## 1 Introduction  
The increase in scientific knowledge in modern biology depends on a few model organisms that represent essential material for fundamental and application-oriented research. Model organisms are extensively used by scientists as references or standards to study cellular and physiological processes in other organisms. This is true when the biology of these models is well understood, usually implying that their genetic variance has been controlled and reduced to a minimum. However, this could restrict their value when the goal is to explore the broad diversity of the tree of life and to extrapolate rules to genetically very different organisms. Hence, in the biological sciences, it is now well recognized that there is a crucial need to investigate new, unconventional model organisms. This especially applies to groups such as microalgae for which biodiversity is high, but also underexplored or underexploited. In the last decades, there has been a growing interest in microalgae due to their importance in ecology, particularly in ecosystem services, as well as in many possible commercial applications. Indeed, microalgae are responsible for the primary productivity in aquatic ecosystems, thus forming the basis of food webs and accounting for more than 50% of the oxygen produced [1]. Due to a huge bio- and chemodiversity, and possibly high growth performances, they constitute a vast renewable resource [2]. However, only a few strains of microalgae are actually exploited on an industrial scale (less than a dozen, including those used as feed in aquaculture). Consequently, microalgae-derived products are currently limited to a few niche markets; however, these organisms can be a valuable source of proteins, lipids, carbohydrates, pigments, vitamins, and high-value antimicrobial, antiproliferative or antioxidant compounds [3; 4; 5; 6; 7]. Aside from the intrinsic fundamental or applied importance of microalgal models, facilitated culture and strain stability can be prerequisites to their development. For diatoms, _Thalassisisira pseudonana_ has been the first species sequenced to provide a whole genome [8], which fostered research using multi-omic approaches. Subsequently, more diatom species have had their genomes sequenced, namely: _Phaeodactylum tricrontum_[9]([PERSON] et al., 2008), _Thalassisira ocanica_[10], _Fistulifera solaris_[11], _Cyclotella cryptica_[12], _Fragiliaropsis cylindtrus_[13], _Pseudo-nitzschia multistriata_[14], _Skeletonem costatum_[15], _Seminavis robusta_[16], _Nitzschia inconspica_[17] and the non-photostrophic Nitzschia sp. Nitz4[18]. All these organisms are marine species, either centric (_T. oceanica, T. pseudonana, S. costatum_) or penate (_F. cylindtrus, F. solaris, P. multiseries, P. multistriata, P. tricrontutum, S. robusta, N. inconspica, Nitzchia sp._). Three of the above-mentioned diatoms are benthic (_S. robusta, F. solaris, F. cylindtrus_), while the rest are planktonic, with the ecological behavior of _P. tricrontutum_ being as diverse as its morphotypes [19; 20]. To date, among these species, sexual reproduction has been evidenced in _C. cryptica_[21], _P. multiseries_[22], _P. multistriata_[23] and _S. robusta_[24]. The microalga _Haslea ostrearia_ ([PERSON] [PERSON] is a marine pennate diatom that produces the very unique blue pigment marennine (Figure 1). This pigment is water-soluble, and it can be fixed on the gills of many invertebrates, particularly oysters (the so-called 'green oysters'). The first mention of the species known today as _H. ostrearia_ was made in 1820 by [PERSON], a French custom receiver but also a botanist, who studied the cause of the greening of bivalves in northern France [25]. Although using his own limited material, an 'inferior microscope' with 'imperfect optical properties' [26], [PERSON] identified microorganisms contributing to this coloration, to which he gave the name _Vibrio ostrearius_.