The Atlantic "Epitonium" blainei appears to be conchologically
indistinguishable from New Zealand's Cirsotrema zelebori, which is the
end-member of an uninterrupted evolutionary lineage stretching back at
least to the middle Eocene, and includes a species that can exceed height
110mm and diameter 36mm (C. lyratum in my collection). There is no doubt
whatsoever that both of these small Recent species belong in Cirsotrema.
Northern NZ C. zelebori is in miniature a close replica of typical C.
lyratum, which is highly variable and in extreme forms resembles C.
varicosum, type species of the genus (of which I am sure Boreoscala is a
synonym, as is Dannevigena; it may be of note that recently I discovered a
new early Paleocene species of Cirsotrema that completely lacks spiral
sculpture and has smooth costae. Southern C. zelebori also has smooth ie
uncrenulated costae).

Assuming that C. blainei and C. zelebori are genuinely conspecific, how did
the species reach the Atlantic from NZ in late Miocene or later times?

One theory, put to me by NZ's now-leading malacologist, is that at the time
of dispersal the deep Pacific Ocean basin, admittedly much narrower then,
would have been an insurmountable barrier to dispersal of a species with
nonplanktotrophic larvae such as C.z. today. However he suggests that at
the time C.z. may have had a planktotrophic larva, allowing it to cross,
carried on the CircumAntarctic Current. Fossil protoconchs have not been
observed to my knowledge.

Another possibility is rafting on floating vegetation or pumice. ETs?

However the malacologist is unhappy with the idea of conspecificity,
because of the wide separation. C. "blainei" is only known from a few spots
in Argentina and Falkland Islands (both unsubstantiated), Florida and
Texas. A South African report is discounted (R. N. Kilburn perscom). An
Australian report is unsubstantiated and highly doubtful. However I suspect
that this is due to collection failure or faulty identification; many
specimens may have been misidentified as the Argentinian C. magellanicum.
And that last-mentioned species may be a descendant or form of C.
"blainei".

Various epitoniids do have wide distributions, such as E. lamellosum
(=commutata, monocycla, perplicatum, perplexum, pseudoscalaris) from
Europe, Mediterranean, IndoPacific to Japan, NZ and west Mexico,
approaching cosmopolitan; and Cirsotrema pumicea (=arcella, cochlea, dalli,
pallaryi and togatum), from Mediterranean, Caribbean, west Mexico and Fiji,
the last being a Pliocene fossil. How did these disperse?

I have only one, slightly worn and protoconchless, specimen of C. "blainei"
and I would like to obtain further and better specimens. Live material with
animal preserved (even dried) would be useful, if I can find someone to do
a dissection and DNA work etc for comparison. Accurate reports of
occurrence would be appreciated. And if anyone happens to have specimens of
the Oligocene Argentinian C. rugulosum to spare, I need material for
comparison with C. lyratum...

Andrew Grebneff