Monops lubbockii Giesbrecht, 1899

Suarez-Morales, Eduardo & Kozak, Eva, 2012, Redescription of the poorly known planktonic copepod Pontellopsis lubbockii (Giesbrecht, 1889) (Pontellidae) from the Eastern Tropical Pacific with a key to species, ZooKeys 234, pp. 1-18 : 2-8

Monops lubbockii Giesbrecht, 1899 Figs 15

Type locality.

Eastern Tropical Pacific (3-6°N, 80-82° W), about 400 km west of the coasts of Colombia and 320 km south of the Panama coast.

Material examined.

Two adult females from the central Pacific of Mexico, 14 December 2010, 19.171°N, 104.912°W, coll. E. Kozak and C. Franco-Gordo, specimens undissected, vial deposited at El Colegio de la Frontera Sur, Chetumal, Mexico (ECO-CHZ-08957). One adult male, same date, site, and collector; specimen dissected, semi-permanent slides sealed with Entellan® (ECO-CHZ-08958). One adult male, 25 October, 2011, same site and collector; specimen dissected in slides sealed with Entellan® (ECO-CHZ-08959). One adult female, 24 October, 2011, 19.171°N, 104.912°W, coll. C. Franco-Gordo; specimen undissected, ethanol-preserved, vial (ECO-CHZ-08960). One adult male, 25 September, 1997, 19.033°N, 104.674°W, coll. C. Franco-Gordo; specimens undissected, ethanol-preserved, vial deposited in ECOSUR (ECO-CHZ-08961). One adult female from Californian coast, 7 October, 1904, 30.67°N, 119.59°W, Albatross cruise, Eastern Pacific Expedition, ethanol-preserved, identified by A. Fleminger (USNM-109384). One adult female from off Ecuador, South Pacific Ocean, 8 November, 1928, 01.531°N, 82.273°W, Carnegie Institution of Washington, ethanol-preserved (USNM-80382), previously examined by P. Pillai.

Female.

Body length of females range between: 2.09 and 2.17 mm (average 2.13 mm, n=5), measured from anterior cephalosome to posterior border of anal somite. Cephalosome robust, widest at level of fully separated first pedigerous somite. Pedigerous somites 4 and 5 fused; posterior corners of fifth pedigerous somite strongly developed, forming large spine-like processes (Fig. 1A, B). Processes straight, posteriorly directed, reaching about halfway along urosome. Cephalosome with rounded forehead, dorsal lenses absent. Rostrum bifid, with long, slender rostral filaments, gap between rostral rami wide (Fig. 1H), in lateral view reaching halfway of second antennular segment (Fig. 1G). Urosome with two segments: genital double somite and anal somite. Genital double-somite representing about 55% of urosome length, excluding caudal rami; somite strongly asymmetrical, with pair of dorsal protuberances arising from distal margin of somite (Fig. 1C, D). In dorsal view, right protuberance subtriangular, curved, posteriorly directed, reaching about half way along anal somite. Left process smaller, also posteriorly directed rounded tapering distally into strongly chitinized bulb-like process (Fig. 1C). Proximal margin of somite bearing lateral spine-like process on each margin, slightly asymmetrical, right one being longer. Ventral surface of genital double somite swollen, with sickle-shaped process arising anterior to genital operculum, posteriorly directed (Fig. 1D, E, F). Anal somite subrectangular, about 1.5 times wider than long, with rounded distomedial process between insertion points of caudal rami. Dorsal surface of anal somite swollen in lateral view, ornamented with rows of minute spinules. Caudal rami weakly asymmetrical, left ramus slightly larger than right, both rami bearing 6 setae: 1 inner, 3 terminal, 1 outer setae plus short, slender dorsal seta.

Antennules (Fig. 2A) symmetrical, 16-segmented. Segments armed as follows (Arabic numbers= setae; Roman numerals= spines, aes=aesthetascs): 1 (I-III) (1), 2 (IV-VII) (9+aes), 3 (VIII-X) (6,I+aes), 4 (XI-XIII) (4,II+3aes), 5 (XIV) (1,I+aes), 6 (XV-XVI) (4,I+ 2aes), 7(XVII) (1+aes), 8(XVIII) (1+aes), 9 (XIX) (1+aes), 10 (XX) (1+aes), 11 (XXI) (1+aes), 12 (XXII) (1), 13 (XXIII) (1), 14 (XXIV) (1,I), 15 (XXV) (2+aes), 16 (XXVI-XXVIII) (4+aes). Larger and longer setae on segments 2, 4, 7, 8, and 13. Modified, wide-based heavily setulated seta proximally inserted on segment 6; same segment with distally blunt, strongly chitinized spine reaching about 2/3 of way along succeeding segment 7 (Fig. 2A).

Antenna (Fig. 2B) biramous: coxa with short plumose distal seta. Basis and first endopodal segment separated, basis bearing 2 setae, one short, one long. First endopodal segment elongate, armed with two small subdistal setae. Second endopodal segment with 9 and 7 setae on proximal and distal lobes, respectively; distal lobe armed with basal outer row of spinules; exopod 6-segmented, setation formula 1, 2, 1, 1, 1,2.

Mandible (Figs 2 C–E) with wide, heavily chitinized gnathobase; mandibular palp biramous, basipod robust, subrectangular, armed with inner basipodal seta. Endopod 2-segmented, first segment armed with 3 long and one short setae; second segment with 6 terminal setae. Exopod 5-segmented, setal formula as: 1, 1,1,1,2. Mandibular distal edge bearing 7 teeth: from ventral margin dentition includes one apical (a), one subapical (sa), two compound medial (med), and three basal (bas) (see Fig. 2C); medial teeth with rounded edges. Clusters of long and short spinules on base of medial teeth; dorsal end of gnathobase with tight row of setae.

Maxillule (Fig. 3A) typical of pontellids, praecoxal arthrite with 14 setal elements; coxal endite (cx end) with 3 long, robust spine-like elements on endite and 9 setae on epipodite (epi); basis with 3 and 1 setae on proximal (bend1) and distal (bend2) endites, respectively; 1st and 2nd endopod segments, each with 2 setae, incorporated into basis, distal endopod segment with 5 apical setae; exopod with 8 setae.

Maxilla (Fig. 2F) uniramous, first praecoxal endite bearing 4 setae, second with 3 setae (one of them shorter and thinner than the others); two coxal endites each bearing 3 setae. Basis with 2 setae; endopod 4-segmented, setal formula of endopod as: 2, 2, 1, 1. Basal and endopodal setae strongly serrate.

Maxilliped (Fig. 3B) uniramous, with praecoxa and coxa fused, three syncoxal endites well developed, with setal formula 2, 2, 3; endites setae strong, serrate. Inner lateral margin of third endite with rows of short setae. Basis fringed with medial row of 5-6 spinules and 2 distal setae. Endopod 4-segmented, setal formula of endopod as: 2, 1, 1, 2.

Leg 1 with 3-segmented endopod; legs 2-4 with 2-segmented endopods and 3-segmented exopods (Figs 3C-F). Coxae with plumose inner seta; basis of leg 4 with slender outer seta, medial patch of spinules on medial anterior margin of legs 3 and 4. First endopodal segment of second leg with inner rounded protuberance (arrowed in Fig. 3D). In one specimen examined, terminal exopodal spine of legs 3 and 4 modified, represented by flexible seta (Italized in setal formula) (Fig. 3G, H). Seta and spine formula (Arabic numbers=setae, Roman numerals=spines) of legs 1-4 as:

Coxa Basis Exopod Endopod

Leg 1 0-1 0-0 I-1;I-1;II,I,4 0-1;0-2;1,2,3

Leg 2 0-1 0-0 I-1; I-1;III,I,5 0-3; 2,2,4

Leg 3 0-1 0-0 I-1; I-1; III,1,5 0-3; 2,2,4

Leg 4 0-1 1-0 I-1; I-1;III,1,5 0-3; 2,2,3

Leg 5 (Fig. 1I, J) biramous, slightly asymmetrical; coxa and intercoxal sclerite fused. Basis subrectangular, naked. Endopod distally bifurcate, about 0.3 times as long as exopodal ramus. Exopod of both legs 1-segmented, elongate, right leg with 3 outer spiniform processes and a large distal inner process; left leg smooth except for two subdistal outer spine-like setae.

Male.

Body (Fig. 4A) robust, slightly smaller than female (1.85-2.07 mm, average: 1.98 mm, n=4). Cephalosome about 3.5 times as long as urosome (caudal rami excluded), dorsal surface of cephalosome pilose, particularly pedigerous somites 1-5. Fifth pedigerous somite with asymmetrical lateral expansions, left process spiniform, reaching posterior margin of first urosomite; right side with long curved, ventromedially directed process with small, distally curved rounded process (Fig. 4B). Urosome (Fig. 4A-C) with 5 somites. Genital double-somite strongly asymmetrical, left side with 2 sensilla on outer distal corner; right side expanded forming rounded process armed with two unequal setae (Fig. 4C). Second urosomite with pair of sensillae on right side; third urosomite as long as succeeding somite, with strong laterally-directed rod-like process on right margin, process armed with anterodistal curved row of teeth-like spinules, a short seta, and terminal rows of spinules (Fig. 4D). Anal somite symmetrical, as long as preceding somite. Caudal rami slightly asymmetrical, approximately twice as long as wide.

Right antennule (Fig. 4 E–G) with 12 segments geniculate between segments 10-11, reaching middle of third pedigerous somite. Antennular segments armed as follows (Arabic numbers= setae; Roman numerals= spines, aes=aesthetascs): 1 (I-III) (1), 2 (IV-VII) (8+2aes), 3 (VIII-X) (2), 4 (?) (2), 5 (?) (2+aes), 6 (X-XIV) (5+ 2aes), 7 (XV-XVI) (4+aes), 8 (XVII) (2,I+aes), 9 (XVIII-XIX) (3+aes), 10 (XX) (1), 11(XXI-XXIII) (1,II), 12 (XXIV-XXVIII) (8+aes). Spine on segment 8 long, slightly curved; segments 9 and 10 with coarse double row of acuminate sharp teeth (Fig. 4F). Segment 11 with proximal process forming fan-like row of strong spines plus two usual stout spines adjacent to segmental margin (Fig. 4G). Anterior margin of segments 10 and 11 with usual spiniform processes parallel to segmental margin. Left antennule as in female except for shorter spiniform process on segment 6 which is also relatively shorter than in female (Fig. 5A).

Leg 5 (Figs 5 B–E) asymmetrical, typical of pontellids. Left leg 5 short; coxa quadrate, basipod (bp) robust, cylindrical, naked. Exopod 3-segmented, segments 2-3 partly fused; first segment cylindrical, with subtriangular process on outer distal margin. Second exopodal segment (Fig. 5E) with medial surface covered by patch of long hair-like setae, segment with inner rounded expansion and subdistal seta on outer lateral margin; third segment with 2 unequal spines plus inner spiniform process. Right leg 5 basis with 2 unequal setae. Exopod with two segments, forming robust, widely open chela; first segment (exp1) forming thumb of chela ending in short, strong process curving inward with inner surface armed with shallow cuticular ridges and small spinules (Fig. 5C). Second exopodal segment forming distal elongate finger, tapering distally, armed with two subequal proximal setae on outer surface plus one proximal and one distal setae inserted on inner surface of segment (Fig. 5D).

Remarks.

Our specimens from the Mexican Pacific were identified as Pontellopsis lubbockii by the females having acute, symmetrical posterolateral corners of the fifth pedigerous somite plus an asymmetrical genital double-somite as long as the anal somite and with two dorsal protuberances. Males have a long, curved process on the right side of the fifth pedigerous somite, a laterally directed process on the third urosomite combined with a pair of long stout setae on the right margin of the genital double somite. Females of this species are easily distinguishable from its congeners by the structure and details of the genital double somite. It is unique in having two conical dorsal processes and also a ventral spine arising from the genital field. One of these processes might have been overlooked in previous descriptions ( Giesbrecht 1889; Pillai 1977) but its presence was confirmed in museum specimens from California (USNM-109384) and off Ecuador (USNM-80382). There are other species of Pontellopsis bearing dorsal processes, like Pontellopsis inflatodigitata Chen & Shen, 1974, Pontellopsis laminata Wilson, 1950, Pontellopsis herdmani Thompson & Scott, 1903, Pontellopsis scotti Sewell, 1932, Pontellopsis macronyx Scott, 1909, and Pontellopsis yamadae Mori, 1937. Only one such dorsal process is illustrated in previous illustrations of Pontellopsis lubbockii , appearing as a single, robust, mammiliform, dorsal process ( Giesbrecht 1893; Pillai 1977), but our redescription shows that there are two conspicuous processes; a similar pattern is present in Pontellopsis albatrossi Wilson, 1950. When two dorsal processes are present, they are differently built; in Pontellopsis laminata , the left process is very large, clearly spiniform, laterally projected, whereas the right one is reduced to a low protuberance (see Pillai 1977). In Pontellopsis herdmani , there are two thorn-like projections on the left side ( Thompson and Scott 1903); Pontellopsis lubbockii also differs from Pontellopsis scotti , which has a single spiniform dorsolateral process and an enlarged right proximal spine. Pontellopsis macronyx has a pair of dorsal spiniform processes, different from the robust, conical processes found in Pontellopsis lubbockii ( Scott 1909; Chen and Shen 1974). A different pattern, with a single globose lateral process tapering distally into a spine was depicted for the same nominal species by Silas and Pillai (1973), but it also diverges from the pattern observed in Pontellopsis lubbockii . The structure of the female genital double-somite of Pontellopsis yamadae is probably the most similar to that of Pontellopsis lubbockii a nd in some cases both species may be confused, but the dorsal processes are quite distinct, digitiform, none of them reaching the dorsal margin of the somite ( Mori 1937; Jeong et al. 2009). Both species also differ in the structure of the thoracic processes, short, rounded in Pontellopsis yamadae and long, spiniform in Pontellopsis lubbockii . The structure of the female leg 5 is also different in both species, with a much shorter and more robust outer ramus in Pontellopsis yamadae (see Mori 1937).

The extremely long spiniform ventral process present in the genital double-somite of Pontellopsis lubbockii , is a unique character of this species and has not been hitherto described in or illustrated in previous works ( Giesbrecht 1893; Pillai 1977). In only a few species of the genus a ventral process related to the genital field has been described: in Pontellopsis albatrossi , Pontellopsis armata , and Pontellopsis villosa ( Brady, 1883) it is a short, curved spine arising from the genital field ( Zheng et al. 1982). Yet another interesting character of Pontellopsis lubbockii is the modification of the distal spines of the third exopodal segment of legs 3 and 4, they are flexible elements, thus contrasting with the usual pattern of stout, spiniform terminal setae. The data available to us from various descriptions suggest that this is a unique character among members of this genus.

The mandibular dentition found in our specimens agrees with the pattern described by Fleminger (1956) for this species and genus; dentition is quite uniform among species of Pontellopsis and its taxonomical value is weak. In addition, this species has the main characters described by Ohtsuka and Onbé (1991) as Type II specialized mouthparts for predation, with serrate maxillar setae, a relatively narrow mandibular edge armed with sharp, blade-like teeth, and clusters of setae and spinules near the base of the teeth. Overall, our analysis supports the notion that this species is a predator, as long known for other species of Pontellopsis ( Lillelund and Lasker 1971).