Paradinium poucheti

Super Group: 
Chatton 1910


Diagnosis_Genus: Paradinium Chatton 1910. Parasitic protists that infect marine, planktonic copepods.
Diagnosis_Species: Paradinium poucheti Chatton 1910. The parasite exists as 8-10 µm long amoeboid cells in the body cavity of its host. The individual cells are interconnected by thin pseudopodia thereby forming a reticulate plasmodium, a filoplasmodium. At more advanced stages of infection, a solid plasmodium is formed. After a time the filoplasmodium
of Paradinium has grown through the body-cavity, creeping on the surface of the organs and bridging the spaces between them; the amoebiform bodies have become multinucleate and more massive, spreading in sheets over the walls of the haemocoele, and the structure of the plasmodium is no longer uniform. The development of the plasmodium prevent the formation of genital glands, leading to the castration of the host. The trophont is now distributed in
two ' genital masses' occupying the region of the female gonad and duets, which are destroyed, pushing out between the bodymuscles to form 'parietal sheets' on the inside of the body-wall, and continuous behind with a perineural investment of parasite which thins out anteriorly. This is developed early in the infection and may penetrate deep into the nervous tissue itself. The abdomen and limbs are never invaded. The yellowish-grey, slightly opaque plasmodium now shows through the body-wall of its host, making it conspicuous amongst its healthy fellows.
Eventually, the plasmodium passes from the body cavity of the host and into the lumen of its intestine whereupon it is expelled through the anus. The plasmodial cell mass then forms a ‘‘cyst’’, a gonosphere (Chatton 1920), that attaches to the urosome of the host. The gonosphere is bounded by a mucoid wall with a reticulate surface. Within a few hours after the formation of the gonosphere, flagellated spores are formed (the sporogeneis is external). These spores measure approximately 12 µm in length and possess two flagella of unequal length. The spores are believed to represent the infectious stage (Chatton 1920), but this has never been documented.
Body_trophont_length: 8-10 µm
Body_spores_length: 12 µm
Sequence_SSU: EU189030


poucheti: in honor of Pr Pouchet, who first observed a Paradinium infecting Acartia longiremis in Concarneau 1890.

Type species

This is the type species of the genus.

Type illustration / Type locality / Type specimen

Type host: Acartia clausi
Type locality: Banyuls-sur-Mer (France)


Substrate: endozoic
Salinity: marine

Life cycle

When release outside its host, the external cycle of Paradinium poucheti is a gameto-meiosis: two homeotypic divisions (mesomitosis) are followed by a meiotic division (metamitosis). The fourth division is homeotypic (Chatton and Soyer 1973).

Generation: <1 month
Reproduction_mode: asexual
Reproduction_mode: sexual
Symbiont: horizontal

Feeding behaviour


Attached phylogeny

Observation site(s)


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