Pleuroxus hardingi, Smirnov & Kotov & Coronel, 2006

Smirnov, Nikolai N., Kotov, Alexey A. & Coronel, Jorge S., 2006, Partial revision of the aduncus-like species of Pleuroxus Baird, 1843 (Chydoridae, Cladocera) from the southern hemisphere with comments on subgeneric differentiation within the genus, Journal of Natural History 40 (27 - 28), pp. 1617-1639 : 1631-1635

publication ID	https://doi.org/ 10.1080/00222930600958870
persistent identifier	https://treatment.plazi.org/id/1A2F87C2-0A19-FF97-04D6-FC0F895BF9B8
treatment provided by	Carolina
scientific name	Pleuroxus hardingi
status	sp. nov.

Treatment

Pleuroxus hardingi View in CoL sp. nov.

( Figures 53–75 View Figures 47–55 View Figures 56–66 View Figures 67–75 )

Pleuroxus aduncus (Jurine) View in CoL in Harding 1955, p 348 –350, Figures 85, 86 (part); Uéno 1967, p 559 –561, Figures 37–40 View Figures 33–38 View Figures 39–46 .

Holotype: parthenogenetic female 0.55 mm long, in 95% alcohol, MGU Ml 57. Label of the holotype: ‘‘ Pleuroxus hardingi sp. nov., 1 parth. fem. from pools in the Cordillera del Tunari near the city of Cochabamba, Bolivia, HOLOTYPE’ ’. Paratypes: five parthenogenetic females from the same sample, MGU Ml 58.

Type locality

Pools of the bofedal system in the cordillera del Tunari (part of the Cordillera Oriental) near the city of Cochabamba, Cercado Province, Bolivia (4000–4400 m a.s.l., 17 u 109560S– 17 u 179190S, 66 u 079620–66 u 229990W). The type series was collected in February 2004 by J. S. Coronel, S. Declerck, and G. Crespo .

Short diagnosis

Body brown, not transparent, dorsum without a medial keel, postero-ventral angle without denticles. Rostrum not reaching apex of labral keel. Head shield with triangular-rounded posterior end, anteriorly makes a blunt rostrum, PP52.5–3 IP. Striation on head shield and valve ill-defined. Setae at posterior half of valve ventral margin situated submarginally. Setules on posterior margin of valve situated on inner face of valve submarginally, but projecting behind the valve edge. Postabdomen long, slightly narrowing distally, with rounded and slightly prominent dorso-distal angle, its anal and preanal portion roughly equal in length, shorter than postanal portion, anal teeth represented in adults as series of setules. Antenna I with a rudimentary basal peg, sensory seta arises from a low prominence on antennular body. On antenna II, one apical seta on each branch shorter than two other setae. On limb I smallest ODL seta thin and armed with long setules, two largest IDL setae subequal in size. On limb II, scrapers 1–3 with size decreasing basally; setules on gnathobase naked, filter plate II with eight setae. On exopodite III setae 1 and 3 unequal in length, filter plate III with eight setae. Filter plate IV with six setae. Limb V with seta 1 of exopodite short and three projections distal to it.

Description

Parthenogenetic female. Body brown, not transparent. In lateral view body widely oval, high (body height/body length50.72– 0.76 in adults), maximum height somewhat anteriorly to middle ( Figures 53 View Figures 47–55 , 56 View Figures 56–66 ). Dorsal margin evenly arched from tip of rostrum to postero-dorsal angle, which is well-defined, posterior margin almost straight, postero-ventral angle welldefined, without teeth, ventral margin prominent in anterior half. Obscure striation expressed only in antero-ventral and postero-ventral portions of valve, while entire valve punctuate, these dots smaller and sparsely located as in P. carolinae ( Figure 56 View Figures 56–66 ). In anterior view body subovoid, without traces of a keel.

Head with long rostrum, protruding downward and slightly posteriorly ( Figure 57 View Figures 56–66 ). Eye markedly smaller than ocellus, distance from tip of rostrum to ocellus greater than that between ocellus and eye. Head shield elongated, with maximum width anteriorly to mandibular articulation, its posteriormost extremity triangular-rounded ( Figure 58 View Figures 56–66 ). Two major head pores, PP52.5–3 IP. Lateral head pores minute. Medial labral keel large, with well-defined apex projecting significantly behind rostrum.

Valves large, with ventral margin armed with numerous setae of different size in its different regions, located exactly marginally in anterior half of the margin ( Figure 59 View Figures 56–66 ), and slightly submarginally in its posterior half ( Figures 60–62 View Figures 56–66 ). A row of fine, relatively long setules situated on inner side of posterior valve margin, close to the margin, their tips projected behind it ( Figures 55 View Figures 47–55 , 61–62 View Figures 56–66 ).

Postabdomen elongated, distinctly narrowing distally, its ventral margin slightly convex ( Figure 63 View Figures 56–66 ). Preanal margin slightly concave, as long as anal margin or somewhat shorter than the latter, preanal and postanal angles well-defined, postanal margin clearly longer than anal margin, dorso-distal angle distinct, slightly prominent distally, inflated basis of claws bordered from postanal margin by a shallow depression ( Figures 64, 65 View Figures 56–66 ). Each side of postanal portion provided with successive series of marginal setules, size of setules increasing distally in each series. Series of setules continues in anal margin, but the size of setules in each series subequal. Laterally to marginal setules, a row of fascicles consisting of short, fine setules. Postabdominal seta relatively short ( Figure 56 View Figures 56–66 ). Postabdominal claw as long as anal margin, massive, slightly curved, with setules along concave margin, and two basal spines, proximal one being less than half length of distal ( Figures 54 View Figures 47–55 , 64, 65 View Figures 56–66 ). In juveniles postabdomen ( Figure 66 View Figures 56–66 ) with more pronounced angles, with shorter postanal portion and thin, sole postanal teeth instead of groups of setules in adults.

Antenna I not reaching tip of rostrum ( Figure 57 View Figures 56–66 ), slightly narrowing distally, with a rudimentary basal peg ( Figures 67, 68 View Figures 67–75 ). Antennular sensory seta slender, longer than half the antennule, arising at one-third of antennular length from distal end on a small projection of the antennular body. Nine short aesthetascs of slightly differing size. Antenna II relatively short ( Figure 56 View Figures 56–66 ), similar to than of P. carolinae , but among endopod apical swimming setae, one seta shorter than two others, and chitinous insertions present within distal segments of all setae ( Figures 69, 70 View Figures 67–75 ).

Limbs very similar to those in P. wittsteini , but smaller seta on ODL of limb I thin and armed with long setules, IDL first seta especially small and thin ( Figure 71 View Figures 67–75 ); limb III with especially thick, bottle-shaped sensillae near setae 2 and 3 ( Figure 72 View Figures 67–75 ); limb IV with thin setules on setae 2–4 and rare setules on basal segment of seta 2 of gnathobase distal armature ( Figures 73, 74 View Figures 67–75 ); limb V with seta 1 of exopodite short and three projections distal to it ( Figure 75 View Figures 67–75 ), instead of two projections in other species.

Ephippial female, male

Unknown.

Size

Parthenogenetic females 0.33–0.55 mm in available material.

Etymology

The species is named after J. P. Harding who recorded it from South America (as P. aduncus ).

Distribution

It is known from the type locality (pools in the cordillera del Tunari ), and from Lagunillas Pond (near Lake Titicaca), both from high altitudes in Bolivian Andes .

Ecology

The pools where the type series was collected are small, shallow with a layer of organic matter about 20–25 cm thick. About 30% of the pool surface was covered with aquatic plants and the rest was uncovered except for some algal mats. The physical parameters from the type locality at the time of collection were as follows: depth 18 cm, temperature 22.0 u C, dissolved oxygen 8.4 mg l 21, pH 6.87. Other information in Coronel et al. (2005).

Comments

This taxon was first found by Harding (1955) and determined as P. aduncus (see Discussion). Then Uéno (1967) described specimens of brown colour, lacking denticles at the postero-ventral angle of the valve and with a peg on antenna I, apparently belonging to the same taxon. At the same time, quite typical P. aduncus was found in the Lake Titicaca region ( Harding 1955, Figures 87–90; Smirnov 1996, Figures 179–185).

As our key below does not deal with Australian and New Zealand species, i.e. those described by Frey (1991), it is necessary to report their differences from a new species for accurate confirmation of its independent status. Pleuroxus harding sp. nov. differs from P. helvenacus Frey, 1991 in having postanal teeth on the postabdomen represented as a series of small setules, and having no tubercles on the valves; from P. hastirostris Sars, 1903 , P. foveatus Frey, 1991 , and P. inermis Sars, 1896 in having no teeth on the postero-ventral angle of the valve (the latter pair also bear strong postanal teeth). In addition, antenna I in all Australian forms are supplied with a peg.

Key to species of the Pleuroxus aduncus group known from the southern