Ovalona pascua Damme, 2016, sp. nov.

• Main Author: Damme, Kay Van
• Format: Text
• Language: unknown
• Published: Zenodo 2016
• Subjects: Biodiversity; Taxonomy; Animalia; Arthropoda; Branchiopoda; Diplostraca; Ovalona; Ovalona pascua; Patagonia; Heard Island; Kay; Seta; Roa; Oldfield; Moai; Antarc*; Antarctica
• Online Access: https://dx.doi.org/10.5281/zenodo.6089697; https://zenodo.org/record/6089697

Ovalona pascua sp. nov. (Figs 1–5) Alona weinecki Studer, 1878 in Dumont & Martens (1996: pp. 84–91; Figs 1 –35) and subsequent publications on Easter Island (Dumont et al. 1998; no figures) not Ovalona weinecki (Studer, 1878) sensu Van Damme & Dumont (2008a: pp. 4–9; Figs 1–2) Etymology. The epitheton pascua for Easter, as the species is described here from Easter Island. The genus name Ovalona Van Damme & Dumont, 2008 refers to the oval egg-like shape of the habitus in lateral view, combined with the name of the original genus, Alona Baird, 1843 (Van Damme & Dumont 2008a). Older O. pascua sp. nov . adult females have a pronounced oval shape in lateral view. Type locality . Walled pool close to road, North of Hanga Roa village, West of Easter Island, Leg. H.J. Dumont and K. Martens, 18.VIII.1990 (sample # 2 in Dumont & Martens 1996). Detailed coordinates unknown, for Hanga Roa: 27.1500° S, 109.4167° W. Type material . Holotype (RBIN INV.138001), ovigerous adult parthenogenetic female. Paratypes (RBIN INV.138002) four adult parthenogenetic females and two ephippia in a separate slide and one ephippial female RBIN INV.138003) and adult male (RBIN INV.138004), each in a slide Type series in four slides mounted in glycerol-formaldehyde and one tube with wet material in 4% formaldehyde.Wet material one tube from type locality with ca. 50 specimens covering all life stages, in 4% formaldehyde (RBIN INV.138005). All type specimens deposited at the Royal Belgian Institute for Natural Sciences (RBIN), Brussels, Belgium. Additional specimens examined. Ovalona pascua sp. nov . All surface samples from 1987 (H.J. Dumont; HJD), 1990 (HJD, K. Martens; KM) and 1993 (K. Desender; KD) in the Dumont collection at RBIN (Accession Number for the collection is INV IG 32.094) from Easter Island were studied. Specimens were retrieved and studied from the following localities (details after Dumont & Martens 1996): shallow pool in walled compound near Te Ihu o Motu Pare (North of Hanga Roa), Easter Island, Coll. by HJD and KM, 18.VIII.1990. Large shallow pool, opposite to Pto Espolon (North of Hanga Roa), Easter Island, Coll. by HJD and KM, 18.VIII.1990. Stone well with drinking water (North of Hanga Roa), Easter Island, Coll. by HJD and KM, 18.VIII.1990. Stagnant water in cave at Anu Ipu Maengo (North of Hanga Roa), Easter Island, Coll. by HJD and KM, 18.VIII.1990. Two eutrophic pools East of Maungo Roiho (North of Hanga Roa), Easter Island, Coll. by HJD and KM, 18.VIII.1990. Stone basin at seashore with seawater seeping in, at Na Manga, Easter Island, Coll. by HJD and KM, 21.VIII.1990. Eutrophic stone basin used for watering horses at Hanga Tuu Hata opposite Rano Raraku volcano, Coll. by HJD and KM, 21.VIII.1990. Pool in crevices on basaltic plateau Vai-Atare, SE of Rano Kau, Easter Island, Coll. by HJD and KM, 23.VIII.1990. Between vegetation in shallow water, Teravaka, Easter Island, Coll. by KD, 20.XII.1993. In reference to the sample numbers listed in Dumont & Martens (1996) for the localities above, animals were found in large numbers and of all life stages (>500) in the 1990 samples #1, 2, 4, 9, 10, 24, 28, 38 collected by HJD and KM and the Teravaka samples collected by KD in 1993. Few (10–50), only parthenogenetic females found in samples #6, 7, 23 and none in #12, 13, 14, 18, 19, 20, 21, 25, 38 collected by HJD and KM in 1990, none in samples from Rano Raraku collected by HJD in 1987. Several samples of the 1990 expedition could not be found, likely in the collection but in other boxes (#3, 5, 11, 15, 17, 18, 26, 29). Additional specimens of O. pascua sp. nov. were deposited under the accession numbers (numbers between brackets refer to sample numbers in Dumont & Martens 1996) RBIN INV.138006 (#4) (wet material, tube), RBIN INV.138007 (#9) (wet material, tube), RINB INV.138008-10 (#4) (slides, including males in RBIN INV.138009). Chydorus sphaericus (O.F. Müller, 1776) from #2, adult parthenogenetic female, deposited under RBIN INV.138011 (this record cannot be confirmed as only one specimen was found in the samples). Specimens for comparison . Three adult parthenogenetic females of Ovalona sp., labeled as Alona cambouei from Patagonia, Chile from the Daday Collection, Natural History Museum of Budapest, Hungary. Accession Numbers Cladocera II-537, II-538 and II-661, labeled “ Alona cambouei 1203-1901 Patagonia – Sylvestri”. Specimens of Ovalona weinecki , loc. freshwater pool, Heard Island, Antarctica, Coll. H.J.G. Dartnall, The Natural History Museum, London (1993.62–71). Description. Adult parthenogenetic female. General Habitus (Figs 1 A & 2A).. Length/width ratio ca. 1.65. Habitus oval, strongly convex dorsal region and convex posterior region of the carapace (Figs 1 A & 2A). Carapace (Figs 1 A & 2A) lacking ornamentation. Valve setae ca. 35–50 (ca. 45 on average), in three main groups, long anterior group, medium small group and intermediate sized posterior group starting just beyond the middle. Setae with fine setules and gradually decreasing in size towards the corner. The last seta is relatively long, therefore the row of setae seems to end abruptly, just before the corner, continuing in fine setules on the margin (not groups) (see habitus drawing Fig. 1 A; Fig. 2 in Dumont & Martens 1996). Posteroventral corner without notch and no posterodorsal angle. Ventral margin of the valves straight, slight depression near the middle (Figs 1 A & 2A). Posteroventral valve corner round. No dorsal keel. Cephalic structures. Ocellus smaller than eye, equidistant between rostrum and latter (Figs 1 A & 2A). Well developed rostrum, round and a round even posterior margin (see Dumont & Martens 1996). Apex of the first antenna reaching rostrum, aesthetascs projecting beyond. Head pores (Fig. 1 E; Dumont & Martens 1996: Fig. 3 and Fig. 24), three main narrowly connected head pores (Fig. 1 E) all of the same size, close to the broadly rounded round posterior head shield margin (Dumont & Martens 1996: Fig. 3). Postpore distance PP less than one interpore distance IP. Small pores between 3/4th IP (Fig. 1 E) to one IP distance (Dumont & Martens 1996: Fig. 24) from the midline and situated at about midway of the main pores (Fig. 1 E). Labrum (Fig. 1 B). Keel short in lateral view, quite convex, no lip present. Variation shown in Dumont & Martens (1996), margin mostly straight yet variable, sometimes wavy (Fig. 1 B). Antennules/A1 (Fig. 1 C). Short, about 2–2.5 as long as wide. Sensory seta at a third from the antennular apex. Setulated on the margin (four to five rows). Aesthetascs of similar length, two slightly longer, all implanted on the apex. Second antennae/A2 (Fig. 1 A, 1D). Coxal spine short. Spinal formula 001/101, setal formula 113/003. Seta on the first exopod segment fine and long, reaching beyond the last exopod segment by at least one third to over half its length. Segments ornamented with small denticles (not shown). First endopod segment spine, reaching half of the second endopod segment; terminal spines about the same lengths as the segments they are implanted on. Terminal setae of similar thickness, one terminal exopod seta markedly shorter. Thoracic structures. Five pairs of thoracic limbs (P1–5). First limb (Figs 3 A–B). Short round epipodite. First endite with just two setae, second endite with three setae, third endite with four similar setae (Fig. 3 A). No anterior elements on en1–2. ODL with one slender seta, with short fine setules in distal half and just longer than longest IDL seta (Fig. 3 B); IDL with two setae implanted with fine setules unilaterally on distal halves, both similar in size and a shorter naked seta about a third to a quarter their length. Short accessory seta on sixth endite, near the base of the ODL ( as in Fig. 3 B). About six anterior setule groups with relatively short setules in each group, strongly decreasing in length ventrally. Short setules on the ventral margin. Ejector hooks very narrow and small, subequal. Gnathobase without a seta but with a small tuft of setules (Fig. 3 A). Second limb/P2 (Fig. 3 C). Exopodite quadrangular, with a short subapical seta and apical setules. Eight scrapers gradually decreasing in size between the exopodite and the gnathobase. Two first scrapers relatively longest, third slightly shorter than the fourth, sixth to eigth slightly thicker. Setulation of all scrapers uniform, no anterior elements at the base of scrapers. Gnathobase with short tuft of setules, three elements and a filter comb with seven setae of which the first short and modified. Third limb/P3 (Figs 3 D–H). Epipodite oval-rectangular with short projection. Exopodite (Figs 3 D–E) with seven setae in 2+5 arrangement. First seta about twice as long as second, both in opposite directions; third seta about twice as long as sixth seta; fourth seta just shorter than sixth, fifth of the same length as the seventh seta and both are half as long as the sixth seta. Fourth seta clearly bent in the middle, oriented away from the epipodite. All setae widely plumose, except for setae six and seven: sixth seta with asymmetric setulation, with strong thicker sparse setules in the second half, seventh seta with short setules. External endite (Fig. 3 F) with three setae (1’–3’) of which first two quite short, setules not seen and with a small naked element between them, third (3’) shorter and with longer setules; four plumose setae with thicker base on inner side (1”–4”) of same length; one naked element and four small naked setae on internal endite (Fig. 3 G); the gnathobase (Fig. 3 H) with a cylindrical sensillum and the typically larger bent seta (plumose) and two elements. Filter comb w ith seven setae (Fig. 3 F, a–g). Fourth limb / P4 (Figs 3 I–K). Pre-epipodite round, epipodite oval with short projection. Exopodite round, with six plumose setae; first two exopodite setae of similar lengths, third seta just slightly longer than second; fourth exopodite seta about half as long as the fourth (or just over half), the fifth 1.5 times as long as the fourth; sixth exopodite seta shortest, about half as long as the fifth. Fifth seta just shorter than third seta. All exopodite setae similar except for fifth and sixth, which are narrower; fifth is setulated asymmetrically. Endite (Figs 3 J–K) with marginal row of four setae (1’–4’), first fine and longer than the flaming torch setae, of which one quite developed and two markedly shorter, each with about five setules (Fig. 3 J). One elongate naked sensillum (Fig. 3 J–K, labeled “s”); gnathobase with one long setae which is typically bent over endite and naked projection at its base; on inner side, three plumose setae (1”–3”) gradually increasing in size towards the gnathobase and a small filter comb with five setae. Fifth limb/P5 (Figs 3 L–M). Pre-epipodite round, with long setules; epipodite oval with short projection. Exopodite (Fig. 3 L) shape oval, about two times as long as wide, with slightly concave setulated margin between setae three and four; four exopodite setae, first (dorsal) two longest, oriented dorsally; third shorter by one quarter of second exopodite seta, fourth exopodite seta half as long as the second; inner portion of limb (Fig. 3 M) with ovally elongated inner lobe with long apical setules (Fig. 3 L); two plumose endite setae (1’–2’), the first reaching over the inner lobe, the second about half as long as the first. Small projection near gnathobase (broad with tuft), but no filter comb or elements (Fig. 3 M). Abdominal/Postabdominal structures. Postabdomen (Figs 1 F). Widest at preanal corner. Dorso-distal angle present, about 90°, length of postabdomen 2–2.5 times as long as wide (measured from deepest point for the width, from the preanal corner to the ventral margin and from the point of implantation of the natatorial setae to the point of implantation of the terminal claw). Even though from measurements, the postabdomen is 2–2.5 times as long as wide, it has a rather elongate shape. Length of the postabdomen and depth of the preanal portion increase in larger adult females (shorter postabdomen in smaller adult females). Ventral and dorsal margins in postanal portion, parallel (to slightly tapering distally). Anal margin about the same length as the postanal margin, and concave, with smooth transition into the postanal margin. Distal margin (dorsodistal angle) slightly or not protruding. Preanal margin straight to convex. Preanal angle well developed, broad and deep, strongly reaching beyond the postanal margin (by about half the terminal claw length). Postabominal armature (Fig. 1 G). Seven to ten groups of marginal denticles. Proximal groups with three to four denticles in each group, distalmost four to three groups with a larger distal conical denticle and always one to two smaller denticles adjacent to them, or groups with equally sized denticles all the way to the distal corner. These marginal denticle groups increase in size distally, the last two to three (maximally four) distal denticles can be markedly larger, or just gradually increasing. The marginal anal denticles in three to four groups, all fine. The lateral fascicles are fine, with no markedly thick distal spine. Lateral fascicles six to nine postanal groups, each fascicle with about 10–20 spinules, distalmost one relatively thicker. Two distalmost spines of the distal fascicles can reach just beyond the margin, or none. In the anal region, there are two to three parallel rows of lateral fascicles. Terminal claw (Fig. 1 F). Between one up to 1.5 times as long as the anal margin, not curved strongly but rather straight. Proximal pecten shorter than half the claw length. Basal spine relatively fine and close to the terminal claw along its length; this spine is about a third or just over a third of the terminal claw length. Basal spinules not shown here, but described, together with pectens on terminal claw, in Dumont & Martens (1996). Male (Fig. 2 D; Dumont & Martens 1996: Figs 12–13, 19–23 & 26–27). Length to width ratio about 1.75, quite elongate habitus with pronounced deep ventral embayment before the middle (Fig. 2 D). No ornamentation of the carapace (only “grainy” appearance). Eye and ocellus of approximately the same size, ocellus equidistant between the rostrum and the eye. Marginal setae ca. 40, long in anterior portion, strongly decreasing in size (more than in female) towards the posterior valve corner. Antennules protruding beyond the rostrum. Labral keel with a strong depression ventrally. The male postabdomen (Figs 2 E & 3A) is two to 2.5 times as long as wide (width in postanal portion), with a strongly truncated broad square distal portion, a generally square shape in the postanal part. Ventral and dorsal distal margin at each side of the claw base of similar length. The gonopore ends just subterminally (Fig. 3 A). Terminal claw short, as long as or just shorter than the anal margin. Basal spine reaching up to half the claw length and with strong pecten on the dorsal margin. Preanal corner deep, well developed but not as a projection, just as a wide triangle, postanal corner not developed. Marginal spinules (Fig. 3 A) short and equal, in groups. Lateral fascicles about five to seven groups with long spinules, distal spinule of each group in the last three to four fascicles reaching over the margin. Several rows of lateral fascicles in the anal portion. The first limb/P1 (Dumont & Martens 1996: Figs 19–22) with a strong, well developed hook consisting of a thick base and a long elongate thin distal portion, about twice as thin as the basal portion (Dumont & Martens 1996: Figs 21–22). Anterior setules on the limb surface shorter than in females and IDL with two terminal setae with well developed setules (Dumont & Martens 1996: Figs 19–20). Ephippial female and ephippium . Ephippial female (Fig. 2 B) with typically high dorsum, light brown color. Ephippium light to dark brown with a single egg, as for the genus (Fig. 2 C). Size. Parthenogenetic female size ranging between 0.31–0.6 mm, average 0.44mm (size distribution in Dumont & Martens 1996). Male size ranging between 0.39–0.41mm (Dumont & Martens 1996). Ephippial female size distribution in Dumont & Martens (1996), ranging according to the authors, up to 0.6mm in the revised specimens. Differential diagnosis. Adult parthenogenetic females of Ovalona pascua sp. nov . are distinct by the combination of three connected headpores and no notches on the headshield, an oval-round habitus, a postabdomen with a wide preanal portion, with deep preanal corner and a right dorsodistal angle (i.e., not protruding strongly or not at all). Additional characters are the groups of marginal denticles (about three per group) on the postabdomen, increasing in length distally with two to four larger conical teeth near the distal corner and the seta on the first endopod of the second antenna reaching a third (up to half) its length over the last endopod segment. For general comparison with other species, see the key and drawings in Sinev (2015). The marginal postabdomen groups of relatively short denticles increasing distally in size (or with two to three distal larger conical teeth), differ from the singular, markedly long teeth with adjacent denticles in most species, as in O. glabra (Sars, 1901), or even more pronounced, in O. altiplana (Kotov, Sinev & Berrios, 2010). It is different from O. archeri (Sars, 1888), which has larger distal teeth towards the distal end of the postabdomen. The long postabdomen with the angular (but not strongly acute) dorsodistal angle is remotely similar to the widespread O. pulchella- like species like O. pulchella (King, 1853), O. cambouei (de Guerne & Richard, 1893), O. glabra (Sars, 1901) and O. bromelicola (Smirnov, 1988). O. pascua sp. nov . differs clearly from O. cambouei in having connected head pores and from O. bromelicola by the presence of a well developed basal spine on the terminal claw. From O. pulchella, it differs in the shape of the postabdomen, not acutely protruding in O. pascua sp. nov ., and in the absence of clear notches on the posterior margin of the head shield. The new species differs from O. glabra and O. pulchella also in the length of the postabdomen. The seta on the first endopod segment of the second antenna is long in O. pascua sp. nov ., reaching a third of its length or more over the last endopod segment, while in O. glabra and O. pulchella the seta is short and reaches just beyond this segment. Similarities with O. weinecki (Studer, 1878) are not obvious from the habitus and postabdomen. The postabdomen is completely different in the latter species, with a strongly round distal angle and with smaller marginal denticles (Fig. 2 F). Finally, O. pascua sp. nov . differs from O. kaingang (Sousa, Elmoor-Loureiro & Santos : Published as part of Damme, Kay Van, 2016, Endemism and long distance dispersal in the waterfleas of Easter Island, pp. 251-272 in Zootaxa 4154 (3) on pages 253-264, DOI: 10.11646/zootaxa.4154.3.2, http://zenodo.org/record/258155 : {"references": ["Dumont, H. J. & Martens, K. (1996) The freshwater microcrustacea of Easter Island. Hydrobiologia, 325, 83 - 99. http: // dx. doi. org / 10.1007 / BF 00028269", "Dumont, H. J., Cocquyt, C., Fontugne, M., Arnold, M., Reyss, J. L., Bloemendal, J., Oldfield, F., Steenbergen, C. L. M., Korthals, H. J. & Zeeb, B. A. (1998) The end of moai quarrying and its effect on Lake Rano Raraku, Easter Island. Journal of Paleolimnology, 20, 409 - 422. http: // dx. doi. org / 10.1023 / A: 1008012720960", "Van Damme, K. & Dumont, H. J. (2008 a) Further division of Alona Baird, 1843: separation and position of Coronatella Dybowski & Grochowski and Ovalona gen. n. 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