an Actinula larva from a jellyfish ?

Franz Neidl · Post by **Franz Neidl** » Wed Jan 11, 2012 12:21 pm

Is this an Actinula larva from the Hydrozoa? It was 137 µm high - without the tentacles.

2 pictures, Obj. 20x and 40x, DIC, flash.

Franz

Mitch640 · Post by **Mitch640** » Wed Jan 11, 2012 3:06 pm

I love the detail you get. Do you know what causes the red tips?

BJ · Post by BJ » Thu Jan 12, 2012 4:45 am

Hello Franz and Mitch,

Franz, I think that you are right, but the actinula larvae that i have seen have had slightly swollen tips to the tentacles. But this can be easily explained if they are a different species or at a different stage of development.

Mitch, i do not know the reason for the colour, but when the larva settles out of the plankton, it explores potential settlement surfaces with the tentacle tips and initially attaches by means of nematocysts in the tips. Once settled, another set of feeding tentacles develop. In Franz´s specimen, these "adult" tentacles are already starting to develop as "buds" at the base of the longer tentacles.

Once more Franz you have produced great images of an interesting specimen - a quick search on the web finds no better images.

thank you for posting,

regards
Brian

Mitch640 · Post by **Mitch640** » Thu Jan 12, 2012 5:07 am

Thanks for the explanation Brian. So it settle for awhile to grow some more? Jellyfish are mobile aren't they? It will eventually let go to go swimming off?

BJ · Post by BJ » Thu Jan 12, 2012 11:51 am

Hi Mitch,

almost certainly this larva would settle and then grow into an attached feeding polyp.

Within the group Hydrozoa there are various different and often rather complicated lifecycles ( http://en.wikipedia.org/wiki/Hydrozoa ). Only some have a free swimming medusa (jellyfish) stage. For example, Hydra is a member of the Hydrozoa and it has no medusa stage.

best wishes
Brian

Mitch640 · Post by **Mitch640** » Thu Jan 12, 2012 12:29 pm

OK, I understand the Hydra. Just didn't know they were the same family.