Myanmarcypris hui Wang et al., 2020

Wang, He, Matzke-Karasz, Renate & Horne, David J., 2022, Mid-Cretaceous coastal amber forest palaeoenvironment revealed by exceptionally preserved ostracods from an extant lineage, Fossil Record 25 (1), pp. 147-172 : 147

publication ID	https://dx.doi.org/10.3897/fr.25.e84604
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scientific name	Myanmarcypris hui Wang et al., 2020
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Figs 1 View Figure 1 , 2 View Figure 2 , 3 View Figure 3 , 4 View Figure 4 , 5 View Figure 5 , 6 View Figure 6 , 7 View Figure 7

Material.

31 specimens, 5 of which were analyzed using 3D X-ray microscopy: adult male, holotype (BA19005-1) - L = 600 µm, H = 356 µm, W ≈ 290 µm; paratypes: adult female, (BA19005-2) - L = 609 µm, H = 382 µm, W ≈ 300 µm; A- 2 juvenile (BA19005-3) - L = 400 µm, H = 261 µm, W ≈ 175 µm; A- 3 juvenile (BA19005-4) - L = 313 µm, H = 204 µm, W ≈ 161 µm; A- 4 juvenile (BA19005-5) - L = 226 µm, H = 156 µm, W ≈ 120 µm; material not tomographed: BA19005-11-36 (Suppl. material 1: Fig. S1).

Emended description.

Carapace (Figs 1 View Figure 1 , 2 View Figure 2 ): Adults small, in lateral view subtriangular. Female with higher and more pointed dorsal peak than male. In dorsal view, anterior and posterior ends blunt, not pointed. Valves thick and strongly reticulate, with prominent transverse muri, except for the dorsal region, which is smooth. In adults, a conspicuous antero-ventral lateral node present on each of the valves (Figs 1E, J View Figure 1 , 2A View Figure 2 ). Antero-dorsally with smooth eye-spot (Fig. 1F View Figure 1 ). Normal pores distributed all over the valves except dorsal area. LV overlaps RV along dorsal and ventral margins. Hinge adont. Well-developed calcified inner lamella in adult carapaces, broader anteriorly than posteriorly, and anteriorly with inner list (Fig. 2C View Figure 2 ). Ventral margin of calcified inner lamella with conspicuous anterior tooth in LV and corresponding socket in RV, and two smaller posterior teeth in LV with corresponding sockets in RV, the latter much less developed than anterior socket (Fig. 2B View Figure 2 ). No central muscle scars preserved. Preserved juveniles show similar carapace ornamentation as adults except for A-4 stage, which is smooth (Fig. 1 View Figure 1 ).

Soft Body (Figs 3 View Figure 3 - 6 View Figure 6 ): A1 (Figs 3A, B, O, P View Figure 3 , 4A View Figure 4 , 5B View Figure 5 ) with eight segments. Segments 1 and 2 fused forming large base, with two setae of unknown length originating dorso-median and long setae situated ventro-distally on segment 2. Only a little more distal, ventro-basally on segment 3, prominent Rome Organ with inflated tip (Figs 4A View Figure 4 , 5B View Figure 5 ). Segment 3 short and sub-triangular. Segment 4 longer than twice its width. Segments 5 to 8 not fused and rectangular, with decreasing widths. Presence of setae confirmed for segments as figured. Setae at least as long as figured, possibly longer.

A2 (Male) (Figs 3C, D View Figure 3 , 5C View Figure 5 ) Segment 1 (coxa) small, with 2 setae ventrally. Segment 2 (basis) elongate and carrying long ventro-apical seta. Segment 3 (first endopodal segment) elongate, with aesthetasc Y (ventro-median) and four natatory setae ventro-apically on the interior side of the appendage. Natatory setae possibly not complete and maximum length not known. Segments 4 and 5 possibly fused, together around half the length of segment 3. Apically with at least one seta subapical-exteriorly and three claws. Segment 6 small with at least one claw apically. Preservation of female A2 not sufficient for detailed chaetotaxy (Fig. 3Q, R View Figure 3 ).

Md (Figs 3E, F, S, T View Figure 3 , 5A View Figure 5 ) Masticatory process of coxa too poorly preserved to describe morphology. Palp consisting of 4 separate segments and straight (i.e., not bent ventrally). Branchial plate not observed. Segment 1 (basis) with two setae ventrally, one at medium-length of the segment, the other more distally. Third seta originating on interio-apical margin. Shape of this segment subrectangular with angulation on dorsal margin. Segment 2 square-shaped, with at least five setae apically (2 dorsally, 3 ventrally). Segment 3 rectangular with at least 5 setae confirmed 3 dorsally, 2 ventrally). Segment 4 much thinner than proximal segments, rectangular, distally with at least 1 claw and 2 setae.

Mxl (Figs 3G, U, V View Figure 3 , 5E, F View Figure 5 ) Protopod with branchial plate with at least 15 marginal setae. Three masticatory lobes (endites 1-3) with distal claws/setae. Palp with two segments, both with at least 3 setae on their apical margins.

L5 Male (Figs 3H, I View Figure 3 , 5D View Figure 5 ) no setae on protopod confirmed. Branchial plate with six marginal setae. Palp (endopod) a jointed clasping organ, carrying a long claw/finger-like process distally, and a shorter (sensory?) process more ventrally. Masticatory process with three or more setae. Female L5 badly preserved (Fig. 3W, X View Figure 3 ).

L6 (Figs 3J, Y, Z View Figure 3 , 5G View Figure 5 ) Walking leg with 5 segments. Segment 1 with setae d1 and d2. Segment 2 elongate with no seta preserved. Segments 3 and 4 separate, not fused. Segment 3 with seta f distally, segment 4 with no seta g observed. Segment 5 with long claw h2.

L7 (Figs 3AA, AB, 5H, I) Distal parts of this appendage not preserved. Bending of this appendage dorsally suggests it being used as a typical cleaning leg. Segment 1 (basis) with setae d1, d2 and dp present. Segment 2 (first endopodal segment) long, with no seta preserved. Segment 3 preserved in one of the male’s L7, however, only partially.

Ur ramus (Figs 3K View Figure 3 , AC, 5J) Elongate, only slightly bent, with two relatively long terminal claws of similar length preserved (approx. half the length of the posterior edge of the ramus). Posterior and anterior setae not observed.

HP (Figs 4D, E View Figure 4 , 6A, B View Figure 6 ) nearly rectangular in lateral view, with outer distal lobe wider and shorter than inner lobe. Several loops of sperm duct preserved in HP (Fig. 4E View Figure 4 ).

Female genital lobes (Fig. 4F View Figure 4 ) formed as spindle-shaped projections towards posterior and extending nearly to the posterior-most end of the soft body (i.e. basis of the UR). Inside the female BA19005-2, several eggs and stored spermatozoa are preserved (Fig. 4G View Figure 4 ).

Zenker Organs (Figs 3L, M View Figure 3 , 4B View Figure 4 , 6D View Figure 6 ) preserved in male BA19005-1 with five whorls of spines, one with the efferent part of the vas deferens attached. Vasa deferentia forming narrow U-shaped loops mid-laterally (Figs 3N View Figure 3 , 4C View Figure 4 ).

Remarks.

In the original description, it was stated that this species (and genus) belongs to the Candonidae because of the morphology of the Zenker Organ. Further, it was assigned to the Paracypridinae and tentatively to the tribe Renaudcypridini ( Wang et al. 2020b) based on the presence of an internal antero-ventral tooth in LV and a corresponding socket in RV. This character has been defined as tribe-specific by Wouters (2001), while in the other tribes of the Paracypridinae the sockets are missing. As specified in the present analysis, the two postero-ventral teeth in LV of M. hui also possess corresponding sockets, albeit less pronounced than the anterior one. The other diagnostic features of the Renaudcypridini on L7 cannot be verified with the investigated specimens, namely the strong, spiny processes situated dorso-distally on each of the segments 3 and 4 and the arrow-shaped setules on the d2 seta. Nevertheless, we here assign this genus to the Renaudcypridini on the basis of the teeth/socket-characters of the valves, hoping that future findings of this species will offer more morphological characters to eventually verify, or falsify, this decision.

Although there is clearly some affinity with the genus Renaudcypris McKenzie, 1980, Myanmarcypris is easily distinguished by its dorsal hump, its strong and exceptional surface ornamentation and the striking antero-lateral nodes of the valves. Some living species of the cypridid subfamily Cypricercinae share carapace morphological characteristics with M. hui , notably the dorsal hump and the anterior tubercles. For example, Strandesia martensi Savatenalinton, 2015 from Thailand has a dorsal hump situated in front of mid-length, but in contrast to M. hui its RV overlaps the LV dorsally and it lacks internal ventral marginal teeth and sockets ( Savatenalinton 2015). The genus Sataracypris Deb, 1983 from India also has a similar dorsal hump and has been tentatively assigned to the Cypricercinae pending redescription ( Savatenalinton 2015). Bradleytriebella tuberculata (Hartmann, 1964) from Thailand has a prominent external tubercle close to the anterior margin of each valve, in a similar position to the node on each valve of M. hui , but it has no dorsal hump or internal ventral marginal teeth and sockets ( Savatenalinton and Martens 2009a). Soft parts of M. hui are broadly similar to those of Cypricercinae , but the morphology of the caudal ramus attachment, which in Cypricercinae features a diagnostic Triebel’s loop, remains unknown for Myanmarcypris and Sataracypris . For now, therefore, we consider the carapace similarities of M. hui with cypricercine species to be examples of homeomorphy rather than close phylogenetic affinity.

Several juvenile specimens were embedded in the same amber piece ( Wang et al. 2020b), allowing for the presentation of an ontogenetic series from A-4 to A-2 (Fig. 1K-Y View Figure 1 ), including soft parts (Fig. 7 View Figure 7 , Suppl. material 3: Movie S1, Suppl. material 4: Movie S2, Suppl. material 5: Movie S3) (no A-1 specimen found). These juveniles lack the pair of antero-lateral nodes present in the adults’ valves. The A-4 specimen even lacks the pronounced surface ornamentations of older stages (Fig. 1U View Figure 1 ).

Family Candonidae Kaufmann, 1900

Subfamily Paracypridinae Sars, 1923