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| Myanmarcypris hui Wang, Matzke-Karasz, Horne, Zhao, Cao, Zhang & Wang, 2020 |
Abstract
The bivalved crustacean ostracods have the richest fossil record of any arthropod group and display complex reproductive strategies contributing to their evolutionary success. Sexual reproduction involving giant sperm, shared by three superfamilies of living ostracod crustaceans, is among the most fascinating behaviours. However, the origin and evolution of this reproductive mechanism has remained largely unexplored because fossil preservation of such features is extremely rare. Here, we report exceptionally preserved ostracods with soft parts (appendages and reproductive organs) in a single piece of mid-Cretaceous Kachin amber (approximately 100 Myr old). The ostracod assemblage is composed of 39 individuals. Thirty-one individuals belong to a new species and genus, Myanmarcypris hui gen. et sp. nov., exhibiting an ontogenetic sequence from juveniles to adults (male and female). Seven individuals are assigned to Thalassocypria sp. (Cypridoidea, Candonidae, Paracypridinae) and one to Sanyuania sp. (Cytheroidea, Loxoconchidae). Our micro-CT reconstruction provides direct evidence of the male clasper, sperm pumps (Zenker organs), hemipenes, eggs and female seminal receptacles with giant sperm. Our results reveal that the reproduction behavioural repertoire, which is associated with considerable morphological adaptations, has remained unchanged over at least 100 million years—a paramount example of evolutionary stasis. These results also double the age of the oldest unequivocal fossil animal sperm. This discovery highlights the capacity of amber to document invertebrate soft parts that are rarely recorded by other depositional environments.
Keywords: ostracods, giant sperm, Cretaceous, sexual reproduction
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| Figure 2. The studied ostracods from Myanmar amber: microtomographic reconstructions. (a,b) Myanmarcypris hui gen. et sp. nov., surface rendering, right view. (a) Male, BA19005-1. (b) Female, BA19005-2. (c) Dorsal view of adult female carapace, surface rendering, BA19005-2. (d,e) Myanmarcypris hui gen. et sp. nov., surface rendering with transparency, right view. (d) Male, BA19005-1. (e) Female, BA19005-2. (f ) Internal view of adult female left valve, surface rendering, BA19005-2. (g–i) Myanmarcypris hui gen. et sp. nov., juveniles, surface rendering, right view. (g) Juvenile (A-2), BA19005-3. (h) Juvenile (A-3), BA19005-4. (i) Juvenile (A-4), BA19005-5. ( j) Sanyuania sp., BA19005-8, surface rendering, right view. (k–m) Myanmarcypris hui gen. et sp. nov., juveniles, surface rendering with transparency, right view. (k) Juvenile (A-2), BA19005-3. (l ) Juvenile (A-3), BA19005-4. (m) Juvenile (A-4), BA19005-5. (n) Sanyuania sp., BA19005-8, surface rendering with transparency, right view. (o,p) Thalassocypria sp., surface rendering, left view. (o) BA19005-6. (p) BA19005-7. (q,r) Thalassocypria sp., surface rendering with transparency, left view. (q) BA19005- 6. (r) BA19005-7. Note: colours for the appendages and soft parts correspond to figure 3 (in which they are labelled). |
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| Figure 4. Preserved body parts in fossils in comparison with modern analogues. Body parts of Myanmarcypris hui gen. et sp. nov. were visualized by tomography and volume rendering of female (BA19005-2) and male (BA19005-1) adult individuals, modern analogues by scanning electron microscopy. (a) Right 5th limb of male with clasping organ (top). (b) Eucypris virens: right 5th limb of male with clasping organ (top). (c) Two eggs in female partly cut open. (d) E. virens: empty egg shell. (e) Zenker organ. (f ) Cyclocypris ovum: Zenker organ. (g) Mass of sperms in location of seminal receptacle in female. (h) Mytilocypris mytiloides: densely packed sperm filling of a seminal receptacle. (i) Paired hemipenes. (j) Fabaeformiscandona subacuta: paired hemipenes. (k) Sperms in female. (l) Pseudocandona marchica: sperms in female. Scale bars, 10 µm (a), (c–g), (k), (l ); 100 µm (b), (h–j). |
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| reconstruction of mating ostracods. Artwork: YANG Dinghua. |
Myanmarcypris hui gen. et sp. nov.
Etymology: Myanmar (the country of origin) + Cypris; hui
(after the collector of the amber piece, Mr Cheng HU).
Type locality and stratigraphy: Hukawng Valley, Kachin
Province, Myanmar; upper Albian–lower Cenomanian.
He Wang, Renate Matzke-Karasz, David J. Horne, Xiangdong Zhao, Meizhen Cao, Haichun Zhang and Bo Wang. 2020. Exceptional Preservation of Reproductive Organs and Giant Sperm in Cretaceous Ostracods. Proceedings of the Royal Society B. DOI: 10.1098/rspb.2020.1661
100-million-year-old amber reveals sexual intercourse of ostracods
