Alona quadrangularis (O.F. Müller, 1776 ), sensu Baird, 1850

Damme, Kay Van & Dumont, Henri J., 2008, The ‘ true’ genus Alona Baird, 1843 (Crustacea: Cladocera: Anomopoda): position of the A. quadrangularis-group and description of a new species from the Democratic Republic of Congo, Zootaxa 1943, pp. 1-25 : 2-10

Alona quadrangularis (O.F. Müller, 1776)

Figs 1–5

Lynceus quadrangularis O.F. Müller, 1776 ; 199, n° 2393 (identity uncertain).

Lynceus quadrangularis O.F. Müller, 1776 in Müller (1785): 72, Plate 9, Figs 1–3 (identity uncertain).

Monoculus quadrangulus Gmelin, 1790 : Gmelin (1790): 3008, 61.

Lynceus (Alona) quadrangularis (O.F. Müller, 1776) sensu Baird (1843) : Plate 3, Figs 9–11 (identity uncertain).

Alona quadrangularis (O.F. Müller, 1776) sensu Baird (1850) : Plate 16, Fig. 4 = nec Lynceus (Alona) quadrangularis O.F. Müller, 1776 sensu Baird 1843 .

nec Lynceus quadrangularis (O.F. Müller, 1776) sensu Fischer (1851) : 189, Plate 9, Fig 3.

nec Lynceus quadrangularis (O.F. Müller, 1776) sensu Leydig (1860) : 221, Plate 8, Fig. 58.

Alona quadrangularis (O.F. Müller, 1776) sensu G.O. Sars (1861) : 132, Plate 96, Fig. 4, Plate 97, Figs 6–8 = A. quadrangularis sensu Baird (1850) : Plate 3, Figs 9–11.

Alona macrops Motas & Orghidan, 1948 .

Alona sulcata Schödler, 1862 .

Alona sanguinea P.E. Müller, 1867 .

For more extensive synonymy we refer to Baird (1850), Smirnov (1971) and Flössner (2000).

Type locality. Denmark (O.F. Müller 1776) .

Material examined. 42 adult parthenogenetic females, Damvallei , Heusden, Belgium, 07.08.2007, Leg. K. Van Damme . 20 adult parthenogenetic females, 5 adult males, Watersportbaan , Ghent, Belgium, 15.08.2007; Leg. K. Van Damme . 15 adult parthenogenetic females and 10 adult males, Firtina Deresi , Tur- key, 18.07.1994. Material at UG Zooplankton collection, Ghent University, Belgium, Dpt. of Biology, Limnology Research Group .

Redescription of parthenogenetic female. Habitus. Medium-sized to large animals, 0.6–0.8mm ( Fig. 1A; 0.50–0.85mm in Flössner, 2001), in life reddish or colourless and transparent, after preservation brownishyellow, depending on amount of haemoglobin. In lateral view carapace widened posteriorly, with high posterodorsal angle ( Figs 1A–B). Posteroventral corner with shallow notch ( Fig. 1B). In dorsal view, body bilaterally compressed with dorsal elevation but lacking a keel ( Fig. 2A). Head. Eye and ocellus of similar size ( Fig. 1A). In specimens from Belgium, eye and ocellus relatively large compared with Sinev & Coronel (2006) and Flössner (2000), feature may be variable; head shield depicted in Flössner (2000) and Sinev & Coronel (2006). Rostrum blunt, aesthetascs projecting beyond its tip ( Fig. 1A). Three main head pores of same size, narrowly connected, small pores less than half distance between midline and lateral margin of head pores ( Figs 1E & 2B). In dorsal view, main head pores elevated, small pores in depressions on each side ( Fig. 2A). Carapace. Ornamentation consisting of both large and ultra-fine striation ( Fig. 1K). Marginal setae in different groups, longest group on frontal margin of carapace and in middle ( Fig. 1A). Posteroventral corner with row of 60–68 setae ending abruptly instead of decreasing in size towards the end, and followed by groups of naked spiniform setae ( Figs 1A&K). Antennules ( Fig. 1F). About three times as long as wide, sensory seta long, implanted at one third from base. Rows of setules on dorsal margin. Antennae ( Figs 1G–J). Coxal setae long, reaching beyond first endopodal segment. Exopod with group of few thicker spines on second segment ( Fig. 1J). Setae: 113/003, spines: 001/101(numbers indicate structures on exo/endo). Terminal setae subequal in length and with long setules, exopod setae with long setules as well ( Figs 1H–I). Labrum ( Figs 1C–D). Lacking lateral projections, labral keel in lateral view quadrangular, with convex margin, with ventral notch and two to three (one minute) ventral groups of setules. First maxilla with two setulated setae ( Fig. 4B).

Postabdomen ( Figs 1M–N, 2D). Broad and robust, widening distally and with convex postanal margin; postanal and ventral margins parallel. Postanal portion expanded, postanal margin up to twice as long as anal margin ( Fig. 1M). Postanal angle over 90°. Marginal teeth 10–13, pyramidal, serrated anterior margin. Each tooth consists of merged denticles, but no individual spines in postanal portion ( Figs 1N, 2F). Lateral fascicles ( Fig. 2F) with setules decreasing in size anteriorly; posteriormost spiniform, thicker and larger than other setules of its group. Posteriormost spine reaching just beyond dorsal margin of postabdomen, but never to apex of marginal teeth ( Figs 1N, 2F). Terminal claw ( Figs 1L, 2E). Long and slender ( Fig. 1L), longer than anal margin, evenly curved ( Fig. 2E). Basal spine also slender, more than two times claw width and less than half claw length ( Fig. 2E). Row of basal spinules of moderate size along dorsal half of terminal claw, no strong spines here ( Fig. 1L).

Five pairs of limbs. First limb ( Figs 3A–D, 4C–D&F). First endite with three setae, the first seta well developed and plumose ( Fig. 3A). Anterior soft setae present but small, accompanied by small element ( Figs 3B, 4F). Second endite with three ventral setae, first two with moderate pecten. One anterior soft seta and additional minute element near base ( Figs 3A–B, 4F). Third endite with four setae, similar in length ( Fig. 3A). Inner distal lobe (IDL) or fourth endite ( Fig. 3C) with three setae, of which one small and naked, two larger, subequal, unilaterally armed with fine denticles in distal half. Outer distal lobe (ODL) or fifth endite ( Fig. 3C) with one single, long seta, implanted on one side with minute denticles in distal half. At base of ODL, before sixth endite, a projection. This projection is visible also on Fig. 4C (between ODL and accessory seta). Accessory seta on sixth endite strongly developed and plumose ( Fig. 3C). Setule rows on anterior and ventral part of limb corm ( Fig. 3D) consisting of seven to eight long singular setules instead of groups. Ejector hooks welldeveloped, subequal in size ( Figs 3A, 4D). Gnathobase I with short setulated process ( Fig. 3A). Second limb ( Figs 3E–G, 4C–E). Exopodite well developed, carrying a long, finely setulated seta and group of setules; this seta about as long as first scraper ( Figs 3E–F). Endites with eight scrapers, first three long, following five gradually decreasing in size towards gnathobase while increasing in thickness ( Fig. 3E). Denticulation of scrapers is fine, last three with relatively thicker denticles ( Fig. 4E). Additional small soft seta at the inner base of the first scraper ( Fig. 3E). Gnathobasic hillock moderately expanded, with fine setules. Small sensillum close to gnathobasic setae. Gnathobase with typical three elements, of which the first a bent seta, second a thick seta, third small and naked. Filter comb with seven setae, of which the first three shorter and of relatively the same size. First filter seta ( Fig. 3G) thicker, with long setules in distal half, implanted on all sides. Third limb ( Figs 3H–L, 4C–E). Pre-epipodite relatively small, with long marginal setules. Epipodite oval- round, without projections. Exopodite ( Figs 3H–J, 4C) with seven setae, of which two on posterior and five on ventral margin. First two exopodite setae long, first longer than second. Third exopodite seta longest, about five times the length of the exopodite itself, following two setae that are very short and of similar size; sixth and seventh setae relatively narrow, fifth longest; all exopodite setae plumose, except for sixth (heterogenous setulation) ( Fig. 3I). Endite ( Fig. 3K) with typical alonine arrangement: close to the exopodite, a row of three well-developed setae, of which the first are unilaterally armed with short denticles in the distal half and have a small reduced seta in between, and a third, thicker seta with fine long setules. In continuation, between the latter row and the gnathobase, five naked setae, of which the first is most reduced. The gnathobase itself ( Fig. 3L) consists of a subapical large bottle shaped sensillum and three apical gnathobasic setae: one large seta, bent over the endopodite and implanted with fine setules, and two well developed straight setae, lacking larger setulation. On the inner side of the endite ( Fig. 3K), four similar plumose (1”–4”) setae precede the gnathobasic filter comb. The latter is strongly developed, consisting of seven long setae with fine plumose setulation. Fourth limb ( Figs 3M–N & 4C–E). Pre-epipodite round, implanted with long marginal setules and slightly larger than the oval-round epipodite. Exopodite ( Fig. 3M) square and large, bearing six setae of which the first four are strongly plumose and similar in morphology, opposed to the last two (5–6 in Fig. 3M), which are much narrower and smaller, implanted with short setules. At the dorsal base of third exopodite seta, a small naked, round process, between third and fourth scraper a setulated hillock. Anteroventral margin of the exopodite straight and implanted with a row of small setules on its margin. Endopodite IV ( Figs 3N, 4E) with four developed marginal setae, of which the first has a scraperlike morphology, i.e. unilaterally armed with short denticles in its distal half, the following three are long “flaming torch” setae (ft's in Fig. 4E). Between scraper and first ft-seta, a minute reduced element. A pore is present below the last scrapers on the anterior side ( Fig. 4E) and towards gnathobase, adjacent to last ft-seta, a round naked seta ( Fig. 3N, indicated “s”). Gnathobase with one large seta, and two smaller basal naked reduced elements Fig. 3N). Large receptor at posterior side of the endite, below the scrapers ( Figs 3N, 4E). On the inner side, a row of three long plumose setae ( Figs 3N, 4E), followed by five slender filter comb setae with fine setulation ( Fig. 3N). Fifth limb ( Figs 3O–P & 4D–E). Pre-epipodite and epipodite oval-round and of similar size, the pre-epipodite with long setules. Exopodite a large flap ( Fig. 3O), with four plumose setae in a 3+1 arrangement, first three setae long, oriented dorsally, fourth seta less than a third of previous exopodite seta. Between third and fourth seta, the exopodite margin is expanded and implanted with setules. Ventral portion of the exopodite widely round. Inner lobe large, with incision in dorsal margin, bearing thick long setules on its ventral margin ( Fig. 3O). Two inner setae long (1’–2’ in Fig. 3O), first one bent over the inner lobe, second exceeding half the proceeding seta, both with long setules ( Figs 3O, 4E). Gnathobase reduced, two naked elements, possibly reduced setae (rs in figs), and a setulated process ( Fig. 3P). Sixth limb. Absent. There is no trace of this limb or a reduced structure, its absence can be seen clearly on SEM images ( Figs 4A–C). Food groove around this region is unsetulated.

Description of male. ( Fig. 5). Smaller and more elongate than female (0.4–0.60mm), with shorter head and wider rostrum ( Fig. 5A). Antennules shorter, with subapical aesthetasc and sensory seta ( Fig. 5B). Postabdomen sexually dimorph, ( Figs 5C–D) broad, gonopores ending subterminally ventrally from the terminal claws ( Fig. 5C); anal margin little shorter than postanal margin; postanal part with marginal row of minute, unmerged denticles ( Fig. 5D); lateral fascicles reaching just beyond margin, spinules strongly decreasing in size per group ( Fig. 5D). Terminal claw relatively short, basal spine half the size of claw. First limb ( Figs 5E– F) with 5–6 anterior groups of setules with more than one setule per group and a well developed clasper ( Fig. 5F), about two times as long as wide, with minute V-like incisions (rugae and furrows) on apex ( Fig. 5F).

Differential diagnosis. A. quadrangularis is morphologically similar to A. boliviana and A. kolwezii , but may be distinguished by the carapace that widens strongly posteriorly, with a high posterodorsal angle (in lateral view); in having a postabdomen with an extended postanal margin in the posterior part with about 13 stout serrated marginal teeth, a long slender terminal claw and basal spine; first limb with only 6–7 single setae on anterior margin and second limb with an exopodal seta about as long as the first scraper. For detailed differences with A. boliviana , see Table 1 and Sinev & Coronel (2006). In Europe, A. quadrangularis is sometimes confused with A. affinis at lower magnifications, but the latter (Alonso 1996) can be distinguished by two major head pores; its larger body size in adult females; a more rectangular habitus (carapace not widening posteriorly); spinule per articulation of antennal swimming setae; much thicker basal spines on the terminal claw, longer and less marginal teeth on a more parallel postabdomen and –a very clear feature- first limb with groups of setules on anterior margin. For differences with A. kolwezii n.sp., see Table 1 and diagnosis below.

Distribution. Due to historical uncertainty of its taxonomical status, the exact worldwide distribution of

A. quadrangularis is unknown. Most likely its distribution is Palaearctic ( Sinev & Coronel, 2006) and maybe Holarctic. Records of A. quadrangularis outside this region should be compared in detail with the populations described in this paper. For example, records from South Africa, South East Asia and Australia (e.g., A. cf. quadrangularis in Frey 1993), may well reveal distinct taxa. An available name for Australia may be Alona whiteleggi Sars, 1896 but identity of the latter (member of quadrangularis- or affinis group?) is unclear. In South America, it may be of interest to check how far the range of A. boliviana extends outside the high Andes, and if other cryptic species will be found on the continent. The same goes for Africa ( A. kolwezii n.sp.).

Ecology and Biology. A. quadrangularis occurs in a wide variety of littoral habitats and ecological conditions, in diverse water types (swamps, lakes, rivers, springs, etc.) but is rare in temporary pools. The species is not bound to vegetation but lives close to substrate, on stones or detritus in waters rich of fine organic matter with population increases following eutrophication; tolerates acid waters (pH 5) but prefers neutral conditions ( Flössner 2000). Reported from caves ( Wood & Greenwood 2001). In comparison to other chydorids, it shows clear preference for mud ( Whiteside et al. 1978). We found it sympatrically with the alonines Leydigia and A. affinis on detritus-rich substrate (rocks, stones, wood) in medium-sized eutrophic, turbid waters rich in decaying plant material (e.g., leaves) and associated algae. Typically lives in flocculent detritus. Gut contents of A. quadrangularis from Belgian populations showed mainly detritus and few algae (e.g., Staurastrum ) (sympatric A. affinis in the same samples contained relatively more algae in gut indicating different diet preferences). We observed live A. quadrangularis , which showed that these are comparatively slower swimmers, keeping closer to the substrate than A. affinis under the same conditions.