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From: mrh@cybvax0.UUCP (Mike Huybensz)
Newsgroups: net.origins
Subject: Re: Tautological Jellyfish
Message-ID: <548@cybvax0.UUCP>
Date: Fri, 24-May-85 17:02:48 EDT
Article-I.D.: cybvax0.548
Posted: Fri May 24 17:02:48 1985
Date-Received: Sun, 26-May-85 20:20:56 EDT
References: <1135@uwmacc.UUCP>
Reply-To: mrh@cybvax0.UUCP (Mike Huybensz)
Distribution: net
Organization: Cybermation, Inc., Cambridge, MA
Lines: 46
Summary: 

In article <1135@uwmacc.UUCP> dubois@uwmacc.UUCP (Paul DuBois) writes:
> 
> > [Mike Huybensz]
> > The fact that an animal today is an obligate parasite in no way requires
> > its distant ancestors to have been obligate parasites.  There are endless
> > examples (I'll list some on request.)  Mesozoa are not really considered
> > likely ancestors anyhow.
> 
> I'm interested, so:  Requested.  "With references, please."

Barnes: Invertebrate Zoology.  Read about nematodes and flatworms.
Oldroyd, Harold: The Natural History Of Flies.  Read about the family
Hippoboscidae and the tstse flies (two obligate parasitic groups) and
what "primitive" flies are thought to have been like.

As an interesting aside, just yesterday I was reading (in the manual for
the Parasitic Hymenoptera V course) of what must be a transition from
obligate parasite to phytophage.  In some groups of parasitic wasps that
normally parasitize gall-forming insects or leafminers, some species
feed first on the host, then the plant; while others don't require a host
at all.

> > Ancestors of today's multicellular animals are still hypothetical.
> > There are no good extant candidates, and fossil candidates will be
> > extremely hard to find (because of size, lack of preservable structures,
> > and difficulties in distinguishing cellular-level distinctions from
> > other organisms.)  After all, how many fossil invertebrate embryos
> > are known?  (They show comparable problems in fossilization.)
> 
> Jellyfish don't fossilize well, either, but we have jellyfish fossils.
> Algae fossils are known, too, even though they aren't very rugged.

So what?

Jellyfish are BIG compared to hypothetical early multicellular animals.

Algae produce cell walls which might be less fragile than early animals.
For example, where are the fossil protozoa of comparable size and durability?
And finally, algae have nice habits of growing in large aggregations.
That's why we have found them as stromatolites.  Early animals might not
have had that property, or might have it and have been mistaken for sponges.
The fineness of detail preserved in a fossil is always less than we
would like....
-- 

Mike Huybensz		...decvax!genrad!mit-eddie!cybvax0!mrh