At the Zoological Society of Japan Board of Directors meeting held on Saturday, June 2, 2018, at the Hokkaido University Tokyo Office, the ZS Editorial Board recommended five papers as candidates for the 2018 Zoological Science Award. As a result of deliberation by the Board of Directors, the 2018 Zoological Science Award was decided to be presented to the following five papers.

Zoological Society of Japan 

[Selection Progress Report]

On April 23, 2018, all Associate Editors and Advisory Board Members of Zoological Science were asked via e-mail to recommend candidate papers (one to several papers published in 2017 (Vol. 34), with a recommendation deadline of May 18). By May 18, a total of 38 nominations (23 unique papers excluding duplicates) were submitted by 1 Editor-in-Chief, 17 Associate Editors, and 3 Advisory Board Members. Based on this list of recommended papers, the Editor-in-Chief and Associate Editors deliberated based on papers receiving multiple recommendations, the validity and significance of the scientific content, and notable contributions to zoology. As a result, the following five papers are reported to the Board of Directors as award candidate papers.

Award-Winning Paper

Clock and Hormonal Controls of an Eclosion Gate in the Flesh Fly Sarcophaga crassipalpisMiki Yamamoto, Koji Nishimura and Sakiko Shiga Zoological Science 34(2): 151–160.
In many insects, eclosion occurs at a specific time of day, a time window known as the "eclosion gate." Although it has been known that the circadian clock is involved in the eclosion gate and that a series of hormone cascades triggers eclosion, it remained unclear when and by what molecules the signal from the circadian clock is generated. In this study, using the flesh fly Sarcophaga crassipalpis, which has a distinct eclosion gate, phase-response experiments of the eclosion rhythm using cold pulses suggested that the circadian clock issues the command to determine eclosion timing no later than 4.5 hours prior to the onset of eclosion. Although administration of 20-hydroxyecdysone caused a delay in eclosion, its sensitivity was not observed after 12 hours before eclosion, suggesting the involvement of a molecule other than ecdysteroids. These findings significantly contribute to the understanding of the mechanism by which the circadian clock sets the timing of ecdysis-related behavioral expression.

A Novel Symbiotic Ciliate (Ciliophora: Peritrichia) in the Hindgut of a Stag Beetle (Coleoptera: Lucanidae) Masahiko Tanahashi, Xian Ying Meng and Takema Fukatsu Zoological Science 34(3): 217–222.
Histological, ultrastructural, and molecular phylogenetic analyses revealed the discovery of a peritrich-related ciliate residing as a symbiont in the adult intestinal tract of the stag beetle *Lucanus maculifemoratus dybowskyi*. All previously reported peritrich-related ciliates are aquatic, and when they are symbiotic with animals, they are epizoic or ectosymbiotic. This study raises many intriguing questions regarding the symbiosis between aquatic ciliates and terrestrial insects, such as: Where do the ciliates come from, and how do they establish symbiosis within the hindgut? Are the ciliates acquired horizontally from the external environment, or are they transmitted vertically? Is their relationship parasitic, commensal, or mutualistic? These are significant research findings that hold great promise for future developments.

Laterality is Universal Among Fishes but Increasingly Cryptic Among Derived GroupsMichio Hori, Mifuyu Nakajima, Hiroki Hata, Masaki Yasugi, Satoshi Takahashi, Masanori Nakae, Kosaku Yamaoka, Masanori Kohda, Jyun-ichi Kitamura, Masayoshi Maehata, Hirokazu Tanaka, Norihiro Okada and Yuichi TakeuchiZoological Science 34(4): 267–274.
The evolutionary ecology of sidedness in fishes can be said to be one of the research fields originating in Japan with a high degree of originality. This paper is a monumental achievement that demonstrates the universality of sidedness in fishes by comprehensively analyzing sidedness across various fish taxa, mapping it onto phylogenetic trees, and analyzing the evolutionary processes. Achieved through the zoological methodology of steadily accumulating observational knowledge from a unique perspective, this research is well-deserving of the Paper Award.

External Asymmetry and Pectoral Fin Loss in the Bamboo SoleHeteromycteris japonica): Small-Sized Sole with Potential as a Pleuronectiformes Experimental ModelQiran Chen, Masako Takagi, Makoto Mogi, Miki Kikuchi, Yudai Saito, Shunya Nakamura, Hayato Yokoi, Tadahisa Seikai, Susumu Uji and Tohru SuzukiZoological Science 34(5): 377–385.
Flounder are teleost fishes that exhibit extreme morphological asymmetry in the position of their eyes and the color of their body surface. Order Pleuronectiformes, family Soleidae (Sasayushinoshita)Heteromycteris japonica), in addition to the left-right asymmetry characteristic of these flatfish, they are characterized by the loss of their pectoral fins during the transition period from larvae to juveniles (metamorphosis). With the goal of understanding the formation mechanism of such unique morphological features, this paper not only established a rearing system for the zebra sole (Brachirus orientalis) from the embryonic stage to the juvenile stage, but also successfully established a microinjection method into fertilized eggs, which is required for embryological research in teleost fish. This research not only paves the way for new embryological studies using flatfish as a model, but is also expected to make a significant contribution to the field of fisheries science.

Laboratory Rearing System for Ischnura senegalensis (Insecta: Odonata) Enables Detailed Description of Larval Development and Morphogenesis in DragonflyGenta Okude, Ryo Futahashi, Masahiko Tanahashi and Takema FukatsuZoological Science 34(5): 386–397.
The development of efficient laboratory rearing systems is an essential first hurdle in establishing model animal species. In particular, dragonflies have been difficult to establish as model species because mass rearing is challenging due to factors such as cannibalism during the larval stage and active flight behavior during the adult stage. In this paper, the authors describe the blue-tailed damselfly (Ischnura senegalensis) as a candidate model species, established an efficient laboratory rearing method, and used this method to provide detailed descriptions of the timing of developmental events from larva to adult, survival rates, and changes in morphological characteristics. This study is a piece of basic research in animal science that holds great promise for the advancement of dragonfly research using *Ischnura senegalensis* as a model species.