Siamopsis planitia, 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 : 28-33

Siamopsis planitia gen. et sp. nov.

urn:lsid:zoobank.org:act:BFF56BA9-BBB4-4B5D-8B3F-221F29768F07

Figs 15– 18 , 19E , 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 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 flagellum-like seta.

Etymology

The specific 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 ).

Paratypes

THAILAND: 1 ♀, stored as the holotype ( MSU-ZOC.208); 1 ♀, carapace stored dry in a micropalaeontological slide ( MSU-ZOC.209); 2 ♀♀ in 70% EtOH.

Other material

THAILAND: Nakhon Ratchasima Province: Sikhiu District, Sub Pradu Reservoir (locality 2 in Fig. 20 ), 14°57′57″ N, 102°05′03″ E, 5 Oct. 2007.Accompanying ostracod fauna: Hemicypris ovata ( Sars, 1903) , Chrissia humilis , Potamocypris sp. and Physocypria sp. 3. – Nakhon Ratchasima Province: Sikhiu District, Lam Taklong Dam (locality 10 in Fig. 20 ), 14°51′49″ N, 101°33′43″ E, 20 Sep. 2005. Accompanying ostracod fauna: Hemicypris exiqua , Physocypria sp. 3 and Strandesia (juveniles); collected on 6 February 2006, accompanying ostracod fauna: Cypridopsis vidua, Cypridopsine sp. and Physocypria sp. 3. – Chiang Mai Province: Mae Kuang Dam (locality 11 in Fig. 20 ), 18°55′17″ N, 99°07′26″ E, 10 Feb. 2006. Accompanying ostracod fauna: Alicenula serricaudata (Klie, 1935) , Cypridopsine sp. and Chrissia (juveniles). – Phetchabun Province: Muang District, Nong Naree (swamp) (locality 6 in Fig. 20 ), 16°26′24″ N, 101°08′29″ E, 9 Oct. 2007. Accompanying ostracod fauna: Bradleycypris vittata , Bradleystrandesia weberi , Strandesia kraepelini , Cypretta sp. 3, Potamocypris sp., Siamopsis renateae gen. et sp. nov., Physocypria sp. 2 and Physocypria sp. 3.

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 conspecta gen. et sp. nov., S. khoratensis gen. et sp. nov. and S. renateae gen. et sp. nov.

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 flat, 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.

Measurements (mean, in μm)

LV (n = 2), L = 667, H = 373; RV (n = 2), L = 599, H = 378.

Description

Female

CARAPACE. In lateral view ( Fig. 15A ) elongated, dorsal margin flat 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, calcified 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, first 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 fifth 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 first endopodal segment. First endopodal segment with five 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 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.

MX 1 ( Fig. 17B ). 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 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 first endite unequally long, length of short one ca half that of long one.

T1 ( Fig. 17 C–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 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

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. 18C ). 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 so far been recorded from five 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°C and a DO range of 3.20 – 8.14 mg /l.

Figures

Fig. 15. Siamopsis planitia gen. et sp. nov., ♀. A. CpL (MSU-ZOC.209). B. LVi (MSU-ZOC.207). C. RVi (idem). D. Valve surface of CpL (MSU-ZOC.209). E. Postero-dorsal part of LVi (MSU-ZOC.207). F. Postero-dorsal part of RVi (idem). Scale bar: A–C = 200 μm; D = 64 μm; E–F = 85 μm.

Fig. 16. Siamopsis planitia gen. et sp. nov., ♀ (MSU-ZOC.207). A. A1. B. A2. C. Md coxa. Scale bar: 50 μm.

Fig. 17. Siamopsis planitia gen. et sp. nov., ♀ (MSU-ZOC.207). A. Md palp. B. Mx1. C. T1, apical setae on protopodite. D. T1. Scale bars: 50 μm.

Fig. 18. Siamopsis planitia gen. et sp. nov., ♀ (MSU-ZOC.207). A. T2. B. T3. C. CR. Scale bars: 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).