On numerous occasions I have find this creature in marine, shallow litoral waterbodies with reduced salinity along the Dutch North Sea Coast. At first I had no idea, but it has been suggested by colleagues in the field that this might be an Edwardiid Actinarian and perhaps N. vectensis.
It is about 3 mm in length with a distinct head and tail (I think). The head appears to have 6 tentacle like structures or perhaps some sort of thickened cuticle, but at least with an apparent distal oral opening with 6 swellings. In this preserved material any tentacles can't be seen, but it is possible that is has more than 6, but perhaps even none. There is also a canal from that oral opening to the anus (?). Just behind the head there are pigment cells inside, surrounding its alimentary canal (?). On the epidermis I cannot find any spicules of some sort, so a sea-cucumber seems to be out of the question.
Any suggestions would be welcome
So it is not marine but brackish? and Cnidaria are not supposed to have an anus. Is it possible to describe a cross section?
For Godried: not in full salinity of the North Sea but less (something like 20-25 ppm): Oosterschelde rare, north sea coast of Ameland and If I remember correctly 'Zandmotor' too, but if you need more exact info, I'll have to check in our database.
Nematostella is usually found in landlocked lagoons and saltmarsh pools. It attains a length of about 15 mm (sometomes 40 mm). Tentacle number is up to 16 (20). So you either have only juveniles or stunted individuals or it is something else.
For sure this is not Nematostella which is much larger when adult and looks different. It could be another species of Edwardsiid actinia but they mostly retract their tentacles during sampling and fixation.
The same photo's as full JPG and an extra photo showing a cross-section of its midpart. The original photos are TIFF (2.5-5mB each). Also I made a simple google-earth map showing the records.
I think your pic is an Edwarsidae sea anemona.The Edwarsidae are burrowing and the end of body have a burrowing organ called physa like you can see on pic.
The longitudinal cross section (half section) you can see the mesenterials filaments;these filaments are in the cannal from the head (oral disc) to the end of body
and this cannal is the throat or actinopharinge (alimentary canal).The oral disc have tentacles and the number of it is variable such the species.
The sea anemones (order Actiniaria) have not head and anus
I think I have found the answer. Just now I have found the Polychaete Eumida broken in half with the pharynx everted from the broken part. And it is this Pharynx (with other intestinal parts?) which is the same as shown in my photos. The bulbous (striated) part shown in the right photo's is positioned near the mouth and the darker part with constriction shown in the left photo's is the posterior part.
You say "just now have the Polychaete Eumida",so I ask you Where are the chaetes?.
You konw all Polychaete have chaetes and every chaetes are formed for two zone,one called parapodia and other notopodia and this last one has two aciculate (=needle-shaped).Did you see that?.
i know, i mean to say that the thing on the photo are in fact the gut-midgut-intestine of the polychaete Eumida, so it is just an internal part of a polychaete. And this is somehow releases from the polychaete when processing a sample.
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