Two new species of Cypricercinae McKenzie, 1971 (Crustacea: Ostracoda) from Thailand

Two new species of the subfamily Cypricercinae McKenzie, 1971 are described from the Western part of Thailand: Pseudostrandesia ratchaburiensis sp. nov. and Strandesia prachuapensis sp. nov. Pseudostrandesia ratchaburiensis sp. nov. is mainly characterized by a fl ange on the anteroventral part of the left valve (LV), a markedly large β seta on the mandibular (Md) palp, serrated bristles on the third endite of the maxillula (Mx1), a slender caudal ramus (CR) with a long claw Ga (length ca half that of the ramus) and a relatively low number (13) of spiny whorls in the Zenker’s organ. The discovery of both males and females of Pseudostrandesia ratchaburiensis sp. nov. in the present study constitutes the fi rst report of a sexual population in this genus, thereby allowing for a comparison of the male reproductive organs (hemipenis and Zenker’s organ) from a new species with those of other genera of Cypricercinae. Strandesia prachuapensis sp. nov. is most closely related to Strandesia odiosa (Moniez, 1892) and Strandesia fl avescens Klie, 1932 as they bear similar anterior fl anges on the right valve (RV). The key diagnostic features of the new Strandesia species are a large carapace (ca 1.5 mm), an angulated antero-ventral part of the LV, a weak and small anterior inner list on the LV, an anterior fl ange on the RV, a markedly small aesthetasc Y on the second antenna, a large β seta on the Md-palp, smooth bristles on the third endite of the Mx1 and a slender CR with a short claw Ga (length ca 1⁄3 of the ra mus). In addition, Pseudostrandesia complexa (Victor & Fernando, 1981) comb. nov. is here proposed.


Material and methods
Forty-five water bodies in the western part of Thailand were investigated in the years 2018-2019. Ostracod samples were taken with a hand net (mesh size 200 µm), instantly preserved in 70% ethanol. In the laboratory, specimens were sorted using a binocular microscope, soft parts were dissected in glycerine under a stereo microscope (Olympus SZ-PT) and later sealed on glass slides. Valves were stored dry in micropalaeontological slides. Soft parts were drawn using a camera lucida attached to a compound microscope. Carapaces and valves were observed and illustrated using a Scanning Electron Microscope (JEOL JSM6460LV -at the Faculty of Science, Mahasarakham University, Thailand). The chaetotaxy of the limbs follows the model proposed by Broodbakker & Danielopol (1982), revised for the A2 by Martens (1987) and for the thoracopods by Meisch (2000). The classification of the Cypricercinae follows that proposed by Savatenalinton & Martens (2009b). All type specimens are deposited in the Ostracod Collection in the Faculty of Science, Mahasarakham University, Maha Sarakham, Thailand.

Diagnosis
Cp in lateral view elongated (length ca 2.2 times of height) with greatest height situated at one third of length, LV overlapping RV along all free margins, LV with flange on antero-ventral part and one anterior inner list, A1 seven-segmented, A2 with long natatory setae, undivided penultimate segment (in both females and males), Md-palp with long α seta and markedly large β seta, two bristles on third endite of Mx1 serrated, T1 without d-seta, T2 with d1 seta longer (ca two times) than d2 seta, f-seta long (reaching far beyond tip of terminal segment), g-, h1 and h3 setae long (length ca ⅓ of that of h2 claw), T3 with pincer organ, e-and f-setae long, CR slender, length of Ga ca half that of ramus, sa slightly longer than Gp, sp thin and long (reaching tip of ramus), CR attachment stout, with Triebel's loop, situated at middle of distal part of main branch, db and vb well-developed, right palp of male T1 anteriorly with triangular lobe and two small apical triangular protrusions, hemipenis with medial shield broadly rounded, lateral shield elongated with blunt distal end, postlabyrinthal spermiduct curved, with 2 loops, Zenker's organ set with 13 spiny whorls, length ca 3.5 times the width.

Repository
The holotype, allotype and all paratypes are deposited in the MSU-ZOC.

Female
Cp in lateral view (Fig. 1A). Elongated (length ca 2.2 times of height), greatest height situated at one third of length, anterior margin rounded with flange on antero-ventral part of LV, posterior margin more narrowly rounded, LV overlapping RV, especially antero-ventrally, valve surface set with short rim-pore setae.
Cp in dorsal view (Fig. 1B). Subelliptical, with greatest width situated slightly behind mid-length, LV overlapping RV anteriorly and posteriorly, anterior and posterior extremities narrowly rounded. lv in internal view (Fig. 1C, E-F). With groove along ventral margin, dorsal margin gently arched, greatest height situated at one third of length, sloping down to anterior and posterior margin, the former more widely rounded than the latter one, antero-ventral part with flange, ventral margin slightly sinuated around mid-length, calcified inner lamella relatively wide anteriorly, with one inner list, posteriorly narrower. rv in internal view (Fig. 1D, G-I). With marginal selvage, calcified inner lamella without inner list, anteriorly broader than posteriorly.   (Fig. 3A). First segment with one short, dorso-subapical seta (reaching tip of segment) and two long ventro-apical setae. Second segment slightly wider than long, with one short dorso-apical seta (slightly beyond tip of segment) and long Rome organ. Third segment bearing two setae: one long dorso-apical seta, reaching halfway penultimate segment, and one short ventro-apical seta (reaching tip of next segment). Fourth segment with two long dorsal setae and two subequal, short ventral setae (the longer one reaching slightly beyond tip of next segment). Fifth segment dorsally with two long setae, ventrally with two (one long, one shorter) setae, the shorter one reaching halfway terminal segment. Penultimate segment with four long setae. Terminal segment with three (two long, one short) apical setae and an aesthetasc y a , the latter ca 4/5 of short apical seta. a2 ( Fig. 3B-C). Exopodite with three (one long, two short) setae, the long one reaching beyond 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 less than half way penultimate segment, aesthetasc Y long, ventro-apical seta long, reaching beyond tip of terminal segment. Penultimate segment undivided, distally with three serrated claws G1-G3, aesthetasc y2 markedly long (reaching far beyond tip of terminal segment), z1-z3 setae long; this segment medially with two (one long, one shorter) dorsal setae (length of the short one ca ⅔ of that of the long one) and four ventral setae of unequal length (t1-t4), t4 shortest seta (not reaching tip of segment). Terminal segment ( Fig. 3C) with two serrated claws (GM and Gm), g-seta and aesthetasc y3 with accompanying seta, length of Gm ca ¾ of that of GM, length of aesthetasc y3 slightly more than half of that of accompanying seta, the latter slightly shorter than Gm, length of seta g ca 3/5 of that of Gm.
Md-palp (Fig. 3D). First segment with two large setae (S1 and S2), one slender, long seta and noticeably long, smooth α-seta. Second segment dorsally with three unequal long apical setae, length of the shortest ca ¼ of that of the longest; ventrally with a group of three long hirsute setae, one shorter hirsute seta and    markedly large β-seta (length ca 5/6 of that of penultimate segment), the latter plumose, cone-shaped and with pointed tip. Penultimate segment bearing three groups of setae: dorsally with a group of four unequal, long, subapical setae; laterally with apical γ-seta and three further apical setae, the former stout, hirsute, long (length ca 2 times that of terminal segment); ventrally with two (one long, one short) apical setae, the latter reaching slightly beyond mid length of terminal segment). Terminal segment bearing three claws and two setae.
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 situated close to palp. Mx1 (Fig. 4B). With two-segmented palp, three endites and large branchial plate; basal segment of palp with a group of four long, unequal apical setae and two (one long, one shorter) subapical setae, the latter reaching beyond tip of terminal segment, terminal segment elongated (length ca twice as long as width), apically with three claws and three setae. Two large bristles on third endite serrated apically. Sidewaysdirected bristles on first endite unequally long, length of short one ca ⅔ of that of long one.
t1. Protopodite ( Fig. 4C) with two short a-setae and long b-seta, distally with 14 (10 apical, four subapical) hirsute setae of unequal length. Endopodite (Fig. 4D) a weakly built palp, slender shape, with three unequal apical setae. t2 ( Fig. 5A-B). With seta d1 ca twice the length of seta d2. Second segment with short e-seta (reaching mid-length of penultimate segment). Penultimate segment divided, proximal segment bearing long f-seta (reaching far beyond tip of terminal segment), distal segment with long g-seta (almost the same length as h1 seta). Terminal segment with two (one dorsally, one ventrally) apical h1 and h3 setae and serrated claw (h2), length of h1 seta ca ⅓ of that of h2 claw, h3 seta slightly shorter than h1 seta. t3 (Fig. 5C). A cleaning limb. First segment with long d1, d2, dp setae. Second segment with long apical e-seta (extending slightly beyond half of the next segment). Third segment with medially long f-seta (reaching beyond tip of segment). Terminal segment with an apical pincer and three setae, one short h1 seta, one claw-like h2 seta and one reflexed subapical h3 seta, length of the latter ca ⅔ of that of third segment. Cr (Fig. 5D). Slender, ventral margin of ramus with tiny setules, Ga and Gp long, serrated, length of Ga ca half of ramus, length of Gp ca ⅔ that of Ga. sa long (slightly longer than Gp), sp thin and long (reaching tip of ramus).
Cr attaChMent (Fig. 5E). Stout, with Triebel's loop situated at middle of distal part of main branch, db and vb well-developed, vb with swollen end.

Male
Carapace and valves as in female, although somewhat smaller (Fig. 2). All limbs as in female, except for last two segments of A2, T1 and reproductive organs (Fig. 6); penultimate segment of A2 with clawlike z1 and z2 setae, considerably reduced claw G1 and with claw G3 reduced to seta (Fig. 6A); T1endopodites forming asymmetrical prehensile palps; right palp ( flange, not close to mouth region, A1 seven-segmented with small Rome organ, A2 with long natatory setae, aesthetasc Y markedly small (short and slender) with insertion situated ca one fourth of segment, β-seta on Md-palp large, two large bristles on third endite of Mx1 smooth, d-seta on T1 present, T2 with d1 and d2 setae (length of d2 seta less than half length of d1 seta), f-seta of intermediate length (not reaching tip of terminal segment), T3 with pincer organ, CR slender, claw Ga ca ⅓ of ramus, claws Ga and Gp and ventral margin of ramus with tiny spine-like setules, sa seta slightly longer than claw Gp, sp seta slender, reaching slightly beyond tip of ramus, CR attachment with Triebel's loop situated at middle of distal part of main branch.

Differential diagnosis
Strandesia prachuapensis sp. nov. resembles S. flavescens Klie, 1932 andS. odiosa (Moniez, 1892). It can be distinguished from them mainly by the narrower anterior flange on the RV, the size of the Cp (ca 1.5 mm), the angulated antero-ventral part of the LV and the small and weak anterior inner list on the LV (for details of the differences, see the Discussion).

Etymology
The species is named after Prachuap Khiri Khan Province, which is also called in short ‛Prachuapʼ, where specimens of the new species were discovered.

Repository
The holotype and all paratypes are deposited in the MSU-ZOC.  Cp in dorsal view (Fig. 7B). Subelliptical, with greatest width situated at mid-length, anterior margin of RV slightly protruded than LV. lv in internal view (Fig. 7C, E-F). With groove along valve margin, dorsal margin arched, greatest height situated slightly in front of mid-length; sloping down to anterior and posterior margin, the former widely rounded, the latter slightly less widely rounded, antero-ventral part angulated, ventral margin slightly sinuated at mid-length; calcified inner lamella relatively wide anteriorly, with a weak and small inner list situated on antero-ventral part, posteriorly narrower. rv in internal view (Fig. 7D, G-H). With inwardly displaced selvage and anterior flange, the latter not close to mouth region, calcified inner lamella without inner list, anteriorly broader than posteriorly. a1 (Fig. 8A-Aʹ). First segment with one dorso-subapical seta of intermediate length (almost reaching tip of segment) and two long ventro-apical setae, Wouters organ absent. Second segment slightly wider than long, with one markedly short dorso-apical seta (reaching tip of segment) and small Rome organ. Third segment bearing two (one dorso-apical and one ventro-apical) setae of intermediate length, both reaching slightly beyond tip of next segment. Fourth segment with two long dorsal setae and two subequal, shorter ventral setae (the short one not reaching tip of next segment, the longer one reaching slightly beyond tip of next segment). Fifth segment dorsally with two long setae, ventrally with two (one long, one shorter) setae, the shorter one reaching beyond tip of terminal segment. Penultimate segment with four long setae. Terminal segment with three (two long, one short) apical setae and aesthetasc y a , the latter markedly long (ca 1.7 times that of short apical seta). a2 (Fig. 8B). Exopodite with three (one long, two short) setae, the long one reaching beyond tip of first endopodal segment. First endopodal segment with five long (reaching tip of terminal claws) and one short natatory setae, length of the shortest seta reaching half way the penultimate segment, aesthetasc Y small (short and slender), insertion situated ca ¼ of segment, ventro-apical seta long, reaching slightly beyond tip of penultimate segment. Penultimate segment undivided, distally with three serrated claws G1-G3, aesthetasc y2 short (not reaching tip of terminal segment), z1-z3 setae long; this segment medially with two (one long, one shorter) dorsal setae (length of the short one ca ¾ of that of the long one) and four ventral setae of unequal length (t1-t4). Terminal segment with two serrated claws (GM and Gm), g-seta and aesthetasc y3 with accompanying seta, length of Gm ca ¾ of that of GM, length of aesthetasc y3 more than half of that of Gm and slightly shorter than accompanying seta, length of g-seta ca ¾ of aesthetasc y3.
Md-palp (Fig. 9A). First segment with two large setae (S1 and S2), one slender, long seta and long, smooth α-seta. Second segment dorsally with three unequal long apical setae, length of the shortest seta less than half of that of the longest seta; ventrally with a group of three long hirsute setae, one shorter hirsute seta and large β-seta (length ca ¾ of that of penultimate segment), the latter large, 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 apical γ-seta and three further apical setae, the former stout, hirsute, long (length ca 1.5 times of that of terminal segment); ventrally with two (one long, one short) apical setae, the latter reaching ⅓ of length of terminal segment. Terminal segment bearing three claws and two setae. Mx1 (Fig. 9B). With two-segmented palp, three endites and large branchial plate; basal segment of palp with a group of five long, unequal apical setae and two (one long, one shorter) subapical setae, the latter reaching half way of terminal segment, terminal segment elongated, apically with three claws and three   setae. Two large bristles on third endite smooth. Sideways-directed bristles on first endite unequally long, length of short one ca half of that of long one. t1 (Fig. 9C). Protopodite with two short a-setae, long b and d-setae, masticatory process distally with 14 (10 apical, four subapical) hirsute setae of unequal length. Endopodite a weakly built palp with three unequal apical setae. t2 (Fig. 10A). With seta d1 more than twice the length of seta d2. Second segment with short e-seta (reaching slightly beyond mid-length of penultimate segment). Penultimate segment divided, proximal segment bearing f-seta of intermediate length (not reaching tip of terminal segment), distal segment with a short g-seta (reaching slightly beyond tip of terminal segment). Terminal segment with two (one dorsally, one ventrally) apical h1 and h3 setae and a serrated claw (h2), h1 and h3 setae subequal in length, length of claw h2 longer than that of penultimate segment. t3 (Fig. 10B). A cleaning limb. First segment with long d1, d2, dp setae. Second segment with long apical e-seta (ca ⅔ of next segment). Third segment with medially short f-seta (not reaching tip of segment). Terminal segment with apical pincer and three setae, one short h1 seta, one claw-like h2 seta and one reflexed subapical h3 seta, length of the latter ca ⅔ of that of third segment.
Cr (Fig. 10C-D). Slender, claws Ga and Gp weakly serrated, claw Ga short (ca ⅓ of ramus), length of claw Gp ca 3/5 of that of claw Ga, sa seta slightly longer than claw Gp, sp seta slender, reaching slightly beyond tip of ramus, ventral margin of ramus with tiny setules.
Cr attaChMent (Fig. 10E). With Triebel's loop situated at middle of distal part of main branch, db and vb well-developed, vb with swollen end.

Male
Unknown.

Pseudostrandesia
One of the discriminating characters between the genera Strandesia and Pseudostrandesia is the occurrence of the d-seta on the T1, which is present in the former and absent in the latter genus (Savatenalinton & Martens 2009b). The terminal part of the T1 protopodite (masticatory process) contains many setae which, in Cypricercinae, are divided into two groups: apical and subapical setae. The former group usually consists of 10 setae while about four setae belong to the latter (see Savatenalinton & Martens 2009a, 2009b, 2010. Frequently, one of the subapical setae is erroneously indicated as a d-seta. For example, in Strandesia mamarilorum Victor & Fernando, 1981, although the presence of T1 d-seta was mentioned in the description, no d-seta appeared in the original illustrations (see Victor & Fernando 1981). The absence of the d-seta on the T1 in this species was confirmed by the redescription, and it was thus transferred to Pseudostrandesia (see Savatenalinton & Martens 2010). A similar case probably occurs in Strandesia complexa Victor & Fernando, 1981. Strandesia complexa was described based on material from the Philippines (Victor & Fernando 1981), and it has not been reported again since its discovery, thus it remains an endemic species of the country. The redescription of S. complexa should confirm the presence/absence of the d-seta on the T1. However, based on the present information with regards, particularly, to its illustrations, the d-seta is absent on the T1 of S. complexa. Thus, here it is tentatively transferred to the genus Pseudostrandesia.
Pseudostrandesia ratchaburiensis sp. nov. described here resembles P. complexa in the presence of an antero-ventral flange of the LV and a similar sized Cp. However, the distinguishing characters are recognized in valves and the soft parts morphology. In the new species, the Cp is more elongated in the lateral view. The diagnostic features of the soft parts are clearly seen in the Md-palp, the T2 and the CR. The β-seta on the Md-palp is somewhat large in the new species, while it was small in P. complexa. The long g and h3 setae of the T2 in the new species are also indicative aspects for discrimination between these two taxa. Moreover, the morphology of the CR shows several distinguishing aspects. The claw Ga is longer in Pseudostrandesia new species appearing half length of the ramus (less than half the length of the ramus in P. complexa). The sa seta is longer than the claw Gp in the new species, whereas it is shorter in P. complexa. In addition, the sp seta of the new species is also longer (slightly beyond the tip of the ramus), while it does not reach the tip of the ramus in P. complexa.
Apart from P. complexa, P. ratchaburiensis sp. nov. is similar to P. phetchabunensis, especially in the carapace shape in the lateral view, at first glance. The presence of the antero-ventral flange of the LV in the new species is clearly an indicative character to separate it from P. phetchabunensis. In addition, the differences between these two species are found in the soft parts morphology. Pseudostrandesia ratchaburiensis sp. nov. is distinguishable from P. phetchabunensis by, for example, the absence of the Additionally, other distinguishing features can be observed in these three related species. Strandesia prachuapensis sp. nov. can be distinguished from S. flavescens by the more arched Cp in the lateral view, the absence of septa-like structures on the LV, the longer claw Ga and the shorter claw Gp.
Strandesia new species differs from S. odiosa by the more elongated Cp, the smooth bristles on the Mx1 third endite (serrated in S. odiosa), the length of the shortest natatory seta on the A2 (longer in the new species) and the shorter f-seta on the T2. It should be noticed that the insertion of the aesthetasc Y on the A2 in S. prachuapensis sp. nov. is rather more proximal, situating ca one fourth of the segment, whereas in other Strandesia species, it is typically approximately mid-length on the first endopodal segment.
Strandesia prachuapensis sp. nov. also shares the presence of an anterior flange on the RV with another Southeast Asian Strandesia, S. feuerborni Klie, 1932. However, the anterior flange of S. feuerborni is considerably larger and slightly slopes downward as well as reaching the mouth region. This notable anterior flange, together with an obvious dorsal hump on the RV are the outstanding indicative characters of S. feuerborni, which cannot be confused with S. prachuapensis sp. nov.
It should be noted that, on the third and the fourth segments of the A1 in S. prachuapensis sp. nov., the ventral setae have an unusual aspect, appearing like aesthetasc-like setae (Fig 8A'). Such setae have also been obviously recognized in other cypricercine species, such as Pseudostrandesia thailandensis, Pseudostrandesia mamarilorum (see Savatenalinton & Martens 2010), Pseudostrandesia striatoreticulata, Tanycypris siamensis Martens, 2009 andBradleytriebella tuberculata (Hartmann, 1964) (see Savatenalinton & Martens 2009b). The A1 seta is known as a swimming appendage in most ostracods and bears several sensory organs/setae, e.g., Rome organ, Wouters organ and aesthetasc y a . Hence, the presence of these modified setae in the Strandesia new species, including other representatives of Cypricercinae, is highly possibly related to sensory reception. The detailed morphology of the A1 setae, together with the comparison of these aesthetasc-like setae and normal setae, will be present elsewhere.
Most cypricercine species have marginal selvage on the RV while in the LV, it lies apart from the valve margin. In Cypricercinae, the anterior flange that occurs on the RV only, is a rare feature as it has been recognized in only a few species. According to the diagrams of the marginal zone structure provided by Horne & Colin (2005), the morphology of the RV anterior flange in Strandesia is similar to that of Cypris O.F. Müller, 1776. Both taxa have an anterior flange on the RV resulting from the inwardly displaced selvage. One-hundred and one species of Strandesia have so far been recorded worldwide covering many zoogeographical regions (see Meisch et al. 2019;Ferreira et al. 2020;present study), and only eight of them, including the new species, possess an anterior flange on the RV, which would indicate that this character is more derived. These eight species can be divided into three groups, on the basis of zoogeographical distribution, namely Oriental and Palaearctic, Afrotropical and Neotropical regions. The former group comprises four species (S. feuerborni, S. flavescens, S. odiosa and S. prachuapensis sp. nov.) while two (S. evae Gauthier, 1951 andS. hancocki (Lowndes, 1931)) and two (S. ewaldi Karanovic, 2006 andS. colombiensis Roessler, 1990) species, respectively, belong to the two latter groups. Since their fossils are unknown, their origins remain obscure.