This is a very interesting contribution where a Devonian foraminiferal taxon is supposed to have had some sort of photosymbiontic activity. Whilst most of the discussion is deeply speculative, the evidence the authors provide does not leave much room for other explanations than kleptoplastidy, at least during limited time frames of the foraminifer cell's life. I feel the authors should go a bit deeper into the life strategy of this taxon as it was indeed restricted to the photic zone but perhaps could have been mixotrophic most of the times and just sporadically host single chloloplasts after digestion of their prey, keeping them alive for as much as they could.  afterall, we are just at the beginning of photosymbiontic strategies for foraminifera and things could have been much more unstalbe as we can observe them today.

Literature they refer to,  is not the most recent one.

Most of the comments are directly on the MS

regards

Antonino Briguglio

This paper is an interesting, well-written contribution to the study of the Photosynthetically- active foraminifera. The conclusion and discussion are speculative. The mode of life concentrate mainly on morphological and habitat comparison with the recent photosymbiont-bearing Peneroplis and the conclusion ofSemitextularia being kleptoplastic is based on the the δ13C enrichment in relation to rock matrix samples.

Endosymbiosis however is a more complex co-evolutionary process and should be discussed involving also different factors such as the temperature during the Devonian; the composition and wall structure of Semitextularia (a thin section of a specimen is important to illustrate in this article); the presence of any remains of plastids. It is also important to discuss the different life strategy adopted by Semitextularia. In this article it is confirmed that they were living in the photic zone and are mixotrophs. Could they have used, however, different sources of energy and carbon, instead of having a single trophic mode.

What is also missing in the manuscript the listing of the foraminiferal assemblages co-existing with vSemitextularia. In order to study accurately the mode of life and plaeoenvironment of this taxon you have to take into account the whole foraminiferal and floral assemblages in the studied thin section/rock sample. For instance, what other foraminifera are also found? Would the shape of their tests implies that they are also kleptoplastic; were fragments of algae found in the rocks? etc..

In my opinion adding all of these information could improve vastly this manuscript and would enrich the conclusion.

Some recent literature are not referred to.

Some extra comments are also in the manuscript.

Best wishes

Marcelle BouDagher-Fadel