Redescription of the poorly known planktonic copepod Pontellopsis lubbockii (Giesbrecht, 1889) (Pontellidae) from the Eastern Tropical Pacific with a key to species

Abstract During a survey of the epipelagic zooplankton carried out off the coast of the Mexican states of Jalisco and Colima, in the Eastern Tropical Pacific, female and male specimens of the poorly known calanoid copepod Pontellopsis lubbockii (Giesbrecht, 1889) were collected. Because previous descriptions and illustrations are largely incomplete and have caused some taxonomical confusion, this species is fully redescribed from specimens from the Mexican Pacific. The species has some characters that have been overlooked, but those related to the female genital double-somite are the most striking, it has two conical dorsal protuberances and a long ventral spiniform process unique of this species. The mouthparts of this species have not been hitherto described and figured, the flexible terminal setae of legs 3 and 4 is noteworthy. The male general morphology agrees in general with previous data, but new details of the leg 5 and geniculate antennule are added. Its mouthparts, with strong, serrate setae on the maxillae and maxillules, and a strong mandibular edge, suggest that this is a predator form. A dichotomous key for the identification of males and females of the species of Pontellopsis known from the Eastern Tropical Pacific is included.


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The genus Pontellopsis Brady, 1883 currently contains up to 33 species (Boxshall and Halsey 2004;Razouls et al. 2012;Walter and Boxshall 2012). As other members of the family Pontellidae, species of Pontellopsis are usually recorded in surface waters (0-10 m) of tropical and warm temperate latitudes (Othman and Toda 2006). In general, pontellids are regarded as good indicators of water masses (Sherman 1963(Sherman , 1964Matsuo and Marumo 1982;Hernández-Trujillo 1989). Because of their morphological complexity and variability (Fleminger 1956(Fleminger , 1967b(Fleminger , 1975Silas and Pillai 1973), their taxonomy is still in flux, partly caused by incomplete descriptions that have raised taxonomic confusion in different regions (Pillai 1977;Jeong et al. 2009). Therefore, in some instances, it is necessary to revise and redescribe species following upgraded modern standards in order to facilitate the identification of these species and related forms (Mulyadi 2002;El-Sherbiny and Ueda 2008). One of these poorly defined pontellid species is P. lubbockii (Giesbrecht, 1889), whose original description and subsequent illustrations by Giesbrecht (1893) Wilson (1950), and Pillai (1977) are limited and lacking in detail. Several important characters of this species have been omitted, not only details of the taxonomically relevant characters, but of the mouthparts and legs 1-4, which still remain undescribed. Besides the occurrence of this species at the type locality off Columbia (Giesbrecht 1889), Wilson (1950) reported this species from the Eastern Pacific; the identity of some of Wilson's specimens were revised by Pillai (1977), who noticed some inconsistencies both in its identification and in the records related to this species. Wilson (1950) identified and labeled female pontellids from the off Sri Lanka, in the South Pacific as P. lubbockii but Pillai (1977) noticed that these were in fact specimens of P. krämeri (Giesbrecht, 1896); in the same sample he found also copepodites of Pontella sp. and of Labidocera acuta (Dana, 1849).
Pontellopsis lubbockii has been relatively rarely taken and is known as a neritic equatorial species endemic to the Gulf of California and adjacent areas of the Eastern Tropical Pacific (ETP) (Brinton et al. 1986, Suárez-Morales andGasca 1998) and extending to Ecuador (Pillai 1977). Overall, the pontellid copepod fauna of the area south of the influence of the California Current and off the Mexican and Central American coasts of the Pacific is still poorly known. Previous regional surveys by Alameda-De la Mora (1980), Álvarez-Cadena (1985, Suárez-Morales and Gasca (1989), Morales-Ramírez (2001), Fernández-Álamo et al. (2000, Álvarez-Silva et al. (2003), and Morales-Ramírez and Suárez-Morales (2009) include only one species of Pontellopsis in this area of the ETP and P. lubbockii was not recorded. In some instances this could be a result of misidentifications or the rarity of the species. In this work we report and redescribe this poorly known pontellid based on female and male specimens collected during a series of zooplankton surveys carried out off the central Mexican Pacific coast. We also provide comments on the morphology of the mouthparts and a key for the identification of the males and females of the species of Pontellopsis recorded in this region.
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.
Leg 5 (Figs 5B-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 P. 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 P. inflatodigitata Chen & Shen, 1974, P. laminata Wilson, 1950 herdmani Thompson & Scott, 1903, P. scotti Sewell, 1932, P. macronyx Scott, 1909, and P. yamadae Mori, 1937. Only one such dorsal process is illustrated in previous illustrations of P. 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 P. albatrossi Wilson, 1950. When two dorsal processes are present, they are differently built; in P. 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 P. herdmani, there are two thornlike projections on the left side (Thompson and Scott 1903); P. lubbockii also differs from P. 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 P. 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 P. lubbockii. The structure of the female genital double-somite of P. yamadae is probably the most similar to that of P. lubbockii and  Mori (1937), Chen & Zheng (1965), Mulyadi (2002), andPalomares-García et al. (1998). 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 P. yamadae and long, spiniform in P. lubbockii. The structure of the female leg 5 is also different in both species, with a much shorter and more robust outer ramus in P. yamadae (see Mori 1937).
The extremely long spiniform ventral process present in the genital double-somite of P. 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 P. albatrossi, P. armata, and P. villosa (Brady 1883) it is a short, curved spine arising from the genital field (Zheng et al. 1982). Yet another interesting character of P. 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).

Distribution of Pontellopsis in the Eastern Tropical Pacific
In the Eastern Pacific, particularly in the California Current region, only a few species of Pontellopsis have been recorded: Pontellopsis occidentalis Esterly, 1906, P. regalis (Dana, 1849), and P. lubbockii. Pontellopsis occidentalis is regarded as endemic of southern California, the Gulf of California, and Baja California area. Pontellopsis regalis is frequently found in waters of the ETP (Fleminger 1967a;Brinton et al. 1986;Hernández-Trujillo 1989, 1994. Additional records of the genus are found south of the California Current region, off the southern sector of Baja California and the Mexican Pacific: P. armata (Giesbrecht, 1889), P. tenuicauda (Giesbrecht, 1889), P. brevis (Giesbrecht, 1889), P. perspicax (Dana, 1849, and P. yamadae Mori, 1937(Hernández-Trujillo 1989, 1994Suárez-Morales and Gasca 1998;Palomares-García et al. 1998;Hernández-Trujillo et al. 2004). So far, only 8 out of the 33 known species of the genus have been recorded in the Eastern Tropical Pacific. The genus is clearly more diverse in the Indo-West Pacific, a region harboring many endemic or presumably endemic forms as a result of the geological history and biogeographic processes related to that geologically complex area (Fleminger 1986).

1A
Posterolateral corners of fifth pedigerous somite with terminally rounded processes (Figs 6A, E)  Genital double-somite with strong, thumb-like process on left margin. Anal somite half the length of genital double-somite (Fig. 6D)  Both lateral margins of genital double-somite expanded forming nearly symmetrical rounded processes, that on the right side globular; anal somite strongly produced between caudal rami (Fig. 6B)  Genital double-somite with asymmetrical, rounded lateral processes, anal somite not strongly produced between caudal rami (Fig. 6F) ......... P. regalis

1A
Posterolateral corners of fifth pedigerous somite with symmetrical or nearly symmetrical processes (Fig. 6G)  Posterolateral corners of fifth pedigerous somite with strongly asymmetrical processes, with long, slender, curved process on the right side (Fig. 6H) .....3 2A Second urosomite with small lateral process on the left margin; second exopodal segment of left leg 5 cylindrical, as long as preceding segment (Fig. 6O Second urosomite without such process on left margin; second exopodal segment of left leg 5 globose, half as long as preceding segment (Fig. 6P), process on first exopodal segment of right leg 5 short, distally acute ............P. villosa 3A Left posterolateral corner of fifth pedigerous somite forming short terminally rounded or broadly subtriangular process, not acute (Fig. 6I)  Left posterolateral corner of fifth pedigerous somite forming relatively long acute process (Fig. 6H)  Second and third urosomites with weak lateral expansions (Fig. 6I), process on first exopodal segment of right leg 5 long, distally truncate (arrow in Fig. 6L)  Right posterolateral corner of fifth pedigerous somite long, acute, tapering distally (Fig. 6I); caudal rami as long as wide, distal segment of chela with protuberance on medial position of inner margin (arrow Fig. 6K) .............P. regalis 6B Right posterolateral corner of fifth pedigerous somite long, slender from insertion, branch-like (Fig. 6H); caudal rami twice as long as wide, distal segment of chela with low proximal expansion on inner margin ........ P. armata 7A Second and third urosomites expanded laterally, process on first exopodal segment of right leg 5 shorter than second exopodal segment (Fig. 6N)  Only third urosomite expanded laterally. Right leg 5 with finger-like process of first exopodal segment longer than second exopodal segment (Fig. 6M)  tera Sur (ECOSUR), Chetumal, Mexico. The comments and valuable suggestions of two referees allowed us to improve a previous version of this contribution, particularly in reference to the interpretation and description of morphological details of the mouthparts. The fine editorial work and processing of the manuscript by Danielle Defaye is deeply appreciated.