Alona lepida Birge, 1982

Sinev, Artem Y., 2013, Cladocerans of Alona affinis group (Cladocera: Anomopoda: Chydoridae) from North America, Zootaxa 3693 (3), pp. 329-343 : 335-341

Alona lepida Birge, 1982

( Figs 4–7 )

Birge 1982: 393–394, Plate XIII. Fig. 19.

Type material: non-existent.

Material: over 40 parthenogenetic females from White lake, Blanden County, North Carolina, USA, 27.02.1979, coll. D.G. Frey, sample DGF 4998, 20 of them deposited as a separate sample, USNM 1207830.

Initial description. “ Length 0.8 mm. Length of male 0.6 mm. Height 0.45 – 0.50 mm. Height of male 0.3 mm. Length postabdomen 0.40 mm. General shape confirms to Alona type. Head depressed, rostrum sub-acute, nearly reaching the level of the ventral margin of the shell. Valves quadrangular, dorsal margin arched, superior posteal angle obtuse, well-marked. Posterior margin oblique, bearing a row of minute spinules. Inferior posteal angle rounded, very slightly emarginate. Ventral margin beset with a row of plumose seta, of ordinary length, which ends abruptly at the posterior angle. Valves marked by close-set, conspicuous, longitudinal striae, alternately stronger and weaker, occasionally anastomosing, running parallel to the dorsal and ventral margins and converging into a reticulated area at the anterior inferior portion of valves. Between the striae lie the braces. Antennule extend nearly to the end of the rostrum: is spindle-shaped, largest near base, provided with anterior sense-bristle and 6 – 8 subaequal sense-hairs. Antennary setae 3 0 0/1 1 3. The terminal setae are of unequal length. All plumose and without spines. The eighth seta is of moderate size, bi-articulated and plumose. Spines of antenna 1 0 1/ 0 0 1. On the middle joint of the inner branch is a circlet of small spines. Ventral margin of labrum often notched just anterior to the posterior angle, which is sharp. Eye moderate in size, showing four or smaller lenses. Macula nigra as large as eye, angular, and somewhat nearer to the eye than to the apex of the rostrum. Postabdomen enlarged posteriorly, lower angle rounded, bearing 15 – 17 serrate postanal denticles and about the same number of squamae. Terminal claw smooth. Basal spine rather large. Abdominal setae of ordinary length.

Male. Antennule cylindrical, with anterior sense-bristle and flagellum. Postabdomen devoid of denticles and with a row of squamae. Vas deferens opens in front of terminal claw. Basal spine large.

Color yellowish to bright yellow, fairly transparent. Lake Mendota, in deeper water, 15 – 20 feet. The species is evidently related to A. elegans Kurz , from which it differs in its greater size, in the reticulation of part of the shell, and in the size, shape and armature of postabdomen. The postabdomen of A. lepida resembles in general that of A. quadrangularis, O.F.M. The species live at the bottom in rather deep water – 15 – 20 or more feet – and is much more abundant in Lake Mendota than elsewhere in the vicinity of Madiso n.”

Diagnosis. Large Alona , length up to 1.06 mm. Body Leydigia -like, carapace height strongly increasing posteriorly, maximum height in the third fourth of the body, height/length ratio 0.52–0.6 in adults. Dorsal margin of carapace convex, postero-dorsal and postero-ventral angles broadly rounded. Posterior margin weakly convex. Ventral margin weakly convex to straight, with over 70 setae. Postero-dorsal angle with 9–12 groups of large setules, with 5–9 setules in each. Carapace ornamentation as well-developed longitudinal lines. Head with short rostrum, eye and ocellus present. Head shield with posterior margin as prominent distal angle with blunt tip, rostrum short and rounded. Two major head pores with a narrow connection between them. PP about 1.2–1.5 IP. Lateral head pores minute, located about 0.7–0.9 IP distance from midline, at level of anterior major head pore.

Labrum with moderately wide keel, with a blunt or rounded apex. Posterior margin weakly convex, with two clusters of short setules. Postabdomen large, subrectangular, moderately high, with straight ventral margin and weakly conveõ dorsal margin; maximum height after the postanal angle. Length about 2.5 height. Distal margin from almost straight to weakly convex; distal angle rounded. Dorsal margin weakly convex in postanal portion and weakly concave to almost straight in anal one, with distal part about 2.5–3 times longer than preanal one, and with postanal portion 2.5–2.8 times longer than anal one. Preanal angle well expressed, postanal angle not defined. Postanal margin with 15–17 well-developed, single sharp denticles, each with 1–4 denticles along anterior margin; size of denticles increasing distally. Postanal portion with 14–15 moderately broad lateral fascicles, posteriormost setae of each fascicle longest, thicker than others. Postabdominal claw of moderate length, longer than preanal portion of postabdomen. Basal spine long and slender, about 0.25 the length of the claw, angle between spine and postabdomen itself about 15° only. Antennule of moderate size, with nine terminal aesthetascs and terminal antennular seta. Antennal formula, setae 0–0–3/1–1–3, spines 1–0–1/0–0–1. Seta arising from basal segment of endopodite thin, not reaching the end of endopodite. Two shortest apical setae on each branch with a spinule at the point of articulation. Spine on basal segment of exopodite significantly longer than middle segment. Spines on apical segments shorter than apical segments. Limb I with accessory seta almost as long as ODL seta. IDL with three setae: seta 1 well-developed, thick, about half length of seta 2; setae 2 and 3 subequal in length. Scrapers of limb II of similar morphology. Exopodite of limb III with seven setae, seta 3 being the longest. Exopodite IV with six setae. Exopodite V bilobed, with four setae, filter plate V present. Limb VI present as elongated lobe.

Description. Parthenogenetic female. General. In lateral view, body Leydigia -like; low in juvenile females ( Fig. 4 A–B), of moderate height in adults ( Fig. 4 D, 5A–D) and moderately compressed laterally. Carapace height strongly increasing posteriorly, maximum height in the third fourth of the body. Height/length ratio 0.52–0.6 in adults.

Carapace. Dorsal margin convex, postero-dorsal and postero-ventral angles broadly rounded. Posterior margin weakly convex. Antero-ventral angle rounded. Ventral margin weakly convex to straight; ventral setae as in the previous species. Postero-dorsal angle ( Fig. 4 F) with 9–12 groups of large setules, with 5–9 setules in each; length and thickness of setules in groups increasing posteriorly, these setules are longer and thinner than in the previous species. A row of about 80 setules of variable length along posterior margin on inner side of carapace; these setules not organized into groups. Carapace ornamentation ( Fig. 5 E) consisting in well-developed longitudinal lines without longitudinal striae between them.

Head relatively small, low triangle-rounded in lateral view. In lateral view rostrum relatively narrow, protruding downwards. Ocellus of moderate size; in most specimens eye of similar size to ocellus, sometimes eye smaller than ocellus. Distance from tip of rostrum to ocellus 1.5 times larger than that between ocellus and eye.

Head shield ( Fig. 4 C, G–H) similar to that of previous species, but with posterior margin less prominent; tip of distal angle blunt. No fine striae on head shield. A small frontal pore is located on ventral side of the rostrum between the bases of antennules ( Fig. 6 J). Two major head pores ( Fig. 4 D, I–J, 5E–G) of same size, with a narrow connection between them. PP about 1.2–1.5 IP in adults. Lateral head pores located in small depressions about 0.7– 0.9 IP distance from midline, at level of anterior major head pore. A single head shield with abnormal head pores ( Fig. 1 K) was found in the sample; anterior pore was of normal morphology, connection between pores was interrupted, and posterior pore was very large, mouth-shaped. A small porelike thickening is located on the valves behind the posterior angle of head shield.

Labrum of moderate size ( Fig. 6 A–C). Labral keel moderately wide, with a blunt or rounded apex. Anterior margin of keel evenly or unevenly convex, posterior margin weakly convex, with two clusters of short setules.

Thorax two times longer than abdomen. Dorsal surface of abdominal segments not saddle-shaped. Abdominal joint not developed.

Postabdomen ( Fig. 6 D–G) large, subrectangular, moderately high, with straight ventral margin and weakly conveõ dorsal margin; maximum height after the postanal angle. Length about 2.5 height. Basis of claws bordered from distal margin by clear incision. Distal margin from almost straight to weakly convex; distal angle rounded. Dorsal margin weakly convex in postanal portion and weakly concave to almost straight in anal one; distal part about 2.5–3 times longer than preanal one; postanal portion 2.5–2.8 times longer than anal one. Preanal angle well expressed, postanal angle not defined. Preanal margin almost straight. Postanal margin ( Fig. 6 H) with 15–17 welldeveloped, single sharp denticles, each with 1–4 denticles along anterior margin; size of denticles increasing distally. Length of longest denticles about 1.5 the width of base of postabdominal claw, more than 3 times exceeding the width of the denticle base. Anal margin with 3–5 groups of marginal spines and setules. Postanal portion with 14–15 moderately broad lateral fascicles, posteriormost setae of each fascicle longest, thicker than others, slightly shorter than neighboring marginal denticles. Anal portion with several smaller fascicles, spaced irregularly. Postabdominal claw ( Fig. 6 I) of moderate length, longer than preanal portion of postabdomen. Basal spine long and slender, about 0.25 the length of the claw, unlike in other species of the group, angle of between spine and postabdomen itself is very small, about 15°only. A row of 9–13 long setules between basal spine and the base of postabdomen.

Antennule ( Fig. 6 J) of moderate size, length abouth 3.5 width, with cluster of 5–6 long setules about one third the length of antennule at anterior face. Antennular seta thin, almost as long as antennule, arising terminally. Nine terminal aestetascs, two of them long and thin, little shorter than antennule itself; the others much shorter, about 2/ 3 the length of antennule.

Antenna ( Fig. 6 K–M) similar to that of the previous species, but basal segments of both branches 1.5 times longer than two others, subequal in size. Two shortest apical setae on both branches with a spinule at the point of articulation; these spinules shorter than in the previous species.

Limb I ( Fig. 7 A–B) similar to that of the previous species, but IDL seta is not claw-like, more thin, about half length of seta 2; setae 2 and 3 subequal in length. Setae of endite 2 shorter than in the previous species, only slightly longer than seta f.

Limb II ( Fig. 7 C) same as in the previous species.

Limb III ( Fig. 7 D–E) similar to that of the previous species, but exopodite seta 7 is much shorter, about halflength of seta 6; basalmost seta (3) of distal endite shorter than scraping setae (1–2)

Limb IV ( Fig. 7 F–H) similar to that of the previous species, but epipodite lack projection; exopodite setae 5–6 longer than seta 4, without visible setules.

Limb V ( Fig. 7 G) similar to that of the previous species, but there is just one sensilla-like structure between inner face setae and filter plate.

Limb VI ( Fig. 7 J) narrower than in the previous species, setulated only on one side.

Ephippial female unknown.

Males were not present in the studied material, see Birge’s description above.

Size. In two studied females of first juvenile instar, length was 0.60 and 0.62 mm, height 0.34 mm in both specimens; in single studied females of second juvenile instar, length 0.84 mm, height 0.44 mm. In adult females, length 0.92–1.06 mm, height 0.49–0.56 mm.

Differential diagnosis: Alona lepida clearly differs from all other species of affinis -group by the body shape, by postabdominal claw with basal spine almost parallel to the claw itself, and by IDL seta 1 being not claw-like.

Distribution. USA, so far reported from Wisconsin and North Carolina only.

Figures

FIGURE 1. Alona ossiani herricki ssp. nov. from Sebago Lake, Cumberland county, Maine, USA. A – B, juvenile females of instar I and II. C – J, adult parthenogenetic female. C, lateral viev. D, ventral margin of valves. E – F, posteroventral corner of valves. G – H, head shields. I, head pores. J, labrum. K, ephippial female. L, adult male. Scale bar: 0.2 mm for A – C, E – F, K – K, 0.1 mm for D and I – J, 0.05 mm for E – F.

FIGURE 4. Alona lepida Birge, 1982 from White lake, Blanden County, North Carolina, USA, A, juvenile female of instar I. B – D, juvenile female of instar II. B, lateral view. C, head shield. D, head pores. E – K, adult parthenogenetic female. E, lateral viev. F, posteroventral corner of valves. G – H, head shields. I – J, head pores. K, abnormal head pores. Scale bar: 0.2 mm for A – C, E, G – H, 0.1 mm for D, I – K, 0.05 mm for F.

FIGURE 5. Alona lepida Birge, 1982 from White lake, Blanden County, North Carolina, USA, adult parthenogenetic females. A – B, lateral view. C – D, dorsal and antero-dorsal view. E, sculpture of dorsal portion of valves. F – G, head pores. H, antenna.

FIGURE 6. Alona lepida Birge, 1982 from White lake, Blanden County, North Carolina, USA, adult parthenogenetic female. A – C, labrums. В – F, outlines of postabdomen. G, postabdomens. H, distal marginal denticles of postabdomen. I, postabdominal claw. J, antennules and outline of rostrum. K, antenna. L – M, distal segments of antenna exopodite and endopodite. Scale bar: 0.1 mm for A – C, G, J – M and B – F, 0.05 mm for H – I.

FIGURE 7. Alona lepida Birge, 1982 from White lake, Blanden County, North Carolina, USA, thoracic limbs of adult parthenogenetic female. A, limb I. B, IDL and ODL of limb I. C, limb II. D, exopodite of limb III. E, distal endite of limb III. F, exopodite of limb III. G – H, inner portion of limb IV and its soft setae. I, limb V. J, limb VI. Scale bar: 0.1 mm.