It looks like a species of Coscinodiscus

Dear Aquilah:

You need to treat the material to eliminate organic matter.

For being sure if your material corresponds to the genus Coscinodiscus (I think that it is a Coscinodiscus) you need to confirm some features (Hasle & Syvertsen in Tomas (1996) Identifying marine phytoplankton)

Areolae loculate; cribra external; foramina internal (SEM).

Marginal rimoportulae, sometimes in more than one ring

Rimoportulae are sometimes also between valve center and margin, irregularly positioned if present in central part of valve.

Rimoportulae usually of two types (shape and/or size).

When you determine conclusively the genus you can follow criterion giving by Hasle & Syverten for distinguished species into the genus.

Valve shape.

Areolae (size) in 10 µm near center and peripheral.

Height of mantle, measured as number of areolae.

Areola pattern on valve face.

Central area, shape (rosette of larger areolae or nonareolated = hyaline).

The presence/absence of hyaline lines (interspaces, wide interstriae).

Shape of the larger processes.

Distance between the larger processes.

Distance between the smaller marginal processes (measured as number

of areolae).

The presence or absence of processes on valve face.

Chloroplast outline

As you can see most part of the generic and specific features are not visible in material if it is not treated. You should treat your material and add pictures taken with light and scanning electron microscopy (if it is possible), in this case other diatomologist could help you with the determination.

Kind regards.

Eugenia

I agree with Dr Kevin and Dr Eugenia.

Thanks everyone for the opinion.

Thank you Eugenia for the detailed explanation and reference. I'll try treating the samples first then have a look at them again.

Dear Aquilah

I agree with Dr. Eugenia and Dr.Kevin. It could be a species of Coscinodiscus probably C.wailesii.

I would like to add a couple of references for you

Hasle, G. R. and Fryxell, G. A. 1995. Taxonomy of diatoms.

Round, F. E., Crawford, R. M. and Mann, D. G. 1990.,The

Diatoms. Biology and Morphology of the Genera. Cambridge

University Press, Cambridge, pp. 747.

Good luck!

I agree that it does look very much like C. wailesii however the diatom in your photo is only about 30 microns wide. C. wailesii is generally much larger than this with a diameter up to around 300-400 microns. Could you be mistaken with the measurements?

See Hasle & Lange 1992, p55, Figs 49-62

Hasle, G.R. & Lang, C.B 1992 Morphology and distribution of Coscinodiscus species from the Oslofjord, Norway and the Skagerrak, North Atlantic. Diatom Research  7, 37-68

Dear Nur:

It is not C. wailesii, this species has 160-500 µm in diameter and the mantle is very deep and vertical. Your specimens measures ca 30 µm in diameter and mantle is shalow.

See Hasle & Syvertsen in Tomas (1997)

I am adding a link showing C. wailesii

http://www.sms.si.edu/irlspec/Coscin_wailes.htm

http://earthguide.ucsd.edu/seafloorscience/pdf/algalbloompaper.pdf

Kind regards.

Eugenia

Hi Jackson, thanks for your opinion. I however agree with Eugenia that the species does not belong to Coscinodiscus wailesii as my diatom is smaller in size.

Kevin, I'm quite sure the measurements are all good. I compared my diatom with my colleague's diatom which is C. wailesii and mine is smaller. I will probably do SEM images to confirm the species.

I was thinking my diatom might be C. radiatus or Actinoptychus sp. 

Dear Nur:

I thought it might be a Coscinodiscus radiatus, but without a proper analysis of the frustules is not possible to know it conclusively, taxonomy has its rules.

I am adding a paper about C. radiatus and C. perforatus

Kind regards.

Eugenia

Dear Eugenia, thank you for the perfect paper concerning Coscinodiscus!

Best wishes

Elena

you need to cleaning organic matter to accurate identification

will do Ahmed. I'm using the cold H2O2 method and hopefully the image will be clearer this time. Thanks for the suggestion.

Is it possible that C. perforatus has a diameter about 30 um? I did sample cleaning and have a look at the sample but I did not have the picture taken yet.

If C. perforatus can't have diameter range of 30 um, then I'm quite sure it's C. radiatus. 

Dear Nur:

The minimum diameter that have registered for perforatus was 80 um. Nevertheless, the paper that I send you discuss more important differences between both species pp. 520.

One importante paragraph says "Coscinodiscus perforatus differs from C. radiatus in the size of the marginal microrimoportulae, larger in C. perforatus Figs 25, 26, 28) than in C. radiatus (Figs 45, 46, 48–50); in the size of the macrorimoportulae, smaller and almost indistinguishable from the microrimoportulae in C. perforatus (Figs 25–28) and larger and easily distinguishable from the microrimoportulae in C. radiatus (Figs 45, 48–50); in the morphology of the macrorimoportulae, similar to the microrimoportulae in C. perforatus (Figs 25–28) and with long thick neck, trilobulate at the top and curved toward the mantle in C. radiatus (Figs 48–50); and in the cribra pattern, complex, with central and subsidiary areas of perforation in C. perforatus (Figs 2–4, 7, 8, 17–20, 22, 31), and simple, without subsidiary areas of perforation in C. radiatus (Figs 40–43)."

Good luck.

Kind regards. 

Eugenia

Dear Nur,

I think Eugenia is right. the species are very similar to Coscinodiscus, and if you want to get rid of organic maters, it is better to treat samples with hydrogen peroxide (%30) for few hours, then see again under light microscope or do SEM.

Dear Nur,

By the way, I forgot to say that you should be very careful while using hydrogen peroxide as it reacts very fast with water or organic mater and being in touch with skin, will burn it.

it's better first to dilute it, then use.

Dear Aquilah, I think its a Coscinodiscus species. 

This is the SEM pictures of Coscinodiscus sp. Is it radiatus?  The diameter size is about 30-40 micron

Dear Aqilah:

It is not a Coscinodiscus it is an Actinocyclus, Hemidiscaceae. Your detail clearly shows the pseudonodulus, characteristic of this genus.

See Hasle & Syvertsen in Tomas (1997) and Round et al. (1990).

All the best.

Eugenia 

Dear Eugenia, 

Thank you very much for your help!

I'll look at the reference. 

This is I think Coscinidiscus sp. 

Dear Kevin and Eldrin:

The material of Aquilah pertain to Actinocyclus. See you additional SEM pictures that she showed.

Kind regards.

Eugenia

Absolutely agree with Dr. Eugenia.

Dear Eugenia, 

Do you think the SEM images showed Actinocyclus octonarius (Ehrenberg, 1837)?