annelida at net.bio.net
RE: Date: Wed, 2 Apr 1997 16:43:29 +1100
Subject: Slow news flash - Annelida not 'dead'
<While we're thinking of matters evolutionary :
<The most important evidence for Hypothesis 2 comes from functional
<morphological considerations; namely the inference that metamerism has
arisen <rom a BORROWING mode of life.
(my capitalization, for effect)
<(1) an errant, epibenthic organism with well-developed prostomium and
<prostomial appendages (antennae and palps), many homonomous segments,
biramous <and well differentiated parapodia, and numerous well-structured
Individual Sabellariidae have all these attributes but, after settling from
the plankton and continuing their lives to sexual maturity and beyond, they
do not leave their tubes...and survive very long.
<(2)a BURROWING organism with small prostomium lacking appendages, which had
<many homonomous segments without parapodia, and only a few simple chaetae.
<(A third hypothesis, which is based primarily on certain morphological
<peculiarities and the presence of exclusively monociliary cells in Owenia,
<and which postulates a sessile stem species, is mentioned only
peripherally: <for the present.)
Oweniidae can unscrew themselves from the sand and are wafted about by
currents, taking their tubes with them as the travel. When the trip gets
boring, or for whatever reason, they can settle back to the bottom and
"screw" themselves back into a sandy substrate (DWK, personal observation)
<(2) the notion that metamerism, and hence the stem species of the Articulata,
<originated from a BURROWING life in the marine environment is unconvincing,
Paleontological and biological literature is replete with references
to "burrows" and "borings" of various kinds and these words are often
utilized to characterize the tubular, cylindrical, elongate; (open or
infilled) artifacts produced by "worms" of various kinds. Many of them
have been given taxonomic names and in doing so have introduced a plethora
of ambiguity and confusion. Most of them cite one or another polychaete
"authority" as justification of their identification.
Webster's New Collegiate Dictionary gives the following definitions:
_boring_ verb _bored_; _boring_ [ME boren; from OE borian akin to OHG
boron to bore; L forare to bore, ferire to strike] verb transitive 1. to
pierce with or as if with a rotary tool 2: to form or construct by boring
_burrow_ noun ME borow]; a hole or excavation made by an animal (as a rabbit)
for shelter and habitation
_burrow_ verb 1. archaic; to hide in or as if in a burrow 2 a: to construct
by tunneling 2 b: to penetrate by means of a burrow 3: to make a motion
suggestive of burrowing with : _NESTLE <she nestles her grubby hand into
mine> ~ verb intransitive 1: to conceal oneself in or as if in a burrow 2 a:
to make a burrow b: to progress by or as if by digging
At first glance, these definitions seem innocuous enough, but if we are going
to use them to define and describe physical processes, interpret artifacts
(such as: e.g., trace fossils), evolutionary characteristics, and
phylogenetic relationships, let us cautiously acknowledge the fact that
certain polychaetes deliberately construct (by secretion and agglutination)
arenaceous and calcareous tubiform exoskeletoid structures (tubes) without
the involvement of any kind of mechanical boring or burrowing activities.
There, I've said it, again. I'll probably rest easier, now.
David W. Kirtley
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