Tonnacypris mazepovae, Meeren, Thijs Van Der, Khand, Yondon & Martens, Koen, 2009

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 : 22-28

Tonnacypris mazepovae n. sp.

( Figs. 14–17 , 21 )

Tonnacypris cf. glacialis ( Mazepova 2006) (p. 219; fig. 14B)

Type locality. Shallow embayment along the southeastern shore of Lake Hövsgöl (50°37’28”N, 100°30’50”E), about 2.5km south from the inflow from the Hilent stream. Sample taken at 1m depth on sandy sediment with few macrophytes.

Type material. Holotype: male (OC.3017), soft parts dissected in glycerine in a sealed slide, valves stored dry in a micropalaeontological slide. Dimensions: L = 1.61 mm, H = 851 µm.

Allotype: female (OC.3018), dissected and stored as the holotype. Dimensions: L = 1.74 mm, H = 933 µm. Paratypes: OC.3019–3024 (most specimens dissected and used for SEM, some whole animals preserved in 70% EtOH).

Material examined. All examined specimens were collected at the type locality. SEM images are presented for OC.3021, 3023, 3030 and drawings of soft parts are included for OC.3019, 3020.

Derivation of the name. The species is named after Dr. G.F. Mazepova () from the Limnological Institute of the Siberian Branch of the Russian Academy of Sciences, who initially identified this species as Tonnacypris cf. glacialis . This is in recognition of her contributions to ostracod taxonomy in Lakes Baikal and Hövsgöl.

Diagnosis. Moderately large species (females about 1.6–2.3 mm). In lateral view slightly higher than half length, anterior and posterior margins broadly rounded. Calcified part of the inner lamella anteriorly narrow, and only slightly narrower posteriorly compared to anteriorly. Inner lamella of the left valve with one anteroventral peg associated with a reduced inner list, posteroventral peg sometimes inconspicuous. A2 with reduced natatory setae, with tips just reaching the terminal segment. Mx1 with tooth bristles on the third endite serrated. Terminal segment of the right clasping palp of the male (T1) with a neck-like marginal indentation near the proximal end.

Description of male. Valves in lateral view ( Fig. 14 A, B) slightly higher than half the length, with greatest height situated at about two-fifth of the length, dorsal margin slightly curving there; dorsal margin almost straight and sloping between this highest point and the rounded, inconspicuous posterodorsal angle in LV; posterior margin widely rounded and evenly progressing towards ventral margin; ventral margin slightly concave; valves in inner view ( Fig. 14 A, B) with calcareous part of the inner lamella anteriorly less than twice as broad as posteriorly, posteroventral about same wide as posteriorly, ventrally only progressively narrowing around indentation; ventral part of the calcified inner lamella with one anterior and one, sometimes inconspicuous, posterior peg.

Wouters organ not seen on A1. Rome organ small. Terminal segment with two long setae, one short claw, and one smaller, slender Y-aesthetasc.

A2 ( Fig. 15 A) with longest natatory setae just reaching the terminal segment, usually these are the first, subequal natatory setae; apical chaetotaxy: z1 and z2 long claws, z3 a subequal seta, G1 a small claw (about twice the length of the terminal segment), G2 longest claw, and G3 a small seta (slightly shorter than G1); terminal segment with long claw GM, shorter claw Gm, seta g, and aesthetasc y3 with a seta fused at the base of this aesthetasc. Last two segments apically with conspicuous protruding reinforcements surrounding the socket of the largest claws; in GM, this reinforcement measuring about half the length of the terminal segment, and about the proximal width of GM (these reinforcements not illustrated because of clarity).

Mdpalp with smooth α-seta; a group of four smooth setae and one hirsute seta associated with slightly serrated β-seta; γ-seta longer, stout, serrated.

Mx1 with seven (5+2) setae on the first segment of the palp; terminal segment of this palp spatulate; tooth bristles of third endite serrated; sideways-directed bristles serrated.

T1 protopodite with process with two a-setae, single b, c and d-seta; masticatory process with 14 setae; exopodite a respiratory plate with six filaments; endopodite developed asymmetrical as two-jointed palp with clasping function: penultimate segment of the right palp with two peg-like sensory organs, equal in size ( Fig. 15 D), penultimate segment of the left palp with three smaller, unequal sensory organs ( Fig. 15 E); terminal segment of the right palp ( Fig. 15 D) with a distinct marginal indentation near the basis, this indentation almost reaching one-third of the width of the base of the terminal segment; left palp ( Fig. 15 E) with a smooth proximal curve at the inner side of the terminal segment; both terminal segments with a distinct, elongated sensory organ at the distal end.

T2 with seta d1 about 0.6 the length of seta d2.

CR ( Fig. 15 F) with proximal seta slightly hirsute, proximally slightly enforced, two distal claws, distal setae about three-fourth the length of the proximal setae; distal half of the posterior side of the ramus set with about 6 or 7 groups of setulae in single rows.

Hemipenis ( Fig. 15 B) with outer lobe slender, not curving, distally tapering and bluntly pointed, reaching only slightly beyond the inner lobe; the latter broadly rounded, serration on inner side; labyrinth of the internal spermiduct with distinctly recurving loop ‘e’; Zenker’s organ ( Fig. 15 G) muscular with numerous (about 43) internal spines.

Additional description of female. Valves in lateral view ( Fig. 14 C,D) as in the male, but larger in all dimensions; posterodorsal angle slightly more rounded than in male; carapace in dorsal view ( Fig. 14 I) subovate and slightly pointed at both sides; surface of the valves covered with polygonal pattern of superficial grooves, most obvious along the dorsal side; radial and false pore canals straight, similar to Tonnacypris tonnensis ( Fig. 10 B); valves in inner view as in the male, but ventral indentation less pronounced and posteroventral calcified part of the inner lamella more narrow in the LV; colour: whitish.

A1 ( Fig. 16 A) as in male.

A2 ( Fig. 16 B) with z-setae shorter than terminal claws, and unequal in length; G2-claw reduced, about 1.6 times the length of the terminal segment.

Mdpalp ( Fig. 16 C) as in male.

Mx1 ( Fig. 17 A) as in male.

T1 ( Fig. 17 E) with endopodite a symmetrical, undivided palp bearing two short setae and one long seta.

T2 ( Fig. 17 B), T3 ( Fig. 17 C, D) and CR ( Fig. 17 G, H) basically as described for the male.

Measurements. Female: L = 1.70–1.77 mm (n = 4), H = 933–976 µm (n = 3), W = 815 µm (n = 1)

Male: L = 1.60–1.62 mm (n = 3), H = 851–911µm (n = 3).

Remarks. Mazepova (2006) gives a range of 1.63–2.30 mm for the length of the female carapace and 1.55–1.97 for the male carapace. Apparently, the species seems to grow significantly larger in deeper water. This could not be checked from our material, as only shallow sites were sampled.

Ecology. Mazepova (2006) reported this species from shallow littoral zones as well as from profundal zones (down to 150 m deep). We found it in late summer on shallow sand with some macrophytes. Due to the reduced natatory setae on A2 and the presence in the profundal zone, the species is believed to crawl in and on sediments. In the type locality, we found a sex ratio close to 1:2 (8 males and 18 females recovered). No juveniles were found.

Differential diagnosis.

The species can be distinguished from:

Tonnacypris estonica by its larger size, less elongated valves, completely rounded posterior margin, more narrow anterior calcified lamella, anterior and posterior pegs on the inner lamella of LV, short claw G2 on AS, group of four setae next to β seta on Md palp, seven setae on the first segment of Mx palp, serrated tooth bristles on third endite of Mx and slender proximal setae of CR.

Tonnacypris tonnensis by its less elongated valves, completely rounded dorsal margin, inconspicuous posterodorsal angle, more narrow anterior calcified lamella, long γ seta on Md palp and serrated tooth bristles on third endite of Mx.

Tonnacypris edlundi n. sp. by its larger size, more narrow anterior calcified lamella, short claw G2 on A2, shorter natatory setae on A2, group of four setae next to β seta on Md palp, serrated tooth bristles on the third endite of Mx, seven setae on the first segment of Mx palp, and distinct indentation on terminal segment of right clasping palp of male.

Tonnacypris glacialis by its broadly rounded posterior margin, anterior and posterior pegs on the calcified lamella of LV, and distinct indentation on terminal segment of right clasping palp of male.

Tonnacypris lutaria by its broadly rounded posterior margin, anterior and posterior pegs on the calcified lamella of LV, and distinct indentation on terminal segment of right clasping palp of male.

Figures

FIGURE 10. Tonnacypris edlundi n. sp. ♂ (A, B) and Ψ (C – I): A) RV, iv (OC. 2994); B) LV, iv (OC. 2994); C) RV, iv (OC. 2995); D) LV, iv (OC. 2995); E) Cp, dorsal view (OC. 3009); F) detail pore canals; G) LV, iv from dorsal side under an angle of about 45 ° (OC. 2990); H) idem, detail anteroventral peg; I) idem, detail posteroventral peg. Scale: C – E = 500 µm; A, B, G = 200 µm; H, I = 20 µm.

FIGURE 14. Tonnacypris mazepovae n. sp. ♂ (A, B, E, G) and Ψ (C, D, F, H, I, J) A) RV, iv (OC. 3023); B) LV, iv (OC. 3023); C) RV, iv (OC. 3021); D) LV, iv (OC. 3021); E) LV, dorsal view on ventral valve margin LV (OC. 3023); F) LV, dorsal view on ventral valve margin LV (OC. 3021); G) dorsocaudal view on ventral valve margin LV (OC. 3023); H) dorsocaudal view on ventral valve margin LV (OC. 3021); I) Cp, dorsal view (OC. 3030); J) detail surface reticulation, dorsal view. Scale: A – F, I = 500 µm; G, H = 200 µm; J = 100 µm.

FIGURE 15. Tonnacypris mazepovae n. sp. ♂ A) A 2, with indication of aesthetascs Y, y 1, y 2, y 3 and claws z 1, z 2, G 1, G 2, GM, Gm and setae z 3, G 3, g; B) Hemipenis, with indication of loop e of the labyrinth; C) T 2, with indication of setae d 1 and d 2; D) T 1, right clasping palp; E) T 1, left clasping palp; F) CR and attachment; G) Zenker’s organ. Scale: A, C, G = 200 µm; B, D, E = 170 µm; F = 100 µm. (OC. 3019)

FIGURE 16. Tonnacypris mazepovae n. sp. 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 palp, with indication of setae α, β, γ; D) Md (plate). Scale: A, B, D = 200 µm; C = 100 µm. (OC. 3020)

FIGURE 17. Tonnacypris mazepovae n. sp. Ψ A) Mx 1, with indication of number of setae on the first segment of the palp, endites incompletely drawn; B) T 2, with indication of setae d 1 and d 2; C) T 3; D) T 3, detail of apical structures (Pincer’s organ); E) T 1, with indication of setae a, b, c, d; F) CR; G) attachment. Scale: A = 100 µm; B, C, E, F = 200 µm; D = 39 µm. (OC. 3020,3021)

FIGURE 21. Length-height plot for Tonnacypris species in this study.