Alona natalensis, Sinev, Artem Yu, 2008

Sinev, Artem Yu, 2008, A new species related to Alona costata Sars, 1862 (Cladocera: Anomopoda: Chydoridae) from South Africa, Zootaxa 1707, pp. 23-36 : 24-31

Alona natalensis sp. n.

Type locality: Lakes Cave Tarn 3, Cobham, KwaZulu-Natal Province, the Republic of South Africa, 29° 39’50’’ S, 29°18’47’’ E, altitude 2190 m.a.s.l.

Material examined: Holotype, parthenogenetic female, ZMMU, Ml-44; Paratypes, 7 parthenogenetic females, ZMMU, Ml-45; Other material: 12 parthenogenetic females from the type locality (dissected and used for SEM); 7 parthenogenetic females from Crane Tarn 3, Mzimkhulwana, KwaZulu-Natal, the Republic of South Africa, 29°42’42’’ S, 29°19’16’’ E, altitude 1950 m, NNS 2002-062; 6 parthenogenetic females from Sentinels Plateau Pool 3, Cobham, KwaZulu-Natal, the Republic of South Africa, 29°38’23’’ S, 29°24’14’’ E, altitude 1978 m, NNS 2002-065; 4 parthenogenetic females from Sentinels Plateau Pool 2, Cobham, Kwa- Zulu-Natal, the Republic of South Africa, 29°38’23’’ S, 29°24’18’’ E, altitude 1978 m, NNS 2002-064; 6 parthenogenetic females from Tarn 6, Sehlabathebe, Lesotho, 29° 51’43’’ S, 29° 7’24’’ E, altitude 2450 m, NNS 2002-052.

Etymology: the species named after its terra typica —KwaZulu-Natal Province of the Republic of South Africa.

Diagnosis. Female. Of moderate size, length up to 0.54 mm. Body oval, of moderate height, length about 1.5 times maximum height, maximum height at the middle of the body. Ventral margin with about 50 setae. Postero-ventral corner without denticles. Whole carapace covered by dense, broad longitudinal lines. Head shield with broadly rounded posterior margin, rostrum short and rounded. Three interconnected major head pores, middle pore located closer to posterior one. Connection between middle and posterior pore wide, connection between middle and anterior pore narrow. PP about 1.1–1.5 IP. Transverse lateral head pores of about 1.0–1.2 IP length, with shallow pocket-like cavities with depth about 1/3 of pore length. Labral keel suboval, with blunt or rounded apex and 1–2 clusters of setules on posterior margin.

Postabdomen wide (length ca. 2.2–2.4 height), narrowing distally, with a clearly defined, acute angle between distal and dorsal margins. Dorsal margin with distal part about 3–3.2 times longer than preanal one, with postanal portion about 1.5 times longer than anal one. Preanal and postanal angles weakly defined. Postanal margin with 8–10 well-developed single marginal denticles, anal margin with 3–5 groups of setules, 10– 12 lateral fascicles of short, very thin setules, distalmost seta of each fascicle longest. Postabdominal claw of moderate length, 1.5 times longer than preanal portion of postabdomen. Basal spine about 0.2 length of claw.

Antennula broad, with nine terminal aesthetascs, longest of them exceeding half length of antennule. Antennal formula, setae 0–0–3/1–1–3, spines 1–0–1/0–0–1. Seta arising from basal segment of endopodite reaching its distal end. Spine on basal segment of exopodite shorter than middle segment. Spine from apical segment of exopodite little longer than this segment. Apical spine of endopodite of same length as this segment.

Limb I with short accessory seta, IDL of limb I with three setae, IDL seta 1 short and slender, two others armed with short setules distally. Exopodite of limb III with seven setae, seta 3 being longest. Exopodite IV with six setae. Exopodite V with four setae. Epipodites IV and V with projections longer than exopodite itself. Limb VI present.

Male unknown.

Diagnosis. Alona natalensis sp. n. clearly belongs to the costata -group of the genus Alona , and has all distinctive characters of the group: (1) transverse lateral head pores with pocket-like cavities below, (2) postabdomen narrowing distally, with well-developed single marginal denticles and weakly developed lateral fascicles of setules, (3) IDL with three setae, (4) limb VI in shape of rounded lobe, and others. Long (1–1.2 IP) lateral pores and acute distal angle of postabdomen separate it from A. rustica Scott, 1900 and related species, A. bicolor Frey, 1965 , A. iheringula Kotov et Sinev 2004 , A. hudeci Sinev, 1999 and A. bessei Dumont, 1983 . It differs from A. costata , A. setigera , and A. cheni by the sculpture of the carapace, composed of dense broad longitudinal lines, which is unusual for the costata -group. In the species listed above, these lines are much thinner and not so densely spaced. A. natalensis differs from A. costata and A. setigera by shallow lateral head pore pockets, and from A. cheni by longer processes of the epipodites IV–V. Other differences between these four species are summarized in Table 1 .

A. costata A. setigera A. natalensis sp. n. A. cheni Description. Parthenogenetic female.

General: In lateral view body regular oval ( Fig. 1 , C, 2, A–C), of moderate height, maximum height at middle of body. In adults length about 1.5 times maximum height, in juveniles – about 1.6–1.7 maximum height ( Fig. 1 , A–B). Dorsal margin uniformly curved. Postero-dorsal and postero-ventral angles broadly rounded. Posterior margin uniformly curved. A row of about 110 setules along the posterior margin ( Fig. 1 , E), at some distance from one on inner side of carapace, these setules not organized into groups. Ventral margin almost straight, with about 50 setae, first 10–14 setae long, next 15 setae short, other setae of moderate length. Antero-ventral angle rounded. Whole carapace covered by dense, broad longitudinal lines ( Fig. 1 , D). Head relatively small, triangular-round in lateral view, rostrum short, pointing downward. Eye larger than ocellus. Distance from tip of rostrum to ocellus slightly greater than that between ocellus and eye.

Head shield with maximum width behind mandibular articulation, without any prominent sculpture ( Fig. 2 , C). Rostrum short, broadly rounded. Posterior margin of head shield broadly rounded. Three interconnected major head pores ( Fig. 1 , F, 2, F), middle pore slightly smaller than others, located closer to posterior pore. Connection between middle and posterior pore wide, connection between middle and anterior pore narrow. PP about 1.1–1.5 IP. Transverse lateral head pores of about 1.0–1.2 IP length, located about 0.5 IP distance from midline, at a level between anterior and middle main head pores. Lateral pore pockets shallow, with depth about 1/3 of pore length.

Labrum of moderate size ( Fig. 3 , A–B). Distal labral plate without setulation. Labral keel of moderate width, with a blunt or rounded apex. Anterior margin of keel convex or wavy, without clearly defined notch at midline, posterior margin with two clusters of setules.

Thorax and a bdomen subequal in length, dorsal surface of abdominal segments not saddle-shaped. No abdominal projections. Second abdominal segment with two transverse rows of short setules.

Postabdomen ( Fig. 1 , G–H, 2, H) wide, narrowing distally, with a clearly defined, acute angle between distal and dorsal margins, length about 2.2–2.4 height. Ventral margin almost straight. Inflated basis of claws bordered from distal margin by clear incision. Distal margin weakly convex to straight. Dorsal margin with distal part about 3–3.2 times longer than preanal one, with postanal portion about 1.5 times longer than anal one. Postanal portion of distal margin straight, anal portion weakly concave. Preanal and postanal angles weakly defined. Preanal margin straight.

Postabdomen with eight–ten well-developed marginal denticles, each with several spinules on anterior margin, and with three–five groups of marginal setules on anal margin. Ten–twelve lateral fascicles of short, very thin setules, distalmost seta of each fascicle longest; additional row of two–three fascicles between lateral fascicles and marginal setules in preanal region. Postabdominal claw of moderate length, 1.5 times longer than preanal portion of postabdomen. Basal spine about 0.2 of length of claw.

Antennule ( Fig. 3 , C), of moderate length, almost reaching the tip of rostrum, with four transverse rows of short setules at anterior face. Antennular sensory seta slender, two times shorter than antennule, arising at 2/3 distance from the base. Nine aesthetascs, two of them 1/4 longer than others, of about 2/3 length of antennule, others of similar size. All aesthetascs projecting beyond anterior margin of head shield.

Antenna ( Fig. 3 , D), of moderate length. Antennal formula, setae 0–0–3/1–1–3, spines 1–0–1/0–0–1. Basal segment robust, branches elongated, slender, all segments cylindrical, with short setules around distal margin. Seta arising from basal segment of endopodite thin, reaching tip of distal segment. Seta arising from middle segment of endopodite of similar size with apical setae. Spine on basal segment of exopodite shorter then middle segment. Spine from apical segment of exopodite little longer than this segment. Apical spine of endopodite of same length with this segment.

Thoracic limbs: six pairs.

Limb I ( Fig. 3 , E), of moderate size. Epipodite oval, without finger-like process. Accessory seta of moderate length. ODL ( Fig. 3 , F), with a long seta, setulation on it not visible under optical microscope. IDL with three setae and four–five clusters of small setules on ventral face, seta 1 small, thin, setae 2 and 3, 2-segmented, subequal in length to ODL seta, both with thin setules in distal part. Endite 3 with four setae, one of them shorter than others. On endite 2 there are three setae, two of them robust, armed with robust setules in distal part, little shorter than ODL setae, third seta similar to endite 3 setae. Endite 1 with two 2-segmented setae, both setulated in distal part, and a flat plumose seta of characteristic shape shifted to limb base. Two slender naked seta on anterior face of limb on endites 1 and 2. Seven rows of thin long setules on ventral face of limb. Two ejector hooks, one of them larger than the other.

Limb II. Exopodite ( Fig. 3 , G), elongated, with one short naked seta. Eight scraping spines ( Fig. 3 , H), increasing progressively in length distally, armed with small setules. Distal armature of gnathobase with three elements, the middle of them armed with denticles. Filter plate with seven setae, the posteriormost considerably shorter.

Limb III: epipodite oval, without finger-like process. Exopodite ( Fig. 3 , I) trapezium-shaped, with seven setae. Seta 3 being longest, setae 6 and 7 of 2/3 and 1/2 length of seta 3, respectively, other setae very short. Setae 6 and 7 naked, all other plumose, setules on seta 3 considerably longer than on short setae. Distal endite with three setae ( Fig. 4 , B), two distalmost members slender, sharp, with distal parts unilaterally armed with sharp, strong denticles; basalmost seta thicker, bilaterally armed with long setules. Basal endite ( Fig. 4 , A), with four stiff setae, increasing in size in basal direction. Gnathobase not clearly separated from basal endite. Four soft setae increasing in size basally, a small sensillum near the base of distalmost seta. Distal armature of gnathobase with four elements. The first one elongated, cylindrical sensillum, second thin, bent seta, others two blunt spines. Filter plate III with seven setae.

Limb IV: Pre-epipodite setulated; epipodite with a finger-like process longer than epipodite itself. Exopodite ( Fig. 3 , J) narrowing to the base, with six setae. Setae 1–3 long, plumose, subequal in length, seta 4 two times shorter, plumose. Setae 5–6 slender, naked, of equal size, longer than seta 4. Inner lobe of limb IV with four setae ( Fig. 4 , C). Distalmost seta slender, sharp, armed with strong, sharp denticles, next to it with inflated base, armed with 7–9 strong, sharp setules, two other slender, with narrow base, in distal part with thin setules. Sensillum rounded. Three soft setae increasing in size basally. Gnathobase with one, 2-segmented seta, and pair of small hillocks distally. Filter plate with five setae.

Limb V ( Fig. 3 , K): pre-epipodite setulated, epipodite with finger-like process longer than epipodite itself. Exopodite divided in two lobes, lateral lobe with three long, densely setulated setae, seta 1 being longest, distal lobe densely setulated, with only a single short seta, twice shorter than seta 1. Inner limb portion an oval lobe, with setulated inner margin. At inner face, two setae, one three times longer than other. Filter plate with three setae.

Limb VI ( Fig. 3 , L) an elongated lobe, its length about twice maximum width, with most of its margin densely setulated.

Ephippial female and male unknown.

Size: In juvenile females of instar I, length 0.35–0.38 mm, height 0.20–0.22 mm, in juvenile females of instar II length 0.4–0.45 mm, height 0.24–0.26 mm. In adult females, length 0.46–0.54 mm, height 0.28–0.33 mm.

Distribution and ecology: A. natalensis sp. n. inhabits small, possibly temporary, water bodies (pools and tarns) in the East Escarpment portion of Drakensberg Mountains within KwaZulu– Natal and Lesotho. At the time of sampling, pH varied from 6 to 7.6, temperature from 16.4 to 22 ºC. Other species of Cladocera cooccurring with A. natalensis are listed in Table 2 .

Figures

FIGURE 1. Alona natalensis sp. n. from Lakes Cave Tarn 3, Cobham, KwaZulu – Natal, the Republic of South Africa: A – juvenile female of instar I, B – juvenile female of instar II, C – G – parthenogenetic female: C – lateral view, D – valve, E – posterior margin of valves, F – head pores, H – G – postabdomen. Scale bars denote 0.1 mm.

FIGURE 2. Alona natalensis sp. n. from Lakes Cave Tarn 3, Cobham, KwaZulu – Natal, the Republic of South Africa, parthenogenetic female: A – B – lateral view, C – antero-dorsal viev, D – E – sculpture of valves, F – head pores, H – postabdomen. Scale bars denote 0.1 mm for A-C, 0.05 mm for D, H, 0.01 mm for E-F.

FIGURE 3. Alona natalensis sp. n. from Lakes Cave Tarn 3, Cobham, KwaZulu – Natal, Republic of South Africa, parthenogenetic female: A – B – labrum, C – antennule, D – antenna, E – F – limb I and its ODL and IDL, H – G – limb II and its exopodite, I – exopodite of limb III, J – exopodite of limb IV, K – limb V, L – limb VI. Scale bar denotes 0.1 mm.

FIGURE 4. Alona natalensis sp. n. from Lakes Cave Tarn 3, Cobham, KwaZulu – Natal, the Republic of South Africa, parthenogenetic female: A – B – inner portion of limb III, С – inner portion of limb IV. Scale bar denotes 0.05 mm.

Tables

TABLE 1. Main differences between A. costata, A. setigera, A. natalensis sp. n., and A. cheni.

Longitudinal lines on carapace	sparse, thin	sparse, thin	dense, broad	sparse, thin
Major head pores	three, connection between central and posterior pore narrow	two	three, connection between central and posterior pore wide	three, connection between central and posterior pore wide
PP/IP ratio	0.5–0.8	1.1–1.3	1.1–1.5	0.7–0.9
Length of lateral head pores	about 0.75 IP	about 0.9–1 IP	about 1–1.2 IP	about 0.9–1 IP
Pockets of lateral head pores	rounded, depth about 2 lengths of pore	rounded, depth about 1.5 lengths of pore	shallow, depth less then 0.4 length of pore	s emicircular, depth about 0.5 length of pore
Labral plate height	about twice maximum width	about twice maximum width	about twice maximum width	about 3 times maximum width
Anterior margin of labral plate	without a notch	without a notch	without a notch	with a defined notch
Projection on epi- podite IV	longer than epipodite itself	absent	longer than epipodite itself	absent
Projection on epi- podite V	longer than epipodite itself	absent	longer than epipodite itself	of same length as epipodite itself