Oxyrrhis is a genus of heterotrophic dinoflagellate, the only genus in the family Oxyrrhinaceae. It inhabits a range of marine environments worldwide and is important in the food web dynamics of these ecosystems. It has the potential to be considered a model organism for the study of other protists. Oxyrrhis is an early-branching lineage and has long been described in literature as a monospecific genus, containing only Oxyrrhis marina. Some recent molecular phylogenetic studies argue that Oxyrrhis comprises O. marina and O. maritima as distinct species, while other publications state that the two are genetically diverse lineages of the same species. The genus has previously been suggested to contain O. parasitica as a separate species, however the current consensus appears to exclude this, with Oxyrrhis being monospecific and containing O. marina and O. maritima as separate lineages of the type species. The genus is characterised by its elongated body which is anteriorly prolonged to a point, its complex flagellar apparatuses which attach to the ventral side of the cell, and the unique features of its nucleus.
Etymology
The name Oxyrrhis is derived from the Greek ‘oxys’, meaning ‘sharp’ and ‘rhis’, meaning ‘nose’. This indicates the anterior extension of the body.
Type species
The type species for this genus is Oxyrrhis marina.
History of knowledge
Oxyrrhis was first described by Félix Dujardin in 1841, having been discovered in a salt marsh habitat in Belgium. There is a broad scope of literature concerning the genus, as it is commonly used in laboratory studies investigating the evolution of protist lineages and responses to environmental changes. The amount of knowledge relating to O. marina is rapidly increasing, with the number of publications having greatly risen in the 1990s. It has been suggested that Oxyrrhis could be an “emerging model organism” as it is widely distributed, small, easily traceable, and useful in addressing a range of ecological questions. Because of this, there is currently good knowledge of the growth, feeding and swimming behavior of Oxyrrhis. [4] Its responses to various stimuli, particularly chemical stimuli, are also well studied and have been included in numeric models assessing a range of ecological processes, giving rise to the rapidly increasing number of citations. Additionally, Oxyrrhis is a food source for several planktivores, so there is some data relating to predation rates upon it.
Between 1938 and 2009, 144 papers were published that featured Oxyrrhis as a keyword. In a survey of 36 papers from 1990-2011 that mention O. marina in the title, approximately 55% were aut- or synecologically based, roughly 40% examined an aspect related to evolutionary or genetic biology, and 5% were associated with distributional patterns. However, only around 5-10% of these papers showed any evidence of rigorous cross-disciplinary evaluation.
Habitat and ecology
Oxyrrhis is widely regarded as having global distribution, but there are limited studies of its geographic range. Most published data describe the range of Oxyrrhis as areas of the Atlantic and Pacific coasts of the USA, the Gulf of Mexico, the Atlantic coasts of Europe, the Mediterranean and Baltic Seas, the Persian Gulf, the Indian Ocean, and the western Pacific. Its presence has been confirmed in the southern hemisphere, such as in or around Australia, South Africa, Brazil, and it is rare or absent in polar seas (northern Norway, Iceland), however there have been small sample sizes in these polar regions. Oxyrrhis is rare in open water but has been found to inhabit the coastal waters of some remote islands including Hawaii and the Azores. The genus shows both widespread distributions and endemicity through its various clades. It has been discovered that one clade of O. marina has widespread distribution, covering both coasts of North America and the eastern Mediterranean Sea, while the other clade is only found in the Baltic Sea and Red Sea.
In terms of habitat, Oxyrrhis is common in many intertidal and coastal habitats. There is potential sampling bias when assessing its distribution, as virtually all samples have been from coastal areas, mainly intertidal pools, rather than the open ocean. Oxyrrhis is unlikely to be exclusively intertidal and is probably a small component of coastal and oceanic plankton communities, while there is anecdotal evidence that it occasionally grows in shallow embayments.
