Pleuroxus scopuliferus Ekman, 1900

Dartnall, Herbert J. G. & Hollwedel, Werner, 2007, A limnological reconnaissance of the Falkland Islands; with particular reference to the waterfleas (Arthropoda: Anomopoda), Journal of Natural History 41 (21 - 24), pp. 1259-1300 : 1274-1276

Pleuroxus scopuliferus Ekman, 1900

This species, described from South America ( Ekman 1900), was only found on Pebble Island. Kotov and Gololobova (2005) found Ekman’s (1900) type material in the Swedish Museum of Natural History and selected the lectotype of P. scopuliferus . Thanks to Frey’s (1993) study on Pleuroxus from the subantarctic islands we could easily identify our juvenile and parthenogenetic female specimens.

Female: 0.6 mm, brown colour, valve with ridge, one denticle at the postero-ventral angle, rostrum longer than labrum, tip of rostrum rounded, anal and post-anal segments of post-abdomen equally long ( Figure 22 ), but both longer than pre-anal region, postabdominal claw stout with two basal spines, the longer one nearly as long as width of claw, shorter one half as long.

Copepoda : we found three calanoid, and three cyclopoid copepods. The calanoids include Parabroteas sarsi and two Boeckella spp. , B. michaelseni and B. poppei , which were familiar from earlier studies on South Georgia ( Dartnall 2005a) and the South Orkney Islands ( Heywood et al. 1979, 1980). Parabroteas sarsi is a powerful swimmer that can avoid plankton nets and is probably more widespread on the Falkland Islands than suggested here.

The specimens of Boeckella poppei , though ‘‘exceptionally variable so that one might suspect at least two species’’ are in fact conspecifics ( Hessen et al. 1989; G. Boxshall, personal communication) .

Two cyclopoid copepods were identified in the field. One of these, a stream-dwelling species from Fox Bay, thought to be Tropocyclops meriodionalis , is sometimes treated as a subspecies of T. prasinus (G. Boxshall, personal communication). The other cyclopoid was subsequently determined to be two species including a larger Acanthocyclops michaelseni and a smaller Diacyclops sp. possibly D. (Acanthocyclops) mirnyi (G. Boxshall, personal communication, who considers the original descriptions of both taxa inadequate and in need of revision).

Harpacticoida : a few small specimens were observed. These have been assigned to two (unidentified) Canthocamptidae one of which was also present at South Georgia (G. Boxshall, personal communication). Attheyella trigonura (Ekman) has been reported from the Falkland Islands ( Ekman 1905; Pugh et al. 2002).

Ostracoda: only one species, Newnhamia patagonica , a new record for the Falkland Islands, was observed.

Amphipoda : freshwater amphipods were regularly encountered and were present at every location except Mount Pleasant. According to Stock and Platvoet (1991) four species are known from the Falkland Islands. Both Falklandella obtusa Schellenberg and Praefalklandella cuspidata (Schellenberg) are eyeless, colourless species and may be emergent-subterranean species though the former has been found in Moody Brook ( Stock and Platvoet 1991). There are also two eyed species, Hyalella curvispina Shoemaker and Hyalella neomoma Stock and Platvoet. All specimens found in this survey were brown and eyed and thus ascribed to the genus Hyalella .

Hexapoda. Diptera : unidentified specimens of a larval midge ( Chironomidae ) were regularly encountered from all locations except Sea Lion Island. A second species was recognized in the field from three Fox Bay locations. Weller (1975) recorded four families in his survey of Falkland Island ponds, while Brooks et al. (2005) consider there to be at least 15 species present from 12 taxa, though none were identified to species. These include carnivorous genera Ablabesyia, Macropelopia , and Apsectrotanypus ; Parochlus , Podonomus , Podonomopsis , and Rheotanytarsus from cool water, the blood worms Chironomus , Phaenopsectra , and Parapsectrocladius , along with two Tanytarsini spp. and three Cricotopus .

Trichoptera : two types of caddis fly larvae were recognized in the field: (1) those that make their protective tubes from reeds and other detritus pieces, and (2) a smaller larva with a transparent flattened cone-shaped tube, open at both ends. The reed-cased specimens comprise two Magellomyia spp. , including M. appendiculata (Ulmer) , with a uniformly coloured head and a slightly curved tube, and Magellomyia stenoptera Schmid , which has a banded head and straight tube. This distinction was not known at the time of the collection when specimens were pooled. The transparent-cased caddis is an Oxyethira spp. probably O. bidentata Mosely though both O. andina Kelley and/or O. vipera Kelley , known from southern Chile and Argentina, are also potential contenders (I. Wallace, P. Barnard and O. S. Flint Jr, personal communication). No caddis larvae were found on either Sea Lion or Pebble Islands.

Coleoptera : two species of diving beetle were found, Lancetes falklandicus and a much smaller bidessine (G. Foster, personal communication). Both are powerful swimmers able to avoid slowly trawled plankton nets but were collected in hand nets and are probably more widespread than indicated.

Hemiptera: unidentified specimens of waterboatman were observed at both Pebble Island and Fox Bay. These powerful swimmers can avoid nets and are probably more widespread than indicated. These records represent the first report of waterboatmen from the Falkland Islands.

Chelicerata. Acarina : only two specimens were found, in the Felton Stream near Stanley and in a stream by the Hawk’s Nest Shanty pond. They have been identified as Soldanellonyx monardi Walter and Mucronothrus nasalis (Willmann) , both of which are ‘‘cosmopolitan’’ freshwater species (P. J. A. Pugh, personal communication).

Vertebrata

Two species of fish were found in this survey, the Falkland Island minnow Galaxias maculates (Jenyns) and the Falkland Island trout Aplochiton zebra Jenyns. Both are diadromous though landlocked populations are known ( McDowall et al. 2001). Neither was particularly common and solitary individuals were usually obtained in hand net sweeps but were noticeably absent from the very small water bodies around Stanley and from Sea Lion Island.

Figures

Figure 22. Pleuroxus scopuliferus, post-abdomen.