Siamopsis suttajiti Savatenalinton 2017, gen. et sp. nov.

Siamopsis suttajiti gen. et sp. nov.

urn:lsid:zoobank.org:act: 9DFC2DC2-82F1-44A2-9762-F817055F8893

Figs 5–7, 19C, 20

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 flagellum-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).

Paratypes

THAILAND: 2 ♀♀, stored as the holotype (MSU-ZOC.196–197); 3 ♀♀, carapaces stored dry in micropalaeontological slides (MSU-ZOC.198–200); 4 ♀♀ in 70% EtOH.

Type locality

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 Victor & Fernando, 1981, Astenocypris papyracea (Sars, 1903), Bradleystrandesia weberi, Bradleytriebella lineata (Victor & Fernando, 1981), Pseudostrandesia calapanensis (Tressler, 1937), P. mamarilorum, Strandesia kraepelini, Tanycypris siamensis Savatenalinton & Martens, 2009, Cypretta sp. 3, Cypridopsis vidua (O.F. Müller, 1906), Siamopsis conspecta gen. et sp. nov. and Physocypria sp. 2.

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 flagellum-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.

Measurements (mean, in μm)

LV (n = 2), L = 577, H = 335; RV (n = 2), L = 584, H = 344; carapace (n = 2), L = 593, W = 258.

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 calcified 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, 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 (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.

A2 (Fig. 6B). 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 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.

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.

MX 1 (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 first 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 reflexed subapical seta, length of latter equal that of third segment.

CR (Fig. 7E). Reduced, flagellum-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.