Songkhramodopsis meischi, Savatenalinton, 2023

Savatenalinton, Sukonthip, 2023, Songkhramodopsis gen. nov., a new genus of Cypridopsinae (Crustacea: Ostracoda) from Thailand, Zootaxa 5254 (1), pp. 51-68 : 53-61

Songkhramodopsis meischi gen. et sp. nov.

( Figs 1–8 )

Etymology. The species is named in honor of Dr. Claude Meisch (National Natural History Museum of Luxembourg, Luxembourg) for his prominent work on ostracod taxonomy.

Diagnosis. Cp in dorsal view elongated, subtriangular; LV overlapping RV all free margins with large overlapping anteriorly; LV and RV with inner list anteriorly, ventrally and posteriorly (very well-developed in LV), and anterior marginal selvage; RV with posterior selvage widely inwardly displaced; valve surface with non-rimmed pore setae, rimmed pore setae in shallow pits and tiny pores; A1 six-segmented, a ventral apical seta on first segment with bifurcate tip, fourth segment with three dorsal apical setae; A2 with natatory setae well-developed (reaching far beyond tip of terminal claws), g seta absent, third section of aesthetasc Y very wide and striated, exopodite with two long and one short setae; two large bristles on Mx1 third endite smooth; T2 without d1 seta, penultimate segment divided; T3 without pincer organ, terminal segment with two setae and one claw-like seta (h2); CR with cylindrical base and present only in female; male prehensile palps asymmetrical, right palp with subtriangular second segment, left palp with strongly sickle shaped second segment; Hp with bird head-shaped ls with blunt inner tip, and widely rounded ms, post-labyrinthal spermiduct with one loop; Zenker organ with blunt ends and eight spiny whorls.

Type material. Holotype. Male, soft parts dissected in glycerine on a sealed glass slide and valves stored dry in a micropalaeontological slide (MSU-ZOC.351).

Allotype. Female, soft parts dissected in glycerine on a sealed glass slide and valves stored dry in a micropalaeontological slide (MSU-ZOC.352).

Paratypes. Two dissected males (MSU-ZOC.353 to 354) stored like the holotype, three undissected males (MSU-ZOC.355 to 357) stored dry in micropalaeontological slides, five dissected females (MSU-ZOC.358 to 362) stored like the holotype, three undissected females (MSU-ZOC.363 to 365) stored dry in micropalaeontological slides, c. four males and eight females in 70% ethanol.

Type locality. Nong Ma Klap Reservoir, Si Songkhram District , Nakhon Phanom Province ( Fig 9 ); coordinates: 17° 38′ 32″ N, 104° 19′ 42″ E; 16 November 2021 .

Measurements (in μm). Male. Cp (n = 3), L = 395–403, H = 176–182, W = 174–176; LV (n = 2), L = 395–400, H = 188–189; RV (n = 2), L = 371–374, H = 192–193. Female. Cp (n = 4), L = 418–442, H = 205–208, W = 200– 203; LV (n = 2), L = 426–439, H = 200–203; RV (n = 2), L = 413–426, H = 200–205.

Description of male

Cp in dorsal view ( Fig 1A ) elongated, greatest width situated at mid-length, anterior and posterior extremities narrowly rounded.

Cp in lateral view ( Fig 1B ) elongated, subtriangular, greatest height situated at mid-length, anterior and posterior margins rounded, anteriorly slightly narrower rounded. LV overlapping RV along free margin, with larger overlap anteriorly. Valve surface with non-rimmed pore setae, rimmed pore setae in shallow pits and tiny pores ( Fig 1C ), setae and pores more abundant at anterior and posterior parts.

LV in interior view ( Figs 2A, 2C–D ) with dorsal margin arched, ventral margin slightly sinuate, anterior and posterior margins rounded, and anterior marginal selvage, calcified inner lamella anteriorly broader than posteriorly, with very well-developed inner list anteriorly, ventrally and posteriorly.

RV in interior view ( Figs 2B, 2E–G ) with anterior marginal selvage, posterior selvage widely inwardly displaced, calcified inner lamella anteriorly broader than posteriorly, with inner list anteriorly, ventrally and posteriorly.

A1 ( Fig 4A ): six-segmented, first segment wide and stout, with small proximal Wouters organ, one long subapical dorsal seta (reaching mid-length of next segment) and two apical ventral setae, one markedly long, the other as half as long as the long one. The shorter seta with long setules, one of which stiff and inserted apically, creating a false bifurcate tip. Second segment slightly wider than long, with one long apical dorsal seta (reaching slightly beyond mid-length of next segment) and large Rome organ. Third segment very elongated, medially bearing one short dorsal seta and one short ventral seta, distally bearing two long apical dorsal setae, one short apical ventral seta and one short subapical ventral seta. Fourth segment with three long dorsal setae and two short ventral setae (longer one reaching mid-length of terminal segment, another one very short). Penultimate segment with four long apical setae. Terminal segment elongated with three (two long, one short) apical setae and aesthetasc ya (short apical seta and aesthetasc ya subequal in length).

A2 ( Fig 4B ): Basal segment with two proximal setae and one long ventro-apical seta. Exopodite with three (two very long, one short) setae, the long setae reaching far beyond tip of first endopodal segment. First endopodal segment with five long setae (reaching beyond tip of terminal claws) and one shorter accompanying seta (half as long as penultimate segment), aesthetasc Y very large, tripartite, third section remarkably wide and striated, apical ventral seta long, reaching far beyond tip of terminal segment. Penultimate segment undivided, distally with large claw G1, claw G2 reduced, appearing smaller and shorter, claw G3 reduced to short and slender seta, z1 and z2 setae transformed into claws (z2 seta smaller than z1 seta), z3 seta intermediate length (c. 2/3 of length of z1 seta), aesthetasc y2 long (reaching tip of terminal segment), this segment medially with two (one long, one shorter) dorsal setae (length of shorter one c. 6/7 of that of long one) and one ventral seta (t seta). Terminal segment subquadrate with very large claw GM, claw Gm reduced to short and slender seta (reaching mid-length of claw GM), g-seta absent, aesthetasc y3 short, length c. 3/4 of that of accompanying seta.

Rake-like organ stout, T-shaped, apically with eight blunt teeth.

Md-palp ( Fig 5A–C ): first segment of palp with two large, hirsute S1 and S2 setae (with very different length, length of S1 seta c. half of that of S2 seta), one long and slender seta and a relatively long α-seta (length c. 1/3 of that of S1 seta), the latter smooth with pointed tip. Second segment dorsally with three subequal long apical setae; ventrally with a group of three long setae, one shorter seta and β-seta, the latter large, cone-shaped and plumose. Penultimate segment with three groups of setae: dorsally with a group of four subequal, long, subapical setae; laterally with hirsute apical γ-seta (length c. 2.3 times of that of terminal segment) and three further smooth apical setae; ventrally with two long apical setae (length c. 2.6 times of that of terminal segment). Terminal segment bearing three claws and two setae.

Md-coxa ( Fig 5E ) elongated, distally with rows of teeth and small setae, and with one slender dorso-subapical seta.

Mx1 ( Fig 6A ) with two-segmented palp, three endites and a large branchial plate (the latter not shown). Basal segment of palp with a group of five long, unequal apical setae, no medial subapical seta. Terminal segment of palp elongated, cylindrical, apically with three claws and two setae. Two large smooth bristles on third endite.

T1 ( Figs 6B–C ): protopodite with two a-setae (one long and one very long), shorter one c. half as long as long one; no b, c, and d-setae, distally with eight hirsute apical setae of unequal length. Endopodite large and elongated, two-segmented, forming asymmetrical prehensile palps, right palp ( Fig 6B ) with two subapical spines on basal segment, terminal segment subtriangular; left palp ( Fig 6C ) with two subapical spines on basal segment, terminal segment strongly hook-like basally with blunt-tipped protrusion.

T2 ( Fig 6D ) with slender d2 seta, no d1 seta. Second segment with medium-long e-seta (length c. 2/3 of that of penultimate segment). Penultimate segment divided, proximal part bearing long f-seta (reaching beyond tip of terminal segment), distal part with a pair of apical setae (long g-seta and one shorter seta). Terminal segment bearing two (one dorsally, one ventrally) apical h1 and h3 setae and a long and curved serrated claw h2, length of h1 c. 2/7 of that of h2, h3 very short (spine-like).

T3 ( Fig 7A ) first segment with short d1 seta and long d2 and dp setae (d2 and dp setae c. twice as long as d1 seta). Second segment with short, hirsute apical e-seta (not reaching middle of next segment). Third segment with medially short, hirsute f-seta (not reaching tip of segment). Terminal segment completely separated and bearing three setae (h1-h3 setae), h1 seta shorter than h2 seta (length c. 2/3 of that of h2 seta), h2 seta claw-like, h3 seta reflexed, hirsute subapical seta, length of h3 seta c. 1.3 times of h2 length.

Caudal ramus absent.

Hp ( Fig 7B ) with ls and ms, the former bird head shaped with blunt inner beak, the latter with widely rounded distal margin, postlabyrinthal spermiduct curved with one loop.

Zenker organ ( Fig 7C ) elongated with blunt ends and set with eight spiny whorls.

Description of female

Carapace and valves as in male, although somewhat bigger ( Fig 1D–I , Fig 3 ). All limbs as in male, except for last two segments of A2 and T1. Penultimate segment of A2 ( Fig 4C ) with three large, serrated claws G1, G2 and G3, claw G2 stronger serrated than claws G1 and G3, z1-z3 setae long (not reaching tip of terminal claws), this segment medially with two (one long, one shorter) dorsal setae (length of shorter one c. 6/7 of that of long one) and four ventral setae of unequal length (t1–t4). Terminal segment subquadrate with large, serrated claw GM, short claw Gm (length c. half of that of claw GM), aesthetasc y3 short (length c. 3/4 of that of accompanying seta), g-seta absent. T1-endopodite ( Fig 8B ) elongated, weakly built palp with three very long apical setae of different lengths, with longest one more than twice as long as endopodite length. T2 ( Fig 8C ) same as in male, except for h3 seta appearing slightly longer. CR ( Fig 8D ) reduced, flagellum-like, with cylindrical base and long subapical seta.

Figures

FIGURE 1. Songkhramodopsis meischi gen. et sp. nov., male (A–C), female (D–I).A. Cp, dorsal view (MSU-ZOC.356). B. Cp, right lateral view (ditto). C. Valve surface (ditto). D. Cp, dorsal view (MSU-ZOC.363). E. Cp, ventral view (MSU-ZOC.364). F. Cp, right lateral view (ditto). G. Valve surface (MSU-ZOC.365). H. Valve surface (MSU-ZOC.364). I. Valve surface (ditto). Scale bars = 100 μm for A–B, D–F, 10 μm for C, G–I.

FIGURE 2. Songkhramodopsis meischi gen. et sp. nov., male (MSU-ZOC.351). A. LV, internal view. B. RV, internal view. C. LV, internal view, posterior part. D. LV, internal view, anterior part. E. RV, internal view, anterior part. F. RV, internal view, posterior part. G. Muscle scars of RV. Scale bars = 100 μm for A–B, 50 μm for C–F, 20 μm for G.

FIGURE 3. Songkhramodopsis meischi gen. et sp. nov., female (MSU-ZOC.352). A. LV, internal view. B. RV, internal view. C. LV, internal view, posterior part. D. LV, internal view, anterior part. E. RV, internal view, anterior part. F. RV, internal view, posterior part. G. Muscle scars of RV. Scale bars = 100 μm for A–B, 50 μm for C–F, 20 μm for G.

FIGURE 4. Songkhramodopsis meischi gen. et sp. nov., male (A–B), female (A’, C). A. A1 (MSU-ZOC.351). A’. an apical ventral seta on A1 first segment (MSU-ZOC.352). B. A2 (MSU-ZOC.354). B’. aesthetasc Y (MSU-ZOC.354, MSU-ZOC.353). C. A2, terminal part of last two segments (MSU-ZOC.352). Scale bars = 50 μm.

FIGURE 5. Songkhramodopsis meischi gen. et sp. nov., male (A–C, E), female (D). A. Md-palp (MSU-ZOC.354). B. terminal segment of Md-palp (ditto). C. S setae of Md-palp (ditto). D. α, β, γ setae of Md-palp (MSU-ZOC.352). E. Md-coxa (MSU- ZOC.351). Scale bars = 20 μm for A–D; 50 μm for E.

FIGURE 6. Songkhramodopsis meischi gen. et sp. nov., male (MSU-ZOC.351). A. Mx1. B. T1, right palp. C. T1, left palp. D. T2. Scale bars = 20 μm for A–C, 50 μm for D.

FIGURE 7. Songkhramodopsis meischi gen. et sp. nov., male (MSU-ZOC.351). A. T3. B. Hp. C. Zenker organ. Scale bars = 50 μm.

FIGURE 8. Songkhramodopsis meischi gen. et sp. nov., female. A. Rake-like organ (MSU-ZOC.352). B. T1 (ditto). C. T2 (ditto). D. CR (MSU-ZOC.360). Scale bars = 20 μm for A–B, D, 50 μm for C.

FIGURE 9. Type locality of Songkhramodopsis meischi gen. et sp. nov.