Ovalona weinecki Studer 1878

IX. Ovalona weinecki (Studer, 1878)

(Figs. 7A–B).

Studer, 1878: 108–109, pl. 3, fig. 3 (Alona); Ekman, 1905: 8–9 (Alona bukobensis var. subantarctica); Sars, 1909: 17–19, Pl.2, fig. 8–11 (Alona subantarctica); Rühe, 1914: 53–55, fig. 18c–d (Alona); Pesta, 1928: 79–80, fig. 1a–b (Alona subantarctica); Frey. 1988: 1400–1410, fig. 57–104 (Alona); Dartnall, Holwedell & Paggi, 2005: 983, fig. 8a–b (Alona); Dartnall & Holwedell, 2007: 1267, fig. 10 (Alona); Van Damme & Dumont, 2008a: 4–9, Fig. 1–2.

Type locality. Kerguelen Island.

Type material. Non-existent.

Diagnosis. Diagnosis is given according to the literature. Parthenogenetic female. General. Length of adult female 0.5–0.65 mm. Body regular oval, of moderate height, height/length ratio 0.64–0.72, maximum height at the middle. Ventral margin with about 40–50 setae. Postero-dorsal angle with about 100 setulae organized into groups.

Head. Posterior part of headshield broadly rounded. Three connected major head pores, PP about 0.6–0.7 IP. Lateral head pores minute.

Labrum. Labral keel of moderate width, with convex anterior margin and blunt or rounded apex, posterior margin of keel without clusters of setulae.

Second abdominal segment without dense setulae. Postabdomen short and wide, with broadly rounded distal part; length about 2 heights. Ventral margin straight. Distal margin convex, distal angle broadly rounded. Dorsal margin with convex postanal portion and concave anal portion. Distal part 1.5 times longer than preanal, anal and postanal portions of similar length. Preanal angle well-defined, postanal angle weakly defined or not defined. 6–8 groups of 3–5 short elementary marginal denticles, 1–2 composite denticles present only in some specimens; postanal margin and anal margin with 4–6 groups of setulae. Seven-nine moderately wide lateral fascicles of short setulae, with distalmost setulae only slightly longer than marginal denticles. Postabdominal claw of moderate length, equal in length to preanal portion of postabdomen. Basal spine about 0.25 length of claw.

Antennule with antennular seta about 1/2 length of antennule, arising at 2/3 distance from the base. Aesthetascs of different length, two longest of them of about 1/2 length of antennule.

Antenna with seta arising from basal segment of endopodite longer than endopodite. Spine on basal segment of exopodite longer than middle segment. Spines on apical segments longer than apical segments.

Limb I with accessory seta about 1/4 length of ODL seta. Limb III with exopodite seta 3 being longest, seta 6 about 1/3 length of seta 3, setae 1 and 4 about 1/4 length of seta 3. Limb IV with epipodite without projection. Exopodite seta 3 longest, setae 1 almost as long as seta 3, length of seta 2 about 2/3 length of seta 3, setae 5 and 4 about 2/3 length of seta 3, setae 6 2 times shorter than seta 4. Flaming-torch setae with well-developed distal portion. Limb V with epipodite without projection. Exopodite seta 4 2.5 times shorter than seta 1.

Ephippial female. Body higher than in parthenogenetic female, dorsal highly arched, postero-dorsal angle expressed, ephippium dark brown.

Male. General. Length 0.48 mm. Body low oval, maximum before the middle of the body, height/length ratio 0.57. Ocellus and eye of same size.

Postabdomen short, slightly narrowing distally, subrectangular in distal portion, dorso-distal angle broadly rounded. Preanal angle well-defined, postanal angle not defined. Distal part of postabdomen 1.5 times longer than preanal. Postabdominal claw 2 times shorter than preanal portion of postabdomen, basal spine of about 0.5 claw length.

Full description. See Frey (1998) and Van Damme & Dumont (2008).

Differential diagnosis. Postabdomen with convex distal margin and broadly rounded dorsodistal angle, armed predominantly with clusters of elementary postanal denticles is an unique feature of the species. O. weinecki differs from O. anastasia, O. azorica and O. setulosa by fully connected main head pores; from O. anamariae by greater size and by broad, subrectangular postabdomen; from O. kaingang by greater size and greater PP/IP ratio; from O. altiplana by broadly rounded distal angle and short marginal denticles of postabdomen.

Taxonomic notes: According to Van Damme & Dumont (2008), O. weinecki probably presents a speciescomplex as morphological differences are present between populations from different islands. But the species has not been revised at the moment.

Distribution. According to Van Damme & Dumont (2008) O valona weinecki is distributed on islands of the Sub-Antarctic and Maritime Antarctic: Falklands, South Georgia, South Orkneys, South Shetland Islands, Prince Edward Island, Kerguelen, Amsterdam, Marion, Macquarie, Heard Islands. There are no records of the species from continents, but the absence of O. weinecki in the southmost part of South America is not confirmed by modern data.