According to Hasle & Syvertesen (1997), in Thomas (ed.) Identifying Marine Phytoplankton, Asteromphalus pettersonii seems conspecific with Asteromphalus sacrophagus. Please indicate if I have misunderstanding. Anyway, both morphospecies frequently found in the temperate to tropical, and coastal to oceanic regions of the North Pacific. Light microscopic image is attached here.

SEM image.

Hi Koji,

Thank for your reply and images. I have a colleague in Tasmania who has a similar SEM image to the one you have posted from sampling in oceanic Temperate waters, although the "top" and short ordinary ray has elongated the valve even further in her specimen than your own specimen (which looks more rounded). At first I thought it was A. sarcophagus, but when you really look at the morphotype (i.e. valve outline) it doesn't really appear to me to be A. sacrophagus, but rather what I would have considered A. pettersonii. I had a look in both Simonsen (1974) and Hernandez-Beccerril (1991) and saw that both are potentially related to A. heptactis and tropical forms. The only recent publication I could find (swiftly looking) was in Itaru Koizumi's paper (plate 3 images no 2 and 3 http://www.sciencedirect.com/science/article/pii/S037783980800100X). Anyway, seems there is little about which is why I posted my question- Simonsen mentions it from the Persian Gulf and Indian Ocean. It wasn't specifically studied by Hernandez-Becerril. Do you have any additional information on your species published or in a report that I could send to my colleague?

I think it is fascinating that you have it up North. I am sure a genetic study is in order if several species from both hemispheres could be isolated and cultured.

Cheerio

Leanne

Hello Leanne and Koji

Attached is the image Leanne referred to ( and kindly identified!) from the Southern Ocean. The image was taken from a sample prepared from a 5m CTD sample, at 47S.

Looking at the images side by side, the SO specimen certainly has a more elongated profile.

Although I have only seen the cell once, there is an accompanying time series from this site at 30m, which I am yet to examine by LM. I will keep you posted if I see any more specimens.

Koji, have you identified the other (small) species in your photo?

Kind regards Ruth

Hi Leanne and Ruth.

Please wait a moment. I'll search my picture folder. Note that I observed many different aspect ratio (apical axis vs. transapical axis) of A. sacrophagus species (complex?). I may attach several example later. I feel that the classification of this genus (and also many others) need revision.

Sincerely,

Koji Sugie

Hi Leanne and Ruth

Several figures and geometric information of A. sacrophagus-like species were gathered as attached. Please check. These were found from ~40N to ~10N in the North Pacific. Areolae pattern seems very similar among specimens which I observed. So, I wonder, do A. sacrophagus and A. pettersonii differ in species level? I think morphological plasticity is actually interesting and controversial matter in diatomology.

Domo arigato gozaimas Koji for the additional photos!.

Its useful to see the range of AL:TL ratios. My cell is within the range you present (~2.5), similar to your specimen 2.

I will send you both any further photos Im able to get, if you like

Hi Kozi and Ruth,

Thanks to you both for the images. Kozi your study images of the morphological differences are quite spectacular. I think I need to find and read the original descriptions for all of these "species". I do not have the original Pettersonii description. I think if Ruth finds more specimens then there is an opportunity to do a short study on the variability. Questions would remain: are they one and the same genetically, and plastic in form due to a environmental factors? I wonder if the S. American diatomists have observed them?

Leanne

Hello, yes in Costa Rica

Figure three is very similar to ours, in the central Pacific of Costa Rica