gread at actrix.gen.nz
Sun Oct 10 21:46:17 EST 1999
Some more thoughts on Capitella (capitata) species complexes.
The latest Capitella sp. I paper to cross my desk is the one by Horng &
Taghon (1999) JMBE 242:41-57. They are looking at organic
contaminants and the effects of fecal pellet formation thereon. Their
Capitella sp. I culture came direct from Judith Grassle. That is probably
fine (except for worries about changes due to inbreeding) but it highlights
what is going on. It is difficult to experiment on your local Capitella sibling
spp because they are not definable - or so people may think.
Horng & Taghon talk of "members of the Capitella sibling species complex"
which is fine, but the previous sentence begins, "Capitella capitata,
originally believed to be a single species, is now known to consist of a
complex of species ..." Oops, we just parted company. Paper after paper
after paper commits this mistake. In my scheme of things C. capitata will
always be a single species. The question is which, if any, of the so far
reported 'siblings' is C. capitata. By the way I would rewrite the above
along the lines of, "the morphologically similar capitellids, originally believed
to be one species, Capitella capitata, are now known to be ..." It's not at all
difficult to be more accurate in name usage.
What annelids do Capitella species resemble? They resemble
oligochaetes. What do oligochaetologists use routinely to distinguish
externally similar species? They use internal anatomy. Have any of the
students of the group of species similar to Capitella capitata proved the
internal morphologies are identical? Not as far as I am aware.
Knowlton (1993) talks of sibling species being artifacts of ignorance. Amen
to that. Usually they become pseudo-sibling species once more
exhaustively examined. Adopting the term 'sibling species' should not be
regarded as an end in itself, nor should the term be used as a crutch. It
James Blake wrote:
> each of those four siblings can be readily separated from
> one another on the basis of prostomial shape, nature of the peristomium,
> shape of the posterior end, distribution of hooded hooks, and several of
> the reproductive and developmental features.
To which can be added genital hook morphology, sperm morphology,
chromosome number and karyotypes - thanks to work by Judith Grassle
and Kevin Eckelbarger.
One thing that worries me is the developmental sequence of capillary setae
replacing hooks. I find it hard to believe no one found any variation in
setigers 1-6 in juveniles at least. I also note in passing that Capitella sp III
(C. jonesi), with capillaries always only on the first three setigers, has
never been a sibling species, although included in papers as such. It just
doesn't fit C. capitata.
Wilcox and Nickell recently (1988: Ophelia 49(2):141-145), and others earlier,
report poecilogony in Capitella capitata. For W&N it is on the basis of a
difference in egg size in the brood tube of one specimen. I don't know
what to make of this observation. Does anyone have any suggestions?
> What is needed is to acquire a collection of adult Capitella from Naples,
> the type locality and to establish and fix a definition of C. capitata from
Jim corrected himself to Greenland. Looking at Fabricius one can see the
type locality appears to be a place called 'Pullateriak,' which is helpful.
However, one can imagine there might be now, if not in Fabricius's day,
more than one species of the complex present there.
Geoff Read <gread at actrix.gen.nz>
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