Ilyocypris thailandensis, Savatenalinton, 2021

Savatenalinton, Sukonthip, 2021, Ilyocypris thailandensis, a new species of freshwater ostracod (Crustacea: Ostracoda: Cypridoidea) from Thailand, Raffles Bulletin of Zoology 69, pp. 403-413 : 404-410

Ilyocypris thailandensis , new species

( Figs. 1–6 )

Material examined. Holotype: Male , soft parts dissected in glycerine on a sealed slide, valves stored dry on a micropalaeontological slide ( MSU-ZOC.307), Phadang Reservoir, Muang District, Phetchabun Province, Thailand, 16°26′46″N 101°05′16″E, coll. S Savatenalinton, 14 February 2006.

Allotypes: one female, stored like the holotype ( MSUZOC.311), same data as holotype .

Paratypes: two dissected males ( MSU-ZOC.308–309) stored like the holotype, one undissected male ( MSUZOC.310) stored dry on micropalaeontological slides, one dissected female ( MSU-ZOC.312) stored like the holotype, one undissected female ( MSU-ZOC.313) stored dry on a micropalaeontological slide, c. 7 males and 10 females in 70% ethanol, deposited in the Science Faculty Museum ( MSU, Thailand) and 5 males and 5 females in 70% ethanol deposited in the Lee Kong Chian Natural History Museum ( Singapore), same data as holotype .

Measurements (μm). Male. Cp: L = 607, W = 248; LV (n=3): L = 586 – 656, H = 327 – 361; RV (n=3): L = 569 – 645, H = 315 – 355. Female. Cp: L = 657, W = 327; LV (n=3): L = 654 – 676, H = 369 – 387; RV (n=3): L = 639 – 666, H = 358 – 376.

Diagnosis. Carapace in dorsal view narrowly elongated (length c. 2.5 times of width in male), with small angular tubercles situated behind mid-length (larger in female), anterior end more compressed and posterior end narrowly rounded; LV in external view elongated (length c. 1.5 times of height), greatest height situated at c. 1/3 of length, dorsal margin straight, sloping towards posterior end, each valve set with three tubercles (two rounded, one angular) and shallow pits; anterior calcified inner lamella of LV with ripplets arranged into two rows and with two inner lists, posterior calcified inner lamella of LV with two inner lists and two main rows of ripplets and minor and short row of ripplets at postero-ventral margin; A1 with very long α-seta (length c. four times of penultimate segment); accompanying seta of A2 natatory setae long (reaching far beyond tip of terminal segment), in male claw G3 reduced to short seta and z1 seta developed to claw-like, female z1 seta markedly short; T2 with long g-seta; hemipenis with subquadrate middle lobe containing tiny pointed corner, inner lobe elongated, rounded knob-like, outer lobe rounded dome-shaped, gaps between lobes present; copulatory process slender with pointed tip; Zenker’s organ length about 2.7 times the width, set with 12 spiny whorls, proximal end remarkably inflated and larger than distal end.

Description of male. Carapace in dorsal view ( Fig. 1D ) narrowly elongated (length c. 2.5 times of width), with small angular tubercles situated behind mid-length. Dorso-median sulci situated at mid-length and before mid-length. LV slightly overlapping RV anteriorly and posteriorly. Anterior end more compressed and posterior end narrowly rounded.

LV in external view ( Fig. 1E ) elongated (length c. 1.5 times of height), greatest height situated at c. 1/3 of length, anterior margin widely rounded, posterior margin narrowly rounded, dorsal margin straight sloping down toward posterior end, ventral margin sinuated at mid-length, anterior and posterior regions with small secondary tubercles; valve surface set with three (two rounded, one angular) tubercles in middle area of valve and upper half of height, no tubercles on lower half of height, and ornamented with shallow pits throughout surface, adductor muscle scars depression situated in central region of valve.

RV in external view ( Fig. 1F ) same as in LV, except for anterior and posterior regions with larger secondary tubercles than those on LV.

LV in interior view ( Fig. 2D, F ): Anterior calcified inner lamella with ripplets arranged into two rows and with two inner lists, posterior calcified inner lamella with two inner lists and with two main rows of ripplets and minor and short row of ripplets at postero-ventral margin.

RV in interior view ( Fig. 2E ) same as in LV, except for anterior calcified inner lamella with one row of ripplets (more robust than those in LV) and postero-ventral margin without ripplets.

A1 ( Fig. 3A ): First segment with one long, dorsal seta (reaching tip of next segment) and two long ventro-apical setae, Wouters organ not seen. Second segment subquadrate with one long dorso-apical seta (reaching beyond tip of next segment), Rome organ not seen. Third segment bearing two setae: one short dorso-apical seta (reaching tip of fifth segment), and one shorter ventro-apical seta (reaching midlength of fifth segment). Fourth segment with two long dorsal apical setae and two ventral apical setae, one long (reaching tip of terminal segment) and one shorter (reaching beyond tip of next segment). Fifth segment with two long dorsal apical setae and two ventral apical setae, one long, one shorter (short one reaching beyond tip of terminal segment). Penultimate segment with four long apical setae and very long α-seta (length c. four times of penultimate segment). Terminal segment with three (one long, two shorter) apical setae and an aesthetasc ya, the latter c. two times of terminal segment.

A2 ( Fig. 3B ): Exopodite with three (one long, two short) setae, the long one reaching slightly beyond tip of first endopodal segment. First endopodal segment with five long natatory setae (reaching far beyond tip of terminal claws) and accompanying seta also long (reaching far beyond tip of terminal segment), aesthetasc Y short, ventro-apical seta long (reaching beyond tip of terminal segment). Penultimate segment undivided, medially with two (one long, one shorter) dorsal setae (length of the short one c. half that of the long one) and four ventral setae of unequal length (t1–t4), t1 seta longest (reaching slightly beyond tip of terminal segment), y1 long, situated at 1/3 of segment; this segment distally with two claws G1–G2 and claw G3 reduced to short seta, aesthetasc y2 long, z1 seta claw-like, z2 and z3 setae long (reaching beyond tip of terminal claws). Terminal segment with two claws (GM and Gm), aesthetasc y3 with accompanying seta, length of Gm c. 6/7 of that of GM, length of aesthetasc y3 c. 3/4 of accompanying seta, the latter slightly shorter than half length of Gm.

Md-coxa ( Fig. 4A ) elongated, distally set with rows of teeth (large dorsally and smaller ventrally) and small setae, and with one dorso-subapical seta, the latter reaching slightly beyond tip of coxa.

Md-palp ( Fig. 4B ): First segment with two large setae (S1 and S2), one long seta and long, smooth α-seta. Second segment dorsally with two unequal long subapical setae; ventrally with a group of three long hirsute setae, one shorter seta and small, plumose β-seta. Penultimate segment dorsally with a group of four unequal, long, subapical setae; laterally with one apical seta; ventrally with three long setae of subequal length. Terminal segment distally bearing three claws and three setae, medially with one long seta (length c. two times of that of terminal segment).

Mx1 ( Fig. 4C ) with two-segmented palp, three endites and large branchial plate; basal segment of palp with a group of four long, unequal apical setae and one subapical seta, the latter reaching tip of terminal segment, terminal segment subquadrate (length as long as width), apically with three claws and three setae.

T1 ( Fig. 4D, E ): Endopodite forming slender prehensile palp. Palp proximally with elongated segment bearing two apical setae, distal part narrower, and with one long subapical seta. Left and right palps symmetrical.

T2 ( Fig. 5A ): First segment with seta d1, seta d2 absent. Second segment with short e-seta (not reaching mid-length of penultimate segment). Penultimate segment undivided, medially with short f-seta (not reaching tip of segment) and long apical g-seta (reaching beyond tip of terminal segment). Terminal segment with two (one anterior, one posterior) apical h1 and h3 setae and serrated claw (h2), length of h1 seta less than half of that of h2 claw, h3 seta short (shorter than half length of h1 seta).

T3 ( Fig. 5B ): First segment with short d1 seta. Second segment with long apical e-seta (extending beyond half of next segment). Third segment with medially long f-seta (reaching beyond tip of segment), long subapical g-seta (reaching tip of h2 seta) and two small apical spines. Terminal segment with three apical h1–h3 setae, h1 and h3 setae long, subequal length, h2 seta shorter (length less than half that of h1 seta).

CR ( Fig. 5C ) with subequal, long claws Ga and Gp (length c. 0.6 times of ramus), seta sa short (length c. 1/3 of that of Ga), seta sp long, situated c. mid-length of ramus.

Hemipenis ( Fig. 6A, B ): Middle lobe subquadrate with distally tiny pointed corner, inner lobe elongated, rounded knob-like (extending c. 2/3 of middle lobe), outer lobe rounded domeshaped; gaps between lobes present; copulatory process with slender end; postlabyrinthal spermiduct curved, with two loops.

Zenker’s organ ( Fig. 6C, D ) set with 12 spiny whorls, length about 2.7 times the width, proximal end remarkably inflated and larger than distal end.

Description of female. Carapace and valves as in male, although somewhat larger and with larger angular tubercles ( Figs. 1A–C , 2A–C, G, H ). All limbs as in male, except for last two segments of A2 ( Fig. 3C ) and T1 ( Fig. 4F ). Penultimate segment of A2 with three claws G1–G3, z2 and z3 setae long (reaching tip of terminal claws), z1 seta shorter (reaching 1/3 of GM claw). T1-protopodite with two long a-setae, distally with 18 hirsute setae of unequal length, endopodite a weakly built-palp with two segments, apically with three unequal hirsute apical setae, length of the shortest seta less than half that of the longest seta. Reproductive organ with large, round lobe anteriorly and slightly smaller, round lobe posteriorly, length of latter lobe about 1/3 of total length of organ.

Etymology. The species is named after Thailand, where the new species was first collected.

Distribution and ecology. Ilyocypris thailandensis , new species, has thus far been collected from one locality (reservoir) which is a permanent water body in the northern part of Thailand. The individuals were collected from the littoral zone in which macrophytes were absent. The vegetation of the shoreline consisted of grasses, most of which were dry. The sediment was a mixture of silt and sand, together with a small quantity of crude dead plant material. Sample was taken from the waters with pH of 7.0 and temperature of 24.2°C.

Remarks. Ilyocypris thailandensis , new species, in the present study consisted of a sexual population comprising both males and females. It should be noted that all dissected females were copulated specimens since sperm cells were observed inside their bodies.

Figures

Fig. 1. Ilyocypris thailandensis, new species. A–C, female; D–F, male. A, carapace, dorsal view (MSU-ZOC.313); B, LV, external view (MSU-ZOC.311); C, RV, external view (ditto); D, carapace, dorsal view (MSU-ZOC.310); E, LV, external view (MSU-ZOC.307); F, RV, external view (ditto). Scale bar: A–F = 200 μm.

Fig. 2. Ilyocypris thailandensis, new species. A–C, G–H, female; D–F, male. A, LV, internal view (MSU-ZOC.312); B, RV, internal view (ditto); C, LV, internal view, postero-ventral part (ditto); D, LV, internal view (MSU-ZOC.308); E, RV, internal view (ditto); F, LV, internal view, postero-ventral part (MSU-ZOC.309); G, LV, internal view, anterior part (MSU-ZOC.312); H, RV, internal view, anterior part (ditto). Arrows indicate lists (l) and rows of ripplets (r). Scale bar: A, B, D, E = 200 μm, C = 94 μm, F–H = 50 μm.

Fig. 3. Ilyocypris thailandensis, new species. A, B, male (MSU-ZOC.307); C, female (MSU-ZOC.311). A, A1; B, A2; C, terminal part of A2. Scale bars: A–C = 50 μm.

Fig. 4. Ilyocypris thailandensis, new species. A–E, male (MSU-ZOC.307); F, female (MSU-ZOC.311). A, Md-coxa; B, Md-palp; C, Mx1; D–E, T1-palp; F, T1. Scale bars: A = 67 μm, B, C, F = 50 μm, D, E = 46 μm.

Fig. 5. Ilyocypris thailandensis, new species, male (MSU-ZOC.307). A, T2; B, T3; C, CR. Scale bars: A–C = 50 μm.

Fig. 6. Ilyocypris thailandensis, new species, male. A, hemipenis (MSU-ZOC.309); Aʹ, copulatory process of A (ditto); B, hemipenis outlines (MSU-ZOC.309, 307, 308; left to right); C, Zenker organ (MSU-ZOC.307); D, Zenker organ (MSU-ZOC.308). Arrows indicate proximal ends. Scale bars: A, D = 50 μm, B = 98 μm, C = 55 μm.