Trichosphaerium is a genus of amoebozoan protists that present extraordinary morphological transformations, both in size and shape, during their life cycle. They can present a testate amoebae that may or may not be covered in spicules. They are related to the family Microcoryciidae, which contains other amoebae with tests, within the clade Corycidia of the phylum Amoebozoa.
Morphology
Trichosphaerium is a genus of
amoebae characterized from other
Amoebozoa by a multiporous
testate amoebae and a specialized non-motile
pseudopodium, known as a dactylopodium, shaped like a digit. The dactylopodium is considered a sensory structure. Its morphology, behavior and life cycle are extraordinary in comparison with other
protists. During its poorly understood life cycle,
Trichosphaerium undergoes dramatic changes in shape and size. They can grow from as small as 10
micrometre to giant cell sizes of over 1
Millimetre, observable by the
naked eye. They can display such varied recognizable
that they can be easily mistaken with other species of amoebae.
Controversial reports describe an alternation of two trophozoite stages within its life cycle: the "schizont", an amoeba surrounded by a test covered in flexible spicules, and the "gamont", an amoeba surrounded by a more flexible and fibrous test without spicules. According to studies written by Germany protozoologist Fritz Schaudinn in 1899, the gamont stage produces , which fuse into a zygote to generate the schizont stage. Although both morphotypes have been observed and kept in laboratory cultures over the decades, this alternation of generations has never been observed in them, which adds a layer of complexity to the unusual, poorly understood behavior of these amoebae.
Systematics
Trichosphaerium is the sole accepted genus of the family
Trichosphaeriidae (sometimes written as
Trichosidae)
and the order
Trichosida.
The phylogenetic placement of
Trichosphaerium has been controversial,
but most recent studies place it within the class
Tubulinea of the phylum
Amoebozoa.
In particular, since 2017,
phylogenomic analyses of Amoebozoa recover a
clade known as
Corycidia, at the base of Tubulinea, containing both
Trichosphaerium and amoebae of the family
Microcoryciidae together.
Synonyms
In 2016, American
protozoologist Thomas Cavalier-Smith described the genus
Atrichosa to comprise an undescribed species of
Trichosphaerium, after considering that the type strain of this species does not belong to the genus
Trichosphaerium but to a distinct, yet related, organism.
This change, however, was not accepted by the 2019 revision of eukaryotic classification, where
Atrichosa is considered a junior synonym of
Trichosphaerium "until the opposite is shown".
Another genus,
Pontifex, is considered to be a synonym of
Trichosphaerium, although with uncertainty.
Species
Up to four species have been described within the genus, mainly based on the morphology of the spicules that cover their test.
-
Atrichosa algivora — described from the only strain of Trichosphaerium that has been DNA sequencing, ATCC 40318.
-
Trichosphaerium platyxyrum
