Strandesia buengkanensis, Savatenalinton, 2025

Savatenalinton, Sukonthip, 2025, Two new species of freshwater ostracods (Crustacea: Ostracoda) from the northeast of Thailand, with notes on sexually reproducing populations of Chrissia and Strandesia, Zootaxa 5717 (2), pp. 235-257 : 245-251

Strandesia buengkanensis sp. nov.

( Figs 7–11 )

Etymology. The species is named after Bueng Kan Province, from which the new species was discovered.

Diagnosis. Cp elongated in lateral view, length c. 760 μm in female (H/L = 0.56–0.57), c. 695 μm in male (H/L = 0.54–0.55), LV overlapping RV along all free margins, larger overlap anteriorly, Cp in dorsal view elongated with greatest W situated in front of mid-length, anterior and posterior margins of LV more protruded than RV; LV internally with groove along valve margin, incomplete inner list and marginal anterior selvage.A1 seven-segmented with large and long RO, small WO, first segment without dorso-subapical seta, aesthetasc ya remarkably long (longer than shortest seta on terminal segment). A2 with long natatory setae, aesthetasc Y large, three segmented, last segment larger than other segments, z1 and z3 setae intermediate length (not reaching tips of apical claws). Male A2 with claw-like z1 and z2 setae and with claw G2 and G3 considerably reduced to thin and short setae, terminal segment with claw GM modified, carrying strong spines on distal half of claw, and with claw Gm strongly reduced to thin and short seta. β-seta on Md-palp large, cone-shaped with needle-like tip, terminal segment with three claws and two setae. Terminal segment of Mx1-palp elongated with three claws and two setae, two large bristles on third endite smooth. d-seta on T1 present. T2 with large d1 and d2 setae (length of d1 seta c. 1.5 times of that of d2 seta), f-seta markedly long. T3 with short f-seta. CR slender, claw Ga less than half length of ramus, claw Gp c. 3/5 of that of claw Ga, sa seta shorter than claw Gp, sp seta thin with flagellum-like tip, reaching beyond tip of ramus. CR attachment with Triebel’s loop situated at middle of distal part of main branch. Hp with medial shield rounded, lateral shield elongated with blunt tip, postlabyrinthal spermiduct curved, with 2 loops. ZO with 17 spiny whorls, length about 3.4 times width.

Type materials: Holotype. Female, soft parts of a dissected specimen preserved in glycerine on a slide, and valves stored dry in a micropalaeontological slide ( MSU-ZOC.430).

Allotype. Male, stored like the holotype ( MSU-ZOC.431).

Paratypes. Four females, stored like the holotype ( MSU-ZOC.432 to 435) ; three males, stored like the holotype ( MSU-ZOC.436 to 438), many whole individuals of females and males in 70% ethanol ( MSU-ZOC.439) .

Type locality. A marshy area next to a weir connecting Bueng Khong Long (marsh) and a rice field, Bueng Khong Long District, Bueng Kan Province, Thailand ( 17º 57.53′ N, 104 º 02.09′ E), coll. S. Savatenalinton, 18 Mar. 2024 .

Measurements (in μm). Female: Cp (n = 1), L = 764, W = 371; LV (n = 2), L = 739–764, H = 421–428; RV (n = 2), L = 732–742, H = 415–418. Male: Cp (n = 2), L = 682–704, H = 376, W = 311; LV (n = 1), L = 689, H = 374; RV (n = 1), L = 666, H = 363.

Description of female. Cp elongated in lateral view (c. 760 μm, H/L = 0.56–0.57), anterior margin widely rounded, posterior margin narrowly rounded, LV overlapping RV along all free margins, larger overlap anteriorly, dorsal margin strongly arched, greatest height situated in front of mid-length, ventral margin somewhat straight, valve surface ( Figs 7A–C ) with tiny tubercles and sparse thin rimmed-pore setae, tiny tubercles less prominent dorsally and ventrally.

Cp in dorsal view ( Fig. 7D ) elongated with greatest W situated in front of mid-length, anterior and posterior margins of LV more protruded than RV.

LV in interior view ( Figs 8A–B, E–F ) with groove along valve margin, marginal anterior selvage, anterior fused zone moderately wide, dorsal margin strongly arched, greatest height situated in front of mid-length, anterior margin widely rounded, posterior margin narrowly rounded with slightly pointed tip, postero-dorsal part angulated, ventral margin somewhat straight; calcified inner lamella relatively wide anteriorly, with incomplete inner list.

RV in interior view ( Figs 8B, G–H ) without marginal groove, with submarginal selvage, inner lamella without inner list, anteriorly broader than posteriorly, ventral margin somewhat straight.

A1 ( Fig. 9A ) seven-segmented. First segment with two long ventro-apical setae, small WO, dorso-subapical seta absent. Second segment slightly wider than long, with one short dorso-apical seta (not reaching mid-length of next segment) and large and long RO. Third segment bearing one long dorso-apical seta (reaching mid-length of fifth segment) and one long, slightly hirsute ventro-apical seta (almost reaching tip of next segment). Fourth segment with two long dorsal setae and two intermediate length ventral setae, shortest seta reaching mid-length of sixth segment. Fifth segment dorsally with two long setae, ventrally with two (one long, one shorter) setae, shorter one reaching mid-length of terminal segment. Penultimate segment with four long setae. Terminal segment with three (two long, one short) apical setae and aesthetasc ya, length of short one c. 2/3 of that of aesthetasc ya, aesthetasc ya remarkably long (c. 2.7 times of that of terminal segment).

A2 ( Fig. 9B ) protopodite with two ventro-proximal setae (third proximal seta not seen) and one long ventrosubapical seta. Exopodite with three (one long, two short) setae, long one reaching tip of first endopodal segment. Endopodite three-segmented. First endopodal segment with five long natatory setae (reaching tip of terminal claws) distally bearing sparsely distributed thin setules, and one shorter accompanying seta (not reaching mid-length of penultimate segment), aesthetasc Y large, three segmented, last segment larger than other segments, ventro-apical seta long (reaching tip of terminal segment), slightly hirsute. Penultimate segment undivided, medially with two (one long, one shorter) dorsal setae (shorter one not reaching tip of segment) and four ventral setae of unequal length (t1–t4); distally with three serrated claws G1–G3 (subequal in length), aesthetasc y2 short (not reaching tip of terminal segment), z1–z3 setae intermediate length, z1 seta shortest (reaching less than half-length of claw G1), z2 and z3 setae not reaching tips of apical claws. Terminal segment with two serrated claws GM and Gm (length of Gm c. 4/5 of that of GM), aesthetasc y3 (length of aesthetasc y3 c. 1/3 of that of Gm and c. 2/3 of that of accompanying seta) and g-seta with same length as aesthetasc y3.

Md-coxa ( Fig. 9D ) elongated, distally set with rows of teeth (large dorsally and smaller ventrally) and small setae, and with one slightly hirsute dorso-subapical seta, the latter thin and short (not reaching base of teeth).

Md-palp ( Fig. 10A ) four-segmented. First segment with two large S1 and S2 setae, one long, smooth seta and one long, smooth α-seta, the latter with wide proximal part. Second segment dorsally with three dorsal apical setae (one long, one medium length and one short), length of the shortest seta c. 1/3 of that of the longest seta; ventrally with a group of three long hirsute setae, one shorter hirsute seta and the β-seta, the latter large, plumose, cone-shaped and with needle-like tip. Penultimate segment dorsally with a group of four unequal, long, subapical setae; laterally with an apical γ-seta and three further apical setae, the former stout, hirsute, long (length c. 2.6 times of that of terminal segment); ventrally with two (one long, one short) apical setae, short one reaching half way of terminal segment. Terminal segment bearing three claws and two setae.

Mx1 ( Fig. 10B ) with two-segmented palp, three endites and large branchial plate; basal segment of palp with group of four long, unequal apical setae, one long subapical setae and laterally one short subapical seta (not reaching tip of terminal segment), terminal segment elongated with three claws and two setae. Two large bristles on third endite smooth. First endite with two unequally long sideways-directed bristles and two basal setae.

T1 ( Fig. 10C ) protopodite with two short a-setae, long, hirsute b and d-setae, distally with 14 (10 apical, four subapical) hirsute setae of unequal length. Endopodite (not illustrated) weakly built palp with three unequal apical setae.

T2 ( Fig. 10D ) five-segmented. Basal segment with large d1 and d2 setae, both hirsute, length of d1 seta c. 1.5 times of that of d2 seta. Second segment with short, hirsute e-seta (reaching mid-length of penultimate segment). Penultimate segment divided, proximal segment bearing markedly long, hirsute f-seta (reaching far beyond tip of terminal segment), distal segment with long g-seta (reaching beyond tip of terminal segment) and tiny spine-like seta. Terminal segment dorsally with long apical h1, ventrally with long h3 seta, h1 longer than h3, laterally with serrated claw h2, length of claw h2 longer than that of penultimate segment.

T3 ( Fig. 10E ) three-segmented. First segment with unequally long d1, d2, dp setae, d2 and dp setae not reaching tip of next segment. Second segment bearing apical e-seta of intermediate length (reaching slightly beyond mid-length of next segment). Third segment medially with f-seta (not reaching tip of segment). Terminal segment with apical pincer and three setae (h1–h3), h1 seta short, h2 seta claw-like, subapical h3 seta long and reflexed, length of the latter c. 3/4 of that of third segment.

CR ( Fig. 11A ) slender, ventral margin of ramus with tiny setules. Claws Ga and Gp serrated, length of claw Ga less than half length of that of ramus, length of claw Gp c. 3/5 of that of claw Ga, sa seta shorter than claw Gp, sp seta thin with flagellum-like tip, reaching beyond tip of ramus.

CR attachment ( Fig. 11B ) stout with Triebel’s loop situated at middle of distal part of main branch, db and vb well-developed.

Description of male. Cp and valves as in female, but somewhat smaller (c. 695 μm, H/L = 0.54–0.55) ( Figs 7E–F ). All limbs as in female, except for last two segments of A2, T1 and reproductive organs. Penultimate segment of A2 with claw-like z1 and z2 setae and with claws G1 and G3 considerably reduced to thin and short setae; terminal segment with claw Gm modified, carrying strong spines on distal half of claw, and with claw GM strongly reduced to thin and short seta ( Fig. 9C ). T1-endopodites forming asymmetrical prehensile palps; right palp ( Fig. 11C ) with elongated basal segment bearing two short apical spines and with triangular terminal segment; left palp ( Fig. 11D ) with elongated basal segment bearing tiny apical spine and tubercle and with elongated, hook-like curved terminal segment. Hp ( Fig. 11E ) with medial shield rounded, lateral shield elongated with blunt tip. Postlabyrinthal spermiduct curved, with two loops. ZO ( Fig. 11F ) set with 17 spiny whorls, length about 3.4 times width, distal and proximal end plates forming crown of petal-like structures.

Distribution. Northeast Thailand.

Figures

FIGURE 7. Strandesia buengkanensis sp. nov., female (A–D), male (E–F). A. LV, external view (paratype, MSU-ZOC.433). B. RV, external view (ditto). C. valve surface of LV (ditto). D. Cp, dorsal view (paratype, MSU-ZOC.435). E. Cp, right lateral view (paratype, MSU-ZOC.438). F. Cp, ventral view (paratype, MSU-ZOC.437). Scale bar: A–B, D–F = 300 μm, C = 100 μm. Arrows point anterior direction.

FIGURE 8. Strandesia buengkanensis sp. nov., female (A–B, E–H), male (C–D). A. LV, internal view (holotype, MSU- ZOC.430). B. RV, internal view (ditto). C. LV, internal view (paratype, MSU-ZOC.436). D. RV, internal view (ditto). E. Posterior part of LV, internal view (holotype, MSU-ZOC.430). F.Anterior part of LV, internal view (ditto). G.Anterior part of RV, internal view (ditto). H. posterior part of RV, internal view (ditto). Scale bar: A–D = 300 μm, E–H = 200 μm.

FIGURE 9. Strandesia buengkanensis sp. nov., female (A–B, B′, D), male (C, C′). A. A1 (holotype, MSU-ZOC.430). B. A2 (ditto). C. Terminal segment of A2 (allotype, MSU-ZOC.431). D. Md-coxa (holotype, MSU-ZOC.430). Scale bar: A–D = 100 μm.

FIGURE 10. Strandesia buengkanensis sp. nov., female (holotype, MSU-ZOC.430).A. Md-palp. B. Mx1. C. T1. D. T2. E. T3. Scale bar: A–B, D–E = 100 μm, C = 50 μm.

FIGURE 11. Strandesia buengkanensis sp. nov., female (A–B), male (C–F). A. CR (holotype, MSU-ZOC.430). B. CR attachment (ditto). C. Right palp of T1 (allotype, MSU-ZOC.431). D. Left palp of T1 (ditto). E. Hp (ditto). F. ZO (ditto). Scale bar: A–B, E–F = 100 μm, C–D = 50 μm.