Stenocypris major major ( Baird, 1859 )

Moonchaisook, Khattiya & Savatenalinton, Sukonthip, 2020, Redescriptions of Stenocypris major major (Baird, 1859) and Stenocypris major sketi Petkovski & Meisch, 1996 (Ostracoda: Crustacea), with discussion on their taxonomic position, Zootaxa 4786 (4), pp. 497-515 : 499-505

Stenocypris major major ( Baird, 1859)

( Figs 1–4 , 9 A–D)

Material examined. Five females (soft parts dissected in a sealed glycerine slide and valves stored dry in a micropalaeontological slide) from two localities (three samples): 1) Canal, Sanam Chai Khet district , Chachoengsao Province, coordinates: 13° 39.174ʹ N and 101° 26.166ʹ E, 4 May 2018 ( MSU-ZOC 279–280 ), 14 October 2016 ( MSU-ZOC 284 , 286 ); 2) Marsh, Kabin Buri district , Prachin Buri Province, coordinates: 13° 59.233ʹ N and 101° 44.961ʹ E, 10 June 2017 ( MSU-ZOC 285 ) and four females (stored dry in a micropalaeontological slide) from two localities (two samples): 1) Canal, Sanam Chai Khet district , Chachoengsao Province, coordinates: 13° 39.174ʹ N and 101° 26.166ʹ E, 4 May 2018 ( MSU-ZOC 281–283 ), 2) Marsh, Kabin Buri district , Prachin Buri Province, coordinates: 13° 59.233ʹ N and 101° 44.961ʹ E, 10 June 2017 ( MSU-ZOC 287 ). Several females from eight other localities in 70 % EtOH ( Table 1) .

Diagnosis. Carapace in lateral view very elongated (length c. 2.8–3.0 times of height), LV slightly overlapping RV, valves surface weakly striated in high magnification. Septa present on all free margins, septa not wide at eye and mouth zones. Posterior inner margins with strongly arched outline or weakly sinuated curve. A1 with dorsal seta on third segment very long (reaching beyond tip of terminal segment), Wouters organ not observed. Natatory setae on A2 long (far beyond end of terminal claws), claw GM slightly shorter than claw G3. Ventro-subapical seta on Md-palp penultimate segment intermediate length (reaching c. mid length of terminal segment). Two large bristles on Mx1-third endite gently serrated. T1 with a, b and d-setae. T2 with d1 and d2 setae, h2 seta of similar length as penultimate segment, h3 seta about 1.4–1.5 times length of h1 seta. CR obviously asymmetrical, right ramus with numerous robust spines and setules on posterior margin, seta Sa c. 3/4 of that of Ga, length of Ga c. 0.4 times of that of ramus, left ramus with small setules on posterior margin, length of Ga c. 0.38 times of that of ramus, length of Gp c. half that of Ga in both CR.

Measurements (μm). LV (n=3), L= 1884–1903, H= 646–688; RV (n=3), L= 1866–1881, H= 644–666; Carapace (n=4), L= 1980–2000, H= 714–725.

Description of female. Carapace in lateral view ( Fig. 1A ) elongated (length c. 2.8–3 times height), anterior margin rounded, posterior margin slightly more narrowly rounded, LV slightly overlapping RV, dorsal margin gently curved, greatest height situated slightly behind mid-length, ventral margin sinuated slightly in front of mid-length, valve surface smooth in medium magnification, but shallowly lineated in high magnification with tiny rimmed-pore setae ( Fig. 1H ).

Carapace in dorsal view ( Fig. 1J ) spindle-like shape, with greatest width situated slightly behind mid-length, LV slightly overlapping RV anteriorly and posteriorly.

LV in interior view ( Fig. 1B , C–D) and RV in interior view ( Fig. 1 E–G, I) elongated, anterior and posterior margins subequally rounded, dorsal margin gently curved, greatest height situated slightly behind mid-length, ventral margin sinuated slightly in front of mid-length, calcified inner lamella relatively wide anteriorly, without inner list, posteriorly narrower, posterior inner margin varies from strongly arched outline (inner margin not parallel to valve margin) to weakly sinuated curve, septa along anterior, ventral and posterior margin slightly widened at mouth zone.

A1 ( Fig. 2A ): first segment with one dorso-subapical seta of intermediate length (almost reaching tip of segment) and two long ventro-apical setae, Wouters organ not observed. Second segment slightly wider than long, with one very short dorso-apical seta and short Rome organ. Third segment bearing two setae: one very long dorso-apical seta, reaching beyond tip of terminal segment, and one short ventro-apical seta, not reaching tip of fourth segment. Fourth segment with two long dorsal setae and two subequal, shorter ventral setae (reaching beyond tip of terminal segment). Fifth segment with two groups (one dorsally and one ventrally) of two setae, all setae very long. Penultimate segment with four long setae and one short dorsal seta (reaching tip of terminal segment). Terminal segment with three (two long, one shorter) apical setae and an aesthetasc Ya, the latter of about similar length as shorter apical seta.

A2 ( Fig. 2 B–C): exopodite with three (one long, two short) setae, the long one reaching tip of first endopodal segment. First endopodal segment with five long (reaching beyond tip of terminal claws) and one short natatory setae, length of the shortest seta almost reaching half way the penultimate segment, aesthetasc Y long, ventro-apical seta of intermediate length, not reaching tip of penultimate segment. Penultimate segment undivided, distally with three serrated claws, aesthetasc y2 long (reaching tip of terminal segment), z1–z3 setae unequally long, longest one reaching slightly beyond tip of apical claws; this segment medially with two subequal dorsal setae and four ventral setae (t1–t4) of unequal length; one of these four setae large, reaching tip of terminal segment. Terminal segment with two serrated claws (GM and Gm), a very short g-seta, an aesthetasc y3 and two short subapical setae (c. the same length of g-seta); length of Gm c. half of that of GM, length of aesthetasc y3 c. 2/3 of that of accompanying seta, the latter slightly shorter than GM.

Md ( Fig. 2 D–E): first segment of md-palp with two large setae (s1 and s2), one slender, long seta and a long, smooth α-seta. Second segment dorsally with three unequal long apical setae, length of the shortest c. half of that of the longest; ventrally with a group of three long hirsute setae, one shorter hirsute seta and the β-seta, the latter plumose, cone-shaped and with pointed tip. Penultimate segment consisting of three groups of setae: dorsally with a group of four unequal, long, subapical setae; laterally with an apical γ-seta and three further smooth apical setae, the former stout, hirsute, long (length c. 1.5 times of that of terminal segment); ventrally with two (one long, one short) subapical setae, the latter reaching c. mid length of terminal segment). Terminal segment bearing three claws and two setae.

Mx1 ( Fig. 3A ) with two-segmented palp, three endites and a large branchial plate; basal segment of palp with a group of five long, unequal apical setae and one short subapical seta, the latter almost reaching tip of segment, terminal segment elongated (length = 1.8 times the width), apically with three claws and two setae. Two large bristles on third endite gently serrated. Sideways-directed bristles on first endite unequally long, length of short one c. 4/5 of that of long one.

T1 ( Fig. 3 B–C): protopodite with two a-setae, long b and d-setae, distally with 9–10 apical and four subapical hirsute setae of unequal length. Endopodite a weakly built palp with three unequal apical setae.

T2 ( Fig. 3D ) with setae d1 and d2, both setae thin and almost the same length. Second segment with long e-seta (reaching c. 2/3 of penultimate segment). Penultimate segment divided, proximal segment (a) bearing long f-seta (reaching beyond tip of segment), distal segment (b) with a pair of apical setae (long g-seta, one spine-like). Terminal segment with two (one dorsally, one ventrally) apical h1 and h3 setae and a long serrated claw (h2), h2 of similar length as penultimate segment, h3 seta about 1.4–1.5 times length of h1 seta.

T3 ( Fig. 3E ) a cleaning limb. First segment with long d1, d2, dp setae. Second segment with long apical e-seta (reaching c. 2/3 of next segment). Third segment with long f-seta medially (reaching tip of segment). Terminal segment with an apical pincer (h2), one short h1 seta and one subapical h3 seta, length of the latter c. 5/6 of that of third segment.

CR ( Fig. 4 A–B) well-developed and asymmetric with right ramus slightly longer and thicker than left ramus. Right ramus ( Fig. 4A ) with strongly serrated posterior margin, bearing c. three groups of spines and setules, first group comprises c. 10 large spines, second group with c. 14 small spines, third group with many tiny setules. Claws Ga and Gp long and strongly serrated, length of Ga c. 0.4 times of that of ramus, length of Gp c. half of that of Ga, claw Ga with large spines on c. 2/3 of Ga length, claw Gp with large spines all along its length. Seta Sa c. 3/4 of that of Ga, seta Sp absent.

Left ramus ( Fig. 4B ) with posterior margin bearing tiny setules. Claws Ga and Gp long and strongly serrated, length of Ga c. 0.38 times of that of ramus, length of Gp c. half of that of Ga, claw Ga with large spines on c. 2/3 of Ga length, claw Gp with large spines all along its length. Seta Sa long (length c. 5/6 of that of Ga), seta Sp absent.

CR attachment ( Fig. 4C ) stout, with triangular basal loop, db and vb well-developed.

Male unknown.

Ecology. Stenocypris major was encountered in 10 localities in the Eastern part of Thailand ( Table 1, Fig. 10 ). Its habitats covered canal, reservoir, rice field and marsh. The species occurred at a pH range of 5.74–8.05, a temperature range of 28.2–34.5°C and a DO range of 2.7–10.7 mg /l.

Remarks. Ferguson (1969) examined the type specimens of S. major (under the name S. cylindrica major ) and provided some information and an illustration of its valves. The Thai specimens (c. 1.98–2.0 mm) are slightly smaller than the Indian specimens (2.0–2.13 mm—Ferguson 1969), while the posterior inner margin in the specimens from Thailand has a strongly arched outline ( Fig. 9 A–D), which resembles the figures provided by Ferguson (1969).

Figures

FIGURE 1. Stenocypris major (Baird, 1859), female. A. Carapace, right lateral view (MSU-ZOC.281). B. LV, interior view (MSU-ZOC.280). C. anterior part of LV, interior view (ditto). D. posterior part of LV, interior view (ditto). E. RV, interior view (ditto). F. anterior part of RV, interior view (ditto). G. posterior part of RV, interior view (ditto). H. valve surface of RV (ditto). I. muscle scars of RV (ditto). J. Carapace, dorsal view (MSU-ZOC.282). K. Carapace, ventral view (MSU-ZOC.283). Scale bars: 200 μm for A–B, E, J–K, 100 μm for C–D, F–G, 10 μm for H, 50 μm for I.

FIGURE 2. Stenocypris major (Baird, 1859), female (MSU-ZOC.279). A. A1. B. A2. C. Terminal segment of A2. D. Md-coxa. E. Md-palp. Scale bars: 100 μm for A, C–D, 115 μm for B, 50 μm for E.

FIGURE 3. Stenocypris major (Baird, 1859), female (MSU-ZOC.279).A. Mx1. B. T1. C. Endopodite of T1. D. T2. E. T3. Scale bars: 100 μm for A–C, 115 μm for D, 140 μm for E.

FIGURE 4. Stenocypris major (Baird, 1859), female (MSU-ZOC.279).A. right CR. B. Left CR. C. CR attachment. Scale bars: 200 μm.

FIGURE 9 Valves (internal view) of Stenocypris major (Baird, 1859) (A–D) and Stenocypris sketi Petkovski & Meisch, 1996 (E–H).A. LV (MSU-ZOC.280). B. RV (ditto). C. LV (MSU-ZOC.284). D. RV (ditto). E. LV (MSU-ZOC.288). F. RV (ditto). G. LV (MSU-ZOC.289). H. RV (ditto). Scale bars: 200 μm.

FIGURE 10 Distribution map of Stenocypris major (Baird, 1859) (black circle) and Stenocypris sketi Petkovski & Meisch, 1996 (white circle) in the Eastern part of Thailand. Numbers refer to the localities in Table 1.