Arctocypris edita, Peng & Zhai & Smith & Wang & Guo & Zhu, 2021

Peng, Ping, Zhai, Dayou, Smith, Robin J., Wang, Qianwei, Guo, Yun & Zhu, Liping, 2021, On some modern Ostracoda (Crustacea) from the Tibetan Plateau in SW China with descriptions of three new species, Zootaxa 4942 (4), pp. 501-542 : 508-514

Arctocypris edita n. sp.

( Figs 7–12 )

Type Locality. Small pond in Rutog, Ngari, Tibet, China, 29.58616ºN, 84.76981ºE, altitude 4626 m (site OS11-29; Table 1 ) .

Type Material. Holotype: a dissected female ( WOC47 ), with appendages mounted on a glass slide and valves stored in a micropalaeontological cavity slide, collected from the type locality (site OS11-29; Table 1 ).

Paratype: a dissected female ( WOC28 ), with appendages mounted on a glass slide and valves stored in a micropalaeontological cavity slide, collected from site OS11-9 ( Table 1 ) .

Other specimens: Seven dissected females ( WOC 25, 33, 34, 60, 65–67), each with appendages mounted on a glass slide and valves stored in a micropalaeontological cavity slide, collected from sites OS11-9, OS11-11 and OS11-80 ( Table 1 ).

Derivation of name. From the Latin editus, meaning high or lofty, and referring to the high altitudes where this species was collected.

Dimensions. Female (LV) length 1.00– 1.29 mm (n = 9), H/L ratio 0.56–0.59 (n = 9).

Diagnosis. In lateral view posterior margin more tightly curved than anterior margin, dorsal margin curved, with slight hump at maximum height, immediately anterior of mid-length. In dorsal view anterior margin slightly laterally compressed. Surface of valves with numerous tiny pits. LV with two closely spaced inner lists on anterior calcified inner lamella, and one list very close to inner edge of posterior calcified inner lamella. RV with single list on anterior calcified inner lamella. Aesthetasc ya on A1 long, over twice as long as terminal segment. Swimming setae extending slightly beyond end of claws of A2. Mx terminal segment with five setae/claws. L5 with no c-seta (see Discussion), but with b and d setae.

Description of female. Carapace ( Figs 7 & 10 ) sub-ovate in lateral view. Dorsal margin moderately arched with highest point situated slightly anterior of mid-length. Ventral margin concave, with small lobe-like expansion at antero-ventral LV. Anterior margin broadly rounded, slightly compressed laterally. Posterior margin narrowly rounded. In interior view, anterior calcified inner lamella much wider than that of posterior. Selvage slightly displaced inwards along posterior and postero-ventral margins of RV. RV with one, LV with two inner lists running in medial area of anterior calcified inner lamella, accompanied by number of striae. Shell surface pitted, covered with fine setae. Colour, in white-shelled phenotype, whitish but stained with small brown patterns, probably due to micro-organism colonization; greenish in green-shelled phenotype.

A1 ( Figs 8A & 11A ) with eight segments, first two of which fused into large base, supporting one shorter dorsal seta and two longer ventro-apical setae. Third segment wide and short, bearing one dorso-apical seta extending to about mid-length of next segment. RO situated on extero-ventral side of this segment, small, with enlarged base and tapering distally. Fourth segment elongate, with one dorso-apical seta and one short ventro-apical seta. Fifth segment sub-quadrate, with two very long dorso-apical setae and two unequal ventro-apical setae. Sixth segment with two very long dorso-apical setae and two ventro-apical setae extending far beyond terminal segment. Seventh segment elongate, with four very long apical setae on interior side and short seta α on exterior side extending somewhat beyond terminal segment. Eighth segment slender, with three distal setae and aesthetasc y a, latter of which slightly longer than total length of three distal-most segments. Ventral seta slightly shorter than y a. Two intermediate setae longer.

A2 ( Figs 8B, C & 11B, E ) basal segment (first protopodal segment) with one lateral seta and two unequal ventro-subapical setae. Second segment robust, carrying one seta with medial curve, extending slightly beyond distal end of third segment. Exopod small, bearing one long seta extending slightly beyond distal end of third segment (first endopodal segment) and two short setae. Third segment elongate, with three-segmented aesthetasc Y situated at about mid-length of ventral margin, and ventro-apical seta reaching basal part of terminal segment. Swimming setae extending beyond terminal claws with 20–30% of length. Sixth seta extending to mid-length of fourth segment (second endopodal segment). Ventro-apical seta of third segment extending to about distal end of terminal segment. Fourth segment elongate and undivided, with two dorso-medial setae. Setae t1–4 unequally long, with t2 being longest, extending beyond middle of terminal claws. Setae t1 and t4 shortest, extending only slightly beyond distal end of penultimate segment. Aesthetasc y1 tiny. Aesthetasc y2 small, extending slightly beyond mid-length of terminal segment. z-setae untransformed, with z2 and z3 longer than z1, extending to or slightly beyond longest terminal claw. G1 somewhat longer than G3 and G2. GM extending to about distal end of G2. Gm extending to or slightly beyond mid-length of GM. All G-claws serrated. Aesthetasc part of y3 extending to mid-length of Gm.

Md palp ( Figs 8D & 11C ) with four segments. First segment (basis) bearing four ventro-apical setae. Setae S1 and S2 on first segment with long pseudochaetae. Accompanying seta smooth, sub-equally long to S1. Seta α slender and smooth. Second segment short, with three unequally long dorso-apical setae, and five ventro-apical setae: stout and setulose seta β, three smooth grouped setae and shorter accompanying seta. Third segment elongate, with total of ten setae, including seta γ, plumose along distal half. Terminal segment with three long and two shorter setae/claws. Vibratory plate with about five wide rays and two small setae.

Mx ( Figs 8E, F & 11D ) palp with two segments. First segment with eight setae. Second segment elongate and cylindrical, with five setae/claws. Tooth bristles on distal protopodal endite with variable serration, with both bristles (WOC66), proximal bristle (WOC28, 33, 34, 65, 67), or no bristle (WOC25, 60) serrated, or only faintly serrated (WOC47).

L5 ( Figs 9A & 12A, B ) protopod with two small setae a, longer setae b and d. Setae b and d setulose in some specimens. Palp with three distal setae, seta h2 very long. Vibratory plate with six rays.

L6 ( Figs 9B & 12C ) robust, with five segments. First segment proximally with elongate anchor structure connecting limb to body, and bearing long seta d1. Seta d2 absent. Second segment carrying pseudochaetae along anterior margin, with seta e extending to about distal end of third segment. Third segment sub-rectangular, with seta f extending somewhat beyond distal end of fourth segment. Fourth segment slightly elongate, with short seta g. Fifth segment small and trapeziform, with robust and serrated claw h2 and short, sub-equally long setae h1 and h2. Seta h1 setulose.

L7 ( Figs 9C & 12D ) comparatively well sclerotized, consisting of three articulated segments. Basal segment with long Setae d1, d2 and dp. Setae e and f setulose distally. Pincer organ present, typical of subfamily. Seta h3 slightly longer than f, not S-shaped.

Ur ( Figs 9D & 12E, F ) ramus slightly curved. Sp situated at 1/6 length of ramus from distal end. Gp significantly shorter than Ga, both serrated.

Males unknown.

Remarks. Specimens of this species are represented by two colour types, green (from sites OS11-29, 80; Table 1 ) and white (sites OS11-9, 11). As there are no obvious morphological differences in carapace shape and chaetotaxy, or size between the two types, we conclude they are conspecific. Differences in the colour of specimens may be related to environmental factors, and similar colour variations have been recorded in other species (e.g. Dolerocypris ikeyai Smith & Kamiya, 2006 ; Smith 2011).

Of the five other species in the genus Arctocypris , three are extant and two are known from valves only. Arctocypris fuhrmanni and A. arctica are found living in Spitsbergen ( Olofsson 1918; Petkovski et al. 2016), while A. mareotica comb. nov. is living in North Africa, parts of Europe, and Central Asia (see review of distribution in Rasouli et al. 2016). Valves of A. mareotica comb. nov. from modern sediments have also been recorded from the Tibetan Plateau (e.g. Li et al. 2010; Song & Wang 2014; Song et al. 2015a; 2015b; Zhang et al. 2013). Arctocypris foveata and A. dulcifons were originally reported from Pleistocene deposits in Canada and Germany respectively, with valves of A. dulcifons later found in Siberia and the Qinghai region of China ( Mischke et al. 2003; Wetterich et al. 2005; Li et al. 2010).

Arctocypris edita n. sp. resembles the type species of the genus, A. fuhrmanni , with an overall similar lateral view of the carapace, similar number and positions of inner lists on the calcified inner lamellas of both valves and similar chaetotaxy of the appendages. Compared to Arctocypris edita n. sp., the carapace of A. fuhrmanni is noticeably less elongate, the dorsal margin more angular and the surface ornamentation more pronounced. The appendages of both species are a close match, but they differ in the length of the A1 y a aesthetasc: this is about twice as long as the terminal segment in A. fuhrmanni (remeasured from the type specimens, somewhat longer than that figured in the original description by Petkovski et al. (2016) —B. Scharf, Bremen, Germany, pers. comm.), but 3–4 times the length of the terminal segment in Arctocypris edita n. sp. The numbers of setae/claws on the terminal segment of the Mx are five in both species (four was reported for A. fuhrmanni by Petkovski et al. (2016), but there are actually five—B. Scharf, Bremen, Germany, pers. comm.). Both tooth bristles on the third endite of the Mx are serrated in A. fuhrmanni , but in Arctocypris edita n. sp. the tooth bristles are rather variable in the amount of serration expressed. Arctocypris arctica and A. mareotica comb. nov. are both smooth and have different lateral outlines of the valves compared to Arctocypris edita n. sp. The original description of A. dulcifons shows a species that is noticeably less elongate than Arctocypris edita n. sp. ( Diebel & Pietrzeniuk, 1969), but later reports of this species figure slightly more elongate specimens (e.g. Wetterich et al. 2005; Fuhrmann 2012). This species can be distinguished from Arctocypris edita n. sp. by its more inflated postero-ventral margin, straighter postero-dorsal margin, stronger ornamentation, less laterally compressed anterior and less elongate lateral outline. Arctocypris foveata is the least elongate species in the genus, with a rather truncated posterior margin ( Delorme 1968), producing a lateral outline quite different to that of Arctocypris edita n. sp.

Arctocypris edita n. sp. was found in shallow waters of ponds and the littoral zone of a lake on either a sandy or muddy substrate, once with submergent macrophytes, at altitudes of 4191–4626 m ( Table 1 ).

Figures

FIGURE 7. Arctocypris edita n. sp., green-shell phenotype, female (A, C, WOC60; others, WOC47, holotype). (A) LV, exterior view; (B) LV, exterior view; (C) RV, interior view; (D) RV, interior view; (E) RV, dorsal view; (F) LV, dorsal view; (G) enlargement of anterior part of (B). Scale bar: A–F = 500 μm; G = 115 μm.

FIGURE 8. Arctocypris edita n. sp., green-shell phenotype, female (WOC47, holotype). (A) Right A1, exterior view; (B) right A2, exterior view; (C) enlargement of distal part of (B); (D) right Md palp, interior view; (E) left Mx palp, interior view; (F) 3rd endite lobe of Mx.

FIGURE 9. Arctocypris edita n. sp., green-shell phenotype, female (WOC47, holotype). (A) Left L5, exterior view; (B) right L6, interior view; (C) left L7, exterior view; (D) right Ur, exterior view.

FIGURE 10. Arctocypris edita n. sp., white-shell phenotype, female. (A) LV, exterior view (WOC25); (B) RV, exterior view (WOC28); (C) RV, interior view (WOC25); (D) LV, interior view (WOC28); (E) RV, dorsal view (WOC34); (F) LV, obliquedorsal view (WOC34); (G) enlargement of antero-ventral part of (D); (H) enlargement of anterior part of (A). Scale bar: A–F = 500 μm; G = 145 μm; H = 105 μm.

FIGURE 11. Arctocypris edita n. sp., white-shell phenotype, female (WOC28). (A) Right A1, exterior view; (B) right A2, interior view; (C) right Md palp, interior view; (D) right Mx, interior view; (E) distal part of (B).

FIGURE 12. Arctocypris edita n. sp., white-shell phenotype, female (A, WOC34; B–F, WOC65). (A) Left L5, exterior view; (B) left L5, interior view; (C) left L6, exterior view; (D) right L7, exterior view; (E) Ur; (F) Ur attachment.