Acroperus africanus, Neretina, Anna N. & Kotov, Alexey A., 2015
publication ID |
https://doi.org/ 10.11646/zootaxa.4039.4.2 |
publication LSID |
lsid:zoobank.org:pub:A12B8539-3EF1-4843-858E-83F5FE31447D |
DOI |
https://doi.org/10.5281/zenodo.5679804 |
persistent identifier |
https://treatment.plazi.org/id/03B53715-A87E-FFC9-FF3C-F90FFD16F8C0 |
treatment provided by |
Plazi |
scientific name |
Acroperus africanus |
status |
sp. nov. |
Acroperus africanus sp. nov.
( Figs. 1–5 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 )
Etymology. This new species is named after Africa, the continent where it was discovered.
Type locality. Bay of Bahir-Dar, Lake Tana, Ethiopia (11.6111° N, 37.3780° E). From this locality, 70 parthenogenetic females were collected in November 27th of 2014 by A.N. Neretina.
Type material. Holotype: an adult parthenogenetic female deposited at the collection of Zoological Museum of Moscow State University, MGU Ml 142. The label of holotype is: “ Acroperus africanus sp. nov., 1 parth. ♀ from Lake Tana ( Ethiopia), HOLOTYPE ”. Paratypes from Lake Tana preserved in 4% formaldehyde: 24 undissected parthenogenetic females (MGU Ml 143: 11.6111 N °, 37.3780 E °, collected in November 27th of 2014 by A.N. Neretina); 17 undissected parthenogenetic females (ANN 2014-008: 11.6023° N, 37.3947° E, collected in November 27th of 2014 by A.N. Neretina) and 3 undissected parthenogenetic females (ANN 2014-017: 11.6117° N, 37.3727° E, collected in November 28th of 2014 by A.N. Neretina).
Other material studied. Bahir-Dar Bay of Lake Tana: 3 adult parthenogenetic females (an ethanol-fixed sample AAK M-2633: 11.6172° N, 37.3831° E, collected by S. Cherenkov in April 2nd of 2013) and 5 juvenile parthenogenetic females (an ethanol-fixed sample AAK M-1454: 11.6116° N, 37.3779° E, collected by A.A. Kotov in February 22nd of 2009).
Eastern Cape, Republic of South Africa: 10 parthenogenetic females from the pool (31.1972° S, 28.1705° E) located near McClear Road, collected in March 26th of 1993 by K. Martens, de Moor & Barber), NNS 2002-119; 10 parthenogenetic females from the Wildebeest River Dam (31.0508° S, 28.3147° E), McClear, collected in March 27th of 1993 by K. Martens, de Moor & Barber, NNS 2002-120.
Description. Parthenogenetic female. General. In lateral view, body ovoid ( Fig. 1 View FIGURE 1 A–B, 3A, 5A), with expressed dorsal keel, maximum height anterior to the middle or at the middle of body (body height/length ratio about 0.6 for adults and juveniles). Body strongly compressed laterally ( Fig. 3 View FIGURE 3 D). Dorsal margin regularly arched in anterior portion, slightly convex in adults ( Fig. 1 View FIGURE 1 A, 5A) and nearly straight in juveniles ( Fig. 1 View FIGURE 1 B) in its posterior half, without a depression between valves and head. Posterodorsal angle expressed ( Fig. 1 View FIGURE 1 A, 5A), posteroventral margin weakly to moderately convex ( Fig. 1 View FIGURE 1 A–B, E, 5A). At inner face of posteroventral margin a row of fine setules, thinning towards posterodorsal angle ( Fig. 1 View FIGURE 1 E–F, 3H). Posteroventral angle broadly rounded ( Fig. 1 View FIGURE 1 A–B, E, 3A, 5A), provided with 1-2 small denticles ( Fig. 1 View FIGURE 1 E, G, 3I –K, 5B). Ventral margin from almost straight to weakly convex, with two groups of setae differing in length: setae are long in anterior portion, then becoming shorter in the first third of margin and then becoming longer again, decreasing in size towards posterior end ( Fig. 1 View FIGURE 1 A–B, E, 5A). A row of setules between each neighboring setae ( Fig. 1 View FIGURE 1 I, 3L–M). Anteroventral angle rounded ( Fig. 1 View FIGURE 1 A, E, 5A). Valves with prominent sculpture consisting of diagonal, never anostomosing lines ( Fig. 1 View FIGURE 1 E, 3A, N, S).
Head small, keeled ( Fig. 1 View FIGURE 1 C, 3B–C). Rostrum relatively short, compound eye larger than ocellus, distance from tip of rostrum to ocellus almost equal to distance between ocellus and eye ( Fig. 1 View FIGURE 1 C). Head keel with three connected major head pores of equal size ( Fig. 3 View FIGURE 3 E), lateral pores small, rounded, located at the level before anterior main pore ( Fig. 3 View FIGURE 3 E: arrow).
Labrum with a narrow subtriangular keel which bears several rows of fine setules ( Fig. 1 View FIGURE 1 C–D, 3F–G); apex of keel rounded.
Thorax relatively long ( Fig. 1 View FIGURE 1 A, 5A). Abdomen short, distal surface of abdominal segments with transverse rows of fine setules ( Fig. 1 View FIGURE 1 A, 2A, 5A).
Postabdomen ( Fig. 1 View FIGURE 1 A, 2A, 5A) long and narrow, with almost parallel dorsal and ventral margins, postabdomen length/height ratio about 2.5-2.7. Ventral margin almost straight, with no ridges or setules ( Fig. 2 View FIGURE 2 A– B, 3 O). Preanal margin short, length of anal margin almost equal to that of preanal margin, postanal margin two times longer than preanal margin ( Fig. 2 View FIGURE 2 A). Preanal and postanal angles well-expressed ( Fig. 2 View FIGURE 2 A). Basis of claws with a group of long setules ( Fig. 2 View FIGURE 2 A–C, 3 O, Q), bordered from distal margin by a clear depression. Postanal margin armed with series of small denticles ( Fig. 2 View FIGURE 2 A–B, 3 O, P); fascicles of thin setules on lateral sides of postabdomen; distalmost setule in each fascicle on postanal portion of postabdomen remarkably longer than following setules ( Fig. 2 View FIGURE 2 B–C, 3P–Q), while all setules in fascicles at anal margin subequal in size ( Fig. 2 View FIGURE 2 B). Postabdominal claw long (as long as anal portion of postabdomen) ( Fig. 2 View FIGURE 2 A–C), almost straight, external side armed in its proximal portion with a row of teeth fluently increasing in size distally; distalmost tooth specially strong; very fine setules on distal half of claw ( Fig. 2 View FIGURE 2 B–C, 3Q); internal side of claw with two successive pectens of setulae. Basal spine long (about 0.3 of claw length), straight and thin, with a row of setulae along its dorsal margin; also there are several short setules at claw base ( Fig. 2 View FIGURE 2 B–C, 3Q).
Antenna I relatively long and narrow (length/diameter at base about 2.7-3), with four transverse rows of short setulae at anterior face ( Fig. 2 View FIGURE 2 D, 3R). Eight terminal aesthetascs, one of them almost two times longer and thicker than others, as long as body of antenna I; a single long lateral aesthetasc located near a slender sensory seta of antenna I ( Fig. 2 View FIGURE 2 D).
Antenna II long for a chydorid ( Fig. 1 View FIGURE 1 A, 2E, 3A, S, 5A). Antennal formula: setae 0-0-3/1-1-3; spines 1-0-1/0- 0-1. Branches of antenna II subequal in size. In adults and juveniles seta on proximal segment of endopod specially short (remarkably shorter that half of middle segment). This feature is difficult to observe in the light microscope due to fine distal part of seta ( Fig. 2 View FIGURE 2 E, F, H–I, 3U, 5C). Seta on middle segment only somewhat longer than apical segment with its spine ( Fig. 2 View FIGURE 2 G) and makes up about half length of endopod itself (in adults and juveniles) ( Fig. 2 View FIGURE 2 E, F, H–I, 3T, 5C). All apical setae subequal in size ( Fig. 1 View FIGURE 1 A, 2E, G, 3A, S, 5A), covered by fine setulae ( Fig. 3 View FIGURE 3 S, V). Spine on proximal exopod segment very short (shorter than 1/4 length of second segment) ( Fig. 2 View FIGURE 2 E, F, H–I, 3S, T, 5C). Spines on both apical segments of exopod and endopod short (less than 0.3 of segment length), subequal in size ( Fig. 2 View FIGURE 2 F–I, 3S, T, 5C).
Thorax limbs: six pairs.
Limb I ( Fig. 4 View FIGURE 4 A–B, 5D–E) relatively large. Accessory seta short. Outer distal lobe ( Fig. 4 View FIGURE 4 B, 5E: ODL) conical and large, bearing a single bisegmented seta with minute setulae on distal segment. Inner distal lobe ( Fig. 4 View FIGURE 4 B, 5E: IDL) with three bisegmented setae of different length: smallest seta short with tiny setulae on the distal segment; middle and largest setae armed by relatively short and thick setulae distally. Endite 4 with three posterior setae ( Fig. 4 View FIGURE 4 A, 5D: a–c) and single anterior seta ( Fig. 4 View FIGURE 4 A, 5D: 1). Endite 3 with three posterior setae ( Fig. 4 View FIGURE 4 A, 5D: d–f), among which setae e and f very long and a rudimentary anterior seta ( Fig. 4 View FIGURE 4 A, 5D: 2). On endite 2 three bisegmented posterior setae ( Fig. 4 View FIGURE 4 A, 5D: g–i) (among which seta “i” very short) and an anterior seta ( Fig. 4 View FIGURE 4 A, 5D: 1). Endite 1 (gnathobase) reduced, without setae. Two serrate ejector hooks of almost equal size ( Fig. 4 View FIGURE 4 A, 5D). Remarkably, that ratio of seta 3/seta 2 length on the limb I is about 3–3.2 (larger, than ratios for these setae in sibling Palearctic species, A. harpae and A. angustatus (see below)).
Limb II ( Fig. 4 View FIGURE 4 C) subtriangular. Exopodite small, ovoid, with a single rudimentary seta ( Fig. 4 View FIGURE 4 C: ext); inner portion of limb with eight scrapers ( Fig. 4 View FIGURE 4 C: 1–8) forming three groups according to size: setae 1-2 longest, with fine setulation; setae 3–5 somewhat shorter, with larger setulae; setae 6-8 shortest, setae 6-7 with thick setulae and seta 8 with fine setulae. Distal armature of gnathobase with four setae; seta 1 represented by a small sensillum. Filter plate with seven seta: distalmost seta thick and short, with specially long setulae, next seta also shorter than other setae increasing in size proximally ( Fig. 4 View FIGURE 4 C).
Limb III ( Fig. 4 View FIGURE 4 D–E). Exopodite trapezium-shaped, with five distal setae (among which two middle setae specially short), and two lateral setae ( Fig. 4 View FIGURE 4 D). Distal endite (in terms of Kotov 2013) with three anterior setae ( Fig. 4 View FIGURE 4 D: 1–3): setae 1 and 2 supplied with robust denticles distally, a small sensillum between their bases ( Fig. 4 View FIGURE 4 D: s); seta 3 with fine setulae. Proximal endite with four small anterior setae (4–7); a small sensillum near seta 4 ( Fig. 4 View FIGURE 4 D–E: s). Four soft setae on posterior face of limb ( Fig. 4 View FIGURE 4 D, a–d). Distal armature of gnathobase with three setae and a thick sensillum ( Fig. 4 View FIGURE 4 E: s). Filter plate with seven setae of subequal size ( Fig. 4 View FIGURE 4 D).
Limb IV ( Fig. 4 View FIGURE 4 F) with ovoid preepipodite and globular epipodite supplied with a long finger-like projection; exopodite subrectangular, with three distal and three lateral setae ( Fig. 4 View FIGURE 4 F). Inner distal portion with four anterior setae: distalmost setae 1 stout, naked; setae 2-4 shorter with inflated basal portion and relatively thick setules distally ( Fig. 4 View FIGURE 4 F). Three thin setae on posterior limb face ( Fig. 4 View FIGURE 4 F). Distal armature of gnathobase with three elements, distalmost one represented by a thick sensillum ( Fig. 4 View FIGURE 4 F: s). Filter plate with five setae subequal in size ( Fig. 4 View FIGURE 4 F).
Limb V ( Fig. 4 View FIGURE 4 G) with ovoid preepipodite and globular epipodite supplied with a long finger-like projection. Exopodite bearing a single distal seta and three lateral setae. Inner limb portion as elongated flap, with setulated margin, with two setulated setae of subequal length ( Fig. 4 View FIGURE 4 G). Filter plate with three small setae ( Fig. 4 View FIGURE 4 G).
Limb VI ( Fig. 4 View FIGURE 4 H) small as compared with other five limbs, represented by a small rounded lobe with setulated margin.
Ephippial female, male. Unknown.
Size. Juvenile females 0.35–0.48 mm in length (height 0.21–0.27 mm; thickness 0.13–0.15 mm). Adult parthenogenetic females 0.55–0.86 mm in length (height 0.37–0.52 mm; thickness 0.22–0.24 mm). Holotype 0.65 mm in length (height 0.39 mm; thickness 0.24 mm).
Variability. The number of denticles on posteroventral margin of valve varies from one to two in different individuals. Remarkably, the most frequent morphotype in the population from Lake Tana has a single denticle on the posteroventral margin ( Fig. 1 View FIGURE 1 A, B, E, 3I, J), whereas individuals with 2 denticles ( Fig. 3 View FIGURE 3 K) are rarely found. Some of the investigated specimens from Lake Tana have asymmetric valves: one with a small denticle ( Fig. 1 View FIGURE 1 G) and the other without denticles (but with tiny hillock on its position) ( Fig. 1 View FIGURE 1 H). On the contrary, specimens from the two localities in Republic of South Africa usually have two denticles ( Fig. 5 View FIGURE 5 B), being the morphotype with a single denticle less common. It is not surprising because the variability of the number of denticles on the posteroventral angle was also shown for other taxa of Acroperus ( Sinev 2009; Sinev & Elmoor-Loureiro 2010; Sinev et al. 2012).
Differential diagnosis. Acroperus africanus sp. nov. could be confused with Palearctic A. harpae and A. angustatus . But the former could be easily distinguished from the latter two taxa in: (1) smaller seta on the proximal segment of antenna II endopod; (2) larger ratio of seta 3/seta 2 length on the first thoracic limb. Other differences from well-described species of Acroperus are summarized in Table 1 View TABLE 1 .
Distribution and ecology. The species is known to date from several localities in Africa ( Ethiopia and Republic of South Africa). Despite the intensive sampling in Ethiopia (there are more than 600 samples from different water bodies in the personal collection of AAK), to date A. africanus sp. nov. was found only in Lake Tana. Type locality, the Bahir-Dar Bay of Lake Tana, is a shallow water body (the maximum depth in the central part is 8.5 m) with a well-developed littoral zone covered by macrophytes ( Ceratophyllum sp., Nymphaea sp., Potamogeton sp. among others). At time of sample collection in November of 2014, temperature was 19.3–23 °C; pH 7.8 and conductivity 125 ΜS cm -1. The findings of A. africanus sp. nov. in the water bodies located in the south part of Africa allows us to presume, that this species is rather common in the continent, but it was misidentified by previous authors as Palearctic Acroperus species.
TABLE 1. Main morphological differences of Acroperus africanus sp. nov. from well-described A. harpae and A. angustatus (with links on original figures in present publication) and A. tupinamba (with links on figures in Sinev & Elmoor-Loureiro (2010 )).
Character Distribution | A. africanus (Fig. 1–5) Africa (Ethiopia, Republic of South Africa) | A. harpae (Fig. 6) Palearctic zone (records from the other localities must be rechecked) | A. angustatus (Fig. 7) Palearctic zone (records from the other localities must be rechecked) | A. tupinamba (fig. 1–3) South America (Brazil) |
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Maximum size of adult parthenogenetic female Setulae on the keel of labrum | 0.86 mm Several rows of setae (Fig. 1C–D, 3F–G) | 0.82 mm A single row of setae (Fig. 6B) | 0.95 mm Several rows of setae (Fig. 7B) | 0.57 mm Dorsal margin of keel without setulae (see fig. 1I, J) |
Number of denticles on the posteroventral angle of valve | (0) 1-2 (Fig. 1E, G, H, 3I–K, 5B) | 1-3 (Fig. 6 C-D) (but 5-9 in A. harpae f. multidentata Sinev, Zawisza & Einarsson, 2012) | 1-3 (Fig. 7 C) | 1-3 (fig. 1E–H and description in the text) |
Branches of antenna II | Subequal in size (Fig. 2E, 3S) | Endopod longer than exopod (Fig. 6E) | Subequal in size (Fig. 7D) | Subequal in size (fig. 1L) |
Seta on proximal segment of endopod | Up to 1/2 length of the middle segment (Fig. 2E, F–I, 3U, 5C) | 2/3 length of the middle segment (Fig. 6E) | As long as the middle segment (Fig. 7D) | Almost as long as the middle segment (fig. 1L) |
Seta on the middle segment of endopod | About half of endopod length (Fig. 2E, F–I, 3T 5C) | About half of endopod length (Fig. 6E) | Subequal in length with endopod (Fig. 7D) | Longer than endopod (fig. 1L) |
Ratio of seta 3/seta 2 length on the first thoracic limb | About 3–3.2 (Fig. 4A, 5D) | About 1.5–1.7 (Fig. 6F) | About 1.6–1.8 (Fig. 7E) | About 1.7 (fig. 3B) |
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