Pseudostrandesia ovata, Savatenalinton & Martens, 2010

Savatenalinton, Sukonthip & Martens, Koen, 2010, On the subfamily Cypricercinae McKenzie, 1971 (Crustacea, Ostracoda) from Thailand, with the description of six new species 2379, Zootaxa 2379, pp. 1-77 : 35-39

Pseudostrandesia ovata sp. nov. ( Figs 22–24)

Holotype. A female, with soft parts dissected in glycerine in a sealed slide, and valves stored dry in a micropalaeontological slide (O.C.3137).

Paratypes. One dissected female ( MSU-ZOC.091) stored as the holotype and three undissected females (O.C.3138, MSU-ZOC.031, MSU-ZOC.032) stored dry in micropalaeontological slides after use for SEM .

Repository. Holotype and one undissected paratype are deposited in the Ostracod Collection of the R. B.I.N.Sc. One dissected and two undissected paratypes are deposited in the Natural History Museum , MSU (Mahasarakham, Thailand).

Type locality. Roadside canal, Wat Boht district, Phitsanulok Province, 26 September 2005, coordinates: 17° 01´51.7˝ N and 100° 18´49.6˝ E (TH042). Accompanying ostracod fauna: Bradleystrandesia weberi ( Moniez, 1892) , Cypretta sp. , Physocypria sp. , Pseudostrandesia gaetani sp. nov., P. mamarilorum (Victor & Fernando, 1981) , Stenocypris sp.

Etymology. After the ovate-shaped appearance of the carapace in dorsal view.

Diagnosis. Carapace in lateral view subovate; greatest height situated at mid-length; LV overlapping RV along anterior, ventral and posterior margins. Carapace in dorsal view ovate, anterior extremity unequal (LV longer than RV); valve surface set with dispersed setae; LV with internal groove along valve margin, calcified inner lamella with one inner list; RV with a marginal selvage; both Wouters and Rome organ long, aesthetasc ya shorter than short apical seta on A1; aesthetasc Y on A2 short, ventro- apical seta on A2-first endopodal segment short; d seta on T1 absent; one of two large bristles on third endite of Mx1 smooth; distal seta of caudal ramus as long as distal claw, proximal seta thin, long (reaching tip of ramus); caudal ramus attachment stout, with Triebel’s loop situated at middle of distal part of main branch, both dorsal and ventral branches well-developed.

Differential diagnosis. Within the genus Pseudostrandesia , the new species is superficially similar to P. calapanensis ( Tressler, 1937) . It is distinguishable from this species by the larger LV/RV overlap at the anterior margin, a narrow marginal selvage on RV and the carapace shape in lateral view (more ovate carapace and arched dorsal margin in P. ovata sp. nov.). Additionally, there are differences between these two species in the morphology of the soft parts. In P. ovata sp. nov., the short apical seta on A1-terminal segment is considerably shorter than that of P. calapanensis . Also, the new species can be distinguished by a short ventro-apical seta on the -first endopodal segment, a short aesthetasc Y, the length of the longest seta of A2-exopodite (longer in P. ovata sp. nov.), the morphology of two large bristles on third endite of Mx1 (one smooth, one serrated in P. ovata sp. nov.), a long distal seta and the longer distal claw on caudal ramus.

Measurements (in µ m). LV (n=1), L=905, H=457; RV (n=1), L=882, H=455; Carapace (n=4), L=896– 920, W=453–476.

Ecology. A few specimens of this new taxon were encountered in the type locality only: a roadside canal with a pH of 6.92 and a temperature of 31.2 °C at the time of collecting.

Description of female. Carapace in lateral view ( Fig. 22A) subelliptical, anterior and posterior margin rounded, dorsal margin arched, greatest height situated at mid-length, ventral margin straight; external valve surface with dispersed, short setae.

Carapace in dorsal view ( Fig. 22B) subovate, greatest width situated slightly behind mid-length, posterior end rounded; LV overlapping RV along anterior, ventral and posterior margins, most widely along anterior margin.

Carapace in ventral view ( Fig. 22C) with ventral margin of LV protruding slightly in front of mid-length.

LV in interior view ( Fig. 22D) with groove along valve margin, dorsal margin curved, greatest height at mid-length, sloping down to anterior and posterior margins, both equally rounded, ventral margin slightly sinuous in front of mid-length; inner lamella calcified, anteriorly widely, with one inner list, posteriorly narrower.

RV in interior view ( Fig. 22E) with marginal selvage; calcified inner lamella without inner list, anteriorly wider than posteriorly.

A1 ( Fig. 23A) first segment with dorso-subapical seta long (reaching tip of segment) and two long, subequal ventro-apical setae, proximal Wouters organ long, tube-like. Second segment slightly wider than long, with one short dorso-apical seta and long Rome organ. Third segment bearing two (one dorso-, one ventro-) apical setae, the former long (reaching tip of fifth segment), the latter short (slightly more than half of length of fourth segment). Fourth segment dorsally with two long setae, ventrally with two (one long, one short) setae, short one c. half of length of next segment. Fifth segment dorsally with two long setae, ventrally also with two (one long, one shorter) setae, the short one reaching tip of terminal segment. Penultimate segment with four long setae. Terminal segment with three (two long, one short) apical setae and short aesthetasc ya, the latter shorter than the short apical seta.

A2 ( Fig. 23B): exopodite with three (one long, two short) setae, the long one reaching tip of first endopodal segment. First segment of endopodite with natatory setae long, reaching slightly beyond tips of end claws, the shortest one slightly more than half of length of penultimate segment, aesthetasc Y short, ventro-apical seta long (reaching tip of penultimate segment). Penultimate segment undivided, distally with three serrated claws (slightly longer than those of terminal segment) and with long aesthetasc y2 (reaching beyond tip of terminal segment), z1–z3 setae long, z1 almost reaching tips of end claws; medially with two (one long, one shorter) dorsal setae (short one c. 2/3 of length of long one) and four ventral setae (t1–t4). Terminal segment with two serrated claws (GM and Gm), short g-seta and aesthetasc y3, the latter slightly shorter than accompanying seta.

Md-palp ( Fig. 23C–D): first segment with two large setae, one slender, long seta and long, smooth α- seta. Second segment dorsally with three (two long, one short) apical setae, length of short one c. 1/3 of that of long one; ventrally with a group of three hirsute setae, one shorter seta and β- seta, the latter plumose, cone-shaped and with pointed tip. Penultimate segment consisting of three groups of setae: dorsally with a group of four long, unequal subapical setae; laterally with apical Ύ–seta long and three smooth apical setae, the former stout, hirsute, long (c. twice length of terminal segment); ventrally with one long and one short (slightly more than half length of terminal segment) apical setae. Terminal segment ( Fig. 23D) bearing three claws and three setae.

Mx1 ( Fig. 24A) with two-segmented palp, basal segment with a group of five unequal long apical setae and two (one long, one shorter) subapical setae, terminal segment elongated, with three claws and three setae. Two (one serrated, one smooth) bristles on third endite large. Sideways directed bristles on first endite unequal, short one with length c. 2/3 of that of long one.

T1 ( Fig. 23F): protopodite with two short a-setae, long b-seta, without d-seta, distally with 14 (10 apical, four subapical) long, hirsute setae. Endopodite a weakly built palp with three unequal, apical setae.

T2 ( Fig. 24B) with two slim d-setae, d2 slightly more than half as long as d1. Second segment with 1 long apical seta (slightly more than half length of penultimate segment). Penultimate segment divided, proximal segment (a) bearing one long apical seta, distal segment (b) with a pair of apical setae (one short, one spinelike). Terminal segment with two (one dorsally, one ventrally) short apical setae and a serrated claw.

T3 ( Fig. 24C) a cleaning limb. First segment with three long setae. Second segment with one long apical seta (c. half length of next segment). Third segment medially with one short seta (less than half length of that segment). Terminal segment with an apical pincer and one long reflexed subapical seta.

Caudal ramus ( Fig. 24E) slender, with ventral margin serrated, distal and proximal claws long, slightly serrated, length of distal claw length c. half that of ramus, length of proximal claw c. 2/3 of that of distal claw. Distal seta as long as distal claw, proximal seta thin, reaching tip of ramus.

Caudal ramus attachment ( Fig. 24D) stout, with Triebel’s loop at middle of distal part of main branch, dorsal branch small, ventral branch well-developed.

Male unknown.

Remarks. Based on the morphology of the valves, Pseudostrandesia ovata sp. nov. can be confused with Strandesia elliptica (Sars, 1901) which belongs to Strandesia s.l. ( Savatenalinton & Martens 2009b). Theoretically, these two species can be distinguished by the generic characters, e.g. absence/presence of the d seta on the T1 (see Savatenalinton & Martens 2009c). However, the incomplete original description and illustrations of the South American S. elliptica does not allow to distinguish the state of this character. Strandesia elliptica could belong either to Pseudostrandesia or to Strandesia s.s. Based on the present information, Pseudostrandesia ovata sp. nov. can be differentiated from S. elliptica by the larger overlap at the anterior margin, the length and the position of insertion of the proximal seta of the caudal ramus and the general morphology of the caudal ramus attachment. Pseudostrandesia ovata sp. nov. is rare. We found five specimens from only one sample in Phitsanulok Province. It is thus far known from its type locality only.