Cypridopsis silvestrii ( Daday, 1902 ) Pérez & Coviaga & Ramos & Lancelotti & Alperin & Cusminsky, 2019

Pérez, Alejandra P., Coviaga, Corina A., Ramos, Lorena Y., Lancelotti, Julio, Alperin, Marta & Cusminsky, Gabriela C., 2019, Taxonomic revision of Cypridopsis silvestrii comb. nov. (Ostracoda, Crustacea) from Patagonia, Argentina with morphometric analysis of their intraspecific shape variability and sexual dimorphism, Zootaxa 4563 (1), pp. 83-102 : 87-93

publication ID	https://doi.org/ 10.11646/zootaxa.4563.1.4
publication LSID	lsid:zoobank.org:pub:FFF1E98B-B7F6-44B7-ADC0-1D13560CABC7
DOI	https://doi.org/10.5281/zenodo.5623497
persistent identifier	https://treatment.plazi.org/id/160A87E4-8870-993B-FF72-FAB3FB5493A4
treatment provided by	Plazi
scientific name	Cypridopsis silvestrii ( Daday, 1902 )
status	comb. nov.

Treatment

Cypridopsis silvestrii ( Daday, 1902) View in CoL comb. nov.

( Figs 2–5 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 )

1902 Potamocypris silvestrii . n. sp. Daday: Tab. XIV, figs. 9–13.

1994 Plesiocypridopsis silvestrii ( Daday, 1902) —Martens and Behen: 43, 64,

1996 Eucypris fontana ( Graf, 1931) View in CoL juvenile—Cusminsky and Whatley: pl. II, fig 14.

2005 Eucypris fontana ( Graf, 1931) View in CoL juvenile—Cusminsky et al.: pl. 2, fig 1

2012 Eucypris cecryphalium Cusminsky et al. 2005 —Ramón Mercau et al.: fig. 4.3.

2015 Eucypris cecryphalium Cusminsky et al. 2005 —Ramón Mercau: fig. A1.5.

2017 Eucypris fontana ( Graf, 1931) View in CoL juvenile—Coviaga et al.

Material examined: 48 females, 20 males and 5 juveniles. Female specimens were recovered from the seven sampled lakes, while males were found only in El Toro lake . Seventeen specimens were dissected and soft parts were mounted on permanent slides. Valves and carapaces were stored on micropaleontological slides. All individuals were deposited in the Micropaleontological collection of the Centro Regional Universitario Bariloche , Universidad Nacional del Comahue under the collection numbers UNC-PMIC 148-164 ( Table 1 View TABLE 1 ). All material was collected by APP, CAC , LR and JL.

Sampled locations ( Fig. 1 View FIGURE 1 ): lakes El Toro, La Proveedora, El Sello, Herradura, Potrero, Martinez 4 and Rodriguez 9.

Diagnosis: Carapace sub-triangular in lateral view. Dorsal margin arched to slightly acuminate. Anterior edge broadly rounded and posterior margin rounded to slightly acuminate. In dorsal view, carapace elliptical, anterior and posterior ends pointed; LV slightly overlaps at both ends. Laterally compressed carapace (W:L approximately 0.40, n = 20). Surface densely and homogeneously covered with setae. Respiratory plate in T1 consists of two equally developed filaments. Teeth bristles in Mx smooth under medium magnification and under high magnification the tooth bristle adjacent to the 2 nd masticatory lobe shows fine serration. Seminiferous tubules: with a simple loop in anterior part of carapace.

Description of adult female. Carapace small, L= 674 ± 19 µm (662–752, n=48), H= 384 ± 20 µm (364–405, n=48). Extremely poorly calcified carapace, mainly in specimens from El Sello lake. Carapace sub-triangular in lateral view. Dorsal margin arched to slightly acuminate. Anterior edge broadly rounded. Posterior margin rounded to slightly acuminate. Dorsal posterior margin falls towards postero-ventral border. Ventral border almost straight. Maximum height situated approximately anterior-mid length, H:L ratio around 58%. Valve surface pitted. Pore canals normal with homogenous distribution of setae ( Fig. 2 A, D View FIGURE 2 , Fig. 3 H, I View FIGURE 3 ). Wart-shaped elevations distributed along anterior and posterior margins in both valves ( Fig 2. D, E View FIGURE 2 ). Carapace elliptical in dorsal view, anterior and posterior end pointed. LV slightly overlaps at anterior and posterior ends ( Fig. 2 G View FIGURE 2 ). Greatest W approximately equal to ½ L. In ventral view, LV overlapping RV. LV slightly overlapping RV anteriorly and posteriorly ( Fig. 2 O View FIGURE 2 ). In interior view, fused zone antero-ventral broadened ( Fig. 2 I, N View FIGURE 2 ). Postero-ventral vestibule well developed ( Fig. 2 K, L View FIGURE 2 ). Inner lamella in ventral margin narrow ( Fig. 2 J View FIGURE 2 ). Posterior CIL of LV with an oblique inner list ( Fig. 2 L, M View FIGURE 2 ). Hinge adont, sulcus in RV and bar in LV ( Fig.2 J, M View FIGURE 2 ). Muscle scars with typical cypridopsine pattern ( Fig. 3 D View FIGURE 3 ).

In lateral view, the posterior margin is rounded in females of the ET bisexual population, while in females from ES, He, Po and Ro9 lakes, posterior border falls towards postero-ventral margin ( Fig. 2 View FIGURE 2 and 3 View FIGURE 3 ). According to morphometric analysis, specimens from ES and ET show significant differences in valve shape (see Geometric Morphometric Results). Non-intraspecific differences between the populations were detected either in morphology or chaetotaxy of the appendages.

A1 ( Fig. 4 A View FIGURE 4 ): Seven articulated segments. First segment with two unequal ventral plumose and one dorsal setae; Wouters organ not seen. Second segment with one anterior seta passing the middle of following segment; Rome organ not seen. Third segment elongated with unequal setae, one ventral and one dorsal. Fourth segment almost as long as wide, with one short ventral and two long dorsal setae. Fifth segment slightly longer than wide, with two short ventral setae and two long dorsal setae. Sixth segment slightly longer than wide, with four long natatory setae. Terminal segment about 4 times as long as wide, with two long natatory and one short seta. Aesthetasc ya around five times longer than terminal segment.

A2 ( Fig. 4 B View FIGURE 4 ): Second protopodal segment with one long ventral seta. Exopodite reduced, bearing one long and two short setae. First endopodal segment with short aesthetasc Y (about 1/3 length of segment) and one distal seta. Five well-developed swimming setae, exceeding the tips of the end claws, accompanying short (6 th) seta, less than half the length of the next segment. Second endopodal segment with two dorsal setae and four unequally developed t-setae. Distally with three z-setae and three claws. G1 and G3 similar in length, slightly longer than claw G2. Terminal endopodal segment with GM reaching the end of G1. Gm slender and shorter than GM. Aesthetasc y3 over half the length of Gm, and g seta shorter than y3. The appendage is partially covered with fine, short pseudochaetae.

Mb ( Fig. 4 D View FIGURE 4 ): Mandibular coxa elongated, set with rows of teeth, a small setae group and a single smooth seta on outer edge. Md palp normally developed. First segment with two long barbed setae, s1 and s2, one long smooth seta and the short (ca. 1/4 the length of accompanying seta), smooth α-seta. Second segment with three unequal dorsal smooth setae, ventrally with three long, smooth setae, one long plumose accompanying seta and a short, hirsute β-seta. Third segment with four unequal dorsal-subapical setae, one shorter than the others. Laterally with three slender, smooth setae and long, relatively robust and smooth γ -seta. Terminal segment with two claws and two equal setae.

Rake, T-shaped like organ with seven to eight teeth. Not drawn.

Mx ( Fig. 4 E View FIGURE 4 ): Palp two-segmented. Terminal segment cylindrical, about twice as long as broad and set with four setae. Teeth bristles of 3 rd masticatory lobe smooth under medium magnification; tooth bristle adjacent to the 2 nd masticatory lobe shows fine serration under high magnification.

T1 ( Fig. 5 B View FIGURE 5 ): Protopod with two a-setae, respiratory plate reduced, consisting of two equally developed filaments only. Endites with eight apical setae, five of which are plumose, arranged more or less in a row. Endopodite palp apically with two unequal long setae and one short seta.

T2 ( Fig. 5 F View FIGURE 5 ): Basal segment, with short d2 seta, d1 missing. Endopod four-segmented, the first one longer than broad with e-seta not reaching the end of following segment. Second segment with long f-seta, reaching the end of the terminal segment. Third segment with a short g-seta. Terminal segment broad with tiny h3 seta, longer h1 seta and well-developed h2 serrated claw.

T3 ( Fig. 5 H View FIGURE 5 ): Basal segment with anterior d1 and d2 and one posterior dp seta. Proximal d2 ca. seven times longer than distal d1. Second segment elongate with short apical e-seta less than half the length of the next segment. Following two segments fused, f-seta protruding from mid-length, g-seta missing. Terminal segment with pincer organ, h3 long and slender, h1 short and h2 long and serrated, with thickened base.

UR ( Fig. 5 I View FIGURE 5 ): Strongly reduced and flagelliform, typical of the subfamily. Triangular base supporting one short subapical and one long apical seta. Genital field with well-developed genital hooks ( Fig. 5 G View FIGURE 5 ).

Description of adult male. Caparace small. L= 664 ± 19 µm (620–709, n=20), H= 380 ± 11 µm (361–403, n=20). Subtle differences between male and female valve shapes ( Fig. 2 View FIGURE 2 B–C, G–H, 3 B–E, C–F), detectable by morphometric analysis (see Geometric Morphometric Results). A1, Md, Mx, T2, T3 similar to those of adult female.

A2 ( Fig. 4 C View FIGURE 4 ): First two endopodal segments more slender than in females. The 1 st endopodal segment is around 2.5 times longer than wide and the 2 nd is around 3 times longer than wide (in females this ratio is ca. 2 in both segments). First endopodal segment with an aesthetasc Y and one long posterior seta passing the distal end of the last segment. Five swimming setae on distal end of this segment; very long, exceeding the tips of the end claws, 6 th swimming seta long, over half the length of the next segment. The length of the five long natatory setae does not differ between males and females, while the 6 th seta is usually longer in males than in females. Second endopodal segment with two setae situated on the dorsal side and two short t-setae on the ventral side. Distally with one longer z2 and two shorter z1 and z3 setae. G1 and G2 similar in length, G3 slightly shorter. Terminal segment with Gm slender and shorter than GM.

T1: Protopod with two a-setae, with endite bearing 8 apical setae. Endopod transformed in two slightly asymmetrical prehensile palps. The left one ( Fig. 5 C View FIGURE 5 ) with thinner and less curved finger than right one ( Fig. 5 D View FIGURE 5 ). Subterminal segments of both palps stout, apical, with one sensory organ.

Hemipenis ( Fig. 5 A View FIGURE 5 ): Symmetrical, with outer and middle lobe separated. Rounded dorsal margin fingershape and curved outwards and bearing a small knob process on its inner margin. Middle lobe with rounded edge distally elongated with labyrinth typical of the subfamily. Zenker organ with 11 chitinous whorls ( Fig. 5 E View FIGURE 5 ).

Seminiferous tubules with a simple loop in the anterior part of carapace ( Fig. 3 C View FIGURE 3 ).

Measurements are summarized in Table 1 View TABLE 1 .

Distribution and Ecology. Cypridopsis silvestrii was recorded in both northern and southern Patagonian environments from 40° to 48° S latitude and from 68° to 71° W longitude. It was also recovered in a lacustrine sequence from ET lake ( Coviaga et al. 2017). The main environmental features of the surveyed lakes are summarised in Table 2 View TABLE 2 . In our study C. silvestrii was found living in stagnant waters with temperatures ranging from 4.6° to 21.3°C (15.3 ± 5.9 C°). Conductivity tolerance was remarkably high, from 126 µScm - 1 in individuals from ES, to 42400 µScm - 1 in ET population. This species preferred alkaline (9.1± 0.4) and well oxygenated waters (11.9±1.2 mgL -1 dissolved oxygen concentration). It is, therefore, a mesothermic and mesohaline species. Overall, these results may explain the wide geographical distribution ranges of C. silvestrii . Particularly, specimens from the northern Patagonian lake ET are mesohaline forms, and show the highest conductivity tolerance, while all southern specimens seem to be stenohaline fresher taxa ( Table 2 View TABLE 2 ).

Geometric morphometric results. Non-metric multidimensional scaling (n-MDS) analysis showed outline valve variation among ET and ES populations ( Fig. 6 View FIGURE 6 ). The main variation of this type was found in the posterodorsal margin. The parthenogenetic population of ES showed a more acuminate postero-dorsal margin than their amphigonic counterparts from ET, and these differences were statistically significant (ANOSIM R =0.79; p=0.1%). Furthermore, the valve outlines of specimens recovered from ETC overlap with C. silvestrii from ET lake morphospace ( Fig. 6 View FIGURE 6 ); no statistically significant shape differences between these groups (ETC-ET) were found (ANOSIM R=0.103; p=1.1%) indicating close similarity between the valve shape of living and subfossil individuals from ET lake. In relation to sexual dimorphism, valve outlines of males and females occupied distinct spaces on the n-MDS plot ( Fig. 7 View FIGURE 7 ) and shape difference was significant (ANOSIM R =0.45; p=0.1%). However, note that the R statistic, which characterises the degree of shape disparity, was lower than the ES-ET comparison, indicating that the valve outline differences between sexes was less marked than the differences between populations. Superposition of virtual mean outlines of both sexes showed that the female left valves were slightly different in the middle anterior area and more acuminate in the postero-ventral margin than males ( Fig. 7 View FIGURE 7 ). Most ETC valves lay well within the ET females’ morphospace, and only five valves from ETC overlapped with the males’ morphospace ( Fig. 6 View FIGURE 6 ). Valve shape dispersion, calculated as the mean area deviation from consensus (MDC), was higher in ES females (MDC±SE= 20.49± 1.63) than ET females (MDC±SE=14.79±0.82), ET males (MDC±SE=16.66±1.24) and ETC individuals (MDC±SE= 16.30±1) (K-W H 3;85 =17.68 p=0.0005). The correlation between length and height in all C. silvestrii populations studied was significant (r = 0.67); however, the coefficient of determination was low (r 2 = 0.447), suggesting that both length and height should be used to evaluate size. Moreover, the shape was not correlated with the length (r = 0.4451) or height (r = 0.1352) of valves, suggesting the absence of allometry. When subfossil individuals from ETC were superimposed, most fell well within the “female side”, while only few valves superimposed onto the “male side” ( Fig. 8 View FIGURE 8 ). Mean size variations, i.e. length, height and H:L are summarized in Figure 9 View FIGURE 9 . Significant differences in the length of carapaces were found between the four groups analysed (F 3,81 =45.7, p=0.001). Cypridopsis silvestrii females from ES were larger (700.9±16.0 µm) than ET females (663.8 ± 18.1 µm, q=9.9, p<0.001), ET males (664.3±19.2 µm, q=9.8, p<0.001) and ETC specimens (642.5±13.7 µm; q=16.5, p<0.001). Non-significant differences were detected between the length of females and males from ET (q=0.1, p=1). Regarding valve heights, significant differences were found between the four groups analysed (F 3; 81 =6.9, p<0.001). Valve heights from ES females (391.8± 13.5 µm) and ET females (391.5 ± 14.1 µm) were similar (q=0.1, p=1), whereas ET females were significantly taller than ET males (380.1±11.2 µm; q=4.1, p=0.02) and ETC individuals (378±10.9 µm; q=4.8, p=0.06). The ratio between H and L was different between groups (F 3,81 =26.7, p<0.001). This ratio was lower in the elongated ES females (0.56± 0.02) than in ET females (0.59 ±0.01; q=10.4, p<0.001). Non significant differences in the H:L ratio were detected between ET females and ETC individuals (0.59 ±0.01; q=0.06, p=1). In sum, our findings showed that individuals of C. silvestrii from ES were significantly different in shape and had greater morphological variability in valve shape than individuals from ET. We also found that ES females were larger, taller and more elongated than those in the ET population. Regarding sexual dimorphism, female specimens were taller than males in ET and it was possible to find valve shape differences between females and males. Finally, we confirmed that the valves recovered from ETC which were identified as E. fontana juveniles ( Coviaga et al. 2017), are actually C. silvestrii adults.