Tonnacypris rectangularis, Yu & Ma & Wang & Zhai, 2022

Yu, Na, Ma, Shunxin, Wang, Qianwei & Zhai, Dayou, 2022, Three new species of non-marine ostracods (Crustacea, Ostracoda) from small water bodies of northern China, ZooKeys 1097, pp. 183-207 : 183

Tonnacypris rectangularis sp. nov.

Figs 7 , 8 , 9

Tonnacypris sp. - Zhai et al. 2017: 488, fig. 11.

Type locality.

A small pond (Y11, Table 1 ) in Inner Mongolia, China.

Type material.

Holotype: one female (dyzoc575) dissected, valves preserved on the micropalaeontological slides. Paratype: five females (dyzoc576-580) dissected, valves preserved on the micropalaeontological slides. All from the type locality.

Other material.

Two undissected females (dyzoc819, dyzoc821) from the type locality, preserved dry on the micropalaeontological slides.

Etymology.

From the English word rectangle, referring to sub-rectangular valve shape in lateral view.

Dimensions.

Female, LV, n = 6, length 1800-2030 μm, height 940-1040 μm; RV, n = 4, length 1804-2010 μm; height 980-1060 μm.

Diagnosis.

Carapace sub-rectangular, dorsal margin sub-parallel to ventral or slightly inclined anteriorly. Peg present on antero-ventral part of LV (Fig. 7C, E, F ). Natatory setae on A2 reduced, first and second setae approximately in same lengths, others increasing in lengths towards anterior edge (Fig. 8B ). Claw G2 on A2 short, not reaching to middle length of claw G3 (Fig. 8C ). Second segment of Md palp with 3+1+ β setae at interior side (Fig. 8E ). Mx palp with terminal segment slightly spatulate. Two tooth-bristles on third masticatory lobe of Mx smooth (Fig. 8F ). Length ratio between d1 - and d2 - setae on L6 0.41 (Fig. 9B ).

Description.

Valves (Fig. 7 ) sub-rectangular, dorsal margin sub-parallel to ventral or slightly inclined anteriorly. When inclined, greatest height posterior of mid-length. Dorsal margin slightly arched posteriorly. Ventral margin concaved (Fig. 7A-E ). Anterior end more rounded than posterior. Calcified inner lamella wider anteriorly than posteriorly. Peg present on antero-ventral part of LV (Fig. 7C, E, F ). Valve surface smooth, with setae. Carapace sub-ovate in dorsal / ventral view (Fig. 7G, H ), with greatest width behind mid-length. Each valve with one outer list running through anterior and ventral margins (Fig. 7G, H, I ).

A1 (Fig. 8A ) seven-segmented. First segment with one short dorsal and two long ventral setae. Second segment with one short dorso-apical seta and a tiny Rome organ. Third segment with one comparative long dorso-apical seta and one short ventro-apical seta. Fourth segment with two long dorso-apical and two short ventro-apical setae. Fifth segment with two long dorso-apical setae and two setae (one long and one short) ventrally. Sixth segment with four long apical setae. Seventh segment with two long setae, one short seta and aesthetasc ya.

A2 (Fig. 8B, C ) four-segmented. Natatory setae reduced, first and second setae almost in same lengths, others decreasing in lengths towards anterior edge. Claws G1 and G3 almost in same lengths. Claw G2 short, not reaching mid-length of claw G3. Claw Gm slim, reaching mid-length of claw GM.

Md coxa (Fig. 8D ) elongated and arched, with masticatory processes on interior end. Palp (Fig. 8E ) four-segmented. Seta α long and slim. Seta β hirsute. Second segment with 3+1+ β setae on interior side. Seta γ slim and smooth.

Mx (Fig. 8F ) palp two-segmented. First segment with seven setae on outer apical edge and one seta in sub-apical position near outer edge. Second segment slightly spatulate with three long and three short setae. Two tooth-bristles on third masticatory lobe smooth.

L5 (Fig. 9A ) with two a -setae, one long b -seta, one short c -seta and one hirsute d -seta.

L6 (Fig. 9B ) five-segmented. Seta d1 slightly shorter than half length of seta d2. Setae e and f short, not reaching end of next segment. Seta g long, slightly exceeding end of terminal segment. Seta h1 longer than seta h3.

L7 (Fig. 9C, D ) first segment with d1 -, d2 - and dp - setae. Second segment with e -seta not reaching end of third segment. Third segment medially with f -seta almost reaching end of this segment. Pincer organ typical of the genus, with comparatively long h3 -seta and slender, gently curved h2 -seta.

UR (Fig. 9E ) with tiny seta Sa. Claw Gp exceeding half-length of claw Ga. Seta Sp slightly exceeding end of stem. UR attachment (Fig. 9F ) with two long branches.

Remarks.

The genus Tonnacypris was first established with the fossil species Tonnacypris loessica Diebel & Pietrzeniuk, 1975. T. rectangularis sp. nov. can be identified as belonging to this genus by the presence of peg on the LV [although not all specimens of this genus have pegs, see e.g., Peng et al. (2021)], presence of the c -seta on the L5, a short d1 - and long d2 - setae on the L6. There are nine extant species in this genus ( Meisch et al. 2019). Among these, T. angulata Yang, 1985 has been described based on valves alone ( Huang et al. 1985), and its generic assignment remains uncertain ( Van der Meeren et al. 2009). The new species can be readily distinguished from all other extant congeners by the valve morphology (e.g., long and sub-parallel or anteriorly sloping dorsal margin, and narrow anterior calcified inner lamella) alone, but its soft parts offer additional diagnostic information. According to the length of the swimming setae on the A2, this species was the most similar to T. mazepovae Van der Meeren et al., 2009. But in T. rectangularis the surface of the carapace and the tooth-bristles on Mx are smooth, while in T. mazepovae the carapace surface is covered with superficial grooves and the tooth-bristles on the Mx are serrated ( Van der Meeren et al. 2009). The present specimens are similar in valve shape and size to T. tonnensis (Diebel & Pietrzeniuk, 1975). However, in T. tonnensis the postero-ventral part of the valve is more narrowly rounded, and its A1 has a very long dorsal seta on the second segment ( Van der Meeren et al. 2009: fig. 8). In addition, the UR attachment is not bifurcated in T. tonnensis . Among the fossil species, the type species T. loessica may resemble the new species in valve morphology ( Fuhrmann 2012). Both species have sub-rectangular valves and their anterior calcified inner lamella is narrow. However, while the dorsal margin of T. rectangularis is sub-parallel to the ventral margin or is inclined anteriorly, the dorsal margin of T. loessica is sloping posteriorly. And the antero-dorsal part of both valves of T. loessica is angular, forming an antero-dorsal corner (cf. Fuhrmann 2012).

Figures

Figure 7. Tonnacypris rectangularis sp. nov. Female A-D dyzoc 575 (holotype) A outer view of LV B outer view of RV C inner view of LV, with peg arrowed D inner view of RV E, F dyzoc 577 E inner view of LV, with peg arrowed F detail of peg in (E) G dyzoc 821, slightly oblique-dorsal view of carapace H, I dyzoc 819 H ventral view of carapace I detail of central part of (H), showing outer lists on both valves. Scale bars: 100 μm (F, I); 500 μm (A-E, G, H).

Figure 8. Tonnacypris rectangularis sp. nov. Female. dyzoc 575 (holotype) A A 1 B part of A 2 C part of A 2 D Md coxa E Md palp F Mx. Scale bars: 100 μm.

Figure 9. Tonnacypris rectangularis sp. nov. Female A dyzoc 580, L 5 B dyzoc 580, L 6 C dyzoc 580 part of L 7 D dyzoc 580, part of L 7 E dyzoc 575, UR F dyzoc 575, UR attachment. Scale bars: 100 μm.