Chrissia muangkanensis, Savatenalinton, 2023

Savatenalinton, Sukonthip, 2023, On Chrissia muangkanensis, new species (Crustacea, Ostracoda) from Thailand, with notes on taxonomic characters of the genus, Raffles Bulletin of Zoology 71, pp. 443-456 : 444-449

Chrissia muangkanensis , new species

( Figs. 1–6 )

Material examined. Holotype: Female , soft parts dissected in glycerine on a sealed slide, valves stored dry on a micropalaeontological slide ( MSU-ZOC.366), a swamp close to Mae Klong River, Tha Muang District, Kanchanaburi Province, Thailand, 13°58.21′ N 99°37.86′ E, coll. S Savatenalinton, 19 October 2018, 13 March 2019.

Paratypes: two dissected females stored in the same way as the holotype ( MSU-ZOC.367–368), two undissected females stored dry on micropalaeontological slides ( MSU-ZOC.369 – 370) .

Measurements (μm). Female. Cp (n=2): L = 2183 – 2310, H = 1040 – 1042, W = 676; LV (n=2): L = 2155 – 2296, H = 1028 – 1070, RV (n=2): L = 2141 – 2169, H = 1014 – 1016.

Diagnosis. Cp in lateral view reniform shaped (length c. 2.2 – 2.3 mm), LV slightly overlapping RV all free margins, greatest height situated slightly behind mid-length, ventral margin sinuated slightly in front of mid-length; both valves with anterior margins rounded, posterior margin bluntly rounded, and with two spines at postero-ventral corner (the ones on RV smaller than those on LV), LV with anterior inner list situated very close to valve margin, and incomplete posterior inner list; A1 with small, unsegmented Rome organ; A2 with long natatory setae (not reaching tip of terminal claws) and slender, four-segmented aesthetasc Y; α-seta on Md-palp smooth with slightly wider base and very long needle-like tip; terminal segment of Md-palp elongated with 5 setae; Mx1-palp with elongated terminal segment (length c. 2.4 times of width), two large bristles on third endite distally serrated; T2 with short, subequal d1 and d2 setae, long g-seta and very short h3 seta; T3 with long h2 seta and very long reflexed h3 seta with bottle neck-like part at mid-length; CR well-developed, asymmetry with right CR larger than left one, Sa seta short, claws Ga and Gp short and strongly serrated with two sets of large spines, right ramus with very robust spines along ventral margin and range of spines-bearing about half-length of ramus, CR attachment with triangular basal loop.

Description of female. Carapace large (c. 2.2 – 2.3 mm), carapace in lateral view ( Fig. 1A ) reniform shape, anterior margin evenly rounded, posterior margin slightly more narrowly rounded (blunt margin), LV slightly overlapping RV, dorsal margin strongly curved, greatest height situated slightly behind mid-length, ventral margin sinuated slightly in front of mid-length, valve surface ( Fig. 1B ) smooth with rimmed-pore setae dispersedly. Carapace in dorsal view ( Fig. 1C ) narrowly elongated.

LV in internal view ( Fig. 1D , 2A ) reniform shape with two spines at postero-ventral corner ( Figs. 1G , 2C ); anterior calcified inner lamella well-developed, wide and with inner list situated very close to valve margin ( Figs. 1H , 2D ); posterior calcified inner lamella narrower than anterior one and with incomplete inner list ( Figs. 1G , 2C ); marginal septa absent.

RV in internal view ( Figs. 1E , 2B ) reniform shape with two tiny spines at postero-ventral corner, spines smaller than those of LV ( Figs. 1J , 2F ); anterior calcified inner lamella well-developed, wide, without inner list ( Figs. 1I , 2E ); posterior calcified inner lamella narrower than anterior one and with incomplete inner list ( Figs. 1J , 2F ); marginal septa absent.

A1 ( Fig. 3A ): first segment with one long dorso-subapical seta (reaching beyond tip of segment) and two long ventro-apical setae, Wouters organ on A1 not observed. Second segment slightly wider than long, with one dorso-apical seta of intermediate length (not reaching mid-length of next segment) and a small, short, unsegmented Rome organ. Third segment bearing two setae: one very long dorso-apical one (reaching mid-length of terminal segment) and one very short ventro-apical setae (reaching mid-length of fourth segment). Fourth segment with two long dorsal setae and two subequal, shorter ventral setae (shortest one reaching tip of next segment). Fifth segment with two groups (one dorsally and one ventrally) of two setae, all setae very long. Penultimate segment with four long setae and one short dorsal seta (reaching tip of terminal segment). Terminal segment with three (two long, one short) apical setae and an aesthetasc Ya, the latter of about two times longer of shortest apical seta.

A2 ( Fig. 3B ): Basal segment with two ventro-proximal setae, one lateral proximal seta and one long ventro-apical seta. Exopodite with three (one long, two short) setae, the long one not reaching tip of first endopodal segment. First endopodal segment with five long natatory setae (not reaching tip of terminal claws) and one short accompanying seta, length of the short seta c. one fourth of that of penultimate segment, aesthetasc Y slender and four-segmented, ventro-apical seta intermediate length, reaching tip of penultimate segment. Penultimate segment undivided, medially with two subequal dorsal setae and four ventral setae (t1–t4) of unequal length; t1 largest than others, reaching beyond tip of terminal segment; this segment distally with three serrated claws, aesthetasc y2 short (not reaching tip of terminal segment), z1–z3 setae unequally long, longest one reaching tip of apical claws. Terminal segment with two serrated claws (GM and Gm), a long g-seta (length c. 2/3 of that of GM), an aesthetasc y3 and two very short apical setae; length of Gm c. half of that of GM, length of aesthetasc y3 c. half of that of accompanying seta.

Md ( Fig. 4A ): first segment of md-palp with two large setae (S1 and S2), one slender, long seta and a long, smooth α-seta, the latter with slightly wider base and very long needle-like tip. Second segment dorsally with three unequal long apical setae, length of the shortest less than half of that of the longest; ventrally with a group of three long hirsute setae, one shorter hirsute seta and the β-seta, the latter coneshaped and set with strong setules. Penultimate segment consisting of three groups of setae: dorsally with a group of four unequally long, subapical setae; laterally with an apical γ-seta and three further slender smooth apical setae (subequal in length), the former large, elongated (length c. 1.3 times of that of terminal segment), distally covered with long setules c. 1/3 of its length, and middle part covered with very short setules; ventrally with two (one long, one short) subapical setae (length of the short one c. 1/3 of the long one). Terminal segment very elongated (length c. two times of width), bearing three claws and two setae.

Mx1 ( Fig. 4B ) with two-segmented palp, three endites and a large branchial plate; basal segment of palp with a group of five long, unequal, ventro-apical setae and one short laterally subapical seta, the latter reaching slightly beyond mid-length of terminal segment, terminal segment very elongated (length c. 2.4 times of width), apically with three claws (one large, two smaller) and three setae. Two large bristles on third endite distally serrated. Sideways-directed bristles on first endite subequally long.

T1 ( Fig. 4C – D ): protopodite with two a-setae, long b and d-setae, b-seta of similar length as d-seta; distally with 10 apical hirsute setae of unequal length and four (three very long, one shorter) subapical setae set with long setules. Endopodite ( Fig. 4C ) a large, elongated, weakly built palp with one very long and two short apical setae, the short one c. 1/3 of the long one.

T2 ( Fig. 5A ) with setae d1 and d2, both setae short and slender. Second segment with long e-seta (reaching beyond mid-length of penultimate segment). Penultimate segment divided, proximal segment shorter than distal segment, proximal segment bearing very long f-seta (reaching beyond tip of terminal segment), distal segment with a pair of apical setae (g-seta, one short seta), g-seta very long (reaching half of h2). Terminal segment with two (one dorsally, one ventrally) short apical h1 and h3 setae (length of h1 seta about that of terminal segment, h3 seta slightly longer than h1 seta) and a long serrated claw (h2), length of h2 c. 1.4 times of that of penultimate segment.

T3 ( Fig. 5B ) a cleaning limb. First segment with long d1, d2, dp setae. Second segment with long apical e-seta (reaching tip of next segment). Third segment medially with long f-seta (reaching slightly beyond tip of next segment). Terminal segment with an apical pincer organ, very long h2 seta, very short h1 seta and long reflexed subapical h3 seta, about first half length of h3 seta wider than distal half appearing bottle neck-like part at mid-length of seta, length of h3 seta c. 5/6 of that of third segment.

CR ( Fig. 5C, D ) well-developed and asymmetry with right CR larger than left one, right ramus slightly shorter than left ramus. CR attachment ( Fig. 5E ) with triangular basal loop, db and vb well-developed.

Right CR ( Fig. 5C ) with very long and robust spines reducing in size along ventral margin of ramus, and range of spines-bearing about half-length of ramus. Claws Ga and Gp short and strongly serrated with two sets of large spines, length of Ga c. 1/3 of that of ramus, length of Gp c. 2/3 of that of Ga. Seta Sa short (length c. 2/3 of that of Ga), seta Sp absent.

Left CR ( Fig. 5D ) with small spines and setules arranging in c. four sets on ventral margin of ramus. Claws Ga and Gp short and strongly serrated with two sets of large spines, length of Ga c. 1/3 of that of ramus, length of Gp c. 2/3 of that of Ga. Seta Sa short (length c. 3/4 of that of Ga), seta Sp absent.

Male. Males have so far only been detected by semen in females.

Etymology. The species is named after Kanchanaburi Province, which is also called in short “Muangkan”, where specimens of the new species were discovered.

Figures

Fig. 1. Chrissia muangkanensis, new species, female. A, Cp, right lateral view (MSU-ZOC.369). B, valve surface (ditto). C, Cp, dorsal view (MSU-ZOC.370). D, LV, internal view (MSU-ZOC.366). E, RV, internal view (ditto). F, Muscle scars of RV (ditto). G, Posterior part of LV, internal view (ditto). H, Anterior part of LV, internal view (ditto). I, Anterior part of RV, internal view (ditto). J, Posterior part of RV, internal view (ditto). Scale bar: A, C–E = 500 μm, B, F = 50 μm, G–J = 100 μm.

Fig. 2. Chrissia muangkanensis, new species, female (MSU-ZOC.367). A, LV, internal view. B, RV, internal view. C, Posterior part of LV, internal view. D, Anterior part of LV, internal view. E, Anterior part of RV, internal view. F, posterior part of RV, internal view. Scale bar: A–B = 500 μm, C–F = 100 μm.

Fig. 3. Chrissia muangkanensis, new species, female (MSU-ZOC.366). A, A1. B, External view of left A2. C, Terminal segment of A2. D, Md-coxa. Scale bars: A–B, D = 100 μm, C = 65 μm. Arrow indicates two apical spine-like setae.

Fig. 4. Chrissia muangkanensis, new species, female (MSU-ZOC.366). A, Md-palp. B, Mx1. C, T1-palp. D, T1. Scale bars: A–D = 100 μm.

Fig. 5. Chrissia muangkanensis, new species, female (MSU-ZOC.366). A, T2. B, T3. C, Right CR. D, Left CR. E, CR attachment. Scale bars: A–D = 100 μm, E = 200 μm.

Fig. 6. Chrissia muangkanensis, new species, juvenile A-2 (MSU-ZOC.368). A, LV, internal view. B, RV, internal view. C, Posterior part of LV, internal view. D, Anterior part of LV, internal view. E, Anterior part of RV, internal view. F, posterior part of RV, internal view. Scale bar: A–B = 200 μm, C–F = 100 μm.