Diaphanosoma macedonicum, Korovchinsky, Nikolai M. & Petkovski, Trajan K., 2014

Korovchinsky, Nikolai M. & Petkovski, Trajan K., 2014, The ancient Balkan lakes harbor a new endemic species of Diaphanosoma Fischer, 1850 (Crustacea: Branchiopoda: Cladocera), Zootaxa 3784 (5), pp. 539-549 : 541-547

Diaphanosoma macedonicum sp. nov.

( Figs. 1–4 )

Daphnella brachyura (Liévin, 1848) : Richard 1892, p. 151,152.

Diaphanosoma brandtianum Fischer, 1850 n. var.: Gjorgjevic 1906, p. 208, 214–217, Fig. 14–17; Georgevitch, 1907: p. 6. Diaphanosoma brachyurum (Liévin, 1848) : Parenzan 1931, p. 40; Popovska-Stankovič, 1958, p. 131; 1990, p. 56, 57; Guseska et al., 2012, p. 940.

Etymology. the species name is derived from the name of the country ( Macedonia), in whose the lacustrine zones the species was originally found.

Type material. Holotype. A female from Lake Dojran with body length 1.31 mm deposited in the collection of type material of the Zoological Museum of M.V. Lomonosov Moscow State University (Ml 125).

Paratypes. Eight females and two males from the same lake in the same collection (Ml 126), other paratypes are deposited in the authors’ collections.

Diagnosis. Body conically elongated, slightly narrowing anteriorly, with head of comparatively large or medium size, having rather strongly developed dorsal part. Swimming antennae long, with the upper branch reaching or surpassing the posterior valve margin; basipodite massive, with a small, sharp spine on the outer side of its apical end. Proximal segment of upper two-segmented antennal branch bearing conspicuous apical spine dorsally. Formula for antennal seta 4–8 / 0–1–4. Shell with conspicuous dorsoposterior angle seeming more chitinized than usual, having conspicuous dorsal and lateral ribs separating shell valves. Posteroventral valve margin armed with a row of 12–27 small comparatively sparsely situated denticles having thin setules between them. Posterior valve margin with rows of marginal and submarginal densely situated spinules and few setules between them but lacking internal submarginal thorn. Male’s antennal basipodite with large apical outer spine. Tl I with large terminal hook, having a number of denticles on its inner margin, and a naked, basally widened seta with a constriction close to it. Copulative appendages tubular.

Description. Parthenogenetic and gamogenetic female. They differ only in the presence of dark resting eggs in brood pouches in the latter ( Fig. 1 I). Body conically elongated, slightly narrowing anteriorly, with head of comparatively large or medium size (length 37.5–43.2 %, 31.3–37.7 % and height 22.1–25.4 %, 17.0–23.0 % of body length in specimens from Lake Dojran and Lake Prespa, respectively), having rather strongly developed dorsal part, shape of which may vary in preserved specimens ( Fig. 1 A, 2A–C).

Eye small (6.0–7.2 %, 6.5–7.6 % of body length) and situated closer to ventral side or anteroventral corner of head.

Antennules small ( Fig. 1 A, C) with nine small aesthetascs and rather long sensory seta.

Swimming antennae long (73.3–84.7 %, 73.2–87.7 % of body length), with the upper branch reaching or surpassing the posterior valve margin (47.5–53.4 %, 49.1–56.1 % of antennal length) ( Fig. 1 A). Their basipodite is massive, with a small, sharp spine on the outer side of its apical end closer to the base of the upper branch ( Fig. 1 D) and long naked seta on the dorsal side of this apex ( Fig. 1 K). A similar seta sits on the posterodorsal side of the basipodital proximal part ( Fig. 1 J). Proximal segment of upper two-segmented antennal branch bears conspicuous apical spine dorsally and outgrowth of slightly varied shape laterally ( Fig. 1 E). Distal segment of this branch with larger spine provided with outer and inner outgrowths near its base ( Fig. 1 F). Proximal segment of lower threesegmented antennal branch fused with the neighboring one internally ( Fig. 1 H), but has a clear articulation with it externally. Formula for antennal seta 4–8 / 0–1–4. Lateral setae of upper branch are comparatively short (25.3–27.3 % of body length) and armed uniformly with rough setules of the “swimming type ”, while the two apical ones are considerably longer (50 % of body length), having proximally the same setules but distally, thin, sparsely situated setules of the “sensory type ”. Three apical setae of lower branch are slightly shorter (38.7–43.3 % of body length) with armament of similar structure.

Shell with slightly arched dorsal side and conspicuous dorsoposterior angle ( Fig. 1 A). It seems more chitinized than usual, having conspicuous dorsal and lateral ribs separating shell valves ( Fig. 1 A, B). Valves with comparatively short posterior margin smoothly connected with ventral margin and forming a comparatively narrow inflection bearing 12–14 long, finely setulated setae, the proximal of which are diminished and sit submarginally ( Fig. 2 D, E, J). One-two similar setae sit on the ventralmost part of posteroventral margin ( Fig. 2 F–H, J), which is armed with a row of 12–27 small comparatively sparsely situated denticles having thin setules between them ( Fig. 2 D–I). Posterior valve margin with rows of marginal and submarginal densely situated spinules and few setules between them.

Postabdomen comparatively narrow with prominent ventrodistal side and long postabdominal setae (about 65 % of body length) ( Fig. 2 K). Terminal claws with three basal spines, the distal of which is longest and rather straight ( Fig. 2 L). Rows of spinules are situated above the basal spines and distally along the outer lateral side of claws.

Six pairs of thoracic limbs, all with epipodites. Structure and armament of the limbs are schematically summarized in Table 2 . Exopodite of tl I comparatively narrow at its end ( Fig. 3 B), while the exopodite widens terminally in limbs tl II–tl VI ( Fig. 3 D, F). Those of tl I–tl V bear 5–6 terminal and 3–5 lateral, unsegmented, thick and long, densely setulated setae. Endopodites of tl I–tl V are inconspicuously subdivided into four segments and bear 29–48 long, two-segmented setulated filtering setae and one (tl I) or two (tl II–tl V) outer setae, similar to those of the exopodite ( Fig. 3 A, D: arrows). Among the latter, the subterminal one is conspicuously shorter than the other ( Fig. 3 D). Small, thorn-like, naked seta on the end of proximal segment above the row of filtering setae of tl I ( Fig. 3 : ns). Gnathobase of tl I with a row of eight–nine two-segmented, distally finely setulated setae, one large twosegmented seta on its distal corner (I) and a shorter, curved, basally widened seta (i) near it ( Fig. 3 C). Gnathobases of tl II–tl V are larger, bearing 22–28 filtering setae and one naked seta (p) proximally and one long, two-segmented seta (I) distally with rough setules; an additional modified naked, hooked seta (J) with few lateral denticles near the previous one is also present (tl III– tl V) ( Fig. 3 D, E). Tl VI small and strongly modified ( Fig. 3 F). Its exopodite reduces up to the terminal plate and is armed with five terminal and one lateral setae. Endopodite with seven similar setae and one thorn. Gnathobase with two long setae and three thorns of different sizes and shapes.

Limb pairs Exopodite (apical Endopodite Gnathobase Epipodite

+ lateral setae)

Male. Most of features are similar to those of females.

Antennules long (44.3–60.7 % of body length), attached to large outgrowths of ventral side of head ( Fig. 4 A, B). Their proximal part is thickened and the distal one bears numerous densely situated setules ( Fig. 4 C).

Antennal basipodite with large apical outer spine ( Fig. 4 D). Tl I with large terminal hook, having a number of denticles on its inner margin, and a naked, basally widened seta with a constriction near it ( Fig 4 F, G). Above it, comparatively short naked setae located on the ends of each of the three previous segments.

Copulative appendages tubular (about 30 % of body length).

Size. Body measurements of species are presented in Table 1 . Female body length 0.75–1.33 mm. Resting eggs ovally-elongated 0.24–0.29 x 0.16–0.18 mm. Male body length 0.67–1.15 mm.

Intra-and interpopulational variability. On the whole, judging from Table 1 , the intrapopulational variability of specimens from both lakes seems to be low. It is slightly higher in specimens from Lake Prespa, which are smaller than those from Lake Dojran and have a smaller head and a less developed basipodite of their swimming antennae – body parts, the development of which seems directly connected. The qualitative variability of some structures, head shape, armament of swimming antennae, and shell margin, is shown in Figures 1 and 2 .

Differential diagnosis. The new species is especially close to D. mongolianum differing from it, first of all, in absence of a thorn near the posterior valve margin. Furthermore, the former possess more strongly chitinized shell integument and lacks setules between setae of the ventral valve inflection. The difference in integument structure is very obvious if specimens of the new species from Lake Dojran are compared with co-occurring representatives of D. mongolianum , which are smaller in size and have a thin, transparent integument. The same features distinguish D. macedonicum sp. nov. from D. lacustris , which also has more numerous denticles (usually 30–50, sometimes up to 60) on posteroventral valve margins. D. orghidani Negrea, 1982 widely distributed in Eurasia, including Balkan lakes, lacks thorn near posterior valve margins but it has quadrangular head, low posterior valve margins, row of marginal valve denticles shifted far ventrally and copulatory appendages of males sole-like, enlarging distally.

Remarks. Taking into consideration that D. macedonicum sp. nov. can co-occur with D. mongolianum or possibly with other congeners, it should be noted that the synonymy of the new species described above is provisional since it might not reflect other different species currently grouped under the names “ D. brachyurum ” and “ D. brandtianum ”. Only a re-investigation of material of previous researchers who studied diaphanosomas from Balkan lakes can unambiguously elucidate this question.

Figures

FIGURE 1. Diaphanosoma macedonicum sp. nov., female, Lake Dojran, Macedonia. A, general lateral view. B, general dorsal view. C, antennule. D, basipodital distal outer end. E, distal part of proximal segment of upper antennal branch of two individuals. F, apical end of distal segment of upper antennal branch. G, distal part of lower antennal branch. H, proximal part of lower antennal branch, inner side. I, resting eggs in brood pouch of gamogenetic female. J, dorsal seta of proximal part of antennal basipodite. K, dorsal seta of distal part of antennal basipodite.

FIGURE 2. Diaphanosoma macedonicum sp. nov., female (A – D, I – Lake Prespa, E – H, J – L – Lake Dojran) A – C, head, lateral view. D, E, posterior part of shell. F – I, armament of ventroposterior valve margin. J, ventral valve inflection. K, postabdomen, lateral view. L, postabdominal claw.

FIGURE 3. Diaphanosoma macedonicum sp. nov., female, Lake Dojran, Macedonia. A, distal part of endopodite of thoracic limb of first pair (tl I). B, apical end of exopodite of tl I. C, gnathobases of tl I. D, thoracic limb of second pair (tl II). E, setae on distal corner of gnathobases of thoracic limb of third pair (tl III). F, thoracic limb of sixth pair (tl VI).

FIGURE 4. Diaphanosoma macedonicum sp. nov., male, Lake Dojran, Macedonia. A, general lateral view. B, head, ventral view. C, setules of distal part of antennule. D, apical end of antennal basipodite, outer side. E, copulatory appendages. F, distal part of thoracic limb of first pair (tl I). G, hook on apical end of tl I.

Tables

TABLE 2. S tructure and armament of thoracic limbs of Diaphanosoma macedonicum sp. nov. from Lake Dojran, Macedonia, November 1989 (for explanations of abbreviations, see above and Figure 3).

I	5 + 5	(n 7 + 1) + (n 4) + (n 4) + (n 30–32)	(n 8–9) + I + i	+
II	6 + 5	(n 7–8 + 1) + (n 4 + 1) + (n 4) + (n 28)	(n 28 + p) + I	+
III	6 + 5	(n 7–8 + 1) + (n 4 + 1) + (n 4) + (n 32)	(n 24 + p) + I + J	+
IV	6 + 5	(n 8 + 1) + (n 4 + 1) + (n 4) + (n 24)	(n 24 + p) + I + J	+
V	6 + 3	(n 7 + 1) + (n 4 + 1) + (n 18)	(n 22 + p) + I + J	+
VI	5 + 1	7 + one thorn	2 + three thorns	+

TABLE 1. Measurements of body and body parts of adult females of Diaphanosoma macedonicum sp. nov. from two populations (in each column from top to bottom: range, M, SD, CV).

BL, mm HL: BL, %	HH: BL, %	DE: BL, %	AnL: BL, %	UB: AnL, %	Number of denticles on postero-ventral valve margins
1. Lake Dojran (n = 20)
1.09 – 1.33 37.5 – 43.2	22.1 – 25.4	6.0 – 7.2	73.3 – 84.7	47.5 – 53.4	13 – 24
1.20 38.9	24.2	6.6	78.9	49.3	18.1
1.43	0.77	0.33	3.45	1.77
3.69	3.19	4.93	4.37	3.58
2. Lake Prespa (n = 15)
0.90 – 1.12 31.3 – 37.7	17.0 – 23.0	6.5 – 7.6	73.2 – 87.7	49.1 – 56.1	12 – 27
1.02 34.1	19.0	7.2	81.0	52.5	20.9
1.62	1.41	0.44	4.18	2.04
4.74	7.43	6.13	5.16	3.89