>Paleozoic corals include two main groups, the Rugosa and Tabulata, both
>originally calcitic. Rugosans can be solitary ('horn corals') or colonial;
>tabulates are all colonial. Like modern hexacorals, rugosans have vertical
>internal partitions, but they have a basically 4-sided symmetry instead a
>6-sided one. The tabulates have horizontal internal partitions. Unless ideas
>have changed about the evolution of corals, neither one is the ancestor of
>the modern scleractinians (hexacorals), which can be solitary or colonial
>and have aragonitic skeletons with vertical internal partitions. That
>end-Permian extinction was a doozy.

If scleractinian corals didn't evolve from rugosans, where DID they
come from? There are no other corals that I can think of  which could
be the ancestors.


Perhaps modern corals from noncalyxforming polyps... those other
scleractinians, the anemones. After all, a coral is but an anemone
which secretes a calcareous "cup" (calyx). But THOSE had to have an
ancestor, and from memory the rugosans are the only possibility which
even comes close.

Calling Tabulata "corals" is a usage of convenience. They are not at
all closely related to corals, and really do not fit the name at all.
If rugosans are ancestral to true corals, then the word can quite
easily be stretched to include them.

Note that like all other metazoans, corals are not truly radially
symmatrical. They are really bilaterally symmetrical. Examination of
the columella (central column of the calyx) shows this, and quite a
few solitary corals are strongly compressed (but is it laterally or
dorsoventrally??) eg Flabellum. And many rugosan calyces are strongly
curved.

MANDATORY MOLLUSCAN CONTENT:
When I was collecting on the depauperated reefs of southern Viti Levu
(Fiji) I collected a small Melanella from an encrusting deep red hard
"soft" coral on the underside of a coral boulder. Does anyone know if
any eulimids parasitize any other prey than echinoderms? I do know of
one species (can't remember which) which is not echinoderm-dependent,
but can't remember the host either.
--
Andrew Grebneff
Dunedin, New Zealand
64 (3) 473-8863
<[log in to unmask]>
Fossil preparator
Seashell, Macintosh & VW/Toyota van nut
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I want your sinistral gastropods!
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Opinions in this e-mail are my own, not those of my institution
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