Siamopsis khoratensis, Savatenalinton, 2017

Savatenalinton, Sukonthip, 2017, Siamopsis gen. nov. and five new species of the subfamily Cypridopsinae Kaufmann, 1900 (Crustacea: Ostracoda) from Thailand, European Journal of Taxonomy 384, pp. 1-39 : 22-28

Siamopsis khoratensis gen. et sp. nov.

urn:lsid:zoobank.org:act:3DCD40C9-3A9B-4E3A-AAAC-BDD6AEA1BD4C

Figs 11–14 , 19D , 20

Diagnosis

Carapace in lateral view elongated, dorsal margin flat 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 flagellum-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 ).

Paratypes

THAILAND: 1 ♀, stored as the holotype ( MSU-ZOC.205); 1 ♀, carapace stored dry in a micropalaeontological slide ( MSU-ZOC.206).

Type locality

THAILAND: Nakhon Ratchasima Province, Muang District, irrigation ditch (locality 1 in Fig. 20 ), 14°43′46″ N, 104°33′56″ E, 5 Oct. 2010. Accompanying ostracod fauna: Cypris subglobosa , Cyprinotus uenoi, Stenocypris cf. orientalis, Siamopsis suttajiti gen. et sp. nov., S. renateae gen. et sp. nov. and S. planitia gen. et sp. nov.

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.

Measurements (mean, in μm)

LV (n = 2), L = 616, H = 371; RV (n = 2), L = 626, H = 373.

Description

Female

CARAPACE. In lateral view elongated, dorsal margin flat 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. 11 A–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, calcified inner lamella with inner lists anteriorly and posteriorly, postero-ventral inner-list internally set with small tubercle-like structures.

A1 ( Fig. 12A ). Seven-segmented, first 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 fifth 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 first endopodal segment. First endopodal segment with five 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; 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.

MX 1 ( Fig. 13B ). With two-segmented palp, basal segment of palp dorsally with group of five 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

serrated) large bristles. Sideways-directed bristles on first endite unequally long, length of short one ca half that of long one.

T1 ( Fig. 13 C–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.

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 reflexed subapical seta, length of latter equal to that of third segment.

CR ( Fig. 14C ). Reduced, flagellum-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.

Figures

Fig. 11. Siamopsis khoratensis gen. et sp. nov., ♀ (MSU-ZOC.204). A. LVe. B. RVe (idem). C. LVi (idem). D. RVi (idem). E. Posterior part of LVi (idem). F. Anterior part of LVi (idem). G. Anterior part of RVi (idem). H. Posterior part of RVi (idem). Scale bar: A–D = 200 μm; E–H = 140 μm.

Fig. 12. Siamopsis khoratensis gen. et sp. nov., ♀ (MSU-ZOC.204). A. A1. B. A2. C. Md coxa. Scale bar: 50 μm.

Fig. 13. Siamopsis khoratensis gen. et sp. nov., ♀ (MSU-ZOC.204). A. Md palp. B. Mx1. C. T1, apical setae on protopodite. D. T1. Scale bars: 50 μm.

Fig. 14. Siamopsis khoratensis gen. et sp. nov., ♀ (MSU-ZOC.204). A. T2. B. T3. C. CR. Scale bar: 50 μm.

Fig. 19. Postero-ventral part of internal RV in Siamopsis spp., showing a smooth inner list and a few tiny tubercle-like structures beneath the inner list. A. S. renateae gen. et sp. nov. B. S. conspecta gen. et sp. nov. C. S. suttajit gen. et sp. nov. D. S. khoratensis gen. et sp. nov. E. S. planitia gen. et sp. nov. Scale bar: 100 μm. Arrows indicate tiny tubercle-like structures under postero-ventral inner list.

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