Siamopsis gen . nov . and five new species of the subfamily Cypridopsinae Kaufmann , 1900 ( Crustacea : Ostracoda ) from Thailand

Siamopsis gen. nov., described here, belongs to a group of genera with the right valve overlapping the left valve in the subfamily Cypridopsinae Kaufmann, 1900 of the family Cyprididae Baird, 1845. The distinguishing characters of the new genus are in the morphology of its valves and soft parts. The postero-dorsal margin of the internal left valve is plate-like protruded. The morphology of this plate varies in different species, e.g., some species bear a tooth-like tubercle on the plate. The posterior margin of the right valve is recurved inwardly at ca mid-height, resulting in the occurrence of a lobe-like expansion that can clearly be seen in the dorsal and caudal views of the carapace. In addition, the other diagnostic soft part features of the new genus are the cylindrical caudal ramus, the presence of two t-setae on the female A2 penultimate segment, the very elongated terminal segment of the Mx1 palp, the morphology of the two large bristles (tooth bristles) of the Mx1 third endite (one smooth, one serrated) and the absence of d-seta on T1. In the present paper, five new species are described under this new genus: Siamopsis renateae gen. et sp. nov., S. suttajiti gen. et sp. nov., S. conspecta gen. et sp. nov., S. khoratensis gen. et sp. nov. and Siamopsis planitia gen. et sp. nov. A key to the species of Siamopsis gen. nov. is also provided.


Introduction
The subfamily Cypridopsinae Kaufmann, 1900, with Cypridopsis Brady, 1867 as type genus, is characterized by a reduced caudal ramus that forms fl agellum-like structures.About 204 species in 17 genera of subfamily Cypridopsinae have so far been recognized worldwide (Martens & Savatenalinton 2011;Higuti & Martens 2012).The subfamily contains six monospecifi c genera: Austrocypridopsis

Material and methods
Samples were collected with a hand net (mesh size 150 μm), preserved in 70% ethanol and sorted using an Olympus SZ-PT stereo-microscope.Soft parts were dissected in glycerine and sealed on glass slides.Valves were stored dry in micropalaeontological slides.Drawings of soft parts were made with the aid of a camera lucida.Carapaces and valves were observed and illustrated using a scanning electron microscopy (JEOL JSM6460LV at the Faculty of Science, MSU and Philips XL30 SEM at RBINS).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).Type material of all species is deposited in the Natural History Museum, MSU (Maha Sarakham, Thailand).The following abbreviations are used for limbs: A1 = fi rst antenna A2 = second antenna CR = caudal ramus Md = mandibula Mx1 = maxillula T1 = fi rst thoracopod (maxilliped) T2 = second thoracopod (walking leg) T3 = third thoracopod (cleaning leg)

Etymology
The genus is named after the country "Siam", the former name of Thailand, where the new taxa were discovered.The name is combined with the suffi x of the existing generic name Cypridopsis.

Differential diagnosis
Siamopsis gen.nov.can be distinguished from other genera of the subfamily Cypridopsinae by the presence of a postero-dorsal internal plate of the LV and the morphology of the posterior inner valve margin of the RV, which is recurved inwardly.Additionally, it differs from its closest genus, Plesiocypridopsis Rome, 1965, by the presence of the A1 Wouters organ, the two t-setae of the female A2 (there are four t-setae in Plesiocypridopsis) and the morphology of the two large bristles (teeth bristles) on the Mx1 third endite, of which one bristle is smooth while the other one is serrated (both setae are serrated in Plesiocypridopsis).

Remarks
The postero-dorsal plate of the internal LV bears tooth-or teeth-like tubercle(s) in several species of Siamopsis gen.nov.The position of these tubercles can vary from species to species, being on, for example, the margin or in the middle of the plate.The degree of the inward curve on the RV posterior margin is different among species.Therefore, these aspects are used as taxonomic characters for identifi cation.

Diagnosis
Carapace in lateral view subtriangular, dorsal margin strongly arched, slightly angulated at posterodorsal part, greatest height situated in front of mid-length, RV overlapping LV anteriorly, ventrally, posteriorly.Valve surface set with long (rim-pore) setae and shallow pits dispersedly.Carapace in dorsal view tumid with even lateral margins.LV in internal view, with large marginal zone anteriorly, both anterior and posterior valve margins subequally rounded, postero-dorsal plate broad with two small marginal teeth-like tubercles, inner lamella calcifi ed, with inner lists anteriorly and posteriorly.RV in internal view with large marginal zone anteriorly, inner lamella with inner lists anteriorly and posteriorly, without small tubercle-like structures under posterior inner list.Mx1 third endite with two (one smooth, one serrated) large bristles, terminal segment of Mx1 palp cylindrical, very elongated.CR of cylindrical shape, with fl agellum-like seta.

Etymology
This species is named after Dr. Renate Matzke-Karasz (Munich University, Germany) in appreciation of her outstanding work on ostracods and also for a long friendship.

Material examined
Holotype THAILAND: ♀, with soft parts dissected in glycerine on a sealed glass slide and valves stored dry in a micropalaeontological slide (MSU-ZOC.190).

Differential diagnosis
Siamopsis renateae gen.et sp.nov.differs from the other species of the new genus by the presence of a strongly arched dorsal margin, resulting in the subtriangular carapace in lateral view (elongated shape in other species), the postero-dorsal plate on LV having two small, teeth-like tubercles on the inner border and the absence of tiny tubercle-like structures under the RV posterior inner list.Additionally, the ya and accompanying seta on A1 are subequal in length in S. renateae gen.et sp.nov.while the length of the accompanying seta is ca ⅔ that of ya in other species of Siamopsis gen.nov.Compared to the g-seta on T2, the length of the seta located next to the g-seta is short (ca ⅓ of g-seta) in S. renateae gen.et sp.nov.The length of this seta is ca half of that of the g-seta in other species of Siamopsis gen.nov.

Description
Female CARAPACE.In lateral view (Fig. 1A) subtriangular, anterior margin rounded, posterior margin narrower rounded, dorsal margin strongly arched and slightly angulated at postero-dorsal part, greatest height situated in front of mid-length, RV overlapping LV anteriorly, ventrally and posteriorly, valve surface set with long setae, long rim-pore setae and shallow pits dispersedly.Carapace in dorsal view (Fig. 1B, G) tumid, with evenly curved lateral margins, greatest width situated at mid-length, posterior extremity round, anterior extremity more pointed.
European Journal of Taxonomy 384: 1-39 (2017) VALVES.LV in internal view (Fig. 1D, H) with large marginal zone anteriorly, both valve margins subequally rounded, ventral margin sinuous at mid-length, postero-dorsal plate broad, with two small marginal teeth-like tubercles, calcifi ed inner lamella with inner lists anteriorly and posteriorly.RV in internal view (Fig. 1E, I) with large marginal zone anteriorly, ventral margin sinuous at mid-length, inner lamella calcifi ed with inner lists anteriorly and posteriorly.A1 (Fig. 2A).Seven-segmented, fi rst segment with large proximal Wouters organ, one long dorsosubapical seta (reaching beyond tip of next segment) and two long ventro-apical setae.Second segment slightly wider than long, with one long dorso-apical seta (reaching tip of next segment) and Rome organ.Third segment bearing two setae: one long dorso-apical (reaching tip of penultimate segment) and one short ventro-apical.Fourth segment with two long dorsal setae and two short ventral setae (both reaching beyond half of fi fth segment).Fifth segment dorsally with two long setae, ventrally with two (one long, one short) setae, short one reaching beyond end of next segment.Penultimate segment with four long apical setae.Terminal segment with three (two long, one short) apical setae and long aesthetasc ya, length of short seta ca ⅓ of aesthetasc ya.A2 (Fig. 2B).Exopodite with three (one long, two short) setae, long one reaching beyond tip of fi rst endopodal segment.First endopodal segment with fi ve long (reaching far beyond tips of terminal claws) and one short natatory seta, length of shortest seta ca half that of penultimate segment, aesthetasc Y long, ventro-apical seta long, extending beyond tip of terminal segment.Penultimate segment undivided, distally with three serrated claws (G1, G2, G3), G2 shorter (length of G2 ca ¾ that of G1), aesthetasc y2 long (ca half of terminal segment), z1-z3 setae long; this segment medially with two subequally long dorsal setae, two ventral setae of unequal length (t1-t2).Terminal segment distally with two serrated claws (GM and Gm), length of Gm ca ⅔ that of GM; medially with short g-seta and ventral aesthetasc y3, length of aesthetasc y3 and accompanying seta subequal.
MD PALP (Fig. 3A).First segment with two large setae, one long and slender seta, and a short, smooth α-seta.Second segment dorsally with three unequal long apical setae; ventrally with group of three long hirsute setae, one shorter hirsute seta and plumose, cone-shaped β-seta with pointed tip.Penultimate segment with three groups of setae: dorsally with group of four unequal, long, subapical setae; laterally with apical γ-seta and three further apical setae (two smooth, one hirsute), the former thin and long (length ca 2.2 times that of terminal segment); ventrally with two subapical setae, one very long (reaching beyond tip of terminal segment), one short (ca half length of terminal segment).Terminal segment elongated, bearing three claws and two shorter setae.MX1 (Fig. 3B).With two-segmented palp, basal segment of palp dorsally with group of fi ve long, unequal apical setae; ventrally with one short subapical seta.Terminal segment very elongated (length ca 2.8 times width), apically with three claws and two setae.Third endite with two (one smooth, one serrated) large bristles.Sideways-directed bristles on fi rst endite unequally long, length of short one ca half that of long one.T1 (Fig. 3C-D).Protopodite with two unequally short a-setae, b-and d-setae absent, distally with ca 12 hirsute apical setae of unequal length.Endopodite with weakly built palp, with one very long, hirsute and two unequally short apical setae.T2 (Fig. 4A).With d2 seta (d1 absent).Second segment with long e-seta (reaching tip of penultimate segment).Penultimate segment divided, proximal segment bearing long f-seta (reaching beyond tip of terminal segment), distal segment with pair of apical setae (g-seta, one short), g-seta very long (with almost the same length as h1 seta).Terminal segment with two (one dorsal, one ventral) apical h1 and h3 setae (length of former ca half that of claw, latter short) and serrated claw (h2), length of h2 longer than that of penultimate segment.European Journal of Taxonomy 384: 1-39 (2017) T3 (Fig. 4B).A cleaning limb.First segment with long d1, d2 and dp setae, d1 and d2 setae subequal in length.Second segment with long apical e-seta (reaching half of next segment).Third segment with medially long f-seta (reaching tip of segment).Terminal segment with an apical pincer and one refl exed subapical seta, length of latter equal to that of third segment.CR (Fig. 4C).Reduced, fl agellum-like, of cylindrical shape, with a small lateral seta and long apical seta, length of latter ca 1.7 times that of ramus.

Male
Unknown.

Diagnosis
Carapace in lateral view elongated, dorsal margin arched, greatest height situated in front of mid-length.Carapace in dorsal view elliptical, with unevenly curved lateral margins (posterior half of carapace), anterior extremity pointed, RV overlapping LV anteriorly, ventrally and posteriorly.Valve surface set with long (rim-pore) setae and shallow pits dispersedly.LV in internal view with large selvage anteriorly, valve margins rounded, broader anteriorly, postero-dorsal plate of LV in internal view elongated, with posterior marginal tooth-like tubercle.RV in internal view with large selvage anteriorly, posterior margin slightly curved inwardly at postero-dorsal part, few small tubercle-like structures set beneath the posterior inner list along postero-ventral corner.Third endite of Mx1 with two large bristles, one distally serrated, the other one smooth.CR cylindrical in shape, with long fl agellum-like seta (ca 2.4 times as long as ramus).

Etymology
This species is named after Prof. Dr. Maitree Suttajit (University of Phayao, Thailand) in appreciation of his encouragement and moral support over the years, especially during my research project on nonmarine ostracods in the southern part of Northeast Thailand.

Material examined
Holotype THAILAND: ♀, with soft parts dissected in glycerine on a sealed glass slide and valves stored dry in a micropalaeontological slide (MSU-ZOC.195).

Differential diagnosis
Siamopsis suttajiti gen.et sp.nov.can be distinguished by the morphology of the carapace in dorsal view and the postero-dorsal plate of the LV in internal view.The carapace in dorsal view is elongated, with unevenly curved lateral margins (the posterior half of carapace narrower) and the LV posterodorsal plate contains a tooth-like tubercle on the posterior marginal.Siamopsis suttajiti gen.et sp.nov. is similar to S. conspecta gen.et sp.nov.and S. khoratensis gen.et sp.nov.as they share a few small septa-like structures under the posterior inner list along the postero-ventral corner.The distinguishing features of S. suttajiti gen.et sp.nov.also appear in the soft parts morphology.For example, the length of the shortest seta on A1 terminal segment is markedly short, when compared to ya (ca ¼ length of ya).In other species of Siamopsis gen.nov., this seta is about half as long as ya.Additionally, the apical fl agellum-like seta of CR is very long (more than two times that of the ramus) in S. suttajiti gen.et sp.nov.while it is less than two times that of the ramus in other species of Siamopsis gen.nov.

Description
Female CARAPACE.In lateral view (Fig. 5A) elongated, dorsal margin arched, greatest height situated in front of mid-length, anterior margin rounded, posterior margin narrower rounded, ventral margin sinuous at ca mid-length, RV overlapping LV anteriorly, ventrally and posteriorly, valve surface set with long setae, long rim-pore setae and shallow pits dispersedly.Carapace in dorsal view (Fig. 5B, D) elliptical, with unevenly curved lateral margins (posterior half of carapace narrower), greatest width situated at midlength, anterior extremity pointed, posterior extremity rounded.
VALVES.LV in internal view (Fig. 5F, H) with large selvage anteriorly, valve margins rounded, broader anteriorly, ventral margin sinuous at mid-length, postero-dorsal plate elongated, with posterior marginal tooth-like tubercle, inner lamella anteriorly broader than posteriorly, without inner list.RV in internal view (Fig. 5G, I) with large selvage anteriorly, ventral margin sinuous at mid-length, posterior margin slightly curved inwardly at postero-dorsal part, inner lamella calcifi ed with inner lists anteriorly and posteriorly, with few tiny tubercle-like structures under posterior inner list along postero-ventral corner.A1 (Fig. 6A).Seven-segmented, fi rst segment with large proximal Wouters organ, one long dorsosubapical seta (reaching mid-length of next segment) and two long ventro-apical setae.Second segment slightly wider than long, with one long dorso-apical seta (reaching tip of next segment) and Rome organ.Third segment bearing two setae: one long dorso-apical (reaching beyond tip of terminal segment) and one short ventro-apical.Fourth segment with two long dorsal setae and two short ventral setae (both reaching end of next segment).Fifth segment dorsally with two long setae, ventrally with two (one long, one short) setae, short one reaching mid-length of terminal segment.Penultimate segment with four long apical setae.Terminal segment with three (two long, one short) apical setae and very long aesthetasc ya, length of short seta ca ¼ that of aesthetasc ya.European Journal of Taxonomy 384: 1-39 (2017) A2 (Fig. 6B).Exopodite with three (one long, two short) setae, long one reaching beyond tip of fi rst endopodal segment.First endopodal segment with fi ve long (reaching far beyond tip of terminal claws) and one short natatory setae, shortest seta reaching end of penultimate segment, aesthetasc Y long, ventro-apical seta long, extending beyond tip of terminal segment.Penultimate segment undivided, distally with three serrated claws (G1, G2, G3), G2 shorter (length of G2 ca 6/7 that of G1), aesthetasc y2 long (ca half length of terminal segment), z1-z3 setae long; this segment medially with two subequally long dorsal setae, two ventral setae of unequal length (t1-t2).Terminal segment distally with two serrated claws (GM and Gm), length of Gm ca ⅔ that of GM; medially with short g-seta and ventral aesthetasc y3, length of accompanying seta ca ¾ that of aesthetasc y3.

European Journal of Taxonomy
MD PALP (Fig. 7A).First segment with two large setae, one long and slender seta, and a short, smooth α-seta.Second segment dorsally with three unequally long apical setae; ventrally with group of three long hirsute setae, one shorter hirsute seta and plumose, cone-shaped β-seta with pointed tip.Penultimate segment with three groups of setae: dorsally with group of four unequal, long, subapical setae; laterally with apical γ-seta and three further apical setae (two smooth, one hirsute), the former thin and long (length ca 2.2 times that of terminal segment); ventrally with two subapical setae, one very long (reaching beyond tip of terminal segment), one short (ca half length of terminal segment).Terminal segment elongated, bearing three claws and two short setae.MX1 (Fig. 7B).With two-segmented palp, basal segment of palp dorsally with group of six long, unequal apical setae; ventrally with one short subapical seta.Terminal segment very elongated (length ca 2.7 times width), apically with three claws and two setae.Third endite with two (one smooth, one serrated) large bristles.Lateral bristles on fi rst endite unequally long, length of long one ca 2.2 times that of short one.T1 (Fig. 6D).Protopodite with two unequally short a-setae, b-and d-setae absent, distally with ca 14 hirsute apical setae of unequal length.Endopodite weakly built palp with one very long, hirsute and two unequally short apical setae.T2 (Fig. 7C).With d2 seta (d1 absent).Second segment with short e-seta (reaching middle of penultimate segment).Penultimate segment divided, proximal segment bearing long f-seta (reaching tip of terminal segment), distal segment with pair of apical setae (very long g-seta, one short), the long one reaching beyond tip of terminal segment.Terminal segment with two (one dorsally, one ventrally) apical h1 and h3 setae (length of former ca ⅓ that of claw, latter spine-like) and serrated claw (h2), length of h2 longer than that of penultimate segment.T3 (Fig. 7D).A cleaning limb.First segment with long d1, d2 and dp setae, d1 and d2 setae subequal in length.Second segment with long apical e-seta (reaching half of next segment).Third segment with medially long f-seta (reaching tip of segment).Terminal segment with an apical pincer and one refl exed subapical seta, length of latter equal that of third segment.CR (Fig. 7E).Reduced, fl agellum-like, of cylindrical shape, with a small lateral seta and very long apical seta, length of latter ca 2.4 times that of ramus.

Male
Unknown.

Ecology
The new species has thus far been collected from only one locality in Phayao Province.It occurs at a pH of 7.1, a temperature of 26.8°C and a DO of 7.16 mg/l.

Diagnosis
Carapace in lateral view elongated, dorsal margin arched, greatest height situated in front of mid-length, RV overlapping LV anteriorly, ventrally and posteriorly.Valve surface set with long (rim-pore) setae and shallow pits dispersedly.LV in internal view with large selvage anteriorly, valve margins rounded, broader anteriorly, postero-dorsal plate of LV in internal view broad, with large tooth-like tubercle at the centre.RV in internal view with large selvage anteriorly, posterior margin curved inwardly at posterodorsal part, outer margin of posterior inner list set with a series of small tubercle-like structures at postero-ventral corner.Third endite of Mx1 with two large bristles, one distally serrated, other one smooth.CR cylindrical in shape, with fl agellum-like seta.

Etymology
The Latin word 'conspecta', meaning conspicuous, refers to the markedly well-developed tooth-like tubercle on the postero-dorsal plate of internal LV.This is the most prominent character of the new species.

Material examined
Holotype THAILAND: ♀, with soft parts dissected in glycerine on a sealed glass slide and valves stored dry in a micropalaeontological slide (MSU-ZOC.201).

Differential diagnosis
Siamopsis conspecta gen.et sp.nov. is similar to S. suttajiti gen.et sp.nov. in terms of the carapace shape in lateral view and the presence of tiny tubercle-like structures along the posterior inner list at the postero-ventral corner of the RV.It can be distinguished by the morphology of the postero-dorsal plate of the LV.The plate is broad and contains a large tooth-like tubercle at the middle in Siamopsis conspecta gen.et sp.nov., whereas it is elongated and has a marginal tooth-like tubercle at the posterior part in S. suttajiti gen.et sp.nov.In addition, compared to the CR length, the apical fl agellum-like seta is shorter in Siamopsis conspecta gen.et sp.nov.(very long in S. suttajiti gen.et sp.nov.).

Description
Female CARAPACE.In lateral view elongated, dorsal margin arched, greatest height situated in front of mid-length, anterior margin rounded, posterior margin narrower rounded, RV overlapping LV anteriorly, ventrally and posteriorly, valve surface set with long setae, long rim-pore setae and shallow pits dispersedly.Carapace in dorsal view elliptical, with greatest width situated at mid-length.
VALVES.LV in interior view (Fig. 8C) with large selvage anteriorly, valve margins rounded, broader anteriorly, ventral margin sinuous at ca mid-length, postero-dorsal plate of LV in internal view broad, with large tooth-like tubercle at centre, inner lamella calcifi ed, anteriorly broader than posteriorly.RV in interior view (Fig. 8D) with large selvage anteriorly, ventral margin sinuous at mid-length, posterior margin curved inwardly at postero-dorsal part, inner lamella calcifi ed with inner lists anteriorly and posteriorly, outer margin of lamella set with a series of small tubercles at postero-ventral corner.A1 (Fig. 9A).Seven-segmented, fi rst segment with large proximal Wouters organ, one long dorsosubapical seta (reaching mid-length of next segment) and two long ventro-apical setae.Second segment slightly wider than long, with one long dorso-apical seta (reaching tip of next segment) and Rome organ.Third segment bearing two setae: one long dorso-apical and one short ventro-apical.Fourth segment with two long dorsal setae and two short ventral setae (one reaching tip of fi fth segment, another one spine-like).Fifth segment dorsally with two long setae, ventrally with two (one long, one short) setae, short one reaching beyond tip of next segment.Penultimate segment with four long apical setae.Terminal segment with three (two long, one short) apical setae and very long aesthetasc ya, length of short seta more than half that of aesthetasc ya.A2 (Fig. 9B).Exopodite with three (one long, two short) setae, long one reaching beyond tip of fi rst endopodal segment.First endopodal segment with fi ve long (reaching far beyond tip of terminal claws) and one short natatory setae, shortest seta reaching tip of penultimate segment, aesthetasc Y long, ventroapical seta long, extending beyond tip of terminal segment.Penultimate segment undivided, distally with three serrated claws (G1, G2, G3), G2 shorter (length of G2 ca 6/7 that of G1), aesthetasc y2 long (ca half that of terminal segment), z1-z3 setae long; this segment medially with two subequally long dorsal setae and two ventral setae of unequal length (t1-t2).Terminal segment distally with two serrated claws (GM and Gm), length of Gm ca ⅔ that of GM; medially with short g-seta and ventral aesthetasc y3, length of accompanying seta ca ⅔ that of aesthetasc y3.
MD PALP (Fig. 10A).First segment with two large setae, one long and slender seta, and a short, smooth α-seta.Second segment dorsally with three unequal long apical setae; ventrally with group of three long hirsute setae, one shorter hirsute seta and plumose, cone-shaped β-seta with pointed tip.Penultimate segment consisting of three groups of setae: dorsally with group of four unequal, long, subapical setae; laterally with apical γ-seta and three further apical setae (two smooth, one hirsute), the former thin and long (length ca 2.2 times of terminal segment); ventrally with two subapical setae, one very long (reaching beyond tip of terminal segment), one short (ca half of terminal segment).Terminal segment elongated bearing three claws and two shorter seta.MX1 (Fig. 10B).With two-segmented palp, basal segment of palp dorsally with group of fi ve long, unequal apical setae; ventrally with one short subapical seta.Terminal segment very elongated (length ca 3 times of width), apically with three claws and two setae.Third endite with two (one smooth, one European Journal of Taxonomy 384: 1-39 (2017) serrated) large bristles.Sideways-directed bristles on fi rst endite unequally long, length of short one ca half that of long one.T1 (Fig. 9D).Protopodite with two unequally short a-setae, b-and d-setae absent, distally with ca 12 hirsute apical setae of unequal length.Endopodite with weakly built palp, with one very long, hirsute and two unequally short apical setae.T2 (Fig. 10C).With d2 seta (d1 absent).Second segment with short e-seta (reaching beyond mid-length of penultimate segment).Penultimate segment divided, proximal segment bearing long f-seta (reaching beyond tip of terminal segment), distal segment with pair of apical setae (long g-seta, one short), length of g-seta almost the same length as that of h1 seta.Terminal segment with two (one dorsally, one ventrally) apical h1 and h3 setae (length of former ca ⅓ that of claw, latter spine-like) and serrated claw (h2), length of h2 longer than that of penultimate segment.

SAVATENALINTON S., A new genus of Cypridopsinae from Thailand
T3 (Fig. 10D).A cleaning limb.First segment with long d1, d2 and dp setae, d1 and d2 setae subequal in length.Second segment with long apical e-seta (reaching half of next segment).Third segment with medially long f-seta (reaching tip of segment).Terminal segment with an apical pincer and one refl exed subapical seta, length of latter equal to that of third segment.CR (Fig. 10E).Reduced, fl agellum-like, cylindrical in shape, with a small lateral seta and long apical seta, length of latter ca 1.5 times that of ramus.

Male
Unknown.

Ecology
The new species has so far been collected from two bodies of water only in the Nakhon Ratchasima and Phayao Provinces.It occurs at a pH range of 7.0-7.1, a temperature range of 26.8-28.5°Cand a DO of 7.16 mg/l.

Diagnosis
Carapace in lateral view elongated, dorsal margin fl at at middle part of carapace, RV overlapping LV anteriorly, ventrally and posteriorly.Valve surface set with long (rim-pore) setae and shallow pits dispersedly.LV in internal view with large selvage anteriorly, valve margins subequally rounded anteriorly and posteriorly, postero-dorsal plate broad, with a small anterior tooth-like tubercle.RV in internal view with large selvage anteriorly, posterior margin curved inwardly at slightly above mid height, posterior inner list internally set with small tubercle-like structures at postero-ventral part.Third endite of Mx1 with two large bristles, one distally serrated, one smooth.CR cylindrical in shape, with fl agellum-like seta.

Etymology
The species is named after Nakhon Ratchasima Province, also called "Khorat", where the new species was discovered.

Material examined
Holotype THAILAND: ♀, with soft parts dissected in glycerine on a sealed glass slide and valves stored dry in a micropalaeontological slide (MSU-ZOC.204).

Differential diagnosis
Siamopsis khoratensis gen.et sp.nov.has S. planitia gen.et sp.nov.as its closest congener.The obvious diagnostic characters are the morphology of the postero-dorsal plate of the LV in internal view and of the RV posterior inner list.The plate is broad and has a small tooth-like tubercle at the anterior part in S. khoratensis gen.et sp.nov., while it is elongated and has no tooth-like tubercle in S. planitia gen.et sp.nov.The RV posterior inner list is set with small tubercle-like structures at the postero-ventral part in S. khoratensis gen.et sp.nov., whereas it is smooth in S. planitia gen.et sp.nov.

Description
Female CARAPACE.In lateral view elongated, dorsal margin fl at at middle part of carapace, both margins subequally rounded anteriorly and posteriorly, RV overlapping LV anteriorly, ventrally and posteriorly, valve surface set with long setae, long rim-pore setae and shallow pits dispersedly (Fig. 11A-B).Carapace in dorsal view elliptical, with greatest width situated at mid-length.
VALVES.LV in interior view (Fig. 11C) with large selvage anteriorly, valve margins subequally rounded anteriorly and posteriorly, ventral margin sinuous at ca mid-length, postero-dorsal plate broad, set with a small anterior tooth-like tubercle, inner lamella anteriorly broader than posteriorly.RV in interior view (Fig. 11D) with large selvage anteriorly, valve margins subequally rounded anteriorly and posteriorly, ventral margin sinuous at ca mid-length, posterior margin recurved inwardly slightly above mid height, calcifi ed inner lamella with inner lists anteriorly and posteriorly, postero-ventral inner-list internally set with small tubercle-like structures.A1 (Fig. 12A).Seven-segmented, fi rst segment with large proximal Wouters organ, one long dorsosubapical seta (reaching beyond tip of next segment) and two long ventro-apical setae.Second segment slightly wider than long, with one long dorso-apical seta (reaching tip of next segment) and Rome organ.Third segment bearing two setae: one long dorso-apical (reaching tip of penultimate segment) and one short ventro-apical setae.Fourth segment with two long dorsal setae and two short ventral setae (both reaching beyond half of fi fth segment).Fifth segment dorsally with two long setae, ventrally with two (one long, one short) setae, short one reaching mid-length of terminal segment.Penultimate segment with four long apical setae.Terminal segment with three (two long, one short) apical setae and very long aesthetasc ya, length of short seta ca half that of aesthetasc ya.A2 (Fig. 12B).Exopodite with three (one long, two short) setae, long one reaching beyond tip of fi rst endopodal segment.First endopodal segment with fi ve long (reaching far beyond tip of terminal claws) and one short natatory setae, length of shortest seta ca half that of penultimate segment, aesthetasc Y long, ventro-apical seta long, extending beyond tip of terminal segment.Penultimate segment undivided, distally with three serrated claws (G1, G2, G3), G2 shorter (length of G2 ca 6/7 that of G1), aesthetasc y2 long (ca half that of terminal segment), z1-z3 setae long; this segment medially with two subequally long dorsal setae and two ventral setae of unequal length (t1-t2).Terminal segment distally with two serrated claws (GM and Gm), length of Gm slightly more than half that of GM; medially with short g-seta and ventral aesthetasc y3, length of accompanying seta ca ⅔ that of aesthetasc y3.
MD PALP (Fig. 13A).First segment with two large setae, one long and slender seta, and a short, smooth α-seta.Second segment dorsally with three unequally long apical setae; ventrally with group of three long hirsute setae, one shorter hirsute seta and plumose, cone-shaped β-seta with pointed tip.Penultimate segment consisting of three groups of setae: dorsally with group of four unequal, long, subapical setae; SAVATENALINTON S., A new genus of Cypridopsinae from Thailand European Journal of Taxonomy 384: 1-39 (2017) laterally with apical γ-seta and three further apical setae (two smooth, one hirsute), the former thin and long (length ca 2.2 times that of terminal segment); ventrally with two subapical setae, one very long (reaching beyond tip of terminal segment), one short (ca half that of terminal segment).Terminal segment elongated, bearing three claws and two shorter setae.MX1 (Fig. 13B).With two-segmented palp, basal segment of palp dorsally with group of fi ve long, unequal apical setae; ventrally with one short subapical seta.Terminal segment very elongated (length ca 3.3 times width), apically with three claws and two setae.Third endite with two (one smooth, one SAVATENALINTON S., A new genus of Cypridopsinae from Thailand serrated) large bristles.Sideways-directed bristles on fi rst endite unequally long, length of short one ca half that of long one.T1 (Fig. 13C-D).Protopodite with two unequally short a-setae, b-and d-setae absent, distally with ca 11 hirsute apical setae of unequal length.Endopodite a weakly built palp, with one very long, hirsute and two unequally short apical setae.T2 (Fig. 14A).With d2 seta (d1 absent).Second segment with short e-seta (reaching mid-length of penultimate segment).Penultimate segment divided, proximal segment bearing long f-seta (reaching beyond tip of terminal segment), distal segment with pair of apical setae (long g-seta, one short), length of g-seta almost the same as that of h1 seta.Terminal segment with two (one dorsally, one ventrally) apical h1 and h3 setae (length of former ca ⅓ that of claw, latter short) and serrated claw (h2), length of h2 longer than that of penultimate segment.European Journal of Taxonomy 384: 1-39 (2017) T3 (Fig. 14B).A cleaning limb.First segment with long d1, d2 and dp setae, d1 and d2 setae subequal in length.Second segment with long apical e-seta (reaching half of next segment).Third segment with medially long f-seta (reaching tip of segment).Terminal segment with an apical pincer and one refl exed subapical seta, length of latter equal to that of third segment.CR (Fig. 14C).Reduced, fl agellum-like, cylindrical in shape, with a small lateral seta and long apical seta, length of latter ca 1.8 times that of ramus.

Male
Unknown.

Ecology
The new species has been encountered at only one locality, in Nakhon Ratchasima Province.It occurs at a pH of 7.0 and a temperature of 28.5°C.

Diagnosis
Carapace in lateral view elongated, dorsal margin fl at at middle part of carapace, RV overlapping LV anteriorly, ventrally and posteriorly, valve surface set with long (rim-pore) setae and shallow pits dispersedly.LV in internal view with large selvage anteriorly, valve margins subequally rounded anteriorly and posteriorly, postero-dorsal plate elongated, without tooth-like tubercle.RV in internal view with large selvage anteriorly, posterior margin curved inwardly at postero-dorsal part, posteroventral part slightly angulate, without small tubercle-like structures under inner list.Mx1 third endite with two (one smooth, one serrated) large bristles.CR cylindrical shape, with fl agellum-like seta.

Etymology
The specifi c epithet "planitia" refers to the appearance of a dorsal margin at the middle part of the carapace in lateral view, which is similar to the summit of a plateau.This is the most prominent character of the new species.

Material examined
Holotype THAILAND: ♀, with soft parts dissected in glycerine on a sealed glass slide and valves stored dry in a micropalaeontological slide (MSU-ZOC.208).

Differential diagnosis
Siamopsis planitia gen.et sp.nov. is closely related to S. khoratensis gen.et sp.nov.The species is characterized by the presence of a fl at, slightly concave dorsal margin at the middle part of the carapace in lateral view, the naked (without tooth-like tubercle) elongated postero-dorsal plate of the LV and the absence of small tubercle-like structures under the inner list at the postero-ventral part of the RV.

Description
Female CARAPACE.In lateral view (Fig. 15A) elongated, dorsal margin fl at at the middle part of carapace, both margins subequally rounded anteriorly and posteriorly, RV overlapping LV anteriorly, ventrally and posteriorly, valve surface set with long (rim-pore) setae and shallow pits dispersedly (Fig. 15D).Carapace in dorsal view elliptical, with greatest width situated at mid-length.
VALVES.LV in internal view (Fig. 15B) with large selvage anteriorly, valve margins subequally rounded anteriorly and posteriorly, postero-dorsal plate elongated, without tooth-like tubercle, calcifi ed inner lamella anteriorly broader than posteriorly, with inner lists.RV in internal view (Fig. 15C) with large selvage anteriorly, posterior margin curved inwardly situated at postero-dorsal part, postero-ventral part slightly angulate, without small tubercle-like structures under inner list.A1 (Fig. 16A).Seven-segmented, fi rst segment with large proximal Wouters organ, one long dorsosubapical seta (reaching mid-length of next segment) and two long ventro-apical setae.Second segment slightly wider than long, with one long dorso-apical seta (reaching mid-length of next segment) and Rome organ.Third segment bearing two setae: one long dorso-apical (reaching tip of penultimate segment) and one ventro-apical spine-like setae.Fourth segment with two long dorsal setae and two short ventral setae (both reaching beyond half of fi fth segment).Fifth segment dorsally with two long setae, ventrally with two (one long, one short) setae, short one reaching beyond tip of next segment.Penultimate segment with four long apical setae.Terminal segment with three (two long, one short) apical setae and very long aesthetasc ya, length of short seta more than half that of aesthetasc ya.A2 (Fig. 16B).Exopodite with three (one long, two short) setae, long one reaching beyond tip of fi rst endopodal segment.First endopodal segment with fi ve long (reaching far beyond tip of terminal claws) and one short natatory setae, length of the shortest seta ca half that of penultimate segment, aesthetasc Y long, ventro-apical seta long, extending beyond tip of terminal segment.Penultimate segment undivided, distally with three serrated claws (G1, G2, G3), G2 shorter (length of G2 ca 6/7 that of G1), aesthetasc y2 long (ca half of terminal segment), z1-z3 setae long; this segment medially with two subequally long dorsal setae, two ventral setae of unequal length (t1-t2).Terminal segment distally with two serrated claws (GM and Gm), length of Gm ca ⅔ that of GM; medially with short g-seta and ventral aesthetasc y3, length of accompanying seta ca ¾ that of aesthetasc y3.
MD PALP (Fig. 17A).First segment with two large setae, one long and slender seta, and a short, smooth α-seta.Second segment dorsally with three unequally long apical setae; ventrally with group of three long hirsute setae, one shorter hirsute seta and plumose, cone-shaped β-seta with pointed tip.Penultimate segment consisting of three groups of setae: dorsally with group of four unequal, long, subapical setae; laterally with apical γ-seta and three further apical setae (two smooth, one hirsute), the former thin and SAVATENALINTON S., A new genus of Cypridopsinae from Thailand long (length ca 2 times that of terminal segment); ventrally with two subapical setae, one very long (reaching beyond tip of terminal segment), one short (ca half length of terminal segment).Terminal segment elongated, bearing three claws and two shorter setae.MX1 (Fig. 17B).With two-segmented palp, basal segment of palp dorsally with group of fi ve long, unequal apical setae; ventrally with one short subapical seta.Terminal segment very elongated (length ca 3 times that of width), apically with three claws and two setae.Third endite with two (one smooth, one serrated) large bristles.Sideways-directed bristles on fi rst endite unequally long, length of short one ca half that of long one.European Journal of Taxonomy 384: 1-39 (2017) T1 (Fig. 17C-D).Protopodite with two unequally short a-setae, b-and d-setae absent, distally with ca 10 hirsute apical setae of unequal length.Endopodite a weakly built palp, with one very long, hirsute and two unequally short apical setae.T2 (Fig. 18A).With d2 seta (d1 absent).Second segment with short e-seta (reaching mid-length of penultimate segment).Penultimate segment divided, proximal segment bearing long f-seta (reaching SAVATENALINTON S., A new genus of Cypridopsinae from Thailand beyond tip of terminal segment), distal segment with pair of apical setae (long g-seta, one short), g-seta reaching tip of terminal segment.Terminal segment with two (one dorsally, one ventrally) apical h1 and h3 setae (length of former ca ⅓ that of claw, latter short) and serrated claw (h2), length of h2 longer than that of penultimate segment.T3 (Fig. 18B).A cleaning limb.First segment with long d1, d2 and dp setae, d1 and d2 setae subequal in length.Second segment with long apical e-seta (reaching half length of next segment).Third segment European Journal of Taxonomy 384: 1-39 (2017) with medially long f-seta (reaching tip of segment).Terminal segment with an apical pincer and one refl exed subapical seta, length of latter equal to that of third segment.CR (Fig. 18C).Reduced, fl agellum-like, cylindrical in shape, with a small lateral seta and long apical seta, length of latter ca 1.8 times that of ramus.

Male
Unknown.

Ecology
The new species has so far been recorded from fi ve localities in Nakhon Ratchasima, Phetchabun and Chiang Mai Provinces.It occurs at a pH range of 6.50-7.38, a temperature range of 24.2-29.3°Cand a DO range of 3.20-8.14mg/l.

Discussion
The new genus is the sixth and third cypridopsine genus reported from the Oriental and Southeast Asian regions, respectively.The present study increases the total number of Southeast Asian cypridopsine species from six (Sars 1903;Victor & Fernando 1981;Savatenalinton et al. 2008;Savatenalinton 2009Savatenalinton , 2010;;Tressler 1937) to 11.In the following, the affi nities among genera of the subfamily Cypridopsinae and the morphological characters of the new genus are discussed.
Siamopsis gen.nov., described here, belongs to the group where the RV overlaps the LV.A key to genera with RV overlapping LV of the subfamily Cypridopsinae is given above.This group comprises nine genera: Martenscypridopsis Karanovic, 2000, Klieopsis Martens et al., 1991, Plesiocypridopsis Rome, 1965, Tanganyikacypridopsis Martens, 1985, Sarscypridopsis McKenzie, 1977, Kapcypridopsis McKenzie, 1977, Thermopsis Külköylüoğlu et al., 2003, Bryocypris Røen, 1956 and Siamopsis gen.nov.Among these genera, the occurrence of a cylindrical CR has been recognized in three genera, Klieopsis, Plesiocypridopsis and Siamopsis gen.nov.These three genera also share other features, e.g., the absence of the ventral apical seta on the Mx1 palp and of the d-seta on T1.The new genus can be distinguished from Plesiocypridopsis and Klieopsis by the presence of a plate-like protrusion on the postero-dorsal part of the internal LV, the morphology of the two large bristles on the Mx1 third endite, one being smooth and the other serrated (both bristles are serrated in Klieopsis and Plesiocypridopsis) and the presence of the Wouters organ on A1.Additionally, Siamopsis gen.nov.can be distinguished from Plesiocypridopsis by the number of t-setae on the female A2 penultimate segment (two in the new genus and four in Plesiocypridopsis) and the fi ve apical setae on the terminal segment of the Mx1 palp (four in Plesiocypridopsis).Siamopsis gen.nov.differs from Klieopsis mainly in the presence of long natatory setae and the absence of a robust internal septa of the RV posterior inner list.The conspicuous morphology of the RV postero-ventral inner list of Klieopsis is the outstanding character that, so far, has not been observed in any other cypridopsine genera (Martens et al. 1991).However, a similar structure appears in three species of Siamopsis gen.nov.(S. suttajit gen. et sp. nov., S. conspecta gen. et sp. nov. and S. khoratensis gen. et sp. nov.).These species have a few tiny tubercle-like structures beneath the postero-ventral inner list of the RV (Fig. 19B-D).Due to their identical positions, this feature in the new genus could be the initiating form of the septa (it is in a well developed form in Klieopsis) and therefore shows the similarity between these two genera.
The Wouters organ on the fi rst segment of the A1 appears in all fi ve species of Siamopsis gen.nov.This is the fi rst report of this organ in the subfamily Cypridopsinae.The length of the ya on the A1 terminal segment varies in different species.However, it was found that the ya was longer, but to different degrees, than the shortest seta of the terminal segment in Siamopsis gen.nov.
It is obvious that the natatory setae on A2 can be either longer or reduced to short setae (as in, e.g., Klieopsis, Thermopsis, Bryocypris and Cavernocypris Hartmann, 1964) in Cypridopsinae (see Meisch 2000;Karanovic 2012).The t-setae on the A2 penultimate segment are different in number between genders and between genera.Based on the occurrence of t-setae in females, there are two groups of genera: with four setae and with two setae.The former group comprises, e.g., Plesiocypridopsis (see Meisch 2000), Thermopsis (see Külköylüoğlu et al. 2003), Bryocypris (see Martens 1989), Tanganyikacypridopsis (see Martens 1985), Cypridopsis (see Meisch 2000) 2000;Dumont & Martens 1996), Klieopsis (Martens et al. 1991) and Siamopsis gen.nov.In males, only one pattern (two t-setae) has so far been recognized (De Deckker 1981;Martens & Meisch 1985;Martens 1989;Martens et al. 1991;Dumont & Martens 1996;Meisch 2000;Külköylüoğlu et al. 2003).Thus, the number of t-setae is a sexual feature in some cypridopsine genera, such as Thermopsis and Bryocypris, in which it is reduced in males.The Md palp is normally developed in the subfamily Cypridopsinae.However, in the new genus, the morphology of the ventro-apical seta on the penultimate segment is similar to that of the γ-seta, showing a plumose and long seta.
The shape of the terminal segment of the Mx1 palp can be divided into two groups: spatulate and cylindrical shapes.While most of the cypridopsine genera have cylindrical terminal segments, the spatula shape occurs in Potamocypris only (see Meisch 2000;Karanovic 2012).Other features of this limb can also be used as generic characters of the subfamily, for example, the occurrence of a ventro-subapical seta on the basal segment of the palp.This seta is absent in, e.g., Siamopsis gen.nov., Plesiocypridopsis and Klieopsis.
The occurrence of a, b, c and d setae on the T1 has been used as a diagnostic feature in several subfamilies.For example, the presence of the c-seta is a distinguishing aspect of the subfamily Eucypridinae (Meisch 2000) and the presence of the d-seta distinguishes Strandesia Stuhlmann, 1888 from Pseudostrandesia Savatenalinton & Martens, 2008 in subfamily Cypricercinae (see Savatenalinton 2009).In the subfamily Cypridopsinae, the presence of only two a-setae is a fundamental pattern in all genera, including Siamopsis gen.nov., while the d-seta has only been seen in Cabelodopsis (Higuti & Martens 2012).
In Cypridopsinae, only the d2 seta is present (d1 absent) in all genera.Thus, this character should be mentioned in the diagnosis of the subfamily.

SAVATENALINTON S., A new genus of Cypridopsinae from Thailand
Although the valve overlap and the shapes of the CR and the terminal segment of the Mx1 palp are the most important diagnostic features (Meisch 2000;Karanovic 2012), there are still many distinguishing characters between the genera of the subfamily Cypridopsinae.The phylogeny of the subfamily, based on morphological characters, including a discussion of generic characters, will be presented elsewhere.
, Maha Sarakham, Thailand MSU-ZOC = Ostracod Collection of the Natural History Museum, Mahasarakham University, Maha Sarakham, Thailand RBINS = Royal Belgian Institute of Natural Sciences, Brussels The following abbreviations are used for valves and carapace: CpC = carapace in caudal view CpD = carapace in dorsal view CpL = carapace in left lateral view CpR = carapace in right lateral view H = height of valves L = length of valves LV = left valve LVe = left valve external view LVi = left valve internal view RV = right valve RVe = right valve external view RVi = right valve internal view W = width of carapace European Journal of Taxonomy 384: 1-39 (2017)

Fig. 20 .
Fig. 20.Sampling localities of species of Siamopsis gen.nov.(for information on locality numbers, see the text).