilosity.

Remarks

These specimens were included in the genus Paracyclops for having the diagnostic characters described by Karaytug (1999) including the presence of a fringe of long setules along the posterolateral margin of the fifth pedigerous somite, caudal rami with transverse rows of spinules on the dorsal surface at base of lateral seta, female antennules with eight segments, antennae with exopodal seta, fifth legs with one strong inner spine and two setae, first segment of male antennules with one modified seta.

Following the comprehensive key of the known species of Paracyclops (Karaytug 1999) , both our female and male specimens key down to Paracyclops carectum because this shares several characters with the new species. In the female these characters include the presence of eight antennular segments, the structure and armature of legs 1–4 and fifth legs, but mainly by the caudal rami bearing ornamented inner margins.

The female of the new species has an ornamentation pattern of the caudal rami that clearly diverges from that known in P. carectum ( Reid 1987; Karaytug and Boxshall 1998b); it has sparsely arranged long setules along the inner margin of the caudal rami and the dorsal and ventral surfaces are naked. The ornamentation of P. carectum has a denser, uniform pattern on the inner margin of rami and also scattered clusters of short spinules on the dorsal surface (see Karaytug and Boxshall 1998b), which are absent in the new species. The innermost terminal caudal seta is clearly shorter in female P. carectum (0.55 times as long as ramus) than in the new species (0.8). The outermost caudal seta is a stout spiniform element armed with an inner row of setules whereas it is a slender, naked seta in the new species. Furthermore, in P. carectum this seta is 0.67 times as long as ramus compared with 0.60 in the new species.

Other differences of the females of P. carectum with respect to the new species include a more compact body and a shorter cephalothorax, almost equally wide as it is long length: width ratio = 1.1 (see Reid 1987); in the new species the cephalothorax is narrower, 1.7 times longer than wide. Both species have a different ornamentation pattern on the dorsal and ventral surfaces of the genital and postgenital somites; the surface of these somites is naked in P. carectum (see Karaytug 1999), whereas it has rows of spinules in the new species. Additional differences in the females of these species include relatively longer caudal rami (length: width ratio = 3.2 in P. carectum compared with 4.1 in P. hirsutus sp. nov.). The legs 1–4 show some additional differences; based on the illustrations by Reid (1987), the ornamentation of all couplers diverges; patterns are weaker in P. carectum . Also, the exopodal spines of legs 2–4 are clearly shorter than in the new species (see Reid 1987, figs 10–12). The length ratio of outer: inner terminal spine of leg 4 endopod is different: 0.37 in P. carectum versus 0.52 in the new species. The new species has a weak distal spinulation of the fifth leg, whereas P. carectum has strong, wide-based spinules near the insertion of the fifth leg setae.

In the new species the ornamentation of the caudal rami is much stronger in the male than in the female, whereas the pattern is similar in males and females of P. carectum . Males of P. hirsutus diverge from P. carectum by having the inner margin and the dorsal and ventral surfaces covered with short hair-like elements, whereas the male of P. carectum has only the inner margin ornamented differently with relatively strong spinules arranged in clusters, but the dorsal and ventral surfaces are otherwise naked. Further, in the new species the anal somite has an extended hairy field on both the dorsal and ventral surface, whereas, aside from the usual ornamentation, this somite is naked in P. carectum ( Karaytug and Boxshall 1998b; Karaytug 1999). Another species with ornamented caudal rami is P. pilosus ; the female of this species has four rows of two to four small spinules on the ventral surface, but the inner margin is naked ( Dussart 1984); the male lacks even this weak ornamentation. As described by Reid (1987) and Karaytug (1999), the caudal rami of the male P. carectum is shorter than in the female (length: width ratio = 3.2 in the female compared with 2.1 in the male); the same pattern is true in the new species (4.1 in the female, 2.25 in the male). Hence, these proportions are additional differences between these two species.

The sixth leg of the male P. carectum is different from that of P. hirsutus sp. nov. In the former species the spiniform seta is longer, reaching well beyond the distal margin of the first postgenital somite, whereas it does not reach this margin in the new species ( Figure 5D ). The spinules at the insertion of the sixth legs are arranged differently and are smaller in the new species (see Reid 1987; Karaytug and Boxshall 1998b; Karaytug 1999). The antennules have the same general segmentation pattern of male Paracyclops (see Karaytug and Boxshall 1999).

Paracyclops hirsutus sp. nov. can be distinguished from the other known neotropical species ( Paracyclops andinus Kiefer, 1957 , P. pilosus Dussart, 1984 , P. carectum Reid, 1987 , P. novenarius Reid, 1987 , P. hardingi Karaytug and Boxshall, 1998b , P. reidae Karaytug and Boxshall, 1998b , P. bromeliacola Karaytug and Boxshall, 1998b , P. punctatus Karaytug and Boxshall, 1998b , P. rochai Karaytug and Boxshall, 1998b ) by the peculiar ornamentation on the caudal rami and the anal somite. Another relevant distinguishing character is the presence of a mid-distal row of long spinules arranged midway along the coxa of leg 1 both in males and females ( Figures 2A , 4E ). This character is present only in P. imminutus Kiefer, 1929 (Karaytug 1999) , but the row is shorter in the new species.

Additional distinguishing characters include the outer seta of the fifth leg; in P. hirsutus sp. nov. it is slightly longer than the inner spine, this proportion is shared with P. hardingi and P. carectum and differs from P. reidae , P. bromeliacola and P. punctatus , in which the length ratio of these elements is close to 1.3; differences are greater in the remaining species: P. rochai (1.45), P. pilosus (1.7) and P. novenarius (2.8).

Further differences include the length: width ratio of the caudal ramus of the male; in the new species it is 2.25. This proportion differs from P. punctatus (2.7), P. pilosus , P. novenarius and P. rochai (2.5), P. carectum and P. reidae (both with 2.1), P. bromeliacola (2.0) and P. hardingi (1.9). In the male of P. hirsutus sp. nov. the length ratio of the medialmost terminal caudal setae: caudal ramus is 0.87, similar to this ratio in P. rochai (0.84), but different from the ratios in P. pilosus (0.66), P. carectum (0.63), P. andinus (1.26), P. novenarius (1.0), P. hardingi (1.2), P. reidae (1.45), P. bromeliacola (1.08) and P. punctatus (1.1).

The male of the new species shares with all its neotropical congeners the presence of one modified seta on the first antennular segment of the antennules (Karaytug 1999). But the number of segments of the male antennule in P. hirsutus sp. nov. differs from P. bromeliacola and P. hardingui (both with 14 segments) and P. novenarius with 12 segments; only P. carectum shares an 11-segmented antennule with the new species. The spine formula in P. hirsutus sp. nov. is 3443 as in its neotropical congeners, except P. novenarius (3433) ( Reid 1987; Karaytug 1999). The length ratio of outer: inner spine of third segment of leg 4 is 0.53 in the new species; which is similar to that of P. rochai (0.54) and P. hardingi (0.50) and differs from those of P. reidae (0.61), P. andinus (0.41), P. pilosus (0.42), P. bromeliacola (0.44), P. novenarius (0.40) and P. carectum (0.37).

The new species seems to be most closely related to P. carectum , but has affinities with the neotropical P. rochai , P. bromeliacola and P. punctatus by the lack of a distal row of spinules from the coxa of legs 2 and 3 and the absence of spinules at the base of the two inner setae on the antennal coxobasis. Furthermore, females of all these species have eight-segmented antennules, whereas the known Nearctic forms have 11 ( P. yeatmani , P. affinis , P. canadensis ) or 12-segmented ( P. smileyi ) antennules (Karaytug 1999).

Figures

Figure 1. Paracyclops hirsutus sp. nov., holotype female from Aguascalientes, Mexico. (A) Antennule; (B) coxobasis of antenna; (C) mandible; (D) maxillule; (E) maxilla; (F) maxilliped. Scale bars: A, 50 µm; B–F, 25 µm.

Figure 2. Paracyclops hirsutus sp. nov., holotype female from Aguascalientes, Mexico. (A) Leg 1; (B) leg 2; (C) leg 3 with separated endopod and exopod. Scale bars A–C, 50 µm.

Figure 3. Paracyclops hirsutus sp. nov., holotype female from Aguascalientes, Mexico. (A) Leg 4 with separated exopod; (B) habitus, dorsal view; (C) urosome showing fifth legs, ventral view; (D) caudal rami, dorsal view. Scale bars: A, D, E, 50 µm; C, 100 µm;

Figure 4. Paracyclops hirsutus sp. nov., allotype male from Aguascalientes, Mexico. (A) Antennule, anterior view; (B) same, posterior view; (C) same, distal segments; (D) leg 1 with separated endopod; (E) coupler of leg 1; (F) coupler, coxa and basis of leg 2; (G) exopod of leg 4. Scale bars: A, B, 100 µm; C–G, 50 µm.

Figure 5. Paracyclops hirsutus sp. nov., allotype male from Aguascalientes, Mexico. (A) Leg 3 with separated endopod; (B) leg 4 with separated endopod and coupler; (C) urosome, dorsal view; (D) same, ventral view. Scale bars: A, B, 50 µm; C, D, 100 µm.