Ilyocypris dui, Ma & Yu, 2018

Ma, Shunxin & Yu, Na, 2018, Freshwater ostracods (Crustacea) from Tiantong National Forest Park and Dongqian Lake, eastern China, with descriptions of two new species, Journal of Natural History 52 (27 - 28), pp. 1825-1868 : 1857-1861

Ilyocypris dui sp. nov.

( Figures 22e–i , 23 , 24 )

Type locality

A stream (29.803581º N, 121.788047º E, elevation 161 m asl) with mud in a peach orchard, Ningbo , Zhejiang province, China; surface water chemistry at 14.24 h (7 September 2014): water temperature 32.9°C, pH 8.8, salinity 0.2‰, dissolved oxygen 0.37 mg /l .

Additional locality

An artificial pond (29.803581º N, 121.788047º E, elevation 161 m asl) with vegetation, surface water chemistry at 14.40 h (7 September 2014): water temperature 29°C, pH 7.8, salinity 0.2‰, dissolved oxygen 9.36 mg /l.

Type material

Holotype: one male (ECNU20140907/TT37). Allotype: one female dissected (ECNU20140907/TT38). Paratype: one female for SEM.

Etymology

The species is named in honour of the late Professor Nanshan Du (1917–2017), the School of Life Science, East China Normal University, for his great contribution to Chinese carcinology.

Dimensions

(Female, n = 2) Length, 0.77–0.91 mm; height, 0.48–0.51 mm; width, 0.30 mm. (Male, n = 1) Length, 0.83 mm; height, 0.45 mm.

Diagnosis

Carapace with two sulci located close to each other. Large tubercle positioned behind sulci. Several small tubercles present on posterior part. Natatory setae of A2 far exceeding tips of terminal claws. L6 four-segmented. L7 with one seta d on the basal segment and two setae (f and g) on the penultimate segment.

Description of male

Carapace Surface of carapace ornamented with shallow pits. Carapace with two sulci located close to each other. Large tubercle positioned behind sulci. Several small tubercles present on posterior part. In lateral view, carapace rectangular. Dorsal margin straight. Maximum height anterior of middle. Both anterior and posterior ends broadly rounded, and anterior end slightly wider than the posterior. Ventral margin concave near middle. Both anterior and posterior margins with several tubercles. Calcified inner lamella narrow at both ends. Fused zone along the anterior margin wide.

A1 seven-segmented. First segment large and wide, with one dorsal seta and two ventral setae. Second segment with one dorsal-distal seta exceeding end of next segment. Third segment with one ventral-distal seta, reaching to end of next segment, and one dorsal-distal seta. Fourth segment with two long dorsal setae and two ventral setae, with long ventral setae reaching to end of terminal segment and short ones only exceeding end of next segment. Fifth segment with two long dorsal setae and two ventral setae of unequal lengths. Sixth segment with four long setae and one short seta, with short one slightly exceeding end of terminal segment. Terminal segment with a claw-like seta, one aesthetasc ya and two long setae.

A2 four-segmented. Exopod consisting of one small plate and three setae (two short and one long), with long seta not reaching to end of first endopodal segment. First endopodal segment with one two-segmented aesthetasc Y, and one strong seta exceeding end of terminal segment; natatory setae far exceeding tips of terminal claws, sixth seta reaching to middle of terminal claws. Second endopodal segment with two smooth dorsal setae (one being slightly short) and four ventral setae t present. Claw G2 slightly shorter than both claws G1 and G3. Claw Gm shorter than claw GM. All claws smooth.

Md palp first segment with seta α short and smooth. Second segment with two equally long setae on outer edge and 3 + 2 setae on inner edge (three long setae equally long, one smooth seta and one pappose seta β). Third segment with four smooth setae towards outer apical edge, one slim γ seta, and three smooth setae on apical inner edge. Terminal segment with three distal claws and one small seta.

Mx1 palp two-segmented, terminal segment enlarged and rectangular with three claws.

L5 prehensile palps two-segmented, slightly asymmetrical. Two smooth distal setae present on end of basal segment of right palp; and only one seta present on left one. One small hirsute seta presents on terminal segment of both right and left prehensile palps. Distal seta claw-like and smooth.

L6 four-segmented. Seta d1 present on basal segment. Penultimate segment completely fused. Setae f and g smooth and short. Terminal segment with one claw and two unequal setae. Seta h1 equalling three times as long as seta h3.

L7 four-segmented. Seta d1 present on basal segment. Second segment hirsute, with e seta reaching to middle of penultimate segment. Penultimate segment with long f and g setae. Row of fine hairs on end of same segment. Terminal segment with three h setae, setae h2 and h3 equally long. All setae on L7 smooth.

UR with slightly curved stem, two setae and two claws. Seta Sp lying behind middle of posterior margin, reaching to end of stem. Seta Sa short and smooth. Claws Ga and Gp equally long.

Hp with all three lobes well defined; medial lobe large, distally dilated. Inner lobe longer than outer one. Outer lobe have a beak-like projection on the end. Chitinous part with an inverted triangle-like shape.

Zenker organ with 21 rows of chitinized rosettes.

Description of female

Prehensile palp of L5 two-segmented, with three h setae distally, two being short.

Remarks

In the genus Ilyocypris , I. dui sp. nov. is morphologically similar to Ilyocypris angulata , Ilyocypris dentifera and Ilyocypris hanguk according to the following characters: carapace rectangular in lateral view, A2 with long natatory setae, four-segmented L6, seta Sp as long as claw Gp on the UR, asymmetrical middle lobe on Hp. However, in dorsal view, I. dui sp. nov., I. angulata and I. dentifera have marginal tubercles on the shell, and of them I. dui sp. nov. and I. angulata have large lateral projections on the shell; moreover, the lateral projections of I. angulata are larger than those of I. dui sp. nov.

Comparing appendages, we found that: (1) the natatory setae on the A2 – the setae exceed tips of the terminal claws by 40% of their total length in I. dui sp. nov. and I. dentifera , and they exceed tips by 10–30% in I. angulata and I. hanguk ; (2) the L 5 in female – it is two-segmented in I. dui sp. nov. and I. angulata and is three-segmented in the other two species; (3) the terminal seta of the L 5 in male – the seta is claw-like in I. dui sp. nov. and I. hanguk , while it is seta-like in I. angulata and I. dentifera ; (4) basal segment of the L5 palp in male – two setae on the segment are present in I. hanguk and I. angulata , and three setae are in I. dentifera , whereas two setae are present on the right L5 and one seta on the left in I. dui sp. nov. (5) the Sp seta on the UR – the seta is shorter and located more medially in I. dui sp. nov. and I. angulata than in I. hanguk and I. dentifera ; (6) Hp – the middle lobe in I. dui sp. nov. is more similar to I. hanguk than to both I. dentifera and I. angulata , and the inner and outer lobe in I. dui sp. nov. is more robust than the other three species.

Zhai et al. (2017) introduced a method of cluster analysis of ostracod specimens based on Canberra Dissimilarity and suggested that the method could be used to discriminate different species based on the lengths of podomeres, claws and setae. In this study we used the same method to examine the morphological dissimilarities among I. dui sp. nov. and the other four Ilyocypris species , such as I. angulata (male and female), I. mongolica (male and female), I. dentifera (female) and Ilyocypris sp. (male and female) that we have. The results showed that the dissimilarities between male and female specimens of the same species are distinctly smaller than 4% (2–3%) and the value is 3% in I. dui sp. nov. The range of dissimilarities between the five species is c. 4– 6% ( Table 2). Zhai et al. (2017) suggested that the morphological dissimilarity between conspecific specimens is less than 4%, and between specimens from different species in the same genus is in the range of 4 to 8%. These data support our identification of the present specimens as a new species.

Figures

Figure 22. (a–d) Ilyocypris angulata Sars, 1903. Female. (a) ripplets on LV; (b) ECNU20150420/TT46, external view of RV; (c) ECNU20150420/TT46, internal view of RV; (d) ECNU20150420/TT4601, dorsal view. (e–i) Ilyocypris dui sp. nov. (e) internal view of LV (f) ripplets on LV; (g) ECNU20140907/TT37, external view of RV (Male); (h) ECNU20140907/TT37, internal view of LV (Male); (i) ECNU20140907/ TT3801, dorsal view (Female). Scale bars: 100 μm.

Figure 23. Ilyocypris dui sp. nov. (a–d, f, g) (ECNU20140907/TT37, male); (e) (ECNU20140907/TT38, female). (a) A1; (b) A2; (c) Md coxa; (d) Md palp; (e) Mx1; (f) left prehensile palp; (g) right prehensile palp. Scale bars: 100 μm.

Figure 24. Ilyocypris dui sp. nov. ECNU20140907/TT37. Male. (a) L6; (b) UR; (c) L7; (d) a photo of Hp; (e) Zenker organ. Scale bars: 100 μm.