## 1 Introduction
Soon thereafter, [PERSON] proposed a new genus encompassing all microorganisms, with a cell shape like a weaver's shuttle and acute at the ends--the genus _Navicula_[27]. He designated _Vibrio tripunctatus_ Muller asthe type species of his new genus, thereafter renamed _Navicula tripunctata_. Accordingly, [PERSON] did the same with _V. ostrearius_, which became _Navicula ostrearia_, the official name of this unique taxon for ca. 150 years. Indeed, in 1974, [PERSON] established the genus _Haslea_ to accommodate all diatoms with peculiar features of frustule morphology, i.e., lanceolate cells, acute ends, fine transverse and longitudinal valve striations; these are all characteristics ascribed to the section/subgenus _Fusiformes_[28]. [PERSON], thus, renamed _N. ostrearia_ as _Haslea ostrearia_, and proposed this taxon as the type species of the genus [29]. In contrast to the two most-studied diatom models, _P. tricornutum_ and _T. pseudonana_, _H. ostrearia_ is a thychopelagic/benthic organism [30]. Its sexual reproduction is well assessed and controlled in the laboratory [31; 32], and it could have an unsuspected impact in natural environments where it blooms [33] ([PERSON] et al. 2017). It displays specific metabolic pathways that lead to the production of compounds, such as marennine, haslenes and highly branched isoprenoids (HBIs), which have a high application potential for the food, feed, health and cosmetic industries [33]. One of the main inadequacies of _P. tricornutum_ or _T. pseudonana_ as models is the absence of known sexual reproduction in these species, which is reflected in the fact that their sizes do not decrease with time. Indeed, due to the rigid frustule being composed of two valves of definite unequal sizes (the larger epivalve and the smaller hypovalve), each daughter cell, after mitosis, inherits only one valve, which becomes the new epivalve. Consequently, in the course of asexual propagation, cells shrink until the original size is restored, due to sexual reproduction. Theoretically, the mechanism and evolutionary path of these species may differ significantly from those in other diatoms, and more models are, thus, needed to better represent the whole taxon. The phenomenon of greening caused by _H. ostrearia_ gives a significant economic added value to oysters produced on the Atlantic coast of France, since green oysters, with a specific flavor and emerald color, are rarer and more expensive than ordinary oysters. Furthermore, it has been shown that in vitro, marennine has biological properties, such as antioxidant, antibacterial and antiviral activities [34; 35; 36], as well as allelopathic effect against other microalgae [37; 38]. Thus, the biological traits of _H. ostrearia_ and the possible applications of its unique pigment marennine make this microalga a highly original biological model. The aim of this review is, thus, to advocate the development of this new microalgal model, presenting past achievements, ongoing research, as well as future objectives to be reached before making this diatom a new reference for biology. Figure 1: Living cell of _Haslea ostrearia_ (NCC 527) observed in light microscopy.