Siamopsis conspecta, 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 : 17-22

Siamopsis conspecta gen. et sp. nov.

urn:lsid:zoobank.org:act:AF502FC5-AE39-4017-8E88-7518CCCC8AC5

Figs 8–10 , 19B , 20

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 flagellum-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 ).

Paratypes

THAILAND: 1 ♀, stored as the holotype ( MSU-ZOC.202); 1 ♀, carapace stored dry in a micropalaeontological slide ( MSU-ZOC.203).

Other material

THAILAND: Phayao Province, Muang District, Kwan Phayao (lake) (locality 9 in Fig. 20 ), 19°09′28″ N, 90°54′39″ E, 6 Oct. 2007. Accompanying ostracod fauna: Cypris subglobosa Sowerby, 1840 , Stenocypris malayica, Astenocypris papyracea , Bradleystrandesia weberi , Bradleytriebella lineata , Pseudostrandesia calapanensis , P. mamarilorum , Strandesia kraepelini , Tanycypris siamensis , Cypretta sp. 3, Cypridopsis vidua , Siamopsis suttajiti gen. et sp. nov. and Physocypria sp. 2.

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

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 flagellum-like seta is shorter in Siamopsis conspecta gen. et sp. nov. (very long in S. suttajiti gen. et sp. nov.).

Measurements (mean, in μm)

LV (n = 2), L = 627, H = 352; RV (n = 2), L = 631, H = 362.

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 calcified, 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 calcified 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, 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 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 fifth 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 first endopodal segment. First endopodal segment with five 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.

MX 1 ( Fig. 10B ). 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 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. 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.

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

CR ( Fig. 10E ). Reduced, flagellum-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°C and a DO of 7.16 mg /l.

Figures

Fig. 8. Siamopsis conspecta gen. et sp. nov., ♀ (MSU-ZOC.201). A. LVe. B. RVe (idem). C. LVi (idem). D. RVi (idem). E. Postero-dorsal part of LVi (idem). F. Postero-dorsal part of RVi (idem). Scale bar: A–D = 200 μm; E–F = 56 μm.

Fig. 9. Siamopsis conspecta gen. et sp. nov., ♀ (MSU-ZOC.201). A. A1. B. A2. C. Md coxa. D.T1. Scale bars: 50 μm.

Fig. 10. Siamopsis conspecta gen. et sp. nov., ♀ (MSU-ZOC.201). A. Md palp. B. Mx1. C. T2. D. T3. E. 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).