Oncocypris rostrata, Savatenalinton, Sukonthip, 2015

Savatenalinton, Sukonthip, 2015, On three new species of non-marine ostracods (Crustacea: Ostracoda) from Northeast Thailand, Zootaxa 3914 (3), pp. 275-300 : 287-295

Oncocypris rostrata n. sp.

( Figures 7–12 )

Holotype. Male, soft parts dissected in glycerine on a sealed slide, valves stored dry in a micropalaeontological slide (MSU-ZOC.119).

Allotypes. Female, stored like the holotype (MSU-ZOC.120).

Paratypes. Two dissected males (MSU-ZOC.121–122) stored like the holotype, three undissected males (MSU-ZOC.123–125) stored dry in micropalaeontological slides, two dissected females (MSU-ZOC.126–127) stored like the holotype, three undissected females (MSU-ZOC.128–130) stored dry in a micropalaeontological slide and c. 20 males and 50 females in 70% EtOH.

Repository. The holotype, allotype and all paratypes are deposited in the Natural History Museum, MSU (Mahasarakham, Thailand).

Type locality. Huay Yang Reservoir, Sakon Nakhon Province. Material collected on 21 December 2011, coordinates: 16° 56΄ 12˝ N and 104° 10΄ 42˝ E. Accompanying ostracod fauna: Thaicythere srisumonae Savatenalinton et al., 2008 , Physocypria sp., Stenocypris sp.

Etymology. The new species is named after the beak-like front, forming a rostrum.

Diagnosis. Carapace in lateral view subovate with evenly arched dorsal margin and large eye tubercles; valve surface strongly ornamentated and set with large granulations and pits (each with a hole in the centre); LV overlapping RV anteriorly, ventrally, and posteriorly; carapace in dorsal view triangular with beak-like anterior part and RV and LV margins subequal and curved rightward.

Terminal segment of A1 divided, Rome organ small, Wouters organ present; third endite of Mx1 with five large serrated bristles; T2 with long, slim seta d2, seta d1 absent, penultimate segment divided, terminal claw with distal furcated; CR whip-like with short base with parallel sides; right prehensile palp with apical long spine and large protrusion on distal margin of first segment, overlapping the second segment; left prehensile palp with long spine and smaller protrusion on distal margin; hemipenis with dorsal lobe elongated, with blunt end, ventral lobe broadly rounded.

Differential diagnosis. Oncocypris rostrata n. sp. is similar to Oncocypris debundshae Green, 1973 and Oncocypris schoutedeni Klie, 1938 . The new species can be distinguished from O. debundshae and O. schoutedeni by the shape of carapace in dorsal view, the bigger eye tubercles, the external valve ornamentation, the chaetotaxy of the limbs, especially the divided terminal segment of A1, and the morphology of prehensile palps and the hemipenis. The beak-like anterior part of carapace in dorsal view has been found in O. rostrata n. sp. and O.

debundshae . However, the feature of this part is different: the RV margin projects in front of LV margin in O. debundshae while margins of RV and LV are subequal and curved rightward in O. rostrata n. sp.

Measurements (mean, in µm). Female, LV (n = 3), L = 574, H = 405; RV (n = 3), L = 579, H = 398; Carapace (n = 3), L = 554, W = 524. Male, LV (n = 3), L = 517, H = 353; RV (n = 3), L = 517, H = 352; Carapace (n = 5), L = 523, W = 454.

Ecology. Oncocypris rostrata n. sp. is thus far only known from its type locality, a reservoir. It occurred at a pH of 7.54, a temperature of 24.3° C and DO of 4.6 mg /l.

Description of female. Carapace in lateral view ( Fig. 7 A) subovate (length 1.5 times width), greatest height situated c. mid-length, dorsal margin evenly arched, anterior margin broadly rounded, posterior margin more narrowly rounded; eye tubercle large and prominent, situated in front of mid-length and at one third of height; valve surface strongly ornamentated, set with large pustules and large pits (each pit with a hole and a seta in the centre) ( Fig. 7 B).

Carapace in dorsal view ( Fig. 7 C) triangular, greatest width situated at c. two thirds of length, anterior part beak-like with right and left valve margins subequal and curve rightward, LV overlapping RV anteriorly, ventrally and posteriorly; both anterior and posterior valve margins with septae between external and internal calcified lamellae, creating a row of ‘chambers’ (lunules) along valve margins.

LV in interior view ( Fig. 7 E) with a flange anteriorly and posteriorly, anteriorly broader than posteriorly, no setae on flanges ( Fig. 8 B), lunules on anterior and posterior parts situated between flange and selvage, calcified inner lamella narrow, with an inner list; selvage not running parallel to valve margin at postero-ventrally part.

RV in interior view ( Fig. 7 F) with large flange anteriorly, wider than LV, setae on flange ( Fig. 8 C), calcified inner lamella narrow, with an inner list, frontal inner lamella with lunules situated between selvage and inner list.

A1 ( Fig. 10 A): first segment with a long dorsal, subapical seta (reaching middle of next segment), with two long, unequal ventro-apical setae and a proximal Wouters organ. Second segment wider than long, with one short dorso-apical seta and a small Rome organ, the former reaching slightly beyond tip of segment. Third segment bearing two (one dorso-, one ventro-) apical setae, the former almost reaching tip of next segment, the latter spinelike. Fourth segment with two long dorsal setae and two shorter ventral setae (the longer one reaching slightly beyond tip of the next segment, the shortest reaching the middle of next segment). Fifth segment dorsally with two long setae, ventrally with two (one long, one shorter) setae, the shorter one reaching middle of terminal segment, the long one reaching beyond tip of terminal segment. Penultimate segment with four long setae. Terminal segment with three (two long, one short) apical setae and an aesthetasc y a, the latter c. twice as long the short apical seta.

A2 ( Fig. 10 B): exopodite with three (one long, two short) setae, the long one reaching middle of penultimate segment. First endopodal segment with natatory setae long, length of shortest seta reaching c. 1/3 of penultimate segment, aesthetasc Y long, ventro-apical seta long (reaching beyond tip of terminal segment). Penultimate segment divided, distally with three long serrated claws (length c. 2.6-2.7 times penultimate segment) and with long aesthetasc y2 (reaching slightly beyond tip of terminal segment), z1–z3 setae long; this segment medially with two (one long, one shorter) dorsal setae (length of short one c. 3/4 of that of long one) and four (three long, one short) ventral setae (t1–t4). Terminal segment with two serrated claws (GM and Gm), long g-seta and an aesthetasc y3, length of Gm c. 2/3 of that of GM, length of aesthetasc y3 c. 5/6 of that of accompanying seta.

Md-palp ( Fig. 10 C): first segment with two large setae, one slender, long seta and α-seta with broad base and flagellum-like tip. Second segment dorsally with three hirsute, unequal long apical setae; ventrally with a group of three hirsute setae, one shorter seta and the 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, but unequal subapical setae; laterally with an apical γ–seta and three further hirsute apical setae, the former stout, hirsute, long (length c. 1.5 times of that of the terminal segment); ventrally with two (one long, one short) subapical setae, the long one hirsute, the short one slightly less than half the length of the terminal segment. Terminal segment bearing three claws and three setae.

Mx1 ( Fig. 11 A) with a two-segmented palp, three endites and a large branchial plate; basal segment of palp with a group of five long, but unequal apical setae and two (one long, one short) subapical setae, the short one reaching beyond tip of basal segment), terminal segment elongated (length c. twice the width), with two claws and two setae. Five large bristles (ZAHNBORSTEN) on third endite distally serrated. Sideways-directed bristles on first endite unequal, length of short one c. half that of long one.

T1 ( Fig. 11 B): protopodite with two a-setae, distally with 10 long, hirsute, apical setae. Endopodite a weakly built palp with three distal setae (not shown).

T2 ( Fig. 11 C) with long, slim d2, d1 absent. Second segment with one long apical e-seta (length c. half of that of penultimate segment). Penultimate segment divided, proximal segment (a) bearing one long apical f-seta (reaching beyond tip of terminal segment), distal segment (b) with short apical g-seta. Terminal segment with two (one dorsally, one ventrally) apical h1 and h3 setae and a claw (h2), the latter with furcate end and outer margin uneven distally (c. 1/3 of length of claw) ( Fig. 11 D).

T3 ( Fig. 11 E) a cleaning limb. First segment with long d2 and dp setae and short d1 seta. Second segment with one long apical e-seta (length c. half of next segment). Third segment with medially one long f-seta (reaching tip of the segment). Terminal segment with three setae (h1-h3), one short h1 seta, one claw-like h2 seta and one long reflexed subapical h3 seta, length of the latter c. 4/5 of that of third segment.

Caudal ramus ( Fig. 11 F) whip-like with wide base, with short proximal seta and distal long seta.

Description of male. Carapace and valves ( Fig. 9 ) as in female, but somewhat smaller. All limbs as in female, except for the last two segments of A2 ( Fig. 12 A–B) and T1 ( Fig. 12 C–D).

Setae z1 and z2 of the penultimate segment of A2 transformed into claws; claws G1 and G3 reduced to setae; Gm on terminal segment of A2 reduced, appearing smaller and shorter (length c. 0.4 time of that of GM).

T1 with asymmetrical prehensile palps (endopodites). Right prehensile palp ( Fig. 12 C) with first segment bearing long apical spine and large protrusion at mid-length of distal margin towards the hook-like second segment. Left prehensile palp ( Fig. 12 D) with first segment bearing a long spine and smaller protrusion on distal margin; second segment narrow and pointed.

Hemipenis ( Fig. 12 E) with ls subtriangular, blunt end, ms broad rounded, internal postlabyrinthal spermiduct with three additional loops.

Zenker organ ( Fig. 12 F) elongated, length c. 4.3 times width, set with c. 17 chitinous spiny whorls.

Remarks. Oncocypris rostrata n. sp. is the first record of this genus in Thailand. The constriction in front of the eye tubercles makes the anterior part of the carapace in dorsal view look like a rostrum. This aspect is also illustrated in some other Oncocypris species, but never this clear. Although the knee segment of T2 was not drawn in several congeneric species, the presence of the d2 and the absence of the d1 setae in several other Oncocypris species, seems to indicate that this is a generic character.

FIGURE 13 Distribution map of the genus Oncocypris G.W. Müller, 1898 (× O. bhatiai Battish, 1982 ; ♦ O. chappuisi Klie, 1939 ; + O. debundshae Green, 1973 ; ♦ O. euglypha Rome, 1962 ; ● O. muelleri (Daday, 1910) ; ˔ O. schoutedeni Klie, 1938 ; ⋅ O. voeltzkowi G.W. Müller, 1898 ; ★ O. rostrata n. sp.).

Figures

FIGURE 7. Oncocypris rostrata n. sp., female. A. carapace, right lateral view; B. valve surface of A.; C. carapace, dorsal view; D. carapace, ventral view; E. LV, internal view; F. RV, internal view. Scale bar = 100 Μm for A, C – F; 25 Μm for B. Arrows point toward the anterior end.

FIGURE 8. Oncocypris rostrata n. sp., female (A – D); Pseudocypretta maculata Klie, 1932 (E – F); Cypridopsis vidua (O. F. Müller, 1776) (G – H). A. posterior part of LV; B. anterior part of LV; C. anterior part of RV; D. posterior part of RV; E. LV, internal view; F. RV, internal view. Scale bar = 20 Μm for A – D; 100 Μm for E – F; 200 Μm for G – H.

FIGURE 9. Oncocypris rostrata n. sp., male. A. carapace, right lateral view; B. valve surface of A.; C. carapace, dorsal view; D. LV, internal view; E. RV, internal view. Scale bar = 100 Μm for A, C – E; 28 Μm for B. Arrow points toward the anterior end.

FIGURE 10. Oncocypris rostrata n. sp., female. A. A 1; B. A 2; C. Md-palp; D. Md-coxa. Scale bar = 50 Μm.

FIGURE 11. Oncocypris rostrata n. sp., female. A. Mx 1; B. T 1; C. T 2; D. Distal part of T 2 terminal claw; E. T 3; F. caudal ramus. Scale bar = 50 Μm for A – C, F; 26 Μm for D; 100 Μm for E.

FIGURE 12. Oncocypris rostrata n. sp., male. A. terminal part of A 2; B. terminal segment of A 2; C. right prehensile palp; D. left prehensile palp; E. hemipenis; F. Zenker organ. Scale bar = 50 Μm for A – E; 100 Μm for F.