In 1886, French biologist Yves Delage[2] published a detailed histological study describing (among other things) the nervous system and the sense organs of the same Roscoff acoela, Convoluta schultzii.

In this article, von Graff also writes about zoochlorella (i.e. micro-algae) "Although they undoubtedly derive from algae ... they represent however, in their current state of adaptation, a specific tissue of the worm dedicated to assimilation".

[5] It is in an academic book entitled Plant-Animals published in 1912 by Frederick Keeble, the co-discoverer of the nature and the origin of micro-algae, where a set of works is describing the specific relationship between Convoluta roscoffensis and its photosynthetic partners.

[7] Luigi Provasoli, a pioneering micro-algologist in the art of isolating and cultivating micro-algae, maintained for several years between 1965 and 1967 in New York (Haskins Laboratories, now in Connecticut) generations of S. roscoffensis directly received from the Station Biologique de Roscoff.

The accumulation of the latter generates reduced, hypoxic or anoxic conditions, which promote the development of anaerobic bacteria releasing compounds such as hydrogen sulfide (H2S) incompatible with the oxygen requirements of the worm.

Colonies of S. roscoffensis are therefore in this place theoretically exposed to the longest light exposure to maximize the photosynthetic activity of micro-algae partners.

The works of Louis Martin refer to the presence of S. roscoffensis in the interstitial seawater flows at low tide nights showing bright reflection of the Sun on the Moon.

In the thermo and photo-regulated chambers where the worms do not physically perceive the rising or falling tide, this vertical oscillation persists for 4 to 5 days and is then gradually lost and evolves in fine in a random occupation of the space in the container.

Another movement characteristic to the species, sometimes observed in puddles of seawater and in the laboratory, brings together hundreds or even thousands of individuals to realize a circular procession.

Under the effect of the abrupt and pronounced decrease of the pH, S. roscoffensis contracts, turns on itself, then gradually expels its algal partners.

This experience mimics the effects of ocean acidification, which is today the major consequence (with the rise in temperatures) of anthropogenic activities, particularly the combustion of fossil fuels, which generates very high concentrations of CO2.

[15] Other works have shown experimentally that if it has the choice, the photosymbiotic worm avoids exposing itself to extreme light conditions: either too weak or too strong.

[17] When one amputates the anterior part ("the head" containing the brain), one can observe a capacity of regeneration of the whole central nervous system in about twenty days with a joint recovery of the normal behavior.

An in-depth study on the behavior of S. roscoffensis in situ explains that the only possibility for the worm to move horizontally is to make a support (invisible to the naked eye) which is nothing other than a matrix synthesized from secreted mucus.

Symsagittifera roscoffensis also has a muscular system consisting of a complex network of transversal, longitudinal, circular and dorsal-ventral muscle fibers.

In the laboratory and depending on the rearing conditions, after 4 to 5 days, the juveniles hatch, escape from the cocoon and begin their quest for the photosynthetic partner.

Regardless of their phylogenetic position within metazoans, acoela may have retained some ancestral traits of bilaterians during evolution and thus represent an object of study that would potentially help to better understand the diversification of body plan organization in animals with bilateral symmetry.

Neither Geddes (1879), who observed the presence of starch and chlorophyll in the green cells present in the tissues, nor Delage (1886) and Haberlandt (1891) had formally been able to identify their origin and nature, however, suspecting micro-algae.

In 1901, in Roscoff, William Gamble and Frederick Keeble began to study these green cells in hospite and tried to isolate them and put them into cultivation—with no success.

This alga has remarkable characteristics, including four flagella, a theca (polysaccharide envelope) and a vacuole (stigma or "eyespot") that contains photo-receptor molecules.

The assimilation of uric acid by S. roscoffensis has attracted the attention of early experimenters, including Louis Destouches aka Louis Ferdinand Céline who carried out work on the physiology of these animals and who concluded in 1920 "that it is therefore very likely that symbiotic exchanges lead to the transformation of uric acid into nitrogenous food for zoochlorella".

[24] However, the author proposes that if exogenous uric acid is not used by the worm and that if its concentration in the medium culture decreases over time it is because of a bacterial activity associated with the animals.

DMSP is a sulfur compound that exhibit, among other things, a repellent property that could confer a chemical barrier explaining the absence of known or observed predators and as a consequence the abundance of worms within colonies.