Hello,

Catch Tentacles in Metridium senile

My research indicated that dissection of Metridium senile failed to discover separate "catch tentacles". Now, anybody who has any experience of this anemone (English Channel specimens) will discover:

1)  catch tentacles appear on certain occasions
2)  introduction of plankton, brine shrimp, fresh seawater can (not always) induce the appearance of the "catch tentacles" in this species.

Certain hypotheses can be thought up from these observations. However, further information would be useful.

The questions are:

1) are "catch tentacles" regularly found in pickled specimens of Metridium senile?
2) what distinguishes the "catch tentacles" in dissected specimens from the ordinary tentacles (apart from the length and size)?

If anybody has investigated this anemone and knows the answers to these questions, I would be very interested. It will help formulate a description of what happens. I might even be able to suggest a reason why. (I have already thought up the reason and now I have to check it out.)

Gosse christened this anemone PLUMOSE, which is widely (almost 100%)  used in the UK and it is a very apt and attractive name.

Cheers

Andy Horton

Replies:

The questions are:
>
> 1) are "catch tentacles" regularly found in pickled specimens of Metridium senile?

Don't know.

> 2) what distinguishes the "catch tentacles" in dissected specimens from the ordinary tentacles (apart from the length and size)?

As I understand it, the cnidome of the catch tentacles should be quite different from that of the feeding tentacles.  I believe the cnidome of catch tentacles (at least in Haliplanella luciae) consists of holotrichous isorhizas, with the mastigophores and spirocysts of the feeding tentacles absent.

David Hesinger

Dear Andy,

Catch tentacles, by definition, differ histologically from normal tentacles.  As I said, they are able to extend further, so when they are contracted, the tissue is denser.  Most importantly, the cnidom is utterly different than it is in normal tentacles.  The transformation to and from catch tentacles has been followed, not in *Metridium*, I believe, but in *Diadumene* or *Haliplanella*.

They are stimulated to form primarily by intraspecific interactions, and sometimes, it seems, in *Metridium* by interspecific interactions.
Jennifer Purcell has published the most on this matter, to my knowledge.

Sincerely,
Daphne Fautin

histology  | hstldi |  n. M19. [f. HISTO- + -LOGY. Cf. Fr. histologie (E19).] The branch of science that deals with the structure and composition of organic tissue, esp. on a microscopic scale; the histological properties of a thing. histologic a. (chiefly US) L19. histological a. M19. histologically adv. as regards histology M19. histologist n. M19.

intraspecific  | ntrspsfk |  a. E20. [f. INTRA- + SPECIFIC.] Produced, occurring, or existing within a (taxonomic) species or between individuals of a single species.

interspecific a. formed or obtained from (individuals of) different species; occurring among individuals of different species: L19.

The "catch tentacles" are used in interference interactions between clones.  Some specimens have them and some don't.  Jenny Percel (and co-authors) has a paper on the formation of catch tentacles in M. senile.
The easy place to find that and more is probably Malcolm Shick's book on the Biology of Sea Anemones.

Cheers

Liz Francis
From: "Dr. Liz Francis" <lfrancis@cc.wwu.edu>