Coronatella rectangula (Sars, 1861) Damme, Kay Van & Dumont, Henri J., 2008
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publication ID |
https://doi.org/ 10.11646/zootaxa.1960.1.1 |
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persistent identifier |
https://treatment.plazi.org/id/B34587DE-9026-CD70-56F2-F9D8FAC3FDBF |
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treatment provided by |
Felipe |
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scientific name |
Coronatella rectangula (Sars, 1861) |
| status |
comb. nov. |
Coronatella rectangula (Sars, 1861) View in CoL comb. nov.
( Figs 3–4 View FIGURE 3 View FIGURE 4 )
Synonymy: see Smirnov (1971), Frey (1988), Flössner (2000) and Sinev (2001b).
Material examined. Type series from Sars’ Collection, 6 specimens from slide F9035 (“Dam ved Lille Fröen”, Norway); 26 specimens including lectotype, Slide F 9036, “Dam paa Egeberg”, Norway, Zoological Museum Oslo. 50 parthenogenetic females from Samber River , Belgium, Coll. K. Van Damme, 20.VIII.2007 ; 10 parthenogenetic females from Boat Racing Canal, Ghent, Belgium, Coll. K. Van Damme, 15.VII.2007 . 5 parthenogenetic females from sand quarry next to Scheldt River , Ghent, Coll. K. Van Damme, 06.V.2006 .
Redescription of adult parthenogenetic female. Habitus ( Figs 3A & E View FIGURE 3 ). For a description of habitus and labrum of material from terra typica, see Frey (1988). Small to medium-sized animals, 0.25–0.4mm (0.26–0.5mm in Flössner (2000); 0.24–0.39mm in Frey, 1988), colourless and transparent. Specimens from Belgium relatively larger (0.3–0.5mm) than types (0.25–0.4mm), but still within range. Carapace rectangular in lateral view, with evenly curved dorsal margin and low posterodorsal angle. Ventral margin rather straight. Posteroventral corner with notch at about 1/4 th of posterior margin. In dorsal view, body compressed lacking a keel. Head. Ocellus smaller than eye. Head shield (in Frey 1988, Alonso 1996) with rounded, wavy posterior margin. Rostrum blunt, round and short, aesthetascs projecting beyond its tip. Three main head pores of same size, narrowly connected, PP distance about one third of IP distance; small pores less than half distance between midline and lateral margin of head pores. In dorsal view, main head pores not elevated. Carapace ( Figs 3A&E View FIGURE 3 ). Ornamentation a wide, well-developed striation, no fine striation. Number of lines 16–20, depending on size of animal. Marginal setae in different groups, long group on frontal margin of carapace, followed by relatively shorter group in middle and another longer group in posterior third of the margin. Marginal row of 30–40 setae decreasing in size towards posteroventral corner and followed by small spinules not arranged in groups. Labrum ( Figs 3D&F View FIGURE 3 ). Labral keel in lateral view short and round with convex margin and obtuse tip. No ventral setules or denticles on labral keel. In specimens from Belgium, labrum keel relatively longer ( Figs 3E&G View FIGURE 3 ) than in types ( Fig. 3D View FIGURE 3 ). Antennules. About two to 2.5 times as long as wide, sensory seta short and implanted at one third from apex. Three rows of setules on dorsal margin. Aesthetascs shorter by one fourth of antennular corm and subequal in length. Second antennae ( Fig. 3H View FIGURE 3 ). Coxal setae not studied. Exopod with group of few (4–6) thicker spines on second segment. Setae: 113/003, spines: 001/101. First endopod spine exceeding length of second endopod segment. First exopod seta short and narrow, not reaching beyond terminal exopod segment. Apical spines well developed about as long as or little longer than ultimate segments. Terminal setae subequal in length.
Postabdomen ( Figs 3I–L View FIGURE 3 ). Relatively short, dorsal margin S–shaped, length about two times as long as wide, anal and ventral margins parallel. Postabdomen in specimens from Belgium relatively more robust than types. Ventral margin shorter than anal and postanal margin. Anal and postanal margins of similar length and shorter than preanal margin. Anal margin concave. Postanal margin convex, tapering distally, distal margin not protruding. Preanal corner moderately developed, triangular, not protruding beyond postanal margin. Marginal denticles well developed, arranged in six up to seven postanal groups. Distal postanal groups consisting of one large denticle with smaller adjacent spine, those closer to the anal margin in groups of two to four long spines of which distal longest. Lateral fascicles five groups in postanal portion, consisting of over seven to ten spinules in each group, parallel to each other, slightly increasing in size distally and with longer and thicker distal spinule. Two to three clusters of marginal denticles and single (in type material) to double row (in specimens from Belgium) of fascicles in anal portion. Terminal claw ( Fig. 3I View FIGURE 3 ). Longer than anal margin, evenly curved, implanted with setules along dorsal side. Relatively slender basal spine, about two times as long as claw width at base and about a third of claw length. Group of two to five short basal spinules, continuing in setules along the dorsal margin of the basal spine. Frey (1988) notes the ridge of 4–5 setae on concave margin as a specific character.
Five pairs of limbs. First limb ( Fig. 4A–C View FIGURE 4 ). Epipodite with long projection. First endite with three marginal setae of which the first well developed, second endite with three setae of which two longer (and subequal in size), third endite with four setae ( Fig. 4A View FIGURE 4 ); anterior elements on en1–2 absent ( Fig. 4C View FIGURE 4 ). ODL with one slender seta as long as or longer than longest IDL seta; IDL with two setae, thickened and with a chitineous ring inside, third seta reduced to minute naked element or absent; armature of IDL setae with few strong proximal spines and narrow distal portion with short denticles ( Fig. 4B View FIGURE 4 ). Accessory seta present, relatively short and plumose. Anterior setule groups with more than three long setules in each groups and strongly decreasing in size ventrally. Ejector hooks subequal and gnathobase with single setulated seta. Second limb ( Figs 4D–G View FIGURE 4 ). Exopodite oval, with one long setulated seta implanted subapically ( Fig. 4E View FIGURE 4 ); endites with eight scrapers of which first four relatively long and slender and of similar morphology, with fine denticulation, scrapers three to five gradually decreasing in size; fifth scraper relatively thicker with stronger denticles and last three much shorter (scrapers 6–8) and of similar size and morphology with heavier denticles ( Figs 4D, F View FIGURE 4 ); gnathobasic ‘brush’ short with group of short spinules, gnathobase with a sensillum and three elements, of which first a bent seta; filter comb with seven setae of which the first two (a–b) much shorter and the first brushlike, with setules implanted around distal half ( Fig. 4G View FIGURE 4 ). Third limb ( Figs 4H–L View FIGURE 4 ). Pre-epipodite round, epipodite oval with small projection; exopodite ( Figs 4H–I View FIGURE 4 ) with rectangular corm and six large setae in 2+4 arrangement; first exopodite seta longer than second; third exopodite seta more than two times as long as fifth exopodite seta, fourth seta short (less than half of fifth seta), sixth seta narrower and less than half as long as fifth ( Fig. 4J View FIGURE 4 ). External endite with three setae (1’–3’) of which first two scraper-like, of similar size and with minute element in between, third (3’) shorter and with long setules ( Fig. 4H View FIGURE 4 ); four well developed plumose setae on inner side (1”–4”) of which first two shorter; one element and four small setae on internal endite preceding gnathobase ( Figs 4K–L View FIGURE 4 ); the latter with a bottle-shaped sensillum and large plumose seta with two naked setae at its base. Filter comb with seven long setae. Fourth limb ( Figs 4M–N View FIGURE 4 ). Pre-epipodite round, epipodite oval-round, with short projection. Exopodite round to square, with six plumose setae of which first three of similar size, fourth shorter by half of fifth and sixth setae, which are of similar length and relatively narrower than others ( Fig. 4M View FIGURE 4 ). Endite with marginal row of four setae, first scraper-like and longer than flaming torch seta, following three ft setae with thick base, all of similar size, and one marginal round naked sensillum ( Fig. 4N View FIGURE 4 ); gnathobase with one long setae, bent over endite and two reduced naked elements; on inner side, three well developed plumose setae (1”–3”) of which first shortest and a filter comb with five setae ( Fig. 4M View FIGURE 4 ).
Fifth limb ( Figs 4O–P View FIGURE 4 ). Pre-epipodite round; epipodite oval, with short projection. Exopodite shape broadly oval, about two times as long as wide, with straight expanded margin between setae three and four; four exopodite setae, gradually decreasing in size, first longest, oriented dorsally ( Fig. 4O View FIGURE 4 ); inner portion of limb ( Fig. 4P View FIGURE 4 ) with inner lobe broadly oval with long terminal setules; two slender endite setae (1’–2’) of which first longest and bent towards inner lobe; behind second endite seta, an elongated element; gnathobase with a naked reduced bump, filter comb absent.
Adult male of C. rectangula not studied here; see Alonso (1996), Frey (1988) and Flössner (2000). Figure of postabdomen after Alonso (1996) in Figure 10 View FIGURE 10 .
Differential diagnosis. For differences between C. rectangula and other smaller Aloninae ( Alona verrucosa , A. monacantha ), see genus diagnosis and discussion. C. rectangula has no denticles on labrum, no denticles or tufts in posteroventral corner of valves, it has a long basal spine on terminal claw (about a third of claw length and two times claw width), and three main connected head pores. C. rectangula differs from the following two species C. anemae and C. holdeni ( Table 1), by relatively small rounded labral plate, well-pronounced notch on the valves, group of long spines on second segment on the exopod of second antenna and the first endopod spine longer than second endopod segment; postabdomen relatively short and broad, about two times as long as wide, with well pronounced concave anal and convex postanal dorsal margin; basal spine about a third of claw length (much longer in C. anemae ). Six to seven postanal marginal groups of denticles and a well-developed distal spine in each lateral fascicle on the postabdomen are also useful characters to recognize C. rectangula . Characters on limbs: ODL setae with modified armature (strong proximal spines and reduced distal part), anterior elements P1 absent; exopodite II with well developed seta; a good character for a short fourth seta on exopodite III (a very useful character for C. rectangula !), setae three and four on exIV of similar length; gnV lacking filter setae.
Distribution and biology. We agree with Frey (1988) that Coronatella rectangula sensu stricto is likely restricted to Western Europe and absent in the Nearctic. In Russia it is common, widespread and shows a remarkable polymorphism, in the Far East other species may be present ( Sinev 2001b). Populations outside this region should be rechecked for cryptic species, but also within Europe a finer resolution is possible and names are available for later division into subspecies. We have no idea about the southern range of C. rectangula sensu stricto (e.g. in Africa), which may overlap with C. anemae n.sp. The C. rectangula -complex has a cosmopolitan distribution, as records of Alona rectangula or Alona cf. rectangula appear worldwide ( Smirnov 1971, Sinev 2001b, Frey 1993). We did not include a detailed distribution map for C. rectangula , the situation is still too complex. Differences in external morphology (habitus, postabdomen) between these congeners are very small. For further comments on distribution, see below taxonomic part. Coronatella rectangula occurs in a wide variety of habitats: temporary pools, lakes, rivers, springs and groundwater; eurythermic, in neutral to alkaline waters; reaches high abundances in productive waters ( Flössner 2000). Prefers littoral, detritus-rich situations at the base of macrophytes but can live on a variety of substrates ( Fryer 1968); may occur in plankton in lakes with algal blooms ( Flössner 2000). One of few chydorid species to thrive at higher salinities ( Flössner 1972, Frey 1993, below). In Belgium, we found it mainly in or close to rivers (e.g., Samber).
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