Stenocypris sancari, Külköylüoğlu & Hutchins & Yavuzatmaca & Schwartz, 2021

Külköylüoğlu, Okan, Hutchins, Benjamin T., Yavuzatmaca, Mehmet & Schwartz, Benjamin F., 2021, Hyporheic ostracods (Crustacea, Ostracoda) from Texas (USA) with six new species, Zootaxa 5046 (1), pp. 1-63 : 17-23

Stenocypris sancari n. sp.

( Figs 9–12 )

Type locality. Colorado River Basin , Llano River at Mason, Mason County , Texas, USA (Lat: 30.661 15, Long: -99.11042), Elevation ~ 376 m ASL .

Etymology. The species is named after Prof. Dr. Aziz Sancar (University of North Carolina School of Medi- cine), 2015 Nobel Prize winner in chemistry, for his continued inspiration for many young people in the World.

Material examined. Holotype: Female dissected in lactophenol solution with soft body parts slide mounted and sealed with translucent nail polish (no: OK-TX-LlM-161116 H3-1); valves in micropalaeontological slides (no: OK-TX-LlM-161116 H3-2). Collected from type locality on 11 November 2016 by Benjamin T. Hutchins and Aaron P. Swink.

Dissected paratypes. Two females from the type locality (no: OK-TX-LlM-161116 H3-3-4). Collected by Benjamin T. Hutchins and Aaron P. Swink.

Non-dissected paratypes: Six females and one juvenile in 70% ethanol. Collected from type locality by Benjamin T. Hutchins and Aaron P. Swink.

Repository. Holotype and all paratypes stored at the Limnology Laboratory of the Biology Department, Bolu Abant İzzet Baysal University, Bolu, Turkey.

Description: Measurements (μm). Female (n=4): LV: L=1680–1710 (mean = 1705), H=610–640 (mean = 630); RV: L=1660–1700 (mean = 1680), H=605–640 (mean = 625); W=300–350 (mean = 330).

Carapace ( Fig. 9 ) opaque white, elongated in lateral view, with greatest height in front of center, anterior margin more rounded than posterior margin ( Figs. 9A, B ); ventral margin slightly concave, dorsal margin curved; valves surface smooth with few small pits ( Fig. 9C ) and normal pores ( Fig. 9H ); LV overlapping RV anteriorly and posteriorly ( Fig. 9E ). Muscle scars as in genus ( Figs. 9G, I ). Carapace ( Fig. 9D ) spindle-shaped in dorsal view, greatest width near center. Calcified inner lamella wider anteriorly than posteriorly ( Fig. 9F ), inner list absent, inner lamella with diamond-shaped ornamentation anteriorly, posterior inner margin with weakly sinuated curve, septa well-developed, wider anteriorly than posteriorly. LV with a short ventral keel ( Fig. 9I ). Hinge adont.

A1 ( Fig. 10A ): Seven-segmented. First segment with smooth, medium-sized dorso-apical seta and two long weakly plumose ventro-apical setae extending to end of third segment; Wouters organ not apparent. Second segment with a very short smooth dorso-apical seta, Rome organ well-developed. Third segment with two smooth setae, long dorso-apical seta extending to terminal segment and short ventro-apical seta slightly exceeding length of next segment. Fourth segment with two long subequal dorsal setae and two long sub-apical ventral setae, all extending slightly past end of terminal segment. Fifth segment with four long setae extending to end of aesthetasc ya. Penultimate segment with four long setae. Terminal segment with two long setae, one short seta and medium sized aesthetasc Ya two times longer than terminal segment.

A2 ( Fig. 10B ): Four-segmented. First segment (protopodite) with two medium sized short basal setae and one long smooth postero-distal seta reaching to end of next segment. Exopodite with one long and two short setae. First endopodal segment with five long and one shorter (sixth seta) natatory setae, aesthetasc Y stout, two-segmented and plumose, ventral seta smooth and reaching tip of terminal segment. Penultimate segment undivided, with three unequally long medium sized ventral t-setae and one short dorsal seta, z1–3 setae thin, lengths: z3>z2>z1, longest reaching tips of claws, aesthetasc y2 about as long as terminal segment, claws weakly serrated, G2 claw 1/2 length of G1 and G3. Terminal segment with GM and Gm claws, Gm claw 1/2 length of GM. Aesthetasc y3 and g seta subequal in length.

Md-palp ( Fig. 10C ): Md-coxa well-developed, with seven strong teeth. First segment with vibratory plate with six unequally long, plumose setae, three long setae (S1 and S2, and one smooth), S1 2 /3 length of S2 seta, alpha seta short and smooth. Second segment dorsally with three unequally long apical setae and ventrally with group of four smooth setae and short, cone-shaped, plumose beta seta. Penultimate segment with four long, smooth dorsal setae, gamma seta well-developed, cone-shaped, thick and two times longer than terminal segment, three apical setae smooth and shorter than beta seta. Terminal segment with three smooth claws and three short setae.

Mx1 ( Fig. 11A ): with Mx1-palp and three endites. Vibratory plate with 14+2 setose setae. Third endite with two smooth bristles. First segment of Mx1 palp with three almost equally long setae (two setose, one smooth), second segment rectangular, with five unequally long smooth claws.

T1 ( Fig. 11B ): with two short a setae and b and d setae, c seta absent. h-setae all smooth, lengths: h2>h1=h3. Vibratory plate with five setose setae.

T2 ( Fig. 11C ): five-segmented. Seta d1 long, seta d2 very short; e, f, and g setae smooth, lengths: e ≈ f> g. Penultimate segment divided. Terminal segment with very short h1 seta, h2 seta claw-like, h3 seta thin claw-like.

T3 ( Fig. 12A ): four-segmented. First segment with three d-setae smooth and slim, lengths: dp> d1 ≈ d2. Second segment with long apical e seta reaching ¾ length of penultimate segment. Penultimate segment undivided, with one lateral smooth f seta. Terminal segment with one long reflexed subapical seta (h3), one serrated claw (h2) and short (h1) seta.

Uropod ( Fig. 12B ): asymmetric, with well-developed rami. Right ramus thicker than left ramus (diagnostic feature). Right ramus strongly serrated posteriorly. Left ramus smooth or with thin setules. Anterior (Sa) seta thin, posterior seta (Sp) absent. Claws strongly serrated.

Uropodal attachment ( Fig. 12C ): with a triangular basal loop, ventral and dorsal branches well-developed. Rake-like organ ( Fig. 12D ): short, with thin teeth.

Genital organ ( Fig. 12E ): rounded, without process.

Males: unknown.

Accompanying ostracod species. See Appendix 2.

Differential diagnosis. Stenocypris sancari n. sp. is distinguished from congeners by the following characteristics: very small H/L ratio, anterior margin rounded, posterior margin slightly pointed, diamond shape ornamentation in calcified lamella visible internally, irregular septa, bulb-shaped Rome organ on A1, unequally long and thin z setae on A2, equally long h1 and h3 setae on T1, very short d1 seta on T2, enlarged h3 seta on T2, group of four setae on Md-palp, two smooth bristles on Mxl, uropod asymmetrical, right uropodal ramus with well-developed spines, left uropodal ramus with very short setules, posterior seta absent, claws with large spines.

Remarks. The septa, elongated carapace and asymmetrical caudal rami are present in all species of Stenocypris . According to Moonchaisook & Savatenalinton (2020), the septa can be in a regular or irregular pattern along the valve margin. Formation of the septa corresponds to the ontogenetic development of the species during which the width continues to increase even after the last stage of maturity ( Moonchaisook & Savatenalinton 2020). In the irregular pattern, septa are typically wide at the ocular and mouth regions. The irregular-type, wide septa is one of the diagnostic characters for several species such as S. orientalis Victor & Fernando , S. hislopi Ferguson , S. intermedia Klie , and S. sancari n. sp.. In contrast, S. malayica, Victor & Fernando , S. major (Baird) and S. sketi Petkovski & Meisch possess regular septa. The valve H and L ratio measured 0.390 in S. orientalis (Victor & Fernando) , 0.433 in S. hislopi ( Ferguson 1969) , 0.362 in S. major , and 0.40 in S. malayica (Victor & Fernando) . The ratio in S. sancari n. sp. is 0.372. Two bristles on the Mxl are smooth in S. orientalis and S. sancari n. sp. but toothed in S. major and S. bolieki (see Ferguson 1962). Additionally, there is no inner groove or list in S. orientalis and S. major , but a weak posterior groove, visible at higher magnification, is present in S. sancari n. sp. Stenocypris hirutai Smith & Kamiya , S. tsukagoshii Smith & Kamiya and S. malayica can be separated from S. hislopi , S. major , S. viridis Okubo and S. sancari n. sp. by features of the appendages. The A2 natatory setae are very short in S. hirutai (see Smith & Kamiya 2006) and S. tsukagoshii (see Smith & Kamiya 2006) but long (reaching to or beyond tips of terminal claws) in S. malayica , S. hislopi , S. major , S. viridis and S. sancari n. sp.. This difference is important from an ecological as well as morphological view; the lack of swimming setae or strongly reduced setae indicates a benthic habitat preference. Additional differences among the species are as follows: alpha seta of Md-palp is very short and thin in S. sancari n. sp. but long in S. orientalis ; Md-palp beta seta is cone-shaped, thick and longer than terminal segment in S. orientalis but smaller and thinner in S. sancari n. sp. Enlarged h3 seta on the T2 occurs in both S. malayica and S. sancari n. sp., but the h3 seta is smooth and thin in S. malayica , but plumose and thick in S. sancari n. sp. S. malayica can also be readily separated from S. sancari n. sp. by the carapace size: 1.24–1.53 mm for S. malayica (see Meisch et al. 2007) and 1.68–1.71 mm for S. sancari n. sp. Table 2 includes additional differences between the two species.

Ecology: Stenocypris is known from various aquatic habitats including springs, canals, reservoirs, rice fields and marshes, and river gravels, primarily in Asia, Europe, and North America. S. sancari n. sp. was found in the hyporheic zone under a small pool in cobbles at the littoral margin of the Llano River ca. 7 m from the riverbank. Water temperature was 17.3°C, dissolved oxygen was 0.70 mg /L, specific conductance was 349 µS/cm, and pH was 7.73. Occurrence of the species in a low-oxygen environment suggests that the species may tolerate hypoxic conditions. Other Stenocypris species have also been reported from waters with reduced oxygen. S. major was reported from canal, reservoir, and rice field habitats in Eastern Thailand where DO ranged between 2.7 and 10.7 mg /L. Alternatively, the low DO value at our site may have been a sampling artifact, as the Bou-Rouch pump can integrate waters from proximal but geochemically distinct horizons within the hyporheic zone.

Figures

FIGURE 9. Stenocypris sancari n. sp. Female. (A) LV and (B) RV external view, (C) ventral view, (D) dorsal view, (E) RV internal view with anterior and posterior septa, (F) RV external view, (G) muscle scars area, (H) pore openings with thin setae, (I) LV internal view with septa and muscle scars (note to short ventral keel). Scale bar: 100 µm.

FIGURE 10. Stenocypris sancari n. sp. Female. (A) A1, (B) A2, (C) Md. Scale bar: 50 µm.

FIGURE 11. Stenocypris sancari n. sp. Female. (A) Mx1, (B) T1, (C) T2. Scale bar: 50 µm.

FIGURE 12. Stenocypris sancari n. sp. Female. (A) T3, (B) Ur, (C) furcal attachment, (D) Rake-like organ, (E) genital organ. Scale bar: 50 µm for A–C, 30 µm for D and E.