Tonnacypris, Diebel & Pietrzeniuk, 1975

Meeren, Thijs Van Der, Khand, Yondon & Martens, Koen, 2009, On Recent species of To n n a c y p r i s Diebel & Pietrzeniuk, 1975 (Crustacea, Ostracoda), with new species descriptions from Mongolia, Zootaxa 2015, pp. 1-41 : 4-16

Genus Tonnacypris Diebel & Pietrzeniuk, 1975

Tonnacypris Diebel & Pietrzeniuk, 1975 (p. 87)

Tonnacypris Diebel & Pietrzeniuk ( Martens et al. 1992; p. 104) Tonnacypris Diebel & Pietrzeniuk (Griffiths et al. 1998; p. 516) Tonnacypris Diebel & Pietrzeniuk ( Meish 2000; p. 301)

Type species. Tonnacypris loessica Diebel & Pietrzeniuk, 1975

Diagnosis. Carapace 1.1–3.2 mm long; valves smooth, without denticles (porenwarzen); elliptical to subovate in dorsal view, LV overlapping RV; valves elongated in lateral view, about twice as long as high, calcified inner lamella narrow to broad, selvage (if present) marginal; LV with small peg on anteroventral side of calcified part of inner lamella, associated with reduced or completely absent inner list; inner list absent in RV; natatory setae on A2 usually (except T. edlundi n. sp.) short; terminal segment of Mx palp trapezoical; seta d1 on T2 usually shorter than seta d2, sometimes subequal.

Species included. Recent: Tonnacypris lutaria Koch, 1838 , T. glacialis Sars, 1890 , T. estonica Järvekülg, 1960 , T. tonnensis Diebel & Pietrzeniuk, 1975 , T. convexa Diebel & Pietrzeniuk, 1975 , T. edlundi n. sp., T. mazepovae n. sp. and T. sp. A–C ( Schornikov 2007).

Fossil: T. loessica Diebel & Pietrzeniuk, 1975 (Weichselian, Germany, opt.cit.), T. turcica Freels, 1980 (Upper Middle-Miocene to lower Upper-Miocene, Turkey, opt.cit.), T. angulata Yang, 1985 (Recent, Tibet, Huang et al. 1985) and T. (?) sp. (Sub-Recent, China, Mischke et al. 2003).

Species excluded. T. sp. sensu Mazepova (2006) is here transferred to the genus Eucypris Vávra, 1891 (based on illustrated characters from both valves and hemipenis).

Remarks. The original description of the fossil (Weichselian) type species did not contain information about soft parts. Martens (1992) and Griffiths et al. (1998) added some of these characters to the generic diagnosis (from Tonnacypris lutaria and T. glacialis respectively). Here, we give a complete description for all limbs of T. estonica (as no soft parts are available for the type species), and we describe differences of other species in comparison with this full description. A differencial diagnosis is provided for described species, this is not included for T. convexa and T. sp. A–C, as no information on the soft parts of these species is available.

Tonnacypris angulata seems to have an aberrant valve shape. Type material from this fossil Chinese species should be re-examined to evaluate the generic assignment.

Tonnacypris estonica ( Järvekülg, 1960) ( Figs. 1 , 2 A, 3, 4, 5D, 6, 21)

Ilyodromus estonicus Järvekülg, 1960 (p. 32; figs. 1–5)

Ilyodromus estonicus (Järvekülg) Danielopol & McKenzie 1977 (p. 309; figs. 9C–F, 10F, 11E) Tonnacypris estonicus [sic] (Järvekülg) Griffiths et al., 1998 (p. 523)

Material examined. Many parthenogenetic females were recovered, mainly from spring habitats (Table 1). From the examined material, representative SEM images are presented for OC.2998, 3004, 3006 and drawings of soft parts are included for OC.2998–3000.

Diagnosis. Carapace small (L: 1.05–1.33 mm) and elongate; in lateral view, anterior margin broadly rounded, posterodorsal margin sloping towards indistinct posterdorsal angle, posteroventral angle evenly rounded; peg at the anteroventral side of the inner lamella of LV variably expressed. A2 with natatory setae reduced, longest just reaching or barely exceeding the proximal side of the terminal segment; claw G2 on A2 only slightly shorter than G1 and G3. Mx1 with tooth bristles on third endite smooth; posterior seta of the CR transformed into slender, feathered claw.

Redescription of female. Carapace in lateral view ( Fig. 1 A) with highest point located at about 3/8 of length; LV higher than RV, overlapping latter anteriorly, posteriorly and ventrally; anterior margin broadly rounded, posterodorsal margin sloping towards indistinct posterdorsal angle, posteroventral angle evenly rounded; ventral margin slightly concave. Carapace in dorsal view ( Fig. 1 B) elongated and slender, maximum width at midlength and lateral surfaces subparallel for about one-third of length; roundly pointed at anterior end, bluntly pointed at posterior end; antero- and posterodorsal lobe-like expansions of the LV distinctly overlapping the RV hinge dorsally; valves in inner view ( Fig. 1 C–F) with broad calcified inner lamella at the anterior and posterior ends, narrower ventrally; inner list reduced in LV, peg on calcified inner lamella variably expressed; few marginal pores, with simple setae and simple, straight radial pore canals ( Fig. 2 A); colour of Cp green with white zones near eyes, central muscle scars and ovaria.

A1 ( Fig. 3 A) with seven segments; first segment with two setae on ventral and one seta and minute Wouters organ on dorsal side; second segment with small Rome organ on ventral side and one seta on dorsal side; third segment with one seta on ventral and one seta on dorsal side; fourth and fifth segments with two setae on ventral and two on dorsal side; sixth segment with four long and one shorter seta; terminal segment with two long setae, one short, stout claw, and an even shorter aesthetasc Ya.

A2 ( Fig. 3 B) with reduced exopod bearing two short and one longer seta; first segment of the endopod with aesthetasc Y on ventral side, on the apical side one large seta and six short natatory setae, the latter unequal in length, the first being the longest; second segment of the endopod with two setae at dorsal side, four t-setae and aesthetasc y1 on ventral side, three z-setae, aethetasc y2, and claws G1, G2 and G3 on apical side, claw G2 distinctly longer than terminal segment, about 0.70–0.95 the length of claw G1; terminal segment with claws GM and Gm, seta g, and aesthetasc y3 with a seta fused at the base of this aesthetasc; all terminal claws set with a row of small teeth.

Masticatory process ( Fig. 3 C) of Md with coxa elongated; Md-palp ( Fig. 4 A) with four segments; first segment with respiratory plate on outer side and a group of four apical setae on inner side: one long seta, two “s”-setae with a double row of setulae, and one short smooth α-seta; second segment with group of three smooth setae on outer side, and a group of three smooth setae, one barbed seta, and one shorter, serrated β-seta on inner side; third segment with a group of four smooth setae on outer side, and five setae and one broader, long and serrated γ-seta on apical side; terminal segment apically with three claws and four setae.

Mx1 ( Fig. 3 D) with three endites and a two-segmented palp; first segment of the palp with eight (5+3) setae; terminal segment spatulate, with three claws and three setae; first endite with serrate sideways-directed bristles; third endite with two smooth tooth bristles.

T1 ( Fig. 4 B) protopodite with two a-setae, a single b- and d-seta, a relatively short c-seta on the basal part; masticatory process with 14 apical setae of different sizes and shapes; exopodite a respiratory plate with six plumose filaments; endopodite an unsegmented palp with three unequal apical setae.

T2 ( Fig. 4 C) a six-segmented walking leg; length of seta d1 (first segment) about 0.65–0.85 of length of seta d2 (second segment); third and fourth segment each with one apical seta; fifth segment with two apical setae; sixth segment with two apical setae and a long claw, with cylindrical shaft and spinose blade.

T3 ( Fig. 4 D, E) a four-segmented cleaning leg; first segment with long setae d1, d2 and dp; second segment with an apical seta e; third segment with medial seta f and distal rows of setulae associated with the pincer organ (modification of the terminal segment).

CR ( Fig. 4 F, G, Fig. 5 D) with proximal seta enforced, sparsely hirsute and distincly claw-like; two distal claws; slender, indistincly hirsute distal seta; posterior side of the ramus almost completely set with about eight indistinct groups of setulae, usually in single rows, the last two groups near the basis of the distal claws; attachment of the CR a simple, bifurcated branch.

Measurements. Female: L = 1.05–1.33 mm (n = 15), H = 539–693 µm (n = 15), W = 438–499 µm (n = 2)

Ecology. This is a crenophylic species, predominantly occurring in oligotrophic environments. Tonnacypris estonica seems to be indicative of good water quality in western Mongolian springs. High abundances have been recorded in shallow, slow-running spring water on silt or sandy substrate, with or without aquatic plants (Table 1). The species is also found in some streams and lakes, crawling on and in the sediment. Järvekülg (1960) reported adult females of this species all year round in coldwater springs (eurychronic). Temperature of the water in Mongolian localities: 3.5–16.8°C, pH 6.9–9.1, conductivity 41–2670 µS/cm. Altitude: 905–2571 m in western Mongolia and around 80 m in northern Estonia. Males unknown.

Distribution. Currently recorded only from Estonia and Mongolia, but is also mentioned in Polish ( Sywula 1974) and Russian ( Kurasov 1995) identification keys. The species is fairly common in springs along the Valley of the Great Lakes and in the northeastern part of the Mongolian Altai mountains (Table 1).

Differential diagnosis.

The species can be distinguished from:

Tonnacypris tonnensis by its smaller size, inconspicuous posterodorsal angle, missing posterior peg on calcified lamella, longer G2 claw on A2, group of three setae next to β seta on Md palp, long γ seta on Md palp, eight setae on first segment of Mx palp and the claw-like proximal setae of CR.

Tonnacypris edlundi n. sp. by its more elongated valves, single peg on the calcified inner lamella, short natatory setae, the claw-like proximal setae of CR.

Tonnacypris mazepovae n. sp. by its smaller size, more elongated valves, broader anterior calcified inner lamella, missing posterior peg on calcified inner lamella, longer G2 claw on A2, group of three setae next to β seta on Md palp, eight setae on first segment of Mx palp, smooth tooth bristles on third endite Mx, and clawlike proximal setae of CR.

Tonnacypris glacialis by its smaller size, longer G2 claw on A2, group of three setae next to β seta on Md palp, eight setae on first segment of Mx palp, smooth tooth bristles on third endite Mx and the claw-like proximal setae of CR.

Tonnacypris lutaria by its smaller size, longer G2 claw on A2, group of three setae next to β seta on Md palp, eight setae on first segment of Mx palp, smooth tooth bristles on third endite Mx and the claw-like proximal setae of CR.

Remarks.

Järvekülg (1960) reported on the discovery of this species from northern Estonia. The similarity between the claw-like proximal setae of this species with the spinous proximal setae typical of Ilyodromus Sars, 1894 (now transfered to Psychrodromus, Danielopol & McKenzie 1977 ) made him classify the new species as such. Danielopol & McKenzie (1977), who took into account more characters of soft parts, suggested that this species could represent a new genus close to Eucypris , but it was later ( Griffiths et al. 1998) transferred to the genus Tonnacypris . The absence of fossil material and the limited modern distribution of the species made the latter authors suggest a relative recent evolutionary origin.

Tonnacypris estonica has a large morphological variability in both valves ( Fig. 6 , see also Fig. 1 C–F) and soft parts ( Fig. 6 ). The ‘typical’ form (the most common form in western Mongolia, with valve shape most similar to the original description) has relatively low valve height, relatively short G2 claw on A2, and relatively short d2 seta on T2. The ‘high’ form has on average the highest valve height, relatively long G2 claws on A2 and long d setae on T2. There are also some ‘intermediate’ forms, which have also relatively high valves, but relatively shorter G2 claws on A2 and d setae on T2 than the ‘high’ form. The forms mentioned here are just morphological groups of individuals, more to illustrate the variability between different specimens and different characters than as an attempt to group some kind of related lineages. The morphological forms co-occur in different sites and habitats in western Mongolia, but the ‘high’ form has only been recorded at the most elevated, alpine sites. There is also considerable variation in the peg on the left valve: sometimes this is well expressed and obvious, sometimes hardly noticeable.

Tonnacypris tonnensis ( Diebel & Pietrzeniuk, 1975) ( Fig. 2 B, 5A, 7, 8, 9, 21)

Amplocypris tonnensis Diebel & Pietrzeniuk, 1975 (p. 93; pl. 2: fig. 1–6)

Tonnacypris tonnensis (Diebel & Pietrzeniuk) Schornikov, 2007 (p. 123; pl. 3: fig. 1)

Material examined. Parthenogenetic females were recovered from several Mongolian waterbodies (Table 1). SEM images are presented for OC.3002, 3007, 3008 and drawings of soft parts are included for OC.3001.

Diagnosis. Large (> 2 mm) species; in lateral view with dorsal margin parallel with ventral margin for about two-fifth of total length, posterodorsal angle rounded but distinct and posterodorsal margin steeply sloping towards narrow, evenly rounded posteroventral angle; calcified inner lamella anteriorly broad, ventrally with more or less pronounced pegs both anterior and posterior to the indentation of the ventral margin; inner list absent. A2 with natatory setae reduced, barely reaching the distal part of the penultimate segment; claw G2 on A2 short; Md-palp with γ-seta stout. Mx1 with smooth tooth bristles on the third endite; length of seta d1 on T2 about 0.6–0.7 length of d2.

Description of the female. Carapace in lateral view ( Fig. 7 A, B, D) with greatest height approximately in the middle; LV higher than RV, also overlapping the latter anteriorly, posteriorly and ventrally; anterior margin broadly rounded, dorsal margin parallel with ventral margin for about two-fifth of total length, posterodorsal angle rounded but distinct and posterodorsal margin steeply sloping towards narrow, evenly rounded posteroventral angle, ventral valve margin slightly curved inwardly; carapace in dorsal view ( Fig.7 C) elongated subovate with maximum width just posteriorly from midlength, slightly pointed at both ends, more roundly pointed anteriorly; valves in inner view ( Fig. 7 A, B, D) with calcified inner lamella very broad at the anterior end (about one-sixth from total length); about half as broad at the posterior end, at the ventral side narrower; LV with two pegs on the ventral side of the calcified inner lamella; lists absent; marginal pores simple, with simple setae and simple, straight radial pore canals ( Fig. 7 G, 2B). Colour: whitish.

A1 ( Fig. 8 A) with Wouters organ minute, Rome organ small; terminal segment with two long setae and one shorter claw, aesthetasc Ya subequal to the latter claw.

A2 ( Fig. 8 B) with natatory setae short but unequal in length, the longest (usually second or third seta) just reaching the proximal edge of the terminal segment; claw G2 distincly shorter than other terminal claws, usually about 1.2 times the length of the penultimate segment.

Md-palp ( Fig. 8 D) with smooth α-seta; serrated β-seta quite short and stout, associated with a group of four smooth setae and one barbed seta; serrated γ-seta stout.

Mx1 ( Fig. 9 A) with seven (5+2) setae on the first segment of the palp; terminal segment of this palp slightly spatulate; tooth bristles on third endite smooth; sideways-directed bristles on first endite serrated; respiratory plate ( Fig. 9 B) with 19+6 filaments.

T2 ( Fig. 9 D) with length of seta d1 about 0.65–0.70 the length of seta d2.

CR ( Fig. 5 A, Fig. 9 G, H) with proximal seta slightly enforced, indistinctly hirsute; posterior side of the ramus almost completely set with about ten groups of setular fields.

Measurements. L = 2.00– 2.15 mm (n = 5), H = 962 µm– 1.04 mm (n = 4), W = 880 µm (n = 1)

Ecology. This species was found in two sites with a spring discharge zone and associated streams, one large lake (permanent), and one temporary pond, which was recently merged with the adjacent lake (Table 1). Water temperature of Mongolian localities: 3.5–12.5°C, pH 7.8–9 and conductivity 282–479 µS/cm. Altitude: 1998–2426 m.

Distribution. Living populations are currently only known from the northwestern part of the Mongolian Altaï mountains (Table 1), and from the Kirgizian Tien-Shan mountains ( Schornikov 2007). Fossil Pleistocene material reported from Germany (Weichselian, Saalian, Elster; Diebel & Pietrzenik 1975; Griffiths 1995), France (Early Würm; Diebel & Pietrzenik 1975; Absolon 1976), Czech (Warthe; Absolon 1976) and the United Kingdom (Early Devesnian, Hoxnian; Green et al. 1983; Preece et al. 2006).

Differential diagnosis.

The species can be distinguished from:

Tonnacypris estonica by its larger size, more conspicuous posterodorsal angle, steeply sloping posterior margin, anterior and posterior pegs on calcified inner lamella of LV, short G2 claw on A2, group of four setae next to β seta on Md palp, stout γ seta on Md palp, seven setae on the first segment of Mx palp and the slender proximal setae of CR.

Tonnacypris edlundi n. sp. by its larger size, more elongated valves, more conspicuous posterodorsal angle, steeply sloping posterior margin, short claw G2 on A2, short natatory setae on A2, group of four setae near β seta on Md palp, stout γ seta on Md palp and seven setae on the first segment of Mx palp.

Tonnacypris mazepovae n. sp. by its more conspicuous posterodorsal angle, steeply sloping posterior margin, broader anterior calcified inner lamella, stout γ seta on Md palp and smooth tooth bristles on third endite Mx.

Tonnacypris glacialis by its more conspicuous posterodorsal angle, steeply sloping posterior margin, anterior and posterior pegs on the calcified lamella of LV, conspiciuous posterodorsal angle, stout γ seta on Md palp and smooth tooth bristles on third endite Mx.

Tonnacypris lutaria by its more conspicuous posterodorsal angle, steeply sloping posterior margin, anterior and posterior pegs on the calcified lamella of LV, conspicuous posterodorsal angle, stout γ seta on Md palp and smooth tooth bristles on third endite Mx.

Remarks.

This species was known as a fossil from Pleistocene sediments and was originally described in the genus Amplocypris Zalányi, 1944, because of the similarity with the elongated valves, pronounced posteroventral angle and occurence of a peg on the anteroventral calcified part of the inner lamella of the left valve in some species of this genus. When Recent specimens of Amplocypris tonnensis were discovered, the species was, based on similarities of soft parts, transferred to the genus Tonnacypris . We here present the first record from Mongolia, and the first description of the soft parts of this species.

Figures

FIGURE 1. Tonnacypris estonica Ψ A) Cp, lateral view (OC. 3006); B) Cp, dorsal view (specimen lost); C) RV, iv (OC. 2998); D) LV, iv (OC. 2998); E) RV, iv (OC. 3004); F) LV, iv (OC. 3004); G) detail of anteroventral peg (specimen lost). Scale: A – F = 200 µm; G = 50 µm.

FIGURE 2. Detail of the anteroventral marginal valve zones with indication of true pore canals (t) and false pore canals (f) A) Tonnacypris estonica; B) Tonnacypris tonnensis; C) Tonnacypris edlundi n. sp. Scale = 50 µm.

FIGURE 3. Tonnacypris estonica Ψ A) A 1, with indication of Rome organ (R) and aesthetasc Ya; B) A 2, with indication of aesthetascs Y, y 1, y 2, y 3 and claws G 1, G 2, G 3, GM, Gm and setae z 1, z 2, z 3, g; C) Md (plate); D) Mx 1, with indication of number of setae on the first segment of the palp, endites incompletely drawn. Scale: A = 200 µm; B = 142 µm; C = 282 µm; D = 147 µm. (OC. 2998, 2999)

FIGURE 4. Tonnacypris estonica Ψ A) Md palp, with indication of setae α, β, γ; B) T 1, with indication of setae a, b, c, d; C) T 2, with indication of setae d 1 and d 2; D) T 3; E) T 3, detail of apical structures (Pincer’s organ); F) CR; G) attachment of CR. Scale: A = 77.8 µm; B = 100 µm; C, D, F, G = 206 µm; E = 41.2 µm. (OC. 2998, 2999)

FIGURE 5. Detail of apical chaetotaxy of CR Ψ A) Tonnacypris tonnensis (OC. 3002); B) Tonnacypris edlundi n. sp (OC. 2995); C) Tonnacypris lutaria (OC. 3003); D) Tonnacypris estonica (OC. 3000). Scale: A = 62,5 µm; B, D = 50 µm; C = 66,6 µm.

FIGURE 6. Measurements for Tonnacypris estonica: Length-Height plot; Length of claw G 2 vs length of claw G 1 (A 2); Length of seta d 1 vs length of seta d 2 (T 2).

FIGURE 7. Tonnacypris tonnensis Ψ (A – E, G) and Tonnacypris lutaria Ψ (F): A) RV, iv (OC. 3002); B) LV, iv (OC. 3002); C) Cp, dorsal view (OC. 3008); D) LV, iv (OC. 3001); E) detail anteroventral peg (OC. 3007); F) idem (OC. 3010); G) detail pore canals, ventral margin. Scale: A – D = 500 µm; E = 50 µm; F = 100 µm.

FIGURE 8. Tonnacypris tonnensis Ψ A) A 1, with indication of Rome organ (R) and aesthetasc Ya; B) A 2, with indication of aesthetasc Y, y 1, y 2, y 3 and claws G 1, G 2, G 3, GM, Gm and setae z 1, z 2, z 3, g; C) Md (plate); D) Md palp, with indication of setae α, β, γ. Scale: A, B = 200 µm; C = 310 µm, D = 141 µm. (OC. 3001)

FIGURE 9. Tonnacypris tonnensis Ψ A) Mx 1, with indication of number of setae on the first segment of the palp, first and second endites incompletely drawn; B) respiratory plate of Mx 1; C) T 1, with indication of setae a, b, c, d; D) T 2, with indication of setae d 1 and d 2; E) T 3; F) T 3, detail of apical structures (Pincer’s organ); G) CR; H) attachment of CR. Scale: A = 15,5 µm; B = 270 µm; C = 200 µm; D = 141 µm; E = 302 µm; F = 61,3 µm; G, H = 283 µm. (OC. 3001)